1

Funding for this work, including publication expenses, was provided by THE SOUTHWEST FISHERIES CENTER HONOLULULABORATORYOF THE NATIONAL MARINE FISHERIES SERVICE, NOAA and THE US. FISH AND WILDLIFE SERVICE 2 WILDLIFE MONOGRAPHS

Roy L. Kirkpatrick, Editor Department of Fisheries and Wildlife Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061

Consulting Editors for this Issue: David G. Ainley, Point Reves Bird Observatory, Stint- son Beach, CA 94970

A. W. Diamond, Department of Zoology, Edward Grey Institute of Field Ornithology, Oxford OX1 3PS, United Kingdom

Editorial Assistant: Thelma J. Kirkpatrick

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,G' The Wildlife Society, Inc. 1983 3

WILDLIFE MONOGRAPHS (ISSN 0084-0173)

A Publication of The Wildlife Society

HAWAIIAN SEABIRD FEEDING ECOLOGY

by CRAIG S. HARRISON, THOMAS S. HIDA, AND MICHAEL P. SEKl

OCTOBER 1983 NO. 85 4

FRONTISPIECE.White tern carrying flyingfish (Parexocoetus brachypterus). French Frigate Shoals. 5

HAWAIIAN SEABIRD FEEDING ECOLOGY

CRAIG S. HARRISON’ US. Fish and Wildlife Service, P.O. Box 50167, Honolulu, HI 96850 THOMAS S. HlDA Southwest Fisheries Center Honolulu Laboratory, National Marine Fisheries Service, NOAA, P.O. Box 3830, Honolulu, HI 9681 2 MICHAEL P. SEKl Southwest Fisheries Center Honolulu Laboratory, National Marine Fisheries Service, NOAA, P.O. Box 3830, Honolulu, HI 96812

.Abstract: The North\vestern Ha\vaiian Islands are the nesting grounds of about 10 millioii seabirds ot 18 species. Fisher! de\elopmeirt prop,osals for this area led to a need for food habit studies (if thrse hirtls to aid in their managemrnt. Food habits are divrrse. \\ itti 56 families of fish. 8 fanlilies of squid. and 11 groups of crustaceans identified Similar to ottitsr tropical seabird comninnities. this cornmunit) feeds largel! on flyingfishes and squids. 111 addition, hou e\er, this comnrnnit! consumes man! Ilacapterzis spp , juvenile goatfishes, juvenile lizardfishes. and mesopelagic fishe\ that rarrl? occur in the tfirts of tropical sealiirtls elsewhere. Albatrosses fed largely on squids and flyingfish eggs. They also ate niany mysids. isopods, leptos- tracans, and shrimps that occur in very deep \vater. Pelecaniforms ate large flyingfishes and Decapterus spp , many of \vhich \\ere more than 25 cm in length Squids, especiall) the wrface-tl\velling Onimastrephidae, \\ere consiimed frequentl! (:ertain booliies ate Pacific sauries. anchob ies. and juvenile goatfishes at some locations. The terns arid sheanvaters that usuall! feed in association \\it11 predator! fishes ate 2-8 cm pre), especially small omrnastrephid squids aiitl juveiiile forms of fl, ingtishes. goatfishes. lizardfishes, aid Decap- term spp. Small nocturnal-feeding procellariiforms ate man) 1-3 cm mesopelagic organisms such as lan- ternfishes, hatchetfishes, bristlemouths, and squids. Small terns ate primaril! juvenile tlyingfishes, goatfishes. lizardfishes, dolphin-fishes, and a cou fish In addition. the blue-gray nodd\ ate minute prty srich as wa- striders and copepeds. Most birds feed most of their )ourrg during the spring and summer Breeding in thr North\vtxstrrn Ha\\ aiian lslaritls is corrrlatetl \r ith and ma! be contrcilletl h! thr period (if inaxinruin a\ail- ability of food. Breeding seasons fcir seahirtls in tropical climates are generally less predictable compartd to seabird communities in temperate or cold \\ atrr regimes. The relative predictabilit) (if the breeding seasmi for tropical seabirds in the Ha\raiian Archipelago ma! he t~xplained13, the fact that most islands there art’ subtropical Many st&ircIs in Hawaii breed at the northmi cxtent (if their range. Some srabird species breed largely during \vinter. Several of these species are adapted for nocturnal feeding. Other \I inter brrt&ng species may be outcompeted for nesting sites during spring antl siimnicr by larger spccirs that have similar nesting requirements. Poor \\rather conditioirs clriring \\ inter may also encourage spring arrtl summer 1lree.d- irig for sonre species. .-\I1 seabirds \\.err (ipportunistic and fed on a \vide variet) of shoaling fish and squid Thvy apparently took air) organism of appropriate size that occurred in surface watrrs. \’ariation in dirt for most species was more correlated \\ ith season than \\ ith locatioii Some resource partitioning among species \vas evident both in the composition antl in the size of prr!. Difference5 in dirt ma) reflect tliffrrt,ncrs among species in morpholog! , feeding technique, time of clay that feeding occurs, srasoiialit) of Iiweding, or feeding location. The most tiitnier~ii~species in this community are tlrose that ate man! squid Tht. population differences among sprcies ins) tie merel! ancithrr e\pressi(in of the proposition that pelagic feeding seabirds are more nunieroris thati irrshort~frctling seabirds iri tropical \\aters. Man! tuntlamental questions concerning the tii(ilog> of tropical and srilltropical seal,irtls cannot be ans\veretl until bettear ~neth(itls of measuring the a\aiiabilit) of pre! art. de\e1oped Our results \vi11 ena~ile\\,ikllife d.rd fishrr) rnariagers to more accriratelv predict the effects of bnrious tisheries (in rnarine Iiirds WILDL. MONOGR. 85, 7-77

1 Present address Environment and Poh Center, The East-\\ est Center, 1777 East-west Road, IIonolulu, HI 96848 6 WILDLIFEMONOGRAPHS

CONTENTS

INTRODUCTION...... 6 Bonin Petrel ...... 37 Acknowledgments ...... 7 Gra y-backed Tern ...... 39 THE NORTHWESTERN HAWAIIAN ISLANDS ...... 8 White Tern (Fairy Tern)...... 40 METHODS ...... 9 Black Noddy ...... 43 Field Collection of Food Samples ...... 9 Bulwer’s Petrel ...... 44 Laboratory Procedures...... 1 1 Sooty Storm-petrel ...... 46 Prey Identification...... 13 Blue-gray Noddy ...... 48 Data Analysis ...... 14 Prey Length Comparisons ...... 49 RESULTS ...... 15 DISCUSSION...... 50 Species Accounts...... 15 Albatrosses ...... 52 Black-footed Albatross ...... 15 Pelecaniformes ...... 55 Laysan Albatross ...... 18 Terns and Shearwaters Associated with Preda- Masked Booby ...... 20 tory Fishes ...... 56 Great Frigatebird ...... 22 Small Nocturnal Procellariiforms ...... 58 Brown Booby ...... 23 Neuston Feeding Terns ...... 59 Red-footed Booby ...... 25 Timing of Breeding Season and Food Avail- Red-tailed Tropicbird ...... 27 ability ...... 60 Wedge-tailed Shearwater ...... 29 Opportunistic Feeding and Diet Diversity ...... 62 Christmas Shearwater ...... 31 CONCLUSIONS...... 62 Brown Noddy ...... 33 LITERATURE CITED ...... 63 Sooty Tern...... 35 APPENDIXES ...... 66

INTRODUCTION nesting grounds of an estimated 10 mil- lion seabirds of 18 species (Table l).Many No comprehensive work has been pub- of their breeding islands have been pro- lished on the diets of Hawaiian seabirds, tected since 1911. Because seabird popu- and most of the information that does ex- lation crashes were correlated with fishery ist is fragmentary or anecdotal (e.g., Mun- development in Peru (Schaefer 1970, Idyll ro 1944, Berger 1972). Brown (1975) gave 1973), Southwest Africa (Crawford and quantitative information on the diets of Shelton 1978), and California (Ainley and sooty terns and brown noddies breeding Lewis 1974) it seemed imperative that the on Manana Island (Oahu), and Ashmole feeding ecology of Hawaiian seabirds be and Ashmole (1967~)presented limited documented before fishery development. information on the diet of the red-footed Few integrated studies of the diets of large, booby on Oahu (scientific names of birds complex seabird communities have been are given in Appendix 1). Feeding habits published. The work on 18 species in the of several species may be inferred from Barents Sea (Belopol’skii 1957), 11 species studies on Christmas Island (Pacific Ocean) on Christmas Island (Ashmole and Ash- by Ashmole and Ashmole (1967b) and mole 1967b, Schreiber and Hensley 1976), Schreiber and Hensley (1976). Christmas and 9 species in the North Sea (Pearson Island is 2,000-3,000 km south of the 1968) elucidated the interspecific feeding Hawaiian Archipelago. relationships of colonial nesting birds in Fishery development proposals for spiny those parts of the world. The present study lobsters, carangids, snappers, and live bait was designed to provide an understanding for tuna fishing in the Northwestern of the trophic structure of the unique sea- Hawaiian Islands (NWHI) prompted the bird community in the subtropical NWHI. US. Fish and Wildlife Service and the Results should be useful to both commu- National Marine Fisheries Service to in- nity ecologists and resource managers. vestigate ecological relationships that could When feasible, ancillary food samples be altered by intensive harvest of various were collected in the main Hawaiian Is- target species. Altered food webs could lands. A preliminary report of this work potentially affect seabirds, which are has been published elsewhere (Harrison abundant in this area. The NWHI are the and Hida 1980). HAWAIIANSEABIRD FEEDING ECOLOGY-HU~~~S~~ et a/. 7

Table 1 Maximum recent population estimate (individual birds), Northwestern Hawaiian Islands *

~~

French Pearl and Frigate Hermes Nprlier Shoals Lisianski Reef hlidwd) Kure I3lack-footed albatross 100 ,350 4,iOO 0 67,000 3,500 14,000 30,000 600 I.aysan albatross tr" 1,800 1,600 tr 550,000 8,000 45,000 500,000 2,400 13onin petrel 0 0 750 0 40,000 1,000,000 1,000 10,000 2,500 Bulwrr's petrel 250,000 200 500 tr 20,000 tr tr 0 0 Wedge-tailed shearwater 25,000 4,500 13,000 tr 1,000,000 500,000 26,500 20,000 1,500 Christmas shrarwatrr 800 0 tr 0 10,000 2,000 tr 100 tr Sooty storm-petrel tr 0 tr 0 2,500 0 7,500 0 0 Red-tailed tropicbird 500 200 450 100 4,000 4,500 200 3,000 2,000 hlasked t,oob) 350 500 1,200 800 2,000 1,200 600 20 100 H rd-f oo t et1 booby 3,500 1,400 750 tr 2,500 3,000 2 00 1,000 600 Ihwn booby 225 50 135 20 250 200 200 tr 100 Great frigatebird 10.000 2,000 1,400 250 8,000 2,500 900 200 500 Soot? tern 100,000 ,50,000 250,000 7*50 2,000,000 1,700,000 80,000 50,000 12,000 Gray-backed tern 10,000 7,500 1,7.50 1,000 40,000 15,000 1 ,900 50 100 13lue-gra) noddy 2.500 2,500 tr tr 0 0 0' 0 0 Brown noddy 20.000 50,000 10,000 5,000 30,000 15,000 8,400 3,000 1,200 Black Irotld!, 2,000 1.000 1 1,000 400 5,000 5,000 4,300 5,000 2,000 U'hitr tern 3,000 600 3,700 400 1,500 500 tr 6,000 tr

The species studied were the black- sooty tern, white tern, brown noddy, and footed albatross, Laysan albatross, Bonin black noddy (Alexander 1954) are wide- petrel, Bulwer's petrel, wedge-tailed spread pantropic species. shearwater, Christmas shearwater, sooty Acknowledgments.-We thank the storm-petrel, red-tailed tropicbird, masked many experts who helped us with identi- booby, red-footed booby, brown booby, fications and contributed significantly to great frigatebird, sooty tern, gray-backed the results of this cooperative study. Wil- tern, blue-gray noddy, brown noddy, black liam F. Smith-Vaniz, Academy of Sci- noddy, and white tern. Both albatrosses ences of Philadelphia, identified the De- nest primarily in the NWHI (Palmer capterus group; Izumi Nakamura, Kyoto 1962). Bonin petrels and sooty storm-pe- University, identified billfish juveniles and trels breed in the Volcano Islands in ad- larvae; Richard E. Young, Department of dition to islands in the study area (King Oceanography, University of Hawaii, 1967). Christmas shearwaters, gray-backed identified squids; Thomas E. Bowman, terns, and blue-gray noddies breed at var- Austin B. Williams, and Isabel Perez Far- ious locations in the tropical Pacific (King fante, National Marine Fisheries Service 1967). Bulwer's petrels nest on islands in Systematic Laboratory, Smithsonian Insti- the warmer waters of the Atlantic and Pa- tution, identified crustaceans; Geoffrey cific but not the Indian Ocean (Alexander Moser, National Marine Fisheries Service, 1954). Red-tailed tropicbirds (Fleet 1974) La Jolla Laboratory, identified fish eggs. and wedge-tailed shearwaters (Alexander John E. Randall, Bernice P. Bishop MLI- 1954) nest in the tropical Indo-Pacific but seum, and Bruce B. Collette, National Ma- not the Atlantic Ocean. The boobies (Nel- rine Fisheries Service Systematic Labora- son 1978), great frigatebird (Nelson 1975), tory, U.S. National Museum of Katurd 8 WILDLIFEMONOGRAPHS

History, supplied reprints, identifications, ies Service, was largely responsible for and referrals; Lanna Cheng, Scripps In- making this interagency cooperative study stitution of Oceanography, identified Ha- possible. Shirley Hernandez patiently lobates species; Walter Matsumoto, Na- typed the various drafts of this paper. Da- tional Marine Fisheries Service, Honolulu vid G. Ainley, Bruce B. Collette, A. w. Laboratory, aided in the identification of Diamond, and R. W. Schreiber made larval and juvenile scombrids; John E. valuable comments on earlier drafts of this Fitch (deceased), California Department manuscript. of Fish and Game, identified several myc- tophid otoliths; Frederick H. Berry, Na- THE NORTHWESTERN HAWAIIAN tional Marine Fisheries Service, Miami ISLANDS Laboratory, helped identify Seriola spp.; Tadashi Kubota, Tokai University, fur- The biologically isolated Hawaiian Ar- nished Decapterus specimens; A. Binion chipelago is 4,000 km from the nearest Amerson, Jr., identified ticks; the captain continental land mass and stretches about and crew of the research vessel Townsend 2,600 km from Hawaii to Kure Atoll (Fig. Cromwell provided logistic support of field 1). Each small island between Nihoa and personnel during the sampling program; Kure is associated with a relatively large Sally H. Kuba wrote the computer pro- bank. Nihoa and Necker are remnant vol- grams used in this study; Bernie M. Ito canic cones of 63 and 17 ha, respectively photographed the fishes; Tamotsu Nakata (Clapp et al. 1977, Clapp and Kridler drew figures. 1977). French Frigate Shoals is a coral Many biologists helped with collections atoll consisting of 12 sandy islets and 1 of samples in the field to make this study volcanic pinnacle on a 360-km’, crescent- possible. Eric P. Knudtson, Maura B. shaped lagoon with a total land area of 45 Naughton, and Audrey L. Newman suf- ha (Amerson 1971). Gardner Pinnacles are fered the deprivations of field camp living 2 small volcanic rocks of approximately for months at a time during collecting pe- 1.2 ha (Clapp 1972). Laysan, 20% of which riods on Laysan Island. John B. Andre, is an interior brackish lagoon (Ely and John V. Gravning, Ruth Ittner, Robert P. Clapp 1973),is a coral island of about 370 Schulmeister, and Susan D. Schulmeister ha atop a massive submerged volcanic collected while resident on Tern Island, peak. Lisianski is a low sandy coral island French Frigate Shoals. The following also of 182 ha at the northern end of a 170- helped collect food samples: Stephen I. km’ bank (Clapp and Wirtz 1975). Pearl Apfelbaum, Gordon H. Black, Dylan A. and Hermes Reef is an atoll comprised of Bulseco, Timothy A. Burr, G. Vernon 9 low, coral islands, 4 of which are non- Byrd, Roger B. Clapp, Richard A. Cole- vegetated sand bars. The land mass of 34 man, Mark Collins, Sheila Conant, Cyn- ha is scattered in a 370-km2lagoon (Amer- thia J. Cookinham, Elisabeth C. Cum- son et al. 1974). Midway is a coral atoll mings, Douglas J. Forsell, J. Brent consisting of 2 islands with a total land Giezentanner, Gilbert S. Grant, Brian W. area of 550 ha, the largest in the NWHI Johnson, Patricia A. Johnson, Ernest F. (Gross et al. 1969). Kure is the northern- Kosaka, Catherine E. Ludwig, Gerald M. most coral atoll in the world, and consists Ludwig, James P. Ludwig, L. A. Paloma, of 2 islands with a land area of about 100 Ted N. Pettit, Mark J. Rauzon, Nelson K. ha and a lagoon with an area of 46 km2 Rice, Donald Richardson, Jennifer Rich- (Gross et al. 1969, Woodward 1972). A ardson, Ralph S. Saito, Nelson Santos, more complete description of each island Robert J. Shallenberger, Elizabeth A. may be obtained by consulting the refer- Sheekey, Daniel L. Stoneburner, and Ka- ences cited above. wika H. Woodside. Northeastern trade winds predominate Richard S. Shomura, Director, Hono- throughout most of the year. Surface water lulu Laboratory, National Marine Fisher- temperatures range from 20-25 C from HAWAIIANSEABIRD FEEDING ECOLOGY-HU~T~SO~ et al. 9

~~ November-February and from 25-27.5 C WINTER (NOV-FEB) I I from April-August (Fig. 1). The Hawai- ian Islands are bathed by central North Pacific water that is seasonally displaced --__ I by the California current extension in --_-LISIANSKI I ---..LAySAN 250 ' GARDNER' PINNACLES '' spring and summer (Seckel 1962). Storms __ .-__I 1 \--/--= FREWY FRIGAlE SWLS , NECKER I and associated high winds and swells are NIHW frequent from November-March.

METHODS During the course of this study, we measured several morphological charac- ters of each seabird species, including SUMMER (APR -AUG 1 -... --.25 C-_ weight, bill width, and culmen length. t 1 KURE I Observations of breeding stage of each MIDWAY IS species by field personnel were recorded PEARL 8 HERMES REEF LISIANSKI I I I to determine the breeding chronologies of , LAYSAN I I 250 1 GARONER PNNACLES t each species. /I FREKH FRIGATE SHWLS ( NECKER I // NIHW ---__ \ I Field Collection of Food Samples 275 C wnu ,' a c.. ~200 ' '\-- HAWAII The 4,315 food samples that provide the --._, basis for this paper were collected from I I I 1978-81 on an irregular series of visits to 175-W /' 110. 165' 160' 155. various islands in the study area. Cruises Fig. 1. The Hawaiian Archipelago with winter and summer in August-September 1978, May 1979, and surface isotherms from Armstrong (1973). June 1980 allowed visits to all islands be- tween Nihoa and Kure (Fig. l).Cruises in February-March 1978 included Laysan and March-April 1979. A 1-day visit to and Midway; May 1978 included French French Frigate Shoals occurred in Janu- Frigate Shoals, Laysan, and Lisianski; July ary 1979. Visits to various islands offshore 1978 included French Frigate Shoals, of the windward Oahu coast took place in Laysan, Lisianski, Pearl and Hermes Reef, July 1978, May 1979, November 1979, and Midway; November 1980 included all July 1980, and November 1980. It is the islands except Lisianski and Kure; Janu- nature of work in a study area as remote ary-February 1981 included Laysan and as the NWHI that collecting visits were Nihoa. Visits to Midway occurred during opportunistic and sampling design could the following months: October and No- not be entirely controlled by the investi- vember 1978; January, February, August, gators. September, October, November, and De- We intended to sample food habits of cember 1979; January, March, and April all species on each island during each 1980. Visits to Kure occurred in Novem- 3-month season, but this proved impossi- ber 1979, March 1980, and October 1980. ble because of personnel limitations and Biologists wrre stationed in a field camp the inherent inaccessibility of many is- on Laysan Island (Fig. 1) and collected lands. Nihoa, Necker, Laysan, Lisianski, food samples March-August 1979 and and Pearl and Hermes Reef could be vis- March-August 1980. Biologists manned a ited only on an expedition supported by a field station at Tern Island (French Frig- large vessel. Bad weather precluded land- ate Shoals) and collected samples from July ing on certain islands during scheduled 1979 until December 1980. A biologist on cruises. Furthermore, many species occur Kure obtained samples March-April 1978 only seasonally in the NWHI. For exam- 10 WILDLIFEMONOGRAPHS ple, Laysan and black-footed albatrosses during periods when parents were feed- were present only November-July, sooty ing young. Young of all species readily storm-petrels were present only January- regurgitated when handled, and adults May, and gray-backed terns were present feeding young usually regurgitated when only March-June. Several species have a captured on the colony. The observation limited distribution within the study area. of a parent feeding a nestling was often Blue-gray noddies are found only on 4 is- used to indicate which bird to sample in lands (Table l), and 2 of these (Gardner order to economize effort in the field. Ad- Pinnacles and La Perouse Pinnacle [French ditionally, collections in the late after- Frigate Shoals]) were inaccessible. Conse- noons and early evenings gave samples of quently, sampling of this species was lim- better condition more readily than at oth- ited to Nihoa and ”ecker Islands at times er times of the day. Samples were taken when vessel support was available and at all hours of the day, but efforts were weather conditions permitted making the maximized from 1600-2100 hours. Sam- hazardous landings. ples that were too digested to be identifi- Finally, the presence of birds on an is- able were often discarded in the field. land did not insure that samples could be All pelecaniforms regurgitated readily obtained. Laysan albatrosses present in if they contained food, and empty birds July were mostly fledglings living off fat often regurgitated digestive juice. Terns reserves, whereas those present in Novem- readily regurgitated or dropped (white ber were adults setting up breeding ter- terns) samples for this study. The 7 pro- ritories and establishing pair bonds (Fish- cellariiforms presented the greatest sam- er and Fisher 1969). In both cases, birds pling problems. Adult albatrosses rarely present on the islands appeared to contain regurgitated, but chicks did immediately no food during those months. Courting, if recently fed. Christmas shearwaters and nonfeeding adults of Bonin petrels, red- wedge-tailed shearwaters could be in- tailed tropicbirds, and great frigatebirds duced to regurgitate by holding the birds were also present. Few black noddy food upside down and applying strong enough samples were obtained from Midway or pressure to the abdomen to visibly stress Kure because this species roosted high in the bird. Our initial samples from sooty ironwood trees (Casuarina equisetifolia), storm-petrels, Bulwer’s petrels, and Bonin and live capture was rarely possible. Sim- petrels consisted only of oil or food so di- ilar problems in food collection occurred gested that only gross identification of prey with black noddies on Nihoa and Necker items was possible. Attempts to induce where roosting sites were faces of sheer Bonin petrels to regurgitate by use of cliffs. emetics (e.g., Radke and Fryendall 1974, We generally captured birds alive by Tomback 1975) were unsuccessful. About hand or with a long-handled polypropyl- 100 birds (wedge-tailed shearwaters, Bo- ene fish net (Ashmole and Ashmole 1967b). nin petrels, and Bulwer’s petrels), many of Some populations on some islands were which were empty, were sacrificed at the small (Table l),and killing individuals for onset of the study to provide sample ma- this study was undesirable (Tomback terial. 1973). Each sample was preserved in 10% for- We sampled adults, chicks, and imma- malin. Because isopropyl alcohol was not ture birds. Upon capture, each bird was used as a preservative due to its less desir- turned upside down. If the bird did not able quality of preserving fish for our regurgitate immediately, it was squeezed identification techniques, we could not or shaken. We quickly learned to deter- identify otoliths (Fitch and Brownell mine when a bird in hand was likely to 1968). After failing to get many identifi- produce a food sample using weight, size, able fish specimens from Bonin and Bul- and distention as criteria. We found that wer’s petrels, a few samples were pre- food samples were most easily obtained served in alcohol so that otolith HAWAIIANSEABIRD FEEDING ECOLOGY-HUW~SOTI et d. 11

identification could be made. Field data known, we believe it is important to show recorded include island, species, date, that many squids were consumed. Squid time, age of bird (adult, juvenile, nest- beaks have been enumerated differently ling), sex of bird (if possible), and any ad- by various investigators. Imber (1973) in ditional comments that seemed pertinent. his study of the food of gray-faced petrels counted the number of lower squid beaks. Laboratory Procedures Ashmole and Ashmole (1967b) counted all squid beaks in a sample as 1 squid. Fish The laboratory procedures used in pro- remains and invertebrate remains were cessing the samples of seabird regurgita- enumerated as 1 whenever the actual tions were similar to those used by Ash- number of individuals could not be deter- mole and Ashmole (1967b), Reintjes and mined. Frequently the posterior parts of King (1953), and King and Ikehara (1956). a fish persisted although the head and oto- The methods used by Schreiber and Hen- liths were digested. Swallowing fish head sley (1976) in their study of the diets of 3 first has been recorded by Imber (1973) pelecaniforms on Christmas Island dif- and is an apparent adaptation to prevent fered from ours in that they analyzed only a bird from being impaled by the spines the fresh or slightly digested material. Ad- and rays (Gochfeld 1975). Fish counts ditionally, they both weighed and mea- were based on the number of caudal pe- sured the volume of individual prey items. duncle-hypural fan sections that were We poured each sample into a strainer, present whenever heads were separated rinsed it with running water, and re- from tail sections or when there were moved any objects not considered to be fragments of fishes. food items. Such objects included sand, Volumes were determined by water twigs, leaves, flies, strands of monofila- displacement using a graduated cylinder. ment line, plastic chips, pumice, and sty- The smallest volume used in our analyses rofoam pieces. These items were weighed was 0.1 ml. This presented a problem with for a subset of the albatross samples. The copepods and sea-striders because 0.1 ml densities of such objects are extremely is greater than their true volume. How- variable, and volumes would have been ever, the volumes of most of the tiny prey misleading. items were measured in aggregate so that We frequently found clusters of fish there was no gross distortion of volume. eggs attached to floating objects in sam- Length measurements of prey items ples taken from Laysan and black-footed were made whenever possible. The lengths albatrosses. We removed the clusters and of most fishes were measured from the tip treated the thousands of eggs as a single of the snout to the tip of the hypural fan mass. Prey items were segregated into (standard length). The lengths of marlins major groups and then identified to the and needlefishes (scientific names of fishes lowest taxon possible. are given in Appendix 2) were measured We recorded the number of individuals from the nostril to the tip of the hypural of each taxon. In many instances ne had fan. The accuracy of the measurements to make a decision regarding what to were ranked as grade 1 for precise and count For example, we encountered a grade 2 for slightly estimated. Grade 2 large number of chitinous squid beaks that fish lengths were good measurements “resist attack by the digestive juices in the where only a small part of the fish was stomach for some time after other tissues missing, i.e., the snout or hypural fan. have been digested” (Clarke 1977:92).We Grade 3 fishes had a larger portion of the followed the method of Pinkas et al. (1971) body missing and were rough estimates. and counted either upper or lower beaks, Grade 4 fishes had most of the body miss- using the count with the highest number. ing and the length was estimated. Although the time it took the predator to Mantle lengths were measured for the accumulate all of the squid beaks is un- squids and total lengths for isopods. For 12 WILDLIFEMONOGRAPHS

a

b

C C Fig. 3. Vertebral comparison of Coryphaena equiselis (a), Seriola sp. (b), and Naucrates ductor(c). Fig. 2. Vertebral comparisons for Oecapterus macTosoma (a), D. tab/ (b), and D. sp. (c).

frequency of occurrence and average per- odd-shaped organisms such as medusae cent volume. and wind-sailers, we measured the largest We often found it necessary to assign a diameter. different grade for the length measure- The stage of digestion of prey items was ment than for the stage of digestion for a graded as 1 for fresh, 2 for slightly di- prey item. Very frequently a well-digest- gested, 3 for advanced state of digestion, ed fish had its axial skeleton intact and a and 4 for bone, squid beak, or exoskeleton fairly accurate length measurement could remains. We assigned grade 5 to prey that be obtained. This was recorded as grade was semidehydrated or dehydrated. The 3 for volume but grade 2 for length mea- latter items were always dropped by white surement because the length was reason- terns, which are well-known for carrying ably accurate. We sometimes encountered food to young lengthwise in the bill fresh chunks of fish that appeared to have (Stonehouse 1962). In comparison to our been chopped; these were graded 2 for method, Ashmole and Ashmole (1967b) volume but 4 for length. We considered recorded the fish and squid remains as parasitic isopods (crustacean ectopara- grade 1 for those in good condition whose sites) to be part of the host and processed lengths could be measured accurately, them as such rather than as independent grade 2 for those that were slightly broken prey items. However, when an ectopara- or digested but fairly accurate measure- site occurred alone, it was processed as a ments could be obtained, and grade 3 for food item. Ashmole and Ashmole (19676) items largely digested for which lengths treated the crustacean ectoparasites of fish were estimated. as food items when they occurred in a The mean, minimum, maximum, and sample, stating that some of the prey items standard error for both length and volume in their samples may have come from the have been presented for common items. stomach of a larger prey item but was re- We restricted those analyses to prey items corded as prey of the seabird. We agree in grades 1 and 2, but used all grades for that food consumed by a prey species may HAWAIIANSEABIRD FEEDING EcoLoGY-Harrison et al. 13

L-d I C"

Fig 4 The cleithrums of 2 hatchetfishes

confonnd the of any food study, Fig. 5. Vertebral comparison of a flyingfish (a) and a halfbeak but it was a minor problem here. (b).

Prey Identification pre-zygapophysis of the posterior verte- A wide variety of prey items that in- brae in D. macrosoma, and the high neu- cluded 78 fish species belonging to 56 ral zygapophysis and presence of the first families, 9 groups of crustaceans, and 7 inferior vertebral foramina on the first squid families encountered in various caudal vertebra identifies D. tab1 (R. L. stages of digestion made identification a Humphreys, pers. commun.). The other challenge. Prey items ranged in size from vertebra illustrated represents either D. tiny sea-striders and copepods measuring muroadsi or D. macarellus. We lack D. a few millimeters and displacing <0.1 ml muroadsi specimens that would aid rec- to adult flyingfishes, juvenile tunas, and ognition of vertebral differences between juvenile dolphin-fishes measuring >340 these 2 species. mm and displacing >300 ml. Very often The similar vertebrae of Coryphaena the prey items were so well digested that equiselis, amberjacks, and pilot fish can be only a few loose bones or squid beaks re- distinguished (Fig. 3). In some cases, the mained. A reference collection of fish ax- presence of just a few pieces of flesh and ial skeletons was made during the course a bone such as the cleithrum of the hatch- of the laboratory work to help identify the etfishes could be adequate to identify the fishes. Many fishes could not be identified prey item to family or genus (Fig. 4). The because key identifying characters were shape of spines in the area of the caudal missing and the reference collection was peduncle helped to distinguish flyingfishes inadequate. from halfbeaks (Fig 5). The young of a Fish vertebrae were prepared by re- swordfish (Xiphias gladius) was identified moving the flesh from either the whole using its unique spined scales. Potthoff and fish or 1 side of the fish and subsequently Richards (1970) used adult characteristics staining it with Alizarin S, a water soluble and features of the axial skeleton to aid in bone stain. A weak concentration of stain their identification of scombrids. was used when soaking overnight to bring Squids were identified by use of their out the finer configurations of the zyg- locking mechanisms, pens, and luminous apophysis and other bony parts whereas a organs. Squid beaks were not identified stronger concentration \vas used for quick because there are no reliable keys for Ha- staining to facilitate the counting of ver- waii (R. E. Young, pers. commun.). The tebrae, fin rays, and spines. identification of squids in the Hawaiian The vertebrae of 3 Decapterus spp. are area is still incomplete, and it would take compared in Fig. 2. The haemal post-zyg- a major effort to collect specimens of all apophysis is overlapped by the haemal species and size ranges. Some researchers 14 WILDLIFEMONOGRAPHS

(Imber 1973) have identified squid beaks these 3 subrankings in a single sequence using Clarke’s (1962) key and illustrations. from lowest to highest to produce a final Crustaceans pose less of a problem of ranking for each prey taxon. This ranking identification because of their digestion- method weights each method equally. Our resistant exoskeleton (Reintjes and King method gives equal weight to each sample 1953, Imber 1973). Identification to order by summing the volumetric percentage of usually presented very little problem, but each item and dividing by the sample size further identification depended upon the to arrive at an average percentage vol- condition of the prey item. Copepods were ume. The aggregate total volume method usually identifiable to genus or species be- (Ashmole and Ashmole 1967b) weights cause their exoskeletons remained fairly large-sample volumes more than small- intact. sample volumes, and a 200-ml sample Numerous keys and guides were con- would have twice the weight of a 100-ml sulted to identify the prey items. The most sample. We compared our ranking meth- useful were Wilson (1932), Rose (1933), od for several seabird species with the one Townsley (1953), Gosline and Brock used by Pinkas et al. (1971) and found (1960), Matsumoto (1963, 1967), Stras- only minor differences in rank for highly burg (1964), Nakamura and Kikawa ranked prey items. (1966), Collette et al. (1969), Lindberg and The ranking of prey taxa gives a good Legeza (1969), Lindberg and Krasyukova idea of their relative importance in the (1971), Ovchinnikov (1971), Tinker (1978), diet without excessive attention to an il- and Tyler (1980). lusory sense of precision, which can come, for example, from a strict comparison of Data Analysis numerical or volumetric data. Matthews et al. (1977) stated that the number of taxa The data are presented as numerical from any 1 category of forage items should abundance, volume, and frequency of oc- not be considered quantitatively because currence. The use of these 3 kinds of data of the differences in taxonomic level to is widespread in food studies in the ma- which the prey items were identified. The rine environment, and we agree that each rankings for prey items by families or ma- measures a different yet important aspect jor groups show which are relatively the of prey utilization (Reintjes and King 1953, most important. The list of genera and Waldron and King 1963, Ashmole and species gives an idea of which species are Ashmole 1967b). Reintjes and King (1953) important within the family or group. It stated that each individual method has must be noted that the categories of un- shortcomings but that a prey item that identified fishes and unidentified remains ranks high in number, volume, and fre- rank high because they are a composite of quency of occurrence is important at the unidentified material presumably from time and place sampled. many species, which by necessity have Various combinations of these basic been pooled together. It is unlikely that types of data have been used to achieve a for any seabird “unidentified fishes” re- single ranking of the importance of prey fers to a single species. items because the repetition of each be- We analyzed the data by grouping ad- comes cumbersome in a textual discussion. jacent islands. The Midway Island group We adopted the ranking method used by also included Kure Island and Pearl and Waldron and King (1963) and Ashmole Hermes Reef. The Laysan Island group and Ashmole (1967b) but modified their included Lisianski Island. The French method of calculating volume. We ranked Frigate Shoals group also included Necker prey organisms separately in terms of and Nihoa Islands. For each group, the number, volume, and frequency of occur- data were analyzed using winter (Jan- rence. We then summed and arranged Mar), spring (Apr-Jun), summer (Jul-Sep), HAWAIIANSEABIRD FEEDING ECOLOGY-Hurrison et al. 15

Table 2. Weights and bill measurements of Hawaiian seabirds from this study.

Bill (cm) Wt (RP Culmen SprClCC N i SE Range Months N lengthb SE Width< SE Black-footed albatross 84 2,820 64 2,025-3,800 Apr-Jun 10 10.40 0.12 3.25 0.04 Laysan albatross 87 2,410 31 1,900-3,075 Apr-Jun IO 11.10 0.12 3.26 0.04 Bonin petrel I68 176 1 150-220 Mar-Oct IO 2.61 0.03 1.11 0.02 Bulwer’s petrel 191 99 1 78-130 Apr-Aug 10 2.04 0.04 0.74 0.01 Wedge-tailed shearwatc-r 124 388 3 320-510 May-Aug 10 3.94 0.07 1.19 0.02 Christmas shearwater 99 356 3 280-415 Apr-Aug 10 3.23 0.04 1.01 0.02 Sooty storm-petrel 61 84 1 66-105 Apr-May 20 1.80 0.05 0.93 0.02 Ked-tailed tropicbird 84 624 5 540-750 Apr- Aug 10 6.09 0.07 2.00 0.08 Masked booby 132 2,160 18 ,770-2,800 Apr-Aug 10 11.50 0.09 3.00 0.04 Ked-footed booby 80 1,110 12 905-1,400 Apr-Aug 10 8.38 0.10 2.57 0.04 Brown booby 43 1,340 18 ,050-1,775 Jun-Sep 10 12.47 0.15 3.30 0.03 Great frigatebird 117 1,440 13 ,060-1,950 Apr-Aug 10 10.90 0.20 3.13 0.07 Sooty tern 94 198 3 153-320 Apr-Jul 10 4.68 0.08 0.99 0.02 Gray-backed tern 83 146 1 115-177 Apr- Aug 10 4.26 0.05 1.00 0.02 Brown noddy 99 205 2 153-275 Apr- Aug 10 4.62 0.05 111 0.02 Black noddy 86 108 I 85-133 Apr-Sep 10 4.76 0.08 0.90 0.02 White tern 109 111 1 92-139 May-Sep 20 4.34 0.04 0.79 0.02 Blue-gray noddy 52 53 1 46-65 Juri 30 2.55 0.02 0.81 0.02

a Wrights from Laysan Island except some Bonin petrel weights were from Midway Islands and all blue-gray noddy weights were from Necker and Nihon Islands h Length from tip to angle of gonys Proxinral rid of gon)s

and fall (Oct-Dec). These groupings were tions, however. Four procellariiforms and necessary because we obtained insuffi- the black noddy feed nestlings during cient samples to compare each month and winter. each island. Prey lengths for common prey items Species Accounts were compared using analysis of variance (ANOVA). Means and standard errors The species are treated in order of de- were calculated for weight, bill width, and creasing body weight, following Ashmole culmen length of each seabird species. and Ashmole (1967b). Black-footed Albatross.-We collected RESULTS and analyzed 172 black-footed albatross samples from 1978-80. Most were from Weights and bill measurements (Table Laysan and Midway Islands, but we also 2) indicate that Hawaiian species are sim- collected at Kure and French Frigate ilar to those studied elsewhere. However, Shoals. Samples were collected from Feb- except for the red-tailed tropicbird, each ruary, when chicks hatch, until June, when species, for which a comparison can be young are abandoned by their parents. made with Christmas Island (Ashmole and Obtaining food samples from adult birds Ashmole 1967b:18, Schreiber and Hensley proved to be difficult. Consequently 84% 1976:245), is heavier in the NWHI (Table of the samples were taken from chicks, 2). The significance of this difference bears and the remainder were taken from adults. further study. The samples averaged 96 ml and con- Most seabirds in this community feed tained an average of 15 items. The sam- most of their young during spring and ples generally were in poor condition, even summer (Fig. 6). There are several excep- when obtained from adult birds or chicks 16 FVILDLIFE MONOGRAPHS

MASKED BOOBY~-l

RED-FOOTED BOOBY ~- BROWN BOOBY >--- GREAT FRIGATEBIRD BBBPBB- ~ -~ SOOTY TERN

__ ~~ ~__~~~ GRAY - BACKED TERN - - _____~~~ -~__-- -. BLUE - GRAY NODDY l2zzaBm- - ~ ~___-~ ~~ ~ BROWN NODDY- ______~_~ - BLACK NODDY - - __ - _. WHITE TERN ~- JAN ' FEB MAR ' APR- ' MAY JUN ' JUL ' AUG ' SEP ' OCT ' NOV ' DEC

that had just been fed by an adult return- fishes gives an indication of the poor con- ing from sea. Consequently, identification dition of samples (Table 3).However, it is of prey beyond family level was very dif- probable that most important taxa are in- ficult. cluded in the species list. Squid rank par- Prey consisted of 4 fish families, 3 squid ticularly high due to the frequent occur- families, an octopus, 8 crustacean groups, rence of digestion-resistant beaks (as many and a variety of other objects (Table 3). as 66 in 1 sample). Although Imber (1973) Samples also contained many floating ob- identified squid from their beaks, we made jects, some of which provided a substrate no effort to identify ours because no suit- for flyingfish ova (Table 4).About 10%of able reference collection of beaks exists the volume of black-footed albatross sam- for the NWHI. Flyingfish ova were the ples was stomach oil, a common feature most important prey item by volume of procellariiformes (Imber 1976, War- (44%), and each egg mass was counted as ham et al. 1976). Our laboratory analysis a single prey item. The abundance in the excluded the oil and found prey to be 30% diet of certain large crustaceans was un- fish, 32% squid, and 5%' crustacean by vol- expected, because they are believed to in- ume. Common food items throughout the habit only very deep water. These include sampling period were squid, especially the mysids Gnathophausia gigas and G. Ommastrephidae, and flyingfish ova. The ingens, the isopod Anuropus branchiatus, high ranking of unidentified remains, un- the leptostracan Nehaliopsis typica, and identified crustaceans, and unidentified the shrimp h'otostomus japonicus. HAWAIIANSEABIRD FEEDINGECOLOGY-Harrison et al. 17

Table 3. Prey items identified to lowest taxon in 172 black- Table 3. Continued. footed albatross samples. Prey items were ranked separately in terms of number, volume, and frequency of occurrence. Per- These 3 subrankings were summed and arranged in a single cent of sequence from lowest to highest to achieve the rank reported samplrs here for each prey taxon. No in "$". w:Fh A;g Prey Rank icms curred vol Per- cent of SIIllples INSECTA No in of which Avg Gerridae 15 organ- oc- R Halobates sericeus 5 1.2 10.1 Prey Rank isms curred vol Caterpillar 23.5 1 0.6 <0 1 FISHES COELENTERATA Carangidae 19 Velellidae 16 Decapferus sp. 1 06 03 Velella oelella I 0.6 06 Exocoetidae 2 TUNICATA Exocoetidae (ova) 139 802 442 Unidentified exocoetid 7 41 18 Pyrosomatidae 8.5 15 4.7 05 Gempylidae 19 1 06 03 ALGAE Sternoptychidae 23 5 1 06 01 sp 23.5 1 0.6 ~0.1 Unidentified fishes 6 24 134 30 Sargassum UNIDENTIFIED REMAINS 3 51 29.7 11.1 SEABIRDS 13 Pufinus sp. 1 0.6 0.1 UNIDENTIFIED MEAT 3 1.7 0.9 P. pacificus 1 0.6 0.2 Pterodroma hypoleuca 1 0.6 0.1 MOLLUSCA Decapoda Measured lengths of intact prey ranged Ommastrephidae 4 S ymplectoteuthis from a 4-mm sea-strider to a 300-mm am- oualaniensis 1 06 02 phipod, the latter probably being the larg- Hyaloteuthis pelagicus 1 06 <01 Unidentified est known (Barnard and Bowman, pers. ommastrephid 47 105 32 commun.). Most length measurements Cranchiidae 23 5 1 06 101 were ommastrephid squids (n = 74 mm, Octopoteut hidae 19 1 06 03 Unidentified squid 1 2182 919 281 Table 5). Some crustaceans were longer Octopoda 17 2 06 02 than the squids. G. gigas and A. bran- CHUSTACEA chiatus averaged 112 and 106 mm, re- Mysidacea 7 spectively. Length data of prey of this Gnathophausia spp. 5 23 01 species must be interpreted with some G. gigas 6 35 09 G. ingens 1 06 <01 caution. They often feed in groups and Unidentified mysid 4 23 01 have strong bills capable of ripping and Euphausiacea 23 5 1 06 <01 Amphipoda 12 tearing flesh. It is probable that many of Alicella sp 1 06 04 the squid fragments occurring in the sam- Unidentified amphipod 2 12 01 ples were not taken whole but were shred- Isopoda 10 Anuropus sp I 06 01 ded from individuals much larger than A. branchiafus 3 17 08 those that we were able to measure or that Parasitic isopod I 06 <01 an albatross could swallow whole. Squid Unidentified isopod I 06 101 Nebaliacea 23 5 arms of at least 200 mm were found next Nehaliopsis typica 1 06 101 to albatross nests on Midway and Laysan Copepoda 11 Penella spp. 17 17 01 Islands, apparently too large for the young Shrimp 85 to swallow. The mantles from such indi- Oplophoridae viduals were certainly much larger than Notosfomus spp 2 12 X0.l N japonicus 2 1.2 0.1 120 mm, the largest ommastrephid squid Unidmtifird oplophorid 1 06 <01 that we measured (Table 5).Flyingfish ova Pasiphaeidae 3 1.7 0.1 clusters averaged 86 ml and appeared to Unidentified shrimp 5 2.9 03 Crab 14 be relatively fresh, perhaps indicating a Brachyura 6 2.3 <0 1 resistance to digestion. The largest egg Grapsidar mass displaced 301 ml and weighed 314 Planes cyaneus 1 0.6 <0.1 Unidentified crustacean 5 39 22 1 1.2 g. We estimated that it contained more than 156,000 ova. Most diameters of in- 18 WILDLIFEMONOGRAPHS

Table 4. Weights and percent of sample by weight of indi- 1940). The black-footed albatross is so re- gestible items in 14 black-footed and 12 Laysan albatrosses: nowned for its habit of following ships and feeding on refuse that Miller (1940) Mean wt of referred to it as the “feathered pig.” indi est Per- ibke rent of Laysan Albatross.-We collected 183 items sample Species (9) SE bywt SE samples from Laysan albatrosses from Black-footed albatross 9.9 1.7 12.2 2.6 1978-80 with samples taken from Laysan, Lavsan albatross 10.6 3.2 14.7 5.2 Midway, Kure, and French Frigate Shoals. Samples were collected February-July a Both species contained squid beaks, squid lens, plastic chips, sty- rofoam, pumice, and monofilament The black-footed albatross also when chicks were being fed by parents. yielded rubber, sponges, and a paper wrapper The Laysan albatross Food samples from adult birds were par- additionally yielded bird bones and a kukui nut (Aleunfes moluccana). ticularly difficult to obtain from this species, and more than 95% of our sam- ples came from chicks. Sample volumes dividual ova were 1.5-1.7 mm, but some averaged 64 ml and contained a mean of were as large as 2.3 mm. 32 items. Samples generally were in an There were few differences in the ma- advanced state of digestion, which limited jor prey items consumed by this predator our ability to identify and measure prey between either winter and spring or items. among any of the 3 island groups of the We identified 9 fish families, 6 squid NWHI. During winter and spring, squid families, a gastropod, 8 groups of crusta- and egg masses of flyingfishes were the ceans, an insect, a coelenterate, and a tu- first and second ranked prey items in each nicate as prey (Table 6). Plastic particles, island group. This order was reversed dur- Styrofoam, and pumice were regularly ob- ing spring in the French Frigate Shoals tained from Laysan albatrosses, but we region, but the number of samples col- kept records of nonfood items from only lected there was relatively low, and we a portion of our samples (Table 4). Ken- attach no importance to this difference. yon and Kridler (1969) also found large These results generally correspond to amounts of indegistible matter, especially anecdotes concerning the feeding habits plastics, in stomachs of Laysan albatrosses. of this species, where it has been reported As with the black-footed albatross, about to feed on flyingfishes (Fisher 1945), 10% by volume consisted of stomach oil shrimps (Anderson 1954), squids, gam- that we ignored in the laboratory analysis. marids, sea urchins (Cottam and Knappen We found the prey to be 9% fish, 65% 1939), fish eggs, sun fish, and algae (Miller squid, 9% crustaceans, and 4% coelenter-

Table 5. Lengths and volumes of some prey items’ of the black-footedalbatross. Length and volume values are not necessarily for the same individuals.

Minimum Maximum Mean SE Sample size Length Vol Length Vol Length Vol Length Vol Prey Length Vol (mm) (ml) (mm) (ml) (mm) (ml) (mm) (ml) FISHES Exocoetidae ova 48 1.4 301 86 10 MOLLUSCA Ommastrephidae 42 36 120 74 3 CRUSTACEA Gnathophausia gigas 3 80 140 112 17 Anuropus branchiatus 3 94 115 106 6 TUNICATA Pyrosomatidae 5 29 72 48 7

Included are prey itrms with sufficient rneasuremrntr in grader 1 and 2 (ser \lethods1 HAWAIIANSEABIRD FEEDING ECOLOGY-Harrison et al. 19

Table 6. Prey items identified to lowest taxon in 183 Laysan Table 6. Continued. albatross samples. See Table 3 for method of calculating rank.

Per- Per- cent of cent of samples samples No in No in of w,hi:h A;g organ- Prey Rank isms curred voI Prey FISHES Shrimp Caridea 2 11 01 Exocoetidae 45 Oplophoridae 3 16 <01 Cypselurus sp. 1 05 05 Notostomus spp. 4 22 02 Exocoetidae (ova) 20 109 36 Acanthephyra sp. 1 05 <01 Unidentified exocoetid 6 27 01 A. exima 1 05 03 Gempylidae 27 1 05 01 Pasiphaeidae 2 11 <01 Gonostomatidae 23 Unidentified shrimp 11 55 03 Vinciguerria spp 6 05 <01 Crab Hemiramphidae 19 Brachyura 3 16 01 Euleptorhamphus viridis 1 05 01 Grapsidae Unidentified hemiramuhid 2 11 <01 Planes cyaneus 11 22 401 Molidae 13 Unidentified crustacean 56 279 28 Ranzania laeois 12 22 09 Unidentified molid 2 11 07 TUNICATA Mullidae 28.5 2 0.5 <0 1 Pyrosomatidae 11 25 44 0.6 hl yctophidae 20 5 2 7 <0.1 INSECTA Scomberesocidae 12 Cololabis saira 13 44 05 Gerridae 28 5 C.saira (ova) 3 I6 <01 Halobates sertceus 2 05 <01 Sternoptychidae 31 COEI.ENTERATA Argyropelecus sp. 1 05 <01 Unidentified fishes 8 24 126 21 Velellidae 6 Velella oelella 668 98 40 MOLLUSCA UNIDENTIFIED REMAINS 3 67 322 108 Decapoda Ommastrephidae 2 Symplectoteuthis spp. 4 11 05 S. oualaniensis 2 11 09 Unidentified ommastrephid 196 268 146 Lepidoteut hidae 18 2 11 09 ates by volume. Squids (especially Om- hlastigoterithidae 26 mastrephidae), flyingfishes, wind-sailers, Mastigoteuthis sp. 1 05 03 Enoplotent hidae 31 and mysids (G. gigas and G. ingens) were Thelidioteuthis the highest ranking prey items (Table 6). alessandrinii 1 0.5 <0.l The ranking of unidentified crustaceans, Onychoteuthidae 21 3 05 03 Histioteuthidae 25 1 0.5 0.4 fishes, and other remains within the top 8 Unidentified squids 1 3,224 82.5 46.6 categories underscores the poor sample Janthinidae 15 condition. Laysan albatrosses very fre- Janthina sp. (ova) 5 2.7 1.8 Unidentified mollusk 22 3 11 0.1 quently ate squid, which occurred in 93% CRUSTACEA of our samples. Flyingfishes (including Mysidacea , ova), the next highest ranked prey, oc- Cnathophausia spp 12 44 10 curred in only 13% of our samples and C. gigas 3 1 1 0.1 C. ingens 7 2.7 0.9 accounted for only 4% of the volume of Unidentified mysid 4 2.2 0.3 the prey (Table 6). By-the-wind sailors Enphausiacea 17 1,415 05 01 ranked below flyingfishes, occurring in Stornatopoda 31 Pserrdosquilla sp 1 05

Table 7. Lengths and volumes of some prey items* of the Laysan albatross. Length and volume values are not necessarily for the same individuals.

Minimum Maximum Mran SE Sample size Length Vol Length Vol Length Vol Length Val Prey Length Vol (mm) (ml) (mml (mll (mm) (ml) (mml (mll FISHES Exocoetidae ova 6 34 195 44 30 MOLLUSCA Ommastrephidae 155 28 144 71 2 Symplectoteuthis spp. 4 77 92 86 3 CRUSTACEA Anuropus branchiatus 7 49 840 187 109 Planes cyaneus 11 8 17 10 1 Amphipoda 7 2 12 0.2 58 0.7 28 0.4 6 0.3 TUNICATA Pvrosomatidae 15 21 80 39 5

a Included are prey items with sufficient measurements In grades I and 2 (see Methods)

Only 229 prey items were sufficiently the Midway region and did not occur dur- intact to measure, and they ranged from ing spring. They occurred sporadically in an 8-mm crab to a 150-mm mysid. Most samples from other regions. Mysids were measurements were of ommastrephid generally found January-June in each of squids, which averaged 71 mm in length the 3 regions but proved to be especially (Table 7). We were unable to obtain length common in the diet of the Laysan alba- or volume data from any fish prey. We tross during this period in the French did measure the volumes of flyingfish ova Frigate Shoals region and during spring at masses that averaged 44 ml. Prey length Midway. data from a species that is known to shred Our results corroborate earlier qualita- its prey before ingestion must be inter- tive reports that this species feeds on squids preted with caution. Squid arms on Lay- (Fisher 1904), shrimps, and fish roe (An- san albatross colonies were found that must derson 1954). Kenyon and Kridler (1969) have come from much larger individuals identified squid beaks from Octopodoteu- than the largest squid (144 mm) that we thidae and Onychoteuthidae in addition were able to measure. Okutani and Ih- to Ommastrephidae. Hsiu (1978) stated that Symplectoteuthis Masked Booby.-We obtained 305 oualaniensis (Ommastrephidae) attains samples from masked boobies from most lengths >460 mm. In addition, some of of the islands within the Hawaiian Archi- the large beaks that we found probably pelago but predominantly from French came from very large squids. Frigate Shoals, Laysan, and Kure. Sam- Our rankings of prey items of the Lay- ples were collected March-November. san albatross showed only minor variation Samples were obtained easily from adults among island groups or seasons. In all 3 (76%),subadults (7%),and nestlings (16%). regions, unidentified or ommastrephid Pooling all samples collected 1978-80, the squids were the highest ranked prey dur- mean volume was 167 ml, and there was ing both winter and spring. Wind-sailers a mean 2.5 prey items/sample. Samples ranked high in the Midway region during from masked boobies generally were in spring but not winter Qnd in the Laysan good condition. More than 97% of the region during winter but not spring. This fishes from these samples were identified prey item did not occur in the French to family and more than 65% to genus or Frigate Shoals region. Pacific sauries were species. consumed both as fish and as egg masses. Fish constituted over 97%of the sample They ranked high only during winter in volumes with squid comprising the re- HAWAIIANSEABIRD FEEDING ECOLOGY-Harrison et al. 21

Table 8. Prey items identified to lowest taxon in 305 masked booby samples. See Table 3 for method of calculating rank.

~~ ~- Per- cent of sam- ples No in in of which Avg organ- w- 5% Prey Rank Isms curred vol Fig. 7. Decapterus sp.. a prey item FISHES Relonidae 11 Platybelone argalus pia t yura 3 07 01 mainder. Fifteen fish families and a single Ablennes hians 1 03 <01 Unidentified belonid 1 03 <01 family of squid were identified. Flying- Carangidae L fishes ranked highest among the prey Decapterus spp. 126 25.6 22.7 D. macarellus 10 2.0 1.7 items, followed by jacks, halfbeaks, squids D macrosoma 71 62 4.6 (Ommastrephidae), and dolphin-fishes Cirrhitidae 18.5 (Table 8). Many of the flyingfishes were Cirrhitops fusciutus 1 0.3 Exocoetus volitans 45 62 37 (Fig. 2). All of the halfbeaks identified Cypselurus spp. 89 262 227 were Euleptorhamphus viridis. Some of C. speculiger 6 20 08 the squids were identified as S. oualanien- C. atrisignis 1 03 03 Unidentified exocoetid 202 439 295 sis and Hyaloteuthis pelagicus. All of the Gempylidae 14 dolphin-fishes were genus Coryphaena Cempylus serpens 3 1.0 10.1 with preponderance being Herniramphidae 3.5 the C. equiselis Euleptorhamphus viridis 31 72 27 rather than C. hippurus. Unidentified hemiramphid 4 07 01 Length measurements were taken for lstiophoridae 13 Tetrapterus angustirostris 1 03 c01 193 prey items and ranged from a 29-mm Unidentified istiophorid 1 03 <01 hawk fish to a 343-mm flyingfish. The Kyphosidae 9 mean for all measured prey was 161 mm. Kyphosus bigibbus 6 13 06 Mullidae 10 10 13 01 The fishes with the longest mean lengths Nonieidae 12 were E. viridis (276 mm), Cypselurus spp. Psenes cyanophrys 3 07 01 (231 mm), and D. macarellus (207 mm) Pomacentridae 15 1 03 03 Sconiberesocidae 16 (Table 9). The lengths of ommastrephid Cololahis sum 2 03 01 squids averaged 90 mm. The few dis- Scornbridae Auxis thazard 2 07 07 placement volumes of prey that we mea- Katsuwonus pefanus 6 I6 15 sured averaged 51 ml and ranged from Unidentified fishes 6 18 59 08 0.7 to 220 ml. MOLLUSCA The families of prey items that ranked Drcapoda high when all data were combined (Table Ommastrephidae 35 Syniplectoteuthis spp h 13 02 8) remained high when the data were sep- S. oualaniensis 4 07 01 arated into seasons and island groups. Hvuloteuthis .welapicus ., 2 03

Table 9. Lengths and volumes of some prey items' of the masked booby. Length and volume values are not necessarily for the same individuals.

Minimum Maximum Mean SE Sample size Length Vol Length Vol Length Vol Length Vol Prey Length Vol (mm) (mi) (mm) (ml) (mm) (ml) (mm) (ml) FISHES Decapterus macarellus 82 185 132 224 139 207 136 54 D. macrosoma 8 66 165 133 14 Decapterus spp. 29 1 66 220 240 220 195 220 6 Parexocoetus brachypterus 11 5 125 34 153 44 136 37 32 Exocoetus volitans 30 3 95 32 184 56 144 47 48 Cypselurus spp. 22 2 134 90 343 102 231 96 13 6 Euleptorhamphus viridis 91 169 53 301 53 267 53 14 MOLLUSCA Ommastrephidae 35 4 46 8 1,280 18 90 12 32 Symplectoteuthis spp. 61 73 13 100 13 88 13 4

a Included are prq items with sufficient measurements in grades 1 and 2 (see Methods) higher throughout the year in the French flyingfishes (Fig. 8). Most were too digest- Frigate Shoals region than elsewhere, and ed to permit identification but Cypselurus were common in the Laysan and Midway spp., Exocoetus volitans, and Parexocoe- regions only during spring. Pacific sauries tus brachypterus were the most common ranked third during winter in the Midway (Table 10) of those identified. The second Island group. Large flyingfishes and De- ranked item was ommastrephid squids. Of capterus spp. dominated the diet of this the few that could be identified, all were booby throughout the seasons and areas Symplectoteuthis, including S. oualan- studied, but some changes in order of iensis and S. luminosa. Ranking third was ranking are evident. Carangidae, mostly Decapterus, especial- The diet of this species in Hawaii is ly D. macrosoma. D. macarellus was also similar to that reported from Christmas identified but is presented in Table 10 as Island (Pacific Ocean) (Schreiber and D. spp. until the vertebrae of this species Hensley 1976) and Ascension Island can be distinguished from D. muroadsi. (Stonehouse 1962, Dorward 1963~).How- Other highly ranked prey items included ever, the diet in Hawaii is unique in the unidentified squids, a filefish (Pervagor importance of Decapterus spp. spilosoma), and halfbeaks. We found few Great Frigatebird.-We collected and sooty terns, but B. Flint (pers. commun.) analyzed 284 regurgitations from great observed hundreds taken during 1980-81 frigatebirds, primarily from Midway, at Tern Island, French Frigate Shoals. Laysan, and French Frigate Shoals. We We obtained lengths from 248 prey obtained samples during all months ex- items. They averaged 83 mrn and ranged cept December and January when 1978- from a 12-mm cow fish to a 272-mm half- 80 are combined. Adults (37%), subadults beak. The flyingfishes E. volitans and P. (17%),and nestlings (45%) were sampled. brachypterus averaged 141 and 135 mm, The samples averaged 104 ml and 4.5 prey respectively (Table 11).Symplectoteuthis items. More than 96% of the fishes were spp. averaged 85 mm. The fact that great identified at least to family. frigatebirds will take cow fish (T = 17 mm) Sample volumes were 85% fish, 14% and filefish (f = 60 mm) in addition to the squid, and 1%juvenile sooty terns. Twen- much larger flyingfishes demonstrates ty-three fish families and a single squid wide flexibility in the size classes of prey family were identified. We found no crus- that may be exploited (Table 11). taceans. The highest ranking prey were Sampling was adequate to allow com- HAWAIIANSEABIRD FEEDING ECOLOGY-Harrison et al. 23

parison among seasons and among the 3 island groups in the NWHI. Flyingfishes ranked very high throughout the year in each island group, usually first or second. ___- YI --- Ommastrephid squids also ranked high &-a throughout the archipelago, but peaked 71 . during spring and were absent from the Midway region during summer. Caran- Fig. 8. Flyingfish, Parexocoetus brachypterus, a prey item. gids were not found in any of 43 samples collected in winter, occurred to a limited degree in spring, but ranked very high in 98% of the fishes being identified to fam- summer and fall, especially at French ily or lower. Frigate Shoals. Dolphin-fishes were very Fish made up 95% of the sample vol- important in the Midway region during umes, and virtually all of the remainder summer but occurred rarely elsewhere. was squid. Eighteen fish families, a single Halfbeaks ranked fairly high throughout squid family, and an isopod were identi- the archipelago, apparently ranking high- fied. The highest ranking family was Ca- est February-June. Pacific sauries ranked rangidae. Most of the fishes from this fam- high during winter in the Midway region, ily were Decapterus, especially D. and filefish ranked high during summer macrosoma, but large numbers of amber- in the Laysan region. Neither of these jacks and fair numbers of pilot fish, Selar fishes occurred in other regions, nor in crumenophthalmus, and Caranx spp. other seasons within the region where they were found (Table 12).Ranking next were were found. This demonstrates the ability flyingfishes and juvenile goatfishes. No at- of the great frigatebird to locally exploit tempt was made to further identify any whatever prey is available, which is usu- of the goatfishes, but 7 species of flying- ally flyingfishes and squids. fishes were identified. Ranking highest The reliance of this species on flying- were E. volitans and P. brachypterus with fishes and squids has also been reported at Cypselurus spp. following very closely. Ascension Island (Stonehouse 1962), Al- Halfbeaks (especially E. viridis) and om- dabra Atoll (Diamond 1974a), and Christ- mastrephid squids (especially Ommas- mas Island (Schreiber and Hensley 1976). trephes spp. and Symplectoteuthis spp.) Great frigatebirds in Hawaii consume ranked next. more Decapterus spp. than other areas The generally good condition of the studied and may feed on fewer juvenile samples allowed length measurement of sooty terns (Beard 1939, Schreiber and 463 prey items. These items had a mean Hensley 1976) than they do elsewhere. of 94 mm and ranged from a 3-mm iso- Brown Booby.-We collected 244 re- pod to a 319-mm halfbeak. The mean gurgitations from brown boobies, primar- lengths of some common prey items in- ily from Laysan and Kure, but including clude D. macrosoma (158 mm), goatfishes samples from Lisianski, Pearl and Hermes (54 mm), E. volitans (128 mm), rudder- Reef, Oahu, and Nihoa. We combined fish (81 mm), and Ommastrephidae (81 samples collected 1978-80, including ma- mm) (Table 13). Brown boobies exploit terial from each month March-Novem- prey over a fairly wide range of lengths. ber. Samples were readily obtained from Few prey items were considered intact adults (22%),juveniles (8%),and nestlings enough to warrant the measurement of (69%).Brown boobies often spontaneously displacement volumes. The volumes we regurgitate upon seeing a human intruder obtained averaged 25 ml, ranging from a in their colony. The samples averaged 100 2-ml squid to a 68-ml halfbeak (Table 13). ml and 12 prey items. The condition of An analysis of seasonal and geographi- samples from this species were aniong the cal differences in this diet suffers from the best in this study, resulting in greater than fact that it was not feasible to collect sam- 24 WILDLIFEMONOGRAPHS

Table 10. Prey items identified to lowest taxon in 284 great Table 10. Continued. fngatebird samples. See Table 3 for method of calculating rank. Per- Per- Cent of cent of sam- sam- ples PI= No. in No. In of which Avg of which Avg Rank organ-isms curredoc- VOI% organ- oc- % Prey Prey Rank isms curred VOI Thunnus alalunza 1 0.4 0.1 FISHES Unidentified scornbrid I 0.4 0.1 Atherinidae 20 Tetracdontidae 13 Pranesus insularum 8 04 01 Lagocephalus Balistidae 26 1 04 <01 lagocephalus 3 11 06 Bramidae 26 Unidentified tetracdontid 1 0.4 0.1 Brama orcini I 04 101 Xiphiidae 26 Carangidae 3 Xiphias gladius I 0.4 0.1 Decapterus spp. 40 70 33 Unidentified fishes 7 32 11.3 1.9 D. macrosoma 74 81 51 D. tab1 11 14 06 SEABIRDS Selar crumenophthalmus 1 04 <01 Sterna fuscata 15 2 07 07 Coryphaenidae 8 MOLLUSCA Coryphaena spp. 4 11 05 C. hippurus 4 14 08 Decapoda Ommastrephidae L C. equiselis 4 14 05 14 32 09 Dactylopteridae 26 Symplectoteuthis spp. 4 14 03 Dactyloptena orientalis 1 04 <01 S. oualaniensis S luminosa 2 04 01 Exocoetidae 1 Parexocoetus Unidentified 209 236 107 brach ypterus 15 11 09 ommastrephid Unidentified squids 5 73116 16 Exocoetus wlitans 35 74 44 Cypselurus spp 51 137 117 UNIDENTIFIED REMAINS 14 3 11 02 C.speculiger 1 04 02 UNIDENTIFIED MEAT 1 04 04 C. simus 1 04 04 C. spilopterus I 04 04 Unidentified exocoetid 346 61 6 425 Gempylidae 21 Gempylus serpens 2 07

Table 11. Lengths and volumes Of some prey items. of the great frigatebird. Length and volume values are not necessarily for the same individuals.

~ ~ ~~ Minimum Maximum Mean SE Sample sue Length Vol Length Vol Length Vol Length Vol Prey Length Vol (mm) (ml) (mm) (ml) (mm) (ml) (mm) (ml) FISHES Decapterus macrosoma 3 147 160 153 4 Pervagor spilosoma 22 42 71 60 1 Parerocoetus brachypterus 11 129 141 135 1 Exocoetus oolitans 20 1 107 54 165 54 141 54 4 Lactoria fornasini 42 12 22 17 <0.5 MOLLUSCA Ommastrephidae 103 1 42 25 118 25 78 25 2 Symplectoteuthis spp. 9 64 105 85 5

1 Included are prey items with sufiicient measurements in grades 1 and 2 (see Methods) percentage total volume in the Midway 73 ml and 5.8 prey items. The condition group, being first during winter (36%)and of the samples was reasonably good, and summer (53%)but fourth during spring more than 97% of the fishes were identi- (13%) and fall (10%).Ommastrephid fied at least to family. squids ranked high only during spring and Fish accounted for more than 72% of summer. Needlefishes (fall) and rudder- the sample volumes with squid represent- fish (winter) ranked high at Midway. This ing most of the remaining 27%. Twenty- analysis demonstrates that overall patterns seven fish families, 1 squid family, a co- are relatively constant, but some subtle pepod, and an insect were found. Pooling changes in diet take place. all years, areas, and seasons, flyingfishes The diet of brown boobies in Hawaii is ranked highest among the prey. Most of distinguished from diets elsewhere in the these fishes could not be identified fur- prevalence of Decapterus spp. and goat- ther, but of those identified, E. volitans, fishes. The brown booby apparently P. brachypterus, and Cypselurus spp. were changes its diet greatly with location. common (Table 14). Ommastrephid squids Murphy (1936:859) mentioned the con- ranked second and included Ommas- sumption of flatfishes, parrot fishes, and trephes spp., Hyaloteuthis pelagicus, S. large prawns. Serventy (1952) listed Ras- oualaniensis, and S. luminosa. Carangi- trelliger kanagurta, Trachurus, and dae ranked third and consisted mostly of Chorinemus lysan as prey in the Sahul Decapterus spp., especially D. macroso- Shelf, Australia. Dorward (1963~)stated ma and D. tabl. Unidentified squids it fed on blennies at Ascension Island. ranked fourth, followed by juvenile goat- However, most authors have found flying- fishes and Pacific sauries (Table 14). fishes to be an important component of We obtained 550 measurements of prey the diet. items with a mean length of 88 mm and Red-footed Booby.-We collected and ranging from a 32-mm balloon fish to a analyzed 369 samples from red-footed 282-mm halfbeak. These data show that boobies from 1978-80. Most were taken red-footed boobies take prey with mean from Midway, Laysan, and French Frig- lengths 50-150 mm, including Decapte- ate Shoals, but some were collected on rus spp. (149 mm), E. volitans (126 mm), each island in the study area with the ex- and S. oualaniensis (82 mm) (Table 15). ception of Pearl and Hermes Reef. Sam- The red-footed booby had fairly wide ples came from all months except Decem- flexibility in the size of prey it consumed. ber and included adults (79%),subadults We had only 41 prey items in good enough (I%),and nestlings (20%).They averaged condition to be measured volumetrically. 26 WILDLIFEMONOGRAPHS

Table 12. Prey items identified to lowest taxon in 244 brown Table 12. Continued. booby samples. See Table 3 for method of calculating rank.

~ Per- Per- cent of cent of ram- sam- pies pier No in No in of which Avg of which Avg organ- oc- I organ- m- 9% Prev Rank isms curred YOI Rank isms curred "01 Scomberesocidae 18.5 FISHES Cololabis saira 4 0.4 0.3 Arnmodytidae 13 Scornbridae 10 Bleekeria gillii 20 12 0.3 Scornber japonicus 2 0.8 0.7 Atherinidae 15 Katsuwonus pelamis 8 2.9 1.4 Pranesus insularum 12 0.4 03 Acanthocybium solandri 3 0.8 0.4 Belonidae 6 Unidentified scornbrid 1 0.4 0.1 Platybelone argalus Sphyraenidae 21 plat yura 50 82 44 Sphyraena helleri 1 04 0.2 Ablennes hians 4 16 01 Unidentified fishes 8 46 17.6 2.3 Blenniidae I4 5 01 04 MOLLUSCA Carangidae 1 Decapterus spp. 145 238 138 Decapoda D. macarellus 8 16 05 Ornmastrephidae 5 D. macrosoma 99 119 72 Ommastrephes spp. 3 08 03 D. tab1 16 45 13 Symplecfoteuthis spp. 2 08 01 Selar crumenophthalmus 5 08 05 S oualaniensis 1 04 01 Naucrates ductor 14 02 02 S. luminosa 1 04 01 Seriola spp. 53 82 35 Unidentified Caranx spp. 9 08 01 ornmastrephid 61 127 37 Unidentifird carangid 13 20 01 Unidentified squids 9 35 61 05 Coryphaenidae 12 CRUSTACEA Coryphaena spp 2 04 02 lsopoda 22 1 04 01 C. hippurus 3 08 <01 C. equiselis 8 16 05 Echeneidae 18.5 Remoropsis brachypterus 2 08 01 Unidentified echeneid I 04 <01 Exiicoetidae 2 5 These items ranged from 0.6 to 129 ml, Parexocoetus averaging 26 ml. brach ypterus 22 29 19 Sampling was generally adequate to Exocoetrrs sp. 1 04 04 E. volitans 56 94 49 compare the most common prey items for Prognichthys gilberti 8 08 05 all seasons in all of the island groups of Cypselurus spp 24 70 54 C. speculiger 4 12 04 the NWHI. Flyingfishes ranked first or C. spilonotopterus 1 04 04 second in almost all seasons for all regions. C atrisignw 5 08 04 Ommastrephid squids also ranked high in Unidentified exocoetid 104 242 11 5 Grmpylidae 17 each season and area sampled, but were Cenipylus serpens 3 12 <01 apparently most important in the French Unidentified gempylid 1 04 01 Frigate Shoals region. Carangids ranked Hemirarnphidae 4 Euleptorhaniphus vrridis 53131 75 highest during summer but were present Nyporhamphus acutus in the species lists for most areas through- pacificus 2 04 01 Oxyporhaniphus out the year. Goatfishes were present at micropterus 1 04 02 low levels throughout the year but ranked Unidentified hemiramphid 75 45 19 highest in the diet of the red-footed booby K)phosidae 7 Kyphosus bigihbua 68 90 36 during spring. Several fishes were com- Labridae 16 mon only during a single season. At Mid- Hemipterouotus leclrrsei 4 01 04 way, Pacific sauries ranked second in win- Mullidar 2.5 1,852 300 15 3 Noniridae I1 ter and anchovies ranked third in fall. Nomeus gronotrii 3 12 01 Neither occurred elsewhere during any Psenes cyanophrys 11 20 06 Unidentified norneid 9 Ih 01 season, nor was found in the diet of this I'riacarr thidae 20 booby during other seasons at Midway. Priacanthus sp I 01 01 Skipjack tunas ranked high only in fall at Unidentified priacanthid 2 04 01 Midway and French Frigate Shoals. Snake HAWAIIANSEABIRD FEEDINGECOLOGY- Harrison et al. 27

Table 13. Lengths and volumes of some prey items. of the brown booby. Length and volume values are not necessarily for the same individuals.

~ ~~ ~ Minimum Maximum Mean SE Sample size Length Val Length Vol Length Val Length Vol Length Val (mm) (ml) (mm) (mll (mm) (ml) (mm) (ml)

~ ~~ FISHES Seriola spp. 27 5 49 6 165 41 100 31 6 6 Decapterus spp. 19 3 63 4 215 24 146.3 11 12 6 D. macrosoma 12 1 110 67 200 67 158 67 7 Mullidae 164 2 37 2 83 2 54 2 <0.5 0 Exocoetidae 11 31 219 115 17 Parexocoetus brachypterus 15 1 129 27 146 27 137 27 1 Exocoetus volitans 32 107 179 128 3 Cypselurus spp. 11 117 234 166 12 Euleptorhamphus oiridis 9 191 319 281 13 Kyphosus bigibbus 24 1 4i 9 170 9 72 96 Psenes cyanophrys 8 51 128 81 10 Cololabis saira 3 218 233 223 5 Platybelone argalus platyura 5 205 248 231 8 MOLLUSCA Ommastrephidae 48 6 41 2 129 50 81 37 4 7

a Included are prey items with sufficient measurements in grades 1 and 2 (see Methods).

mackerels ranked fourth at Laysan during fish families, 2 squid families, stomato- winter. These changes in relative abun- pods, and shrimps (Table 16). Prey items dance of dietary components implies some were 82% fish and 18% squid by volume, differences of availability within a fairly and a few crustaceans. Flyingfishes were constant framework. the most prominent prey. Seventy-eight Our results correspond generally with percent of these could not be identified previous studies that indicate the preva- further, but E. volitans and Cypselurus lence of flyingfishes and ommastrephid spp. were common among those identi- squids in the diet of this species at Oahu, fied. Ommastrephid squids ranked second Hawaii (Ashmole and Ashmole 1967a), and were primarily S. oualaniensis, Om- South America (Murphy 1936:869), Al- mastrephes spp., and Hyaloteuthis pelag- dabra Atoll (Diamond 1974b), and Christ- icus. The third ranked prey were the ca- mas Island (Pacific) (Schreiber and Hens- rangids, mostly Decapterus macrosoma. ley 1976). The diet of Hawaiian birds is Ranking fourth and fifth were unidenti- unique because carangids, goatfishes, and fied squids and dolphin-fishes, respective- Pacific sauries are common components. ly (Fig. 9). The latter were Coryphaena Red-tailed Tropicbird.-We collected and included more C. equiselis than C. and analyzed 270 samples from red-tailed hippurus. Other common prey items were tropicbirds. Most were taken from French truncated sunfish and balloonfish. Frigate Shoals, Laysan, and Midway, with We obtained 169 prey items that were others coming from Lisianski, Nihoa, and in good enough condition to measure. Kure. By pooling all samples together from Their mean length was 101 mm and 1978-80, samples representing each month ranged from a 10-mm stomatopod to a except January were collected. Samples 237-mm balloonfish. Decapterus spp. had were taken from adults (28%),subadults a mean length of 168 mm and squids (12%),and chicks (60%).They contained ranged 70-90 mm (Table 17). One flying- an average of 57 ml and 4 prey items. The fish was only 13 mm. condition of the samples was fairly good, The distribution of our sarnpling effort allowing for identification to family of limits comparisons we can make among more than 90% of the fishes. island groups and anlong seasons because The prey of this species consisted of 24 most samples were collected during spring 28 WILDLIFEMONOGRAPHS

Table 14. Prey items identified to lowest taxon in 360 red- Table 14. Continued footed booby samples. See Table 3 for method of calculating rank. Per- cent of sam- Per- ples cent of No in sam- of which Avg ples organ- oc- R No I" PW? Rank isms curred YOI of which Avg organ- oc- 9% Prey Rank isms curred voI Nomeidae 14 5 Psenes cyanophrys 4 03 01 FISHES Unidentified nomeid 10 11 01 Ammodytidae 12 Priacanthidae 20 2 06 01 Bleekeria gillii 59 33 03 Scomberesocidae 5 Belonidae 24 Cololabis saira 59 64 43 Ablennes hians 1 03 02 Scornbridae 8 Carangidar 3 Katsu won us pelamis 19 44 25 Decupterus spp 124 139 65 Thunnus sp. 1 03 03 D. macurellus 1 03 03 Unidentified scornbrid 3 08 03 D. niacrosoma 67 50 26 Sphyraenidae 30 1 03 <01 D tab1 32 22 08 Synodontidar 21 3 08 <01 Seriola sp I 03 01 Tetraodontidae 30 Unidentified carangid 6 08 01 Lagocephalus lagocephalus 1 03 101 Cheilodactylidar 00 Unidentified fishes i 39 106 11 Cheiloduct ylus vittatus 1 03 <01 MOLLL'SCA Coryphaenidae 11.5 Coryphaena spp 2 06 <01 Decapoda C. hippurus 3 08 01 Onimastrrphidae 2 C. equiselis 3 06 c01 Ommastrephes spp. 9 08 03 Diodontidar 30 1 03 <01 Symplectoteuthis spp. 41 83 19 Engraulidar 10 S ouulaniensis 57 72 32 Stolephorus buccaneeri 131 28 07 S. luminosa 11 08 05 Exocoetidae I Hyuloteuthis pelagicus 16 19 03 Parexocoetus Unidentified brachypterus 22 33 23 ommastrephid 508 375 190 Exocoetus volitans 59 94 47 Unidentified squids 4 130 142 20 Cypselurus spp. 38 100 7 1 CRITSTACEA C speculiger 7 17 11 Copepoda 25 5 C. atristgnis 1 03 01 Prnnellidae C spilopterus 3 11 07 03 <01 Unidentified rxiic(irtid 319 503 294 Penclla spp. 2 Gempylidar 11 INSECTA 30 1 03 <01 Genipylrrs serpens 32 58 05 CNIDENTIFIED REMAINS 17 3 08 02 Ilnidentified grmpylid 1 03 101 Gonorhynchidar 18 Gonorhynchus gonorh ynchua 7 06 01 Goriostomatidae 16 or summer. Flyingfishes ranked highest at Vinciguerria spp 2 0.3 c0.1 most locations for all seasons in which V. nimbaria 33 0 3 0 1 tlemiramphidar 9 sampling was possible. Ommastrephid Euleptorhamphus uiridis 11 3.1 1.1 squids also ranked high throughout the Oxyporharnphris micropierus 10 1.7 0.8 year but were apparently more so during L'iiideritifird hemiramphid 2 0.6 0.2 spring than during summer. Decapterus €~oli~crntridae 22 5 spp. were common during summer but not Sargocentron sp 1 0.3

Table 15. Lengths and volumes of some prey items' of the red-footed booby. Length and volume values are not necessarily for the same individuals.

~ ~ hlinimum Maximum Mean SE Sample size Length Vol Length Val Length Vol Length Vol Prey Length Vol (mm) (ml) (mm) (ml) (mm) (ml) (mm) (ml) FISHES Decapterus tabl 8 62 177 97 16 Decapterus spp. 9 83 214 149 13 D. macrosoma 4 147 173 163 5 Stolephorus buccaneeri 45 57 83 69 1 Oxyporhamphus micropterus 8 5 111 12 180 38 141 25 8 5 Parexocoetus brachypterus 10 3 113 19 142 33 131 27 3 4 Exocoetus volitans 36 3 76 16 208 26 126 21 5 3 Mullidae 3 54 60 58 2 MOLLUSCA Ornrnastrephidae 256 17 40 6 208 43 78 24 1 2 Symplectoteuthis spp. 32 1 08 13 117 13 70 13 3 S. oualaniensis 45 3 54 12 131 26 82 21 2 5 Hyaloteuthis pelagicus 14 49 110 60 4

a lncludrd arr prey items with sufficient measurements in grades I and 2 (ser Methods)

160 mm flyingfishes and Decapterus spp. 8.4 prey items. More than 96% of the fish- and 70-90 mm ommastrephid squids. es could be identified to family, and 51% Flyingfishes (especially Cypselurus spp. could be identified to genus or species. and E. volitans) and squids are known to We found 21 fish families, a squid fam- occur in the diet of this species at Christ- ily, an octopus, a stomatopod, an isopod, mas Island (Indian) (Gibson-Hill 1947), a crab, an insect, and a coelenterate (Ta- Kure (Fleet 1974), Christmas Island (Pa- ble 18). By volume, the prey constituted cific) (Ashmole and Ashmole 1967b), and 66% fish, 28% squid, and 1%crustaceans. Aldabra Atoll (Diamond 1975). The diet As with all procellariiformes, stomach oil of this species in Hawaii is unique in the was regurgitated, but we ignored this prevalence of carangids, dolphin-fishes, component in our laboratory analysis. and sun fish. Pooling all months, years, and locations, Wedge-tailed Shearwater.-During the highest ranked prey was goatfishes 1978-80, we collected 233 samples from (Fig. 10). No attempt was made to further wedge-tailed shearwaters. Collections were identify this family because samples were possible only May-November. This species comprised of juveniles, many of which does not visit its colonies between breed- were very well-digested. The second ing seasons, and courting adults that come ranked prey item was Carangidae, includ- to shore in early spring apparently live off ing Decapterus macrosoma, D. tabl, and fat reserves and have empty stomachs. probably D. macarellus and D. muroadsi. Most of our samples were taken from The third and fourth ranked prey items Oahu, Laysan, and Midway, but some were Ommastrephidae (including S.oual- were taken from each island in our study aniensis) and unidentified squids. It is area except Necker and Lisianski. Many likely that most of the unidentified squids of the samples were in fairly advanced were ommastrephids. Other common prey states of digestion. For this reason 80% of items included filefish, flyingfishes, and the samples were taken from adults and gobies. 20% from dependent young because adults The lengths of the 212 prey items that had less-digested samples. Samples dis- were in good enough condition for reli- placed an average 16 ml and contained able measurement averaged 57 mm, rang-

. ... 30 WILDLIFEMONOGRAPHS

Table 16. Prey items identified to lowest taxon in 270 red- Table 16. Continued tailed tropicbird samples. See Table 3 for method of calculat- ing rank. PW rent of sam- ples No in of which Avg organ- Dc- % .- . Prey Raiik isms curred "01 of whiih A;g organ- or- PW, Rank isms curred vnl Tetraodontidae x ~~ Lagocephalus FISHES lagocephalus 13 4.8 3.2 Ammodytidae 29 Llnidentified tetraodontid 4 1.1 06 Bleekeria gillii 1 04 01 Siphiidae 12 Relonidae 19 Xiphias gladius 7 2.6 1.5 Ablennes hians 1 04 01 Tetrodontoidei (puffer) 25.5 1040.1 Unidentified belonid 1 0.4 0.2 Ilniderrtified fishes A 50 16.7 40 Carangidae 3 MoLl.cISc4 Decapterus spp. 53 159 9.5 D. macrosoma 29 48 36 Decapoda D. tab1 1 0.4 0.1 Ommastrrphidae 2 Naucrates ductor 1 04 04 Onimastrephes sp 1 04 101 Coryphaenidae 5 Symplectoteuthis spp. 20 63 22 Coryphaena spp. 13 4.8 2.9 S. oualaniensis 16 48 24 C. hippurus 9 33 2.4 Hyaloterithis pelagicus 1 04 01 C. equiselis 18 67 39 Unidentified ommastre- Diodontidae 14 phid 139 244 101 Diodon spp. 3 1.1 0.3 On) choteuthidae 18 D. hystrix 1 0.4 0 1 Onychoteuthis spp 2 04 04 Unidentified diodoritid e 0.7 02 Llnidrntifird choteir- Echeneidae 21 thid 1 0.3 <0.1 Remoropsis brachypterus 1 0.4 0.1 I'nidentified squids 4 354 17.4 2.6 Unidentified echeneid 1 0.4 0.1 CR USTACE.4 Exocoetidae I Stornatopoda 24 Parexocoetus Lysiosqrrilla spp. 2 04 <01 brachypterus 3 0.7 05 L~ntdcnt ified stomatopod Exocoetus oolitans 22 74 32 1 04 <01 Shrimp 29 1 04 <01 Cypselurus spp. 20 5 9 3.4 C speculiger 1 0.4 0.3 L'NIDENTIFIED REhlAlNS 29 1 04 <01 C. spilopterus 1 0.4 0.4 I!nidentifird exocoetid I67 396 24 1 Gempylidae 1 :3 Gempylus serpens 8 0.0 0.3 Unidentified gempylid 1 0.4 <0 1 Hemiramphidae 11 ing from a 4-mm sea-strider to a 145-mm Errleptorhamphus uiridis 10 2 6 1.6 Unidentified hemiramphid 5 15 04 D. macrosoma (Table 19). Juvenile goat- Istiophnridae 22 1 0.4 0.4 fishes had a mean length of 54 mm, and Kyphosidae 15 5 Kyphosus bigibbus 4 11 06 ommastrephid squids had a mean length Molidae 7 of 63 mm. Unfortunately, we only had a Ranzania laeois 23 ,5 2 4.3 few Decapterus spp. measurements, but Mast 71 ius lanceola t us 2 07 05 hlonacanthidae 23 2 04 0.1 those we had were in the 80-100 mm hlallidae 17 5 1 5 0.3 range. hl? ctophidae 29 1 04 <01 Our inability to collect samples from Nomeidae 15 5 C.'rrbiceps pauctradiatua I 04 01 several places in the archipelago during Unidentified nonit-id 4 15 02 some seasons precludes a detailed analysis Pomaceritridae 855 10.40.1 Priacanthidar 29 of changes in diet with season and island Priacanthua sp 1 04 <01 group. It is apparent that goatfishes ranked Scmnberescrcidae 9 highest during spring and continued to (hlolalris saira 18 11 11 Scombridae 16 rank high in the Laysan region but not .\UXlS spp 2 07 05 Midway during summer. Ommastrephid Katsuwonus pelaniis 7 26 22 squids ranked high in the Midway region Unidentified scombrid 3 11 07 SI nodoii tidae 20 11 0.1 01 throughout the 3 seasons sampled and ranked first at Oahu during fall. These HAWAIIANSEABIRD FEEDING ECOLOGY-Harrison et ai. 31

u Fig. 9. Dolphin-fish, a prey item. 1 cm

Fig. 10. Goatfish, a prey item. squids also ranked high in the Laysan re- gion during spring but less so during sum- mer. Carangids ranked higher in the Lay- san Island group than Midway, especially an Ocean (Bailey and Bourne 1963) indi- during summer when they constituted 60% cates that squids are consumed by this by volume at Laysan, but they did not species elsewhere. occur in any of the 12 samples from Mid- Christmas Shearwater.-During 1978- way. Lanternfishes ranked high only dur- 80 we collected and analyzed 182 samples ing spring at Midway, and filefishes were from Christmas shearwaters. Most came important only in the Laysan Island group. from Laysan, but some were collected on Wedge-tailed shearwaters fed heavily on each island in the Hawaiian Archipelago ommastfephid squids during fall but sup- with the exceptions of Necker and Oahu. plemented this food source with prey items Because this species does not make land- that were not taken during spring or sum- fall when it is not breeding, our sampling mer. These included anchovies, crabs, and was restricted to March-September. Al- stomatopods in the Midway region and though a few samples were taken from gobies in the Oahu region, neither of nestlings (4%), most (96%) were taken which were taken anywhere during spring from adults. The samples had a mean vol- or summer. This species fed heavily on ume of 15 ml and contained a mean of goatfishes, Decapterus spp., and ommas- 5.4 prey items. This is half the number of trephid squids in the 50-100 mm size class prey items per sample found by Ashmole and took other prey items when available. and Ashmole (1967b). Despite the fairly Fragmentary information from the Indi- digested condition of many of the sam-

Table 17. Lengths and volumes of some prey itemsBof the red-tailed tropicbird. Length and volume values are not necessarily for the same individuals.

~~ ~~ Minimum Maximum Mean SE Sample size ______Length Vol Length Val Length Vol Length Vol Pre, Length Vol (mm) (ml) (mm) (ml) (mm) (ml) (mm) (ml) FISHES Decapterus spp. 6 140 216 168 13 D. macrosoma 5 1 131 65 181 65 153 65 8 Coryphaena hippurus 3 2 111 12 189 78 148 45 23 33 C. equiselis 4 134 183 163 11 Exocoetidae 11 13 201 133 14 Exocoetus volitans 16 2 124 36 159 46 140 41 3 5 Ranzania laevis 5 1 123 34 1-10 34 130 34 4 MOLLUSCA Ornrnastrephidae 58 23 128 82 3 Symplectoteuthis spp. IO 52 120 80 6 S. oualaniensis 14 1 60 32 113 32 90 32 4

~~~~ ~~~ a Included are prq items with sufficient measurements in grades 1 and 2 (see Methods) 32 WILDLIFEMONOGRAPHS

Table 18. Prey items identified to lowest taxon in 233 wedge- Table 18. Continued tailed shearwater samples. See Table 3 for method of calcu- lating rank. Per- cent of Sam- Per- ples cent of No in sam- of which Avg ples organ- OE- ’% No in Prey Rank isms curwd vol of which Avg organ- oc- % Rank isms curred VOI Unidentified ommastre- phid 138 25.8 15.0 FISHES Unidentified squids 4 281 21.5 6.4 Amrnodytidae 30.5 Octopcda 24 2 0.4 04 Bleekeria gillii 1 04 <01 CRUST.4CEA 2 Carangidae Stomatopoda 23 64 133 85 Decapterus spp. Lysiosquilla spp. 5 04 02 D macrosoma 55 146 115 Parasitic isopod 255 2 09 01 D. tab1 19 64 47 Crab 19 5 Selar crumenophthalmus 4 09 02 Brachyrira 1 04 <01 Seriola sp. 1 04 02 Crab inegalopa 19 04 02 Unidentified carangid 2 09 01 Unidentified crustacean 12 24 I3 06 Clupeidae I5 Sardinella marquesensis 7 09 05 INSECTA Chryphaenidae 17 Gerridae 21 Coryphaena sp 1 04 101 Halobates sericeus 3 1.3 0.1 C. equiselis 3 13 02 Dactylopteridae 30.5 COELENTERATA Dactyloptena orientalis 1 04 <01 Scyphozoa 305 1 04 101 Engraulidae 14 UNIDENTIFIED REMAINS 11 15 64 32 Stolephorus buccaneeri 8 09 08 Exocoetidar 8.5 Parexocoetus brachypterus 1 04 04 Unidentified exocoetid 22 77 34 ples, 95% of the fishes could be identified Fistulariidae 30 5 1 04 <01 Gernpylidae 19 5 at least to family. Genipylus serpens 4 13 01 Prey items came from 17 fish families, Gobiidae 7 Pterebot ris 2 squid families, and a crustacean. Ignor- heteropterus 517 26 I4 ing the stomach oil component of the sam- Gonostomatidae 13 ples, we found the prey to be 50%fish and Vinciguerria spp. 38 09 04 Holocentridae 17 6 21 01 48% squid by volume. The highest rank- Kyphosidae 30 5 ing prey item was Ommastrephidae (Ta- Kyphosus bigihhus 1 04 <01 ble 20), including S. oualaniensis and H. Monacanthidae 6 Peroagor spilosonra 13 09 07 pelagicus. Ranking next were goatfishes. Unidentified Flyingfishes ranked third and although monocant hid 33 69 30 Mulhdae 1 521 318 176 few were identified, E. volitans was pres- M yctophidae 8 5 28 47 38 ent. The fourth ranking family was Ca- Norneidae 10 rangidae, consisting entirely of the genus Psenes sp I 04 01 Unidentified nomrid 24 39 15 Decapterus, and included D. macrosoma. Priacanthidae 27 I 04 04 Other common prey families included Scornbridae 17 squirrelfishes and rudderfish (Table 20). Katsuwonus pelamis 4 17 02 Synodont idae 22 4 09 01 We obtained 198 measureable prey Tetraodontidae 25 5 2 09 01 items. The mean prey length was 65 mm, Leptocephalus larvae 30.5 I 04 <01 a Unidentified fishes 5 53 150 58 ranging from a 25-mm squid to 134-mm D. macrosoma. Most measurements were hlOl.I.USCA Decapoda squids, with a mean length of 62 mm for Ornrnastrephidae 3 Ommastrephidae (Table 21). Average Symplectoteuthis spp. 21 64 40 lengths for commonly consumed fishes S. oualaniensis 9 30 25 Hyaloteuthis pelaglcus 1 04 03 ranged from 53 mm (goatfishes) to 126 mm (Decapterus spp.). HAWAIIANSEABIRD FEEDINGECOLOGY-Harrison et al. 33

Table 19. Lengths and volumes of some prey items' of the wedge-tailed sheawater. Length and volume values are not necessarily for the same individuals.

~ ~~ ~~~ Minimum Maximum Mean SE Sample size Length Vol Length Vol Length Vol Length Vol Prey Length Vol (mm) (ml) (mm) (ml) (mm) (ml) (mm) (ml) FISHES hlullidae 41 48 64 54 1 Ptereleotris heteropterus 30 20 22 0.2 30 0.2 28 0.2 <0.5 0 M yctophidae 14 14 80 71 5 MOLLUSCA Ommastrephidae 69 29 115 63 3 Symplectoteuthis spp. 21 39 112 67 4 S. oualaniensis 9 57 100 85 5

a Included are prey items with sufficient measurements in grades 1 and 2 (see Methods)

Sampling was adequate to discuss sea- whereas Christmas Island birds consumed sonal changes only for the Laysan region. many tunas and bristlemouths. Birds at It is apparent that Ommastrephidae was both locations commonly took flyingfishes. the highest ranked prey item in the diet Brown Noddy.-We collected and ana- of the Christmas shearwater in virtually lyzed 354 samples from brown noddies, all island groups and seasons sampled. most coming from Pearl and Hermes Reef, Goatfishes ranked high during winter, Lisianski, Laysan, and French Frigate spring, and summer on Laysan. They Shoals. Some samples were obtained from comprised much more of the prey volume each island in the archipelago. Samples during spring (30%) than summer (6%). were collected March-November with In contrast, flyingfishes were ranked high- many more (84%)coming from adults than est there during summer, climbing from subadults (5%)or nestlings (11%).Pooling 1% by volume in spring to 21% in sum- all samples collected 1978-80, the mean mer. The limited sampling in the Midway volume was 14 ml and contained an av- and French Frigate Shoals regions indi- erage 7.7 prey items/sample. Sample con- cated flyingfishes were eaten whenever dition was relatively good, enabling 97% samples were obtained. Carangids were of the fishes to be identified to family. not present in the Midway samples, but The sample volumes contained 66% fish this may have been due to insufficient and 33% squid. Thirty-three fish families, sampling. In the Laysan region, where 2 squid families, 2 crustacean groups, and sampling was sufficient, carangids were a marine insect were found (Table 22). more important by volume in summer The highest ranking prey was juvenile (25%) than spring (5%). Lizardfishes goatfishes. Ommastrephid squids ranked ranked second in the Laysan area during next and included S. oualaniensis, S. lu- winter, and rudderfish ranked first during minosa, and Ommastrephes spp. Juvenile summer in the Midway region. Christmas lizardfishes ranked third. Carangids, most shearwaters exploited many food sources of which were Decapterus spp., ranked but fed most heavily on ommastrephid fourth. Other common prey families were squids, goatfishes, flyingfishes, and De- flyingfishes (especially E. volitans) and capterus spp. in the 50-100 mm range. snake mackerels. Hawaiian birds consumed less squid We found 460 measureable prey items. (48% vs. 71%, by volume) than shear- They averaged 48 mm and ranged from waters on Christmas Island (Ashmole and a 3-mm sea-strider to a 185-mm Decap- Ashmole 1967b). In addition, Hawaiian terus sp. Goatfishes and ommastrephid birds ate many goatfishes and carangids squids had mean lengths of 58 and 53 mm, 34 WILDLIFEMONOGRAPHS

Table 20. Prey items identifiedto lowest taxon in 182 Christ- Although sampling was somewhat in- mas shearwater samples. See Table 3 for method of CalCu- lating rank. adequate during fall and winter, some in- teresting patterns emerge from a compar- Per- ison of the 4 island groups and 4 seasons. centam- of Goatfishes ranked highest throughout the No ';: Hawaiian Archipelago in spring, but de- organ-of whichoc- ";g clined in summer, especially in the 2 Prey Rank isms curred VOI northern island groups. They remained FISHES fairly common during- fall and winter but Ammodytidac 14 much less so compared to spring and sum- Bleekeria gillii 10 38 04 mer. Ommastrephid squids ranked higher Carangidae 4 Decapterus spp 57 154 106 than goatfishes during fall and winter, D. macrosoma 6 27 18 ranking first in both areas sampled. They Unidentified carangid 2 05 05 ranked second in most island groups dur- Coryphaenidae 19 Coryphaena hippurus 1 05 <01 ing spring and summer and were conse- C. equiselis 1 05 01 quently a very common prey item Dact ylopteridae 22 Dactyloptena orientalis 2 11 <01 throughout the year. Lizardfishes ranked Exocoetidae 3 highest of the fish prey during winter. Exocoetus volitans 1 05 02 They also ranked high during spring but Unidentified exocwtid 81 264 96 Cempylidae 12 declined considerably during summer Gempylus serpens 8 44 09 when other prey resources were eaten. Gonorhynchidae 16 Conorhynchus During summer and fall, goatfishes oc- gonorhynchus 5 2.7 0.2 curred in only 1 of 36 samples at Midway. Conostomatidae 11 Decapterus spp. did not occur in any of Vinciguerria spp. 39 2.2 1.4 Hemiramphidae 20 15 fall or 40 winter samples, yet ranked Ox yporhamphus high during spring and very high during micropterus 1 0.5 0.5 summer, especially in the Laysan Island Holocentridae 7 25 7.1 2.3 Istiophoridae 24 1 0.5 0.1 group. Flyingfishes were highly ranked Macrorhamphosidae 15 only in summer, especially in the Midway Macrorhamphosus gracilis 5 1.6 0.5 Island group where many E. volitans were Monacanthidae 21 2 0.5 0.2 Mullidae 2 256 35.2 14.2 taken. A few flyingfishes were taken dur- Nomeidar 8 22 4.4 24 ing winter and spring. Many were taken Scombridae 13 Katsuwonus pelamis 6 2.7 0.8 on Midway during October. Dorward and Sternoptychidae 17 3 1.1 0.2 Ashmole (1963:453) found that brown Synodontidae 9 28 4.9 0.7 noddies took few E. volitans on Ascension 6 31 148 2.3 Unidentified fishes Island, even though other seabirds ob- MOLLUSCA tained it. Snake mackerels were regularly Decapoda Ommastrephidae 1 taken in all island groups during all sea- Symplectoteuthis spp. 42 126 70 sons, whereas squirrelfishes were most im- S. oualaniensis 7 33 15 Hyaloteuthis pelagicus 12 38 20 portant only during summer at the north- Unidentified ern end of the archipelago. Anchovies ommastrephid 260 478 31 7 occurred only during fall at Midway, Onychoteuthidae 18 2 05 05 Unidentified squids 5 58 203 53 ranking second there. These results dis- CRUSTACEA play intriguing changes in diet with sea- Crustacean larvae 23 4 0.5

Table 21. Lengths and volumes of some prey items’ of the Christmas shearwater. Length and volume values are not neces- sarily for the same individuals.

Minimum Maximum Mean SE Sample size Length Vol Length Vol Length Vol Length Vol Prey Length Vol (mm) (ml) (mm) (ml) (mm) (ml) (mm) (ml) FISHES Decapterus spp 4 120 131 126 3 Mullidae 7 51 57 53 1 Exocoetidae 15 38 125 80 6 MOLLUSCA Ommastrephidae 109 25 107 62 2 Symplectoteuthis spp. 39 4 30 1 99 17 61 7 3 4 S. oualaniensis 7 1 74 12 94 12 84 11 3 Hyaloteuthis pelagacus 10 53 64 58 1

a Included are prey items with sufficient measurements in grades I and 2 (see Methnds)

squids at Ascension Island. At Christmas carangids (especially Decapterus spp.), Island (Pacific), most fishes were flying- nomeids, and squirrelfishes. fishes, tunas, and snake mackerels (Ash- Reliable length measurements were mole and Ashmole 1967b). taken of 326 prey items. They ranged from Sooty Tern.-We collected 356 sam- a 1-mm gastropod to a 120-mm needlefish ples from sooty terns, obtaining some from and averaged 48 mm. All of the common each island group in the Hawaiian Archi- prey items for which adequate measure- pelago. Most came from Laysan, Lisian- ments were available were 20-70 mm ski, and French Frigate Shoals. Because (Table 25). The smallest of the highly this species does not make landfall when ranked prey, the squirrelfishes, averaged not breeding, collecting was restricted to 25 mm whereas the largest, Exocoetus March-September. We took samples from volitans, averaged 71 mm. A few of the adults (68%),subadults (8%),and nestlings prey items were in good enough condition (24%).Pooling all samples from 1978-80, for reliable volumetric measurements. the mean sample volume was 10.4 ml, and Ommastrephid squids and E. volitans had a sample contained an average 4.5 prey average volumes of 5 and 6 mi, respec- items. Sample condition was reasonably tively (Table 25). good with 97% of the fishes identified to Although we could not obtain samples family. from sooty terns during fall, some inter- Sample volumes were 46% fish and 53% esting patterns of seasonal and geograph- squid, a separation almost identical to that ical variation in diet are evident. Squids reported by Brown (1975).Twenty-six fish were commonly eaten in all island groups, families, 1 squid family, 1 shrimp, and 2 ranking either first or second in winter, coelenterate groups were identified (Ta- spring, and summer. If the unidentified ble 24). Squids were clearly the highest squids, which are probably Ommastre- ranked prey items, with ommastrephid phidae, were to be added to those that squids ranking first and the unidentified were definitely from this family, the im- ones ranking third. Most of those identi- portance of ommastrephid squids in the fied were Symplectoteuthis spp., includ- diet would be further underscored. Goat- ing S. oualaniensis. Ommastrephes spp. fishes were most prominent during spring and H. pelagicus were also present. Goat- and were also commonly eaten during fishes ranked highest among fish families. winter and summer. Flyingfishes were Next were flyingfishes, especially Cypse- eaten seasonally. They did not occur in lurus spp. and E. volitans. Other highly any of the 33 samples collected during ranked prey included snake mackerels, winter, occurred in only a few of the sam- 36 WILDLIFEMONOGRAPHS

Table 22. Prey items identified to lowest taxon in 354 brown Table 22. Continued. noddy samples. See Table 3 for method of calculating rank. Per- Per- cent of cent of sam- Sam- ples ples No in of which Avg Noof whichin organ- oc- 93 organ- oc- Prey Rank isms curred vol Prry Rank isms curred vol Myctophidae 24 4 0.6 0.4 FISHES Nomeidae 20.5 13 0.8 0.3 Ammodytidae 19 Pomacentridae 31 4 08 <01 Bleekeria gillii 10 20 02 Scomberesocidae 39 Blenniidae 155 20 28 01 Cololabis saira 1 03 <01 Bothidae 39 1 03 101 Scombridae 12 Bramidae 39 Katsuwonus pelamis 6 17 03 Pteraclis uelifer 1 03 <01 Thunnus alalunga 1 03 101 Carangidae 4 Unidentified scombrid 8 14 01 Decapterus spp, 68 116 65 Sph yraenidae 15 5 D. macrosoma 24 25 18 Sphyraena helleri 1 03 03 D. tab1 11 20 09 Unidentified sphyraenid 6 17 01 Selar crumenophthalmus 7 14 08 Synodontidae 3 682 237 59 Naucrates ductor 1 03 101 Tetraodontidae 26 5 Seriola sp. 1 03 <01 Lagocephalus Unidentified carangid 6 08 <01 lagocephalus 2 03 01 Chaetodontidae 39 1 03 <01 Unidentified Cheilodactylidae 26 5 tetraodontid 2 06 cO1 Cheilodactylus vittatus 4 08 01 Leptocephalus larvae 10 17 31 05 Cirrhitidae 29 5 Unidentified hshes 9 50 127 16 Cirrhitops fasciatus 5 03 02 MOLLUSCA Clupeidae 11 Spratelloides delicatulus 67 08 08 Decapoda Ommastrephidae 2 Coryphaenidae 28~~ Coryphaena equiselis 2 0.6 0.3 Ommastrephes spp. 4 0.6 0.3 Engraulidae 17 Symplectoteuthis spp. 51 9.0 4.9 Stolephorus buccaneeri 9 08 06 S. oualaniensis 6 1.7 1.1 Exocoetidae 5 S lurninosa 3 0.3 0.1 Parexocoetus brachypterus 2 06 06 Unidentified ommastre Exocoetus oolitans 10 28 23 phid 228 33.6 21.6 Cypselurus spp. 5 14 06 Onychoteuthidae 34 Unidentified exocoetid 59 124 54 Onychoteuthis sp 1 0.3 0.1 Fistulariidae 35 2 03 101 Unidentified squids 7 58 14.1 4.8 Gempylidae 6 CRUSTACEA Gempylus serpens 83 121 25 Euphausiacea 25 28 0.3 0.1 Unidentified gempylid 2 06 02 Stomatopoda 29.5 Gobiidae 32 L ysiosquilla sp. 1 0.3

Table 23. Lengths and volumes of some prey items. of the brown noddy. Length and volume values are not necessarily for the same individuals.

~~~ Minimum Maximum Mea" SE Sample size Length Vol Length Vol Length Vol Length Vol Prey Length Vol (mm) (ml) (mm) (ml) (mm) (ml) (mm) (ml) FISHES Holocentridae 25 14 15 0.1 38 0.4 24 0.2 1 0 Decupterus spp. 7 21 185 93 21 Mullidae 95 2 40 2 108 2 58 2 20 Monacanthidae 7 31 60 45 4 Blenniidae 16 20 21 24 1 Spratelloides delicutulus 37 21 47 39 1 Synodontidae 84 6 24 0.2 55 0.4 40 0.3 1 0 MOLLUSCA Ommastrephidae 89 3 19 2 96 28 53 13 28 Symplectoteuthis spp. 30 9 27 1 72 10 47 4 21

~ ~ ~~

a Included are prey items with sufficient measurements in grades 1 and 2 (see Methods)

in any of the 33 samples taken during handled June-January would not regur- winter but were ranked fairly high during gitate, and stomachs from sacrificed birds spring and summer. Squirrelfishes ranked were empty during those months. Samples highest during summer at the northern were well-digested. Nevertheless, more end of the Hawaiian Archipelago, and 75 than 74% of the individual fishes could be of the 76 individuals found in this study identified at least to family. Sample vol- were collected July-September. Striped umes averaged 5.9 ml and contained on hawkfish, skipjack tuna, bristlemouths, and an average 4.5 prey items. nomeids ranked fairly high at certain areas We found 12 fish families, 3 squid fam- and seasons. Sooty terns ate ommastrephid ilies, 7 crustacean groups, 1 insect, and a squids throughout the year and supple- tunicate in the diet of this species (Table mented this with seasonally available fish- 26). By volume, the prey consisted of 47% es from several families in the 20-70 mm fish, 21% squid, 7%crustaceans, and 24% size range. unidentified remains. The highest ranking Sooty terns fed heavily on ommastre- prey categories were unidentified squids, phid squids and flyingfishes at Ascension unidentified fishes, and unidentified re- Island (Ashmole 1963b), Christmas Island mains. These categories are not very use- (Pacific) (Ashmole and Ashmole 1967b), ful because each may be an aggregate of and Oahu (Brown 1975). Squid and fish many taxa. Midwater lanternfishes and species changed with location. Goatfishes hatchetfishes ranked as the most impor- and Decapterus spp. were common in the tant identifiable families. Two of the lan- diet in Hawaii but unreported elsewhere. ternfishes were identified by John E. Fitch Bonin Petrel.-During 1979-80, we using otoliths to be Hygophum sp. and collected 144 samples from Bonin petrels. Myctophum sp., and 2 of the hatchetfish- A single sample was obtained in Decem- es were Argyropelecus spp. Juvenile goat- ber and the remainder March-June. All fishes and sea-striders were also high rank- but 2 were from adults (99%)and, except ing components of the diet. The most for 5 samples from Midway, all came from common squid family was Ommastrephi- Laysan or Lisianski. Although Bonin pe- dae. trels will make landfall during almost any We obtained only 57 reliable prey month, we had extreme difficulty collect- lengths, which averaged 28 mm and ing samples during months when adults ranged from a 3-mm sea-strider to a 112- were not feeding their young. Most birds mm conger eel. Our best measurements 38 WILDLIFEMONOGRAPHS

Table 24. Prey items identified to lowest taxon in 356 sooty Table 24. Continued tern samples. See Table 3 for method of calculating rank. Per- Per- cent of cent of sam- sam- o1-c-- ples No in No. in of which Avg of which organ- oc- % organ- oc- A;g Prey Rank isms curred vol Prey Rank isms curred vol Scombridae 10 FISHES Katsuwonus pelamis 28 5.3 1.6 Ammodytidae 14 Thunnus sp 1 0.3 0.1 Bleekeria gillii 18 31 07 Unidentified scombrid 7 2.0 0.7 Atherinidae 28 Syndontidae 12 27 3.7 0.5 Pranesus insularuni 1 03 <01 Xiphiidae 22 Belonidae 27 Xiphias gladius 2 0.6 0.1 Ablennes hians 1 03 <01 Unidentified fishes 9 38 9.3 1.5 Blenniidae 18 10 08 01 MOLLUSCA Bramidae 23 Pteraclis oelifer 1 03 01 Decapoda Carangidae 55 Ommastrephidae 1 Decapterus spp. 21 48 27 Ommastrephes sp. 1 0.3 0.3 D. macrosoma 9 22 18 Symplectoteuthls spp. 80 13.8 8.4 D. tab1 26 42 20 S. oualaniensis 19 3.9 2.8 Naucrates ductor 2 06 02 Hyaloteuthis pelagicus 7 1.7 0.6 Unidentified carangid 1 03 <01 Unidentified Cheilodactylidae 21 ommastrephid 294 39.6 28.6 Cheilodactylus oittatus 2 06 02 Unidentified squids 3 113 24.4 12.7 Cirrhitidae 16 7 14 02 CRUSTACEA Clupeidae 17 Shrimp 28 1 0.3 <0.1 Spratelloides delicatulus 27 03 03 COELENTERATA 19 Coryphaenidae 28 Vellellidae Coryphaena hippurus 1 03 <01 Velella oelella 4 0.6 0.1 Dactylopteridae 28 Scyphozoa 2 0.3

Table 25. Lengths and volumes of some prey itemsaof the sooty tern. Length and volume values are not necessarily for the same individuals.

Minimum Maximum Mea" SE Sample sizr Length Vol Length Vol Length Vol Length Vol Prey Length Vol (mm) (ml) (mm) (ml) (mm) (ml) (mm) (ml) FISHES Holocentridae 17 4 16 0.1 39 0.4 25 0.3 20 Mullidae 35 38 61 53 1 Spratelloides delicatulus 11 22 45 31 2 Exocoetus oolitans 10 5 32 2 114 19 71 6 83 Nomeidae 10 14 78 51 8 Cantherhines spp. 6 3342 57 5 43 4 41 MOLLUSCA Ommastrephidae 94 11 18 1 104 18 51 22 Symplectoteuthis spp. 44 24 79 46 2

=Included are prey items wtth sufficient measurements in grades 1 and 2 (see Methads) on 58% squid, 28% fish (lanternfishes and fourth and consisted of both Coryphaena bristlemouths), and 12% crustaceans in hippurus and C. equiselis. Round her- New Zealand (Imber 1973). The Bonin rings, crabs, and man-o-war fish (Fig. 11) petrel is unique among Pterodroma in its also ranked high in the diet. heavy reliance on fish instead of squid. We obtained 1,092 reliable prey lengths. Gray-bucked Tern.-We collected and The smallest was a 3-mm sea-strider and analyzed 272 regurgitations from gray- the largest a 138-mm blue marlin, with an backed terns in 1978-80, including each average of 20 mm. The cowfish had a month March-August. Most were collect- mean length of 15 mm and ranged as large ed on Laysan, Lisianski, and Pearl and as 25 mm (Table 29). Except for the crab Hermes Reef, but others were obtained on megalopa and insects, most common prey Nihoa, Necker, and French Frigate Shoals. items had average lengths 15-40 mm, in- We collected half of the samples from cluding flyingfishes (Cypselurus spp., 38 adult birds and half from dependent mm), dolphin-fish (C. hippurus, 32 mm), young. Samples averaged 4 ml and 8.8 and goatfishes (41 mm). prey items. The sample condition was We collected enough samples to make generally very good, and 96%of the fishes some geographical and seasonal compari- could be identified at least to family. sons, although our analysis suffers from the We found the volume of the prey to be fact that we could not collect samples dur- 92% fish, 4% squid, and 3% crustaceans. ing fall. Cowfish ranked first in all areas The diet proved to be complex, consisting and seasons except during summer in the of 41 families of fish (the highest for any Midway Island group. Flyingfishes consis- species in this study), 3 mollusk families, tently ranked second or third during the 5 groups of crustaceans, 3 insects, and a 3 seasons for which we have samples but coelenterate (Table 28). The highest- ranked lowest during spring at Midway. ranked prey item was a cowfish, which Goatfishes occurred seasonally. Only 1 oc- occurred in two-thirds of the samples and cured in the 24 samples collected during accounted for 42%of the sample volume. winter, yet they ranked within the top 3 The next ranked family was flyingfishes. families during spring and summer in both Most of the 167 specimens we obtained the Laysan and French Frigate Shoals re- could not be identified further, but 17 gions. At Midway, they did not occur in were identified as Cypselurus spp. Goat- any of 24 samples collected during sum- fishes ranked third. Dolphin-fishes ranked mer. Dolphin-fishes generally ranked high 40 WILDLIFEMONOGRAPHS

Table 26. Prey items identified to lowest taxon in 144 Bonin only during spring and Summer in the petrel samples. See Table 3 for method of calculating rank. Laysan and Midway Island groups. Round PW herrings ranked high during summer at crrrtIanl~ of Midway. They occurred only in small pltY numbers elsewhere and were found in but No in which ~VR 1 of 161 samples collected in the Laysan llrgall~ <,c- s; I+<.) Hank ,SmS rurrr<~ vo~ Island group. Man-o-war fish did not oc- FISHES cur during winter, ranked second during 26 I 07 <01 summer aT Midway, and yet did not occuy 26 I 07 ~01at Laysan during that season. Crabs oc- I6 5 3 21 05 curred in small numbers in most areas and 21 2 11 01 I1 seasons sampled, but ranked highest dur- 1 28 03 ing spring at Midway. Striped hawkfish, 1 0.7 02 10 bristlemouths, and flying gurnards ranked 21 ti3 12 high at certain locations during a single 4 14 I)J season. We concliide that gray-backed 26 I Oi <01 20 2 0 7 0 6 terns fed heavily at all times on cow fish. -r, 36 76 71 There are no previous studies of the diet 1 1 07 <01 of this species, but Vunro (194461) found I 0 7

Table 27. Lengths and volumes of some prey itemse of the Bonin petrel. Length and volume values are not necessarily for the same individuals.

Minimum Maximum Mean SE Sample- size Length Vol Length Vol Length Val Length Vol Prpy Length Val (mm) (ml) (mm) (ml) (mm) iml) (mm) (ml) FISHES Mullidae 9 46 56 51 1 SQUID Ornrnastrephidae 6 20 72 46 7 CRUSTACEA Anuropus sp. 11545 54 5 54 5 Arnphipoda 3 11 40 23 9 Crab rnegalopa 3 7 7 7 0 INSECTA Halobates sericeus 18 2 3 0.1 4 0.1 4 (0.1 0

a Inclodrd are prey items with suficieot measurements in grades 1 and 2 (see Methods) prey items. Lengths averaged 46 mm and mer they were not present in any of 50 ranged from a 12-mm snake mackerel to samples taken at Midway, yet they ranked a 200-mm needlefish. Most of the impor- first in the Laysan Island group. The rank- tant prey items averaged 30-80 mm, in- ing of ommastrephid squids shows no pat- cluding goatfishes (35 mm), ommastre- tern, but they commonly occurred in all phid squids (50 mm), and Cypselurus spp. island groups and seasons. Dolphin-fishes (80 mm) (Table 31). We included all sam- did not occur anywhere during winter, nor ples for this analysis, even some dropped at Midway or French Frigate Shoals dur- fishes collected under roosting young that ing spring. However, this family ranked may have been too long for them to swal- high during both spring and summer at low. However, it seems unlikely that a tern Laysan. The young of the striped hawk- would take a fish that would be too long fish ranked high, especially at Midway, for adult consumption. Some nestlings during winter and spring but did not oc- were seen perched with a fish tail pro- cur during summer or fall. Silversides truding from the bill, indicating that some ranked high during summer at Midway, long fishes were consumed by the young. but were never common elsewhere. Lan- Our sampling was throughout the year ternfishes only occurred at the Midway Is- only in the Midway Island group and was land group, where they ranked first dur- generally restricted to spring and summer ing spring. Anchovies occurred only at for the Laysan and French Frigate Shoals Midway during fall, where they ranked groups. Our results concerning seasonal first. Snake mackerels, lizardfishes, bristle- and geographical patterns are difficult to mouths, halfbeaks, and needlefishes interpret because the diet of this species ranked within the top 5 prey during cer- is particularly varied. Flyingfishes were tain seasons at certain island groups. These not found in any of 16 samples taken dur- findings indicate that white terns prey op- ing winter. One flyingfish was found in 17 portunistically on most any species of ap- samples collected during spring at Mid- propriate size that is available in surface way, yet this family ranked second high- waters, especially those between 30-80 est at both Laysan and French Frigate mm. Shoals in that season. Flyingfishes were The white tern has a diversified diet most common during summer, ranking wherever it has been studied. It fed on at first or second in each of the 3 island least 16 fishes at Ascension Island, prin- groups. Goatfishes ranked first during cipally cutlass fishes, blennies, and flying- spring at each island group. During sum- fishes (Stonehouse 1962, Dorward 1963b). WILDLIFEMONOGRAPHS

Table 28. Prey items identified to lowest taxon in 272 gray. Table 28. Continued backed tern samples. See Table 3 for method of calculating rank. Per- cent of Per- Idm- cent of pies sam- No in ples of which AVP organ- oc- %I No in Prey Rank isms curred vol of which Avg organ- oc- % Prey Rank isms curred vnl Istiophoridae 17 lstiophorus platypterus 3 0.7 0.2 FISHES Tet ranterus Ammodytidae 52 5 angustirostris 1 04 01 Bleekeria gillii 1 04 101 Makaira nigricans 3 11 04 Atherinidae 52 5 Unidentified istiophorid 6 22 03 Pranesus insularum I 04 <01 Kyphosidae 29 Balistidae 13 Kyphosus bigibbus 5 15 04 Xanthichthys mento 11 26 14 Macrorhamphosidae 18 5 Unidentified halistid 15 26 03 Macrorhamphosus gracilis 17 40 07 Belonidae 42 5 Macrouridae 52.5 1 04 <01 Ablennes hians 1 04 101 Monacanthidae 23 Unidentified belonid 1 04 <01 Peroagor spilosoma 3 07 04 Blenniidae 34 3 11 02 Alutera scripta 5 07 02 Bramidae 42 5 Unidentified monacanthid 2 07 01 Brama orcini 1 04 <01 Mugilidae 27 7 15 03 Pteraclis velifer 1 04 01 Mrillidae 3 173 169 74 Carangidae 9 Myctophidae 20 11 29 09 Decapterus spp. 19 26 03 Nomeidae 8 D. macrosoma 1 04 01 Nomeus gronovii 48 63 23 Naucrates ductor 10 33 03 Psenes cyanuphrys 2 07 01 Seriola spp 10 15 03 Unidentified nomeid 65 40 10 Carangoides ferdau 1 04 01 Ostraciontidae 1 Unidentified carangid 9 29 08 Lactoria fornasini 708 665 41 8 Chaunacidae 16 75 33 10 Peg asi d a e 10 Cheilodactylidae 14 5 Pegasus papilio 48 88 23 Cheilodactylus vittatus 22 48 14 Pomacentridae 31 7 15 01 Clupeidae 5 Priacanthidae 39 2 07 04 Spratelloides Scombridae 45 delicatulus 182 66 54 Katsuwonus pelamis 2 04 <01 Congridae 48 1 04 01 Unidentified tuna 1 04 <01 Coryphaenidae 4 Serranidae 49 Coryphaena spp. 19 51 07 Odontanthias elizabethae 2 04 <01 C. hippurus 76 114 23 Soleidae 42.5 C equiselis 57 40 08 Aseraggodes kobensis 1 04 101 Dactylopteridae 28 Unidentified soleid 1 04 01 Dact yloptena orientalis 7 1.1 0.4 Sphyraenidae 46.5 2 07 <01 Diodontidae 18.5 Sternoptychidae 26 Diodon spp. 5 1.8 0.3 Sternoptyr diaphana 1 04 04 Unidentified diodontid 9 2.6 0.4 Unidentified Echeneidae 46 5 sternoptychid 4 15 03 Rhornbochirus osteochir 2 07 <0.l Synodontidae 32 5 18 01 Exocoetidae 2 Tetraodontidae 36.5 Parexocoetus Lagocephalus brachypterw I 04 03 lagocephalus 1 04 01 Exocoetus monocirrhus I 04 02 Unidentified Prognichthys gilberti 4 15 04 tetraodontid 3 07 <01 Cypselurus spp. 17 48 14 Xiphiidae 24 Unidentified exocoetid 143 268 7 1 Xiphias gladius 7 26 05 Gempylidae 22 Unidentified fishes 6.5 83 19.1 25 Genipylus serpens 9 26 08 MOLLUSCA Gonorhynchidae 52 5 Couorh ynchus Decapoda gonorhynchus 1 04 101 Ommastrephidae 14 5 Gonostomatidae 21 Syrnplectoteuthis spp. 2 07 0.1 Vinciguerria nimbaria 20 15 11 Unidentified ommastrephid 15 4.4 2.0 Hemiramphidae 53 Unidentified squids 11 29 7.0 17 Oxyporhamphus Janthinidae 40 micropterus 1 04 <01 Janthina spp. 2 0.4 0.1 Holocentridae 30 8 11 02 HAWAIIANSEABIRD FEEDINGECOLOGY-Harrison et ai. 43

Table 28. Continued.

~~ ~ Per- cent of Sam ples No in of which organ- oc- 1* Pre) Hank isms curred voI --- I I. pallida 2 04 <01 I cm J prolongata 1 04 <01 Cavolinidae 53 Fig. 11. Man-0-war fish, a prey item Caoolinia tridentata 1 04 101 (:RUSTACEA Euphausiacea 365 I4 04 01 lsopoda 35 Black Noddy.-During 1978-80 we Parasitic isopod 3 I1 <01 collected 494 samples (the largest sample Unidentified isopod 3 07 <01 Copepoda 53 size in this study) from black noddies, most Pontellidae coming from Laysan, Lisianski, and Pon t ella at lan t ica I 04 <01 French Frigate Shoals. Other samples were Shrimp 33 5 15 01 Crab 65 collected on Kure, Midway, and Pearl and Rrachyura 6 22 04 Hermes Reef. Collections included sam- Unidentified megalopa 167 63 22 ples from all 12 months. We collected Portunidae Planes cyaneus 6 11 04 samples from both adults (79%) and de- Port unid megalopa 1 04 <01 pendent young (21%).The samples aver- INSECTA aged 5 ml and 12.6 prey items. We iden- Gerridae 12 tified 94%of the fishes to family or better. Halobates sericeus 135 99 06 By volume, the prey was 92% fish, Lepidoptera (moth) 2 07 <01 7% Orthoptera (grasshopper) squid, and 1%crustaceans. We were able Euconocephalus nasutus 1 04 01 to identify 36 fish families, 2 squid fami- COELENTERATA lies, 3 groups of crustaceans, and an insect \'elellidae 25 (Table 32). The highest ranked prey fam- Velella oelella 11 18 02 ily was goatfishes, followed by lizardfish- UNIDENTIFIED REMAINS 425 2 07 01 es. Round herrings (Fig. 12) ranked third. Next were flyingfishes, of which the most common of the 5 species identified was E. volitans (Table 32). Other common prey Dorward also found that it ate hatchet- items included gobies, ommastrephid fishes and lanternfishes. On Christmas Is- squids, and snake mackerels. land (Pacific), white terns fed about half We had 1,038 prey items for which we on ommastrephid squids and half on fishes could make reliable length measurements. by volume (Ashmole and Ashmole 1967b). These items averaged 34 mm and ranged A wide variety of fishes was consumed from a 5-mm crab megalopa to a 167-mm there, among which the most important leptocephalus larvae. The highest ranked were blennies, flyingfishes. halfbeaks, lan- taxa had mean lengths in the 20-50 mm ternfishes, and bristlemouths. In Hawaii, range and included ommastrephid squids white terns have been reported to feed on (32 mm), lizardfishes (38 mm), and goat- halfbeaks (Fisher 1903:785), anchovies, fishes (45 mm) (Table 33). We made 142 and silversides (Anderson 1954). All work- reliable volumetric measurements. ers have found the condition of prey taken Although sampling was inadequate for from this species to be excellent due to its some areas and seasons, several general- habit of bringing fishes to young crosswise izations can be made regarding geograph- in the bill, and such specimens have been ical and seasonal changes in diet. Goat- used to identify new fish species (Tyler fishes ranked first or second in each season and Paxton 1979). in the Laysan Island group. At French 44 WILDLIFEMONOGRAPHS

Table 29. Lengths and volumes of some prey items of the gray-backed tern. Length and VOlUme Values are not necessarily for the same individuals.

Minimum Maximum Mean SE Sample size ____ Length Vol Length Vol Length Val Length Vol Prey Length Vol (mm) (ml) (mm) (ml) (mm) (ml) (mm) (ml) FISHES Seriola spp. 10 3 18 0.3 32 0.7 23 0.5 1 <0.5 Mullidae 14 3 28 0.7 65 2.1 41 1.3 3

Included are prey items with sufficient measurements in grades 1 and 2 (see Methods)

Frigate Shoals, they ranked third in all spring. Our data indicate that black nod- seasons except spring, when they ranked dies fed most heavily on goatfishes and first. In the Midway Island group, goat- lizardfishes throughout the Hawaiian Ar- fishes occurred only during spring and chipelago throughout the year. Other prey were absent from all 28 samples taken in in the 20-50 mm size range were also tak- the remainder of the year. Lizardfishes en. ranked high during each season in the The diet of black noddies in Hawaii is Laysan and French Frigate Shoals re- unique because of the common occur- gions, either first or second. They also rence of goatfishes, lizardfishes, and round ranked second during fall and winter in herrings. At Ascension (Stonehouse 1962) the Midway Island group, and their ap- and Christmas Island (Ashmole and Ash- parent absence during spring and summer mole 1967b),black noddies fed on flying- there may be an artifact of inadequate fishes, halfbeaks, blennies, and an ancho- sampling. Round herrings were not found vy (Engraulis sp). This bird has been in any of the 76 samples collected during reported feeding on Stolephorus delicat- winter, yet ranked third and fourth dur- ulus (we believe this could be Stolephorus ing spring and summer at Laysan and buccaneeri or Spratellodes delicatulus) in French Frigate Shoals. Flyingfishes were the Marshall Islands (Marshall 1951). very common during summer, ranking Bulwer’s Petrel.-During 1978-80 we first at French Frigate Shoals. Bristle- could collect only 100 samples from Bul- mouths were commonly eaten during wer’s petrels. Samples were taken during winter at Midway and Laysan while dur- the breeding season, May-September, be- ing the same season at French Frigate cause this species rarely comes to land in Shoals gobies ranked very high. Ommas- other months. Most samples were collect- trephid squids ranked third or fourth at ed on Laysan, but 2 were obtained on Ni- several locations during fall, winter, and hoa. Sample condition was generally poor, HAWAIIANSEABIRD FEEDING ECOLOGY-HUW~SO~ et al. 45

Table 30. Prey items identified to lowest taxon in 241 white Table 30. Continued. tern samples. See Table 3 for method of calculating rank.

Per- Per- cent of cent of Sam- sam- ples ples No. in No in of which of which organ- oc- organ- oc- "ig Prey Rank tsms curred vol Prey Rank isms curred vol Oxvvorhamvhus FISHES micropterus 7 25 15 A therinidae 75 Unidentified hemiramphid 3 08 02 Pranesus insularum 16 33 32 Holocentridae 17 Belonidae 6 Myripristis chryseres 1 04 04 Ablennes hians 17 54 39 Unidentified holocentrid 11 17 14 Unidentified beionid 1 04 10 1 Hoplichthyidae 30 5 Blenniidae 15 Hoplichthys sp. I 04 04 Plagiotrenius goslinei 3 08 05 Istiophoridae 11 5 Unidentified blenniid 9 17 11 Istiophorus platypterus 8 29 28 Bramidae 30 5 Makarra nigricans 1 04 <01 Pteraclis uelifer 1 04 04 Macrorhamphosidae 24 Cant higasteridae 33 5 Macrorhamphosus gracilis 3 12 09 Canthigaster sp. 1 04 02 Monacanthidae 30 5 Carangidae 75 Cantherhines sp. 1 04 04 Decapterus sp. I 04 04 Mugilidae 20 5 17 13 D macrosoma 3 04 01 Mullidae 1 185 295 195 Naucrates durtor 6 17 07 Myctophidar 15 Seriola sp 1 04 04 Benthosema fibulatum 1 04 04 Caranx spp. 2 08 08 Unidentified rnyctophid 6 25 25 Unidentified carangid I 04 04 Nomeidae 23 Chaetodontidae 35 Nomeus gronovii 3 12 09 Chaetodon sp 1 04 01 Unidentified nomeid 1 04 02 Cheilodactylidae I1 5 Pomacentridae 22 Cheilodactylus oittatus 8 33 29 Chromis uanderhilti I 04 01 Clupeidae 15 C. struhakeri 1 04 04 Spratellordes Unidentified pomacentrid 3 12 05 delicatulus 13 2 1 Ih Scombridar 27 Coryphaenidae 5 Katsuwonus pelamis 1 04 02 Coryphaena spp. 3 08 04 Unidentified tuna 1 04 01 C. hippurus 8 21 17 Serranidae 33 5 C. equiselis 9 37 22 Cranimatonotus laysanus 1 04 02 Diodontidar 25 5 Soleidae 365 1 04 01 Diodon sp. 1 04 04 Synodontidae 9 Unidentified dicdontid 1 04 01 Synodus sp I 04 04 Echeneidae 19 Unidentified synodontid 21 37 10 Rhombochirus osteochir 6 21 07 Tetraodontidae 305 I 04 04 Remora sp 1 04 <0 1 Xiphiidae 36 5 Unidentified echeneid 2 08 <0 1 Xiphias gladrus I 04 01 Engraulidae 21 Unidentified fishes 10 13 SO 15 Stolephorus buccaneeri 13 08 08 MOILUSCA Exocoetidae 2 Parexocoetus Derapoda brachypterus 2 08 02 Omrnastrephidae 3 Exocoetus oolitans 66 8 7 68 Symplecioteuihis spp 5 17 17 E. monocrrrhus 2 08 08 S. oualaniensis 1 04 04 Prognichthys gilberii 2 08 07 Hyaluteuthis pelagicus 2 04 04 Cypselurus spp. 17 7 1 hO Unidentified C speculiger 2 08 08 ornrnastrephid 32 95 79 C.otrisignis I 04 03 Unidentified squids 18 8 33 12 (Inidentified exoroetid 44 129 66 CRUSTACEA (krnpylidae 13 Shrimp 28 Genrpylirs serpens I1 2') 13 Peiiaridae L'nidentified gernpvlid 3 04 0 1 1 04 01 Gonorhvnchidae 25 5 Cennadus sp Gonorhynchus gonorhyn L'nidcntifird wnaeid 1 04 01 chus 2 08 0 5 Hernirarnphidae h Euleptorhamphus ewidis 4 12 12 IIyporhaniphus ucutiis pacificus 9 25 I (> 46 WILDLIFEMONOGRAPHS

Table 31. Lengths and volumes of some prey items’ of the white tern. Length and volume values are not necessarily for the same individuals.

Maximum Mean SE

Sample size Minimum ~ ~ -Length Vol Length Vol Length Vol Length Vol Prey Length Vol (mm) (ml) (mm) (ml) (mm) (ml) (mm) (ml) FISHES Mullidae 89 38 15 0.1 65 4 35 1.2 1 <0.5 Pranesus insularum 9 7 22 0.1 63 3 45 1.1 5

aIncluded are prey items with sufficient measurements in grades 1 and 2 (see Methods).

with many regurgitations being rejected gyropelecus spp. was common. Other in the field because they were only oil or common prey included sea-striders and because the prey items were digested be- flyingfish ova. We found small plastic par- yond recognition. We also experienced dif- ticles in some of the samples which, as in ficulty in getting this species to regurgi- the albatrosses, could have been ingested tate. Most samples (78%)were taken from while feeding on fish eggs that were at- adult birds, but 22% came from nestlings. tached to these floating particles. The relatively poor condition is reflected We had measurements of only 30 prey in the fact that by volume 5%of the sam- lengths. These averaged 23 mm and ples were unidentified remains, 20% were ranged from a 3-mm sea-strider to a 130- unidentified squids, and 30% were un- mm flyingfish. Five ommastrephid squids identified fishes. However, 67% of the in- had a mean length of 57 mm (range 38- dividual fishes collected were identified to 68 mm). family or better. It is likely that some of The distribution of sampling made it the unidentified fishes were midwater impossible to draw conclusions for any species for which we lacked a reference area except Laysan Island. There, 16 sam- collection of skeletal material. Food sam- ples were collected during spring and 82 ples from this bird yielded an average vol- during summer. Bulwer’s petrels fed more ume of 3 ml and contained an average of on squids during spring (61% by volume) 3.9 prey items. than summer (13%).During summer, lan- We found 7 fish families, 1 squid fam- ternfishes (20%) and hatchetfishes (19%) ily, a gastropod, an annelid, 4 groups of were common prey. The samples con- crustaceans, and an insect (Table 34). By tained no midwater fishes during spring. volume, ignoring stomach oil and uniden- Sea-striders ranked high during both sea- tified remains, the prey was 71% fish, 22% sons. Bulwer’s petrels fed primarily on squid, 4% crustaceans, and 3% sea-strid- squids and mesopelagic fishes, most of ers. The 2 highest ranked categories were which were

Table 32. Prey items identified to lowest taxon in 494 black Table 32. Continued. noddy samples. See Table 3 for method of calculating rank. Per- Per- cent of cent of sam- sam- ples ples No ~n No in organ-Of whichoc- Rank isms curred vol Prey Rank isms curred "01 Istiophoridae FISHES 30 Makaira nigricans 3 04 <01 Ammodytidae 29 Unidentified istiophorid 2 04 01 Bleekeria gillii 5 0.4 0.2 K yphosidae 32 A therinidae 14.5 Kyphosus bigibbus 4 02 02 Pranesus insularurn 27 2.0 1.8 Macrorhamphosidae 20 Balistidae 45.5 1 0.2 <0.1 Macrorharnphosus gracilis 13 26 06 Belonidae 28 Molidae 24 Platybelone argalus Ranzania laevis 9 12 04 platyura 2 04 02 Monacanthidae 37 Ablennes hians 2 04 <01 Pervagor spilosoma 2 02 02 Blenniidae 25 11 10 02 Mugilidae 455 1 02 101 Bothidae 38 3 04 <01 Mullidae 1 1,204 498 312 Carangidae 12 Myctophidae 33 6 02 01 Decapterus spp. 22 14 03 Nomeidae 17 5 D.rnacrosoma 7 08 04 Nomeus gronooii 9 16 05 D. tab1 2 04 01 Psenes cyanophrys 4 04 01 Naucrates ductor 8 12 03 Unidentified nomeid 7 08 02 Unidentified carangid 12 14 03 Pomacentridae 31 Cheilodactylidae 16 Chromis sp. 1 02 <01 Cheilodact ylus vit tatus 23 30 08 Unidentified pornacentrid 5 10 101 Cirrhitidae 34 4 06 C01 Scornberesocidae 39 5 Clupeidae 3 Cololabis saira 2 04 <01 Spratelloides Scombridae 13 delicatulus 560 11.9 102 Katsuwonus pelarnis 9 10 01 Coryphaenidae 19 Thunnus alalunga 5 04 01 Coryphaena spp. 6 1.2 0.4 Unidentified tuna 20 24 101 C. hippurus 2 0.4 0.1 Unidentified scombrid 15 18 01 C. episelis 11 1.8 0.3 Scombrid larvae 6 04 <01 Dactylopteridae 41 Tuna larvae 18 08 01 Dactyloptena orientalis 1 0.2 0.1 Sph yraenidae 355 2 04 01 Echeneidae 39 5 Sternoptychidae 42 2 02 <01 Remora remora 1 0.2 <0.l Synodontidae 2 2365 453 207 Rhornbochirus osteochir 1 0.2 <0.1 Tetraodontidae 45 5 Engraulidae 26 Lagocephalus Stolephorus huccaneeri 25 1.0 0.1 lagocephalns 1 02

Table 32. Continued.

Per- cent of sam- ples No in

organ-Of whichoc- Prev Rank isms curred vol - I cm Penaeidae Penaeus marginatus 15 06 101 Fig. 12. Round herring, a prey item. Unidentified penaeid 4 04 <01 Aristaeidae 1 02 <01 Caridea 31 02 01 Unidentified shrimps 20 28 01 Crab megalopa 21 3414 02 lected on Nihoa (46%)and Necker (54%). INSECTA We could obtain samples only during Caterpillar 455 1 02 <01 February, May, June, and August. Except UNIDENTIFIED REMAINS 27 4 08 02 for 4 samples, all were taken from adult birds (96%).The samples had a mean vol- ume of 1.8 ml and averaged 55 prey items. Even eliminating the large numbers of sea- Nihoa. This species breeds only in inac- striders, the blue-gray noddy had an av- cessible islands during winter and spring, erage of 31 prey items/sample, by far the making sampling difficult. We also had largest number for any of the 18 seabirds difficulties inducing birds to regurgitate, in this study. The condition of the samples and many of the samples that we did col- was relatively good, yet only 46% of the lect were entirely stomach oil. All samples fishes could be identified to family be- came from adults. The advanced state of cause of their extremely small size. digestion of the samples made identifica- By volume, our samples were 61%fish, tion difficult, but aside from unidentified 1.5%squid, 18%crustacean, and 19%in- remains and stomach oil, we found 23% sect. We could identify 28 fish families, 1 fish, 29%squid, 12%coelenterates, and 5% squid family, 8 groups of crustaceans, 2 crustaceans by volume (Table 35). We coelenterates, and a marine insect (Table could not identify any squid family and 36). The highest ranking prey item was identified only I fish family, the hatchet- sea-striders, which occurred in 81%of the fishes. Wind-sailers and sea-striders ranked stomachs sampled and accounted for 19% high among prey items. These data give of the prey volume. Unidentified fishes an indication of the types of prey eaten ranked second. These accounted for 16% by this species, but the unlikely result that of the prey volume and were therefore a the common seabird tick accounted for substantial component of the diet, but 10% of the volume emphasizes the fact probably included many families and that conclusions must be limited. Small species. Lizardfishes ranked third. Flying- plastic particles occurred in samples from fishes and goatfishes also were common. this species. Copepods, almost exclusively Pontella at- The length measurements of only 7 prey lantica, ranked seventh. This species was items were taken that averaged 11 mm reported by Wilson (1950) in the Hawai- and ranged from a 2-mm tick to a 27-mm ian Archipelago and is associated with sur- wind-sailer. We do not have enough in- face waters around islands. Stomatopods formation to draw any conclusions con- also were common and included 5 genera, cerning geographical or seasonal changes especially Pseudosquilla and Coronida. in the diet of sooty storm-petrels. Blue-gray noddies ate the smallest fish- Blue-gray Noddy.-We collected 111 es and invertebrates of all seabirds in this samples from blue-gray noddies from study. Mie measured 635 prey items. They 1978-81. Because of the limited distribu- averaged 10 mm, ranging from a 2-mm tion of this species, all samples were col- sea-strider to a 50-mm halfbeak. The most HAWAIIANSEABIRD FEEDING ECOLOGY- Harrison et d. 49

Table 33. Lengths and volumes of some prey items. of the black noddy. Length and volume values are not necessarily for the same individuals.

Minimum Maximum Mean SE Sample size Length Vol Length Vol Length Vol Length Vol Leneth Vol (mm) Iml) (mm) Iml) (mml lml) lmm) iml) FISHES Holocentridae 44 9 56 19 2 Mullidae 95 7 20 0.3 61 3 45 1.5 1 <0.5 Pranesus insularum 11 32 86 64 4 Spratelloides delicatulus 130 20 29 0.2 61 3 45 1.5 1 <0.5 Exocoetidae 32 18 52 33 2 Exocoetus volitans 23 32 67 48 2 Ptereleotris heteropterus 161 54 13 0.1 35 0.3 27 0.2 <0.5 0 Synodontidae 266 21 25 0.1 65 1 38 0.4 C0.5 0 MOLLUSCA Ommastrephidae 48 11 67 32 1 CRUSTACEA Stomatopod larvae 9 11 40 23 4 Caridean shrimp 22 9 9 9 0 Squilla spp. 10 4 12 0.1 41 0.2 35 0.1 3 0

a Inchided are prey items wth sufficient measurement3 in grades 1 and 2 (see Methods)

common fishes had average lengths 10-30 (75%),squid (lo%),and other inverte- mm, including flyingfishes (16 mrn), goat- brates (16%) (Ashmole and Ashmole fishes (18 mm), and lizardfishes (32 mm). 1967b). Snake mackerels ranked highest The crustaceans and insects were smaller: among the fishes, followed by flyingfishes, Pseudosquilla spp. (9 mm), Pontella at- tunas, and blennies. Sea-striders (H. mi- lantica (5 mm), and sea-striders (3 mm). cans) and copepods (Pontella sp.) also These lengths and displacement volume were common. These findings are similar data, where many common prey items had to ours, but Hawaiian birds also fed on mean volumes <0.1 ml, give a good in- lizardfishes and goatfishes. dication of the minute prey on which blue- gray noddies fed (Table 37). Prey Length Comparisons We cannot make any geographical comparisons, but we can draw some ten- Prey length comparisons, using all prey tative conclusions concerning seasonality from all taxa of grades 1 and 2, indicate in the diet of the blue-gray noddy. Com- that larger predators take larger prey (Fig. paring winter with spring, the only simi- 13). It is useful to compare the same prey larities are the high rankings of unidenti- taken by seabirds with similar diets dur- fied fishes and lizardfishes. During winter, ing the spring-summer chick feeding pe- blue-gray noddies fed on shrimp, flounder riod (Fig. 6). Masked boobies took larger larvae, and squids. During spring sea- flyingfishes than the other 4 pelecani- striders, flyingfishes, and goatfishes ranked forms (ANOVA, P < 0.001), which had high. Few samples were collected during no statistical differences among them. winter, but it is probable that this species Pooling all Decapterus spp., the smallest fed most heavily on lizardfishes, supple- 4 species again had no differences among menting this with various other items. The them, but the masked booby fed on larger small prey size and reliance on crusta- fishes (ANOVA, P < 0.01). Masked and ceans and insects is consistent with the brown boobies had no significant differ- findings of Ashmole and Ashmole (19676). ence between them for ommastrephid At Christmas Island, they fed on fish squids, nor were there differences among 50 WILDLIFEMONOGRAPHS

Table 34. Prey items identified to lowest taxon in 100 Bul- Table 35. Prey items identified to lowest taxon in 10 sooty wer's petrel samples. See Table 3 for method of calculating storm-petrel samples. See Table 3 for method of calculating rank. rank.

Per- Per- cent of cent of Sam- samplrs PIPS No in No I" of which Avg of uhich ,4>g organ- oc- !% organ- oc- c Prry Hank ism5 curred YOI Prry Rank isms currrd YOI FISHES FISHES Sternoptychidae 8 1 100 10.0 Carangidae 13 Unidentified fishes 3 5 40.0 13.0 Decapterus inacrosonia 1 10 04 Exocoetidar I M0LLUSC:A Exocoetus volitans 1 1.0 06 Umdentifird squids 1 7 60.0 28.8 Exocoetidae (ova) 6 60 32 CRUSTACEA Unidentified exocoetid 2 10 02 Gonostomatidae 11 Euphausiacea 13 10 0 01 Vinciguerria sp 1 10 01 .4mphipoda IO 10 0 13 V nimbaria 2 10 10 1 Isopoda 9 IO 0 17 Diplophos sp 1 10 0 3 Shrimp 6 20 0 15 bl yctophidae 3 C'nidrritified crristacran 11 10 0 04 Hygophum spp 2 20 04 INSECT4 Myctophurn sp 1 10 06 (krridae J Lanipan yctus spp 2 20 12 Halohates sericeus 8 300 11 Diaphus spp 3 10 04 Caterpillar 12 1 100 03 Symbolophorus sp. 1 10 03 Unidentilied myctophid 49 360 131 TICKS Norneidae 19.5 1 1.0 <0.1 Argasidae 7 Oi'isthol)roctidar 19 5 Ortiit hodorus capensis 2 100 100 Opisthoprocttrs sp 1 10 <01 Sternnptychidar 4 COELENTER 4TA Argyropelecrrv spp 23 170 52 Vrlellidar 2 Ilnidentified sternopt) chid 31 25.0 10.5 Velella uelella 9 400 119 Pleuronectoidei (Oatfish) 165 1 10 01 L'NIDEIL'TIFIED REMAINS 4 3 300 101 Unidentified fishes 1 67 480 29.5 MOLLUS(:A Decapoda Omrnastrephidae 10 h 30 09 L'nidentified squids 2 90 460 198 took smaller goatfishes than these 4 species, (;astropoda 10 I65 I 01 and white terns ate smaller ones than black ANNELLlD.4 noddies (ANOVA, P < 0.001). Both Polychaeta 165 1 10 01 shearwaters took larger squids than brown (:RUSTA(:EA noddies, sooty terns, or white terns, all of Amphipods 8 16 50 15 Copepoda 12 7 10 01 which took larger squids than black nod- Shrimp 165 1 10 01 dies (ANOVA, P < 0.001). Lizardfishes Crab megalopa 14 1 1.0 0.3 Unidentified crnstacean 9 8 5.0 19 eaten by brown noddies were larger than those taken by black noddies (ANOVA, INSECTA C;erridar 6 P < 0.05). Flyingfish were taken in suc- Halobates sericeus 5' 12 0 2 6 cessively decreasing lengths by Christmas C'NIDENTIFIED REMAINS 5 13 130 52 shearwaters, sooty terns and brown nod- dies, white terns, and black noddies (AN- OVA, P < 0.05). Gray-backed terns ate larger prey than blue-gray noddies, in- red-tailed tropicbirds, red-footed boobies, cluding goatfishes (ANOVA, P < 0.01), or great frigatebirds. The former 2 species flyingfishes (P < O.OOl), and crab megalo- took larger squids than the latter 3 (AN- pae (P 0.001). OVA, P < 0.05). There were no significant differences DISCUSSION among goatfishes eaten by wedge-tailed shearwaters, Christmas shearwaters, sooty It is evident from the preceding species terns. or brown noddies. Black noddies accounts that the diets of seabirds in the HAWAIIANSEABIRD FEEDING ECOLOGY-HUW~SO~ et al. 51

Table 36. Prey items identified to lowest taxon in 111 blue- Table 36. Continued. gray noddy samples. See Table 3 for method of calculating rank. Per- cent of Per- Sam- cent of ples No in Sam- of which No plestn organ- oc- Prey Rank tsms curred voI or;:"- "::Fh A;g Prey Rank isms curred vu1 Scombridae 15 11 7.2 0.6 Soleidae 42.5 1 0.9 <0.1 FISHES Sphyraenidae 37.5 1 0.9 0 1 Ralistidae 40 2 0.9 <0.1 Synodontidae 3 Relonidae 35 Trachinocephalus myops 1 09 <01 Ablennes hians 2 09 01 Unidentified synodontid 319 586 146 Rlenniidae 18 11 72 04 Xiphiidae 14 Unthidae 13 Xiphias gladius 11 81 06 Rothidae larvae b 09 04 Leptocephalus larvae 295 3 27 01 Unidentified bothid 13 54 09 Unidentified fishes 2 1,259 784 161 Carangidae 28 MOLLUSCA Naucrates ductor 1 09 <0 1 Seriola spp 3 18 01 Decapoda Coryphaenidae 33 Omrnastrephidae 37.5 1 0.9 0.1 Coryphaena sp. I 09 <0 1 Unidentified squids 10 34 16.2 1.4 C. hippurus 1 09 01 CRUSTACEA Dactylopteridae 21.5 Dactylopfena orientalis Crustacean larvae 375 1 09 01 11 54 03 Mysidacea Diodontidae 27 12 Siriella spp Diodon spp. 02 14 36 02 6 18 Unidentified rnysid Unidentified diodontid 4 09 <0 1 16 72 03 Euphausiacea Echeneidae 33 17 23 72 03 Stomatopoda 7 Rhombochirus osteochir 1 09 01 Remora sp. Pseudosquilla spp. 105 126 16 1 09 <0 1 Squilla spp. Eleotridae 42.5 4 36 03 Lysiosquilla spp Asterropteryx sp. <0 1 15 63 06 1 09 spp. Exocoetidae 4 Coronida 75 153 20 Odontodact ylus spp. Cypselurus sp. 1 09 02 20 81 06 Unidentified stomatopod Unidentified exocmtid 314 450 9 45 04 10 7 Amphipoda Cempylidae 11 19 25 36 04 Isopoda 23 Gempylus serpens 13 8 1 15 Parasitic isopod Unidentified gernpylid <0 1 4 36 02 2 09 Unidentified isopod Gobiidae 21.5 2 18 02 Ptereleotris Copepda 6 Pontellidae heteropterus 3 27 02 1 09 01 Unidentified gobiid Pontella spp. 4 27 03 4 27 02 P. atlantica Gonorhynchidae 33 319 207 24 Gonorhynchus Calanoid copepod 14 27 03 gonorh ynchus Unidentified copepod 11 27 03 2 18 01 Shrimp Hemiramphidae 25 8 Sergestidae Euleptorhamphus oiridis 2 18 02 22 09 02 Hyporhamphus acutus Lucifer spp. 13 45 02 pacificus C!nidentified shrt.nps 88 423 32 1 09 01 Crab megalopa Unidentified hemiramphid 4 18 01 9 247 288 37 Holocentridae 24 5 45 05 INSECTA Istiophoridae 20 Gerridae 1 Makaira nigricans 3 27 04 Ila/obates sericeus- 2,652 81 1 188 Istiophorus spp. 2 09 01 Unidentified istiophorid 1 09 03 COELENTERATA 16 Macrorharnphosidae 37 5 Velellidae Macrorhamphosus gracilis 1 09 01 Velella oelella 5 36 03 Mullidae 5 238 423 10 4 Scyphozoa 11 27 02 Norneidae 29.5 UNIDENTIFIED HEMAINS Nomeus gronovii 2 18 01 425 1 09 <01 unidentified nomeid 1 09 <0 1 Ostraciontidae 26 Lactoria fornasint 7 27 03 LJnidentified ostraciontid 1 09 <01 Hawaiian Archipelago are complex. We Poniacentridae Scomberesoridae !k5 h: <:; found 56 families, 86 genera, and 74 species of fish, and 8 families, 8 genera, and 5 species of squid. We also found an 52 WILDLIFEMONOGRAPHS

Table 37. Lengths and volumes of some prey items. of the blue-gray noddy. Length and volume values are not necessarily for the same individuals.

Minimum Maximum Mean SE

Sample Size ______~ ____ Length Vol Length Vol Length Vol Length Vol Prey Length vol (mm) (ml) (mm) (ml) (mm) (ml) (mm) (mi) FISHES Blenniidae 10 6 10 <0.1 13 <0.1 12

a Included are prey items with sufficient measurements in grades 1 and 2 (see Methods)

octopod, 2 gastropod families, an annelid, Each species requires a food source near 11 groups of crustaceans, 2 coelenterates, the surface of the water, and diversifica- a tunicate, 3 seabirds, and an alga in the tion of foraging patterns in such a struc- diets (Appendix 3). Plastic particles were turally simple habitat is limited compared found in the stomachs of 4 species, indi- to colder waters. We recognize that many cating that this potential problem (Baltz differences in prey consumption may be and Morejohn 1976, Ohlendorf et al. 1978) a result of relative rather than absolute is not restricted to northern waters. prey abundance, but absolute prey abun- Nevertheless, it is also evident that rela- dance data are unavailable. Without such tively few of these prey items comprise data, it is difficult to assess the “impor- most of the food consumed by this seabird tance” of a prey item. We believe that community in terms of number, volume, any prey that ranks high during any sea- or frequency of occurrence. It is possible son (especially when nestlings are fed) to that some of the prey items that occur be important. We acknowledge the prob- infrequently are necessary to survival in ability that some prey rank high simply the absence of other food (Ashmole and because they are seasonally abundant. We Ashmole 1967b). have no other objective criterion to judge For ease of discussion, we have grouped the importance of forage items. the 18 species into 5 guilds. These are the albatrosses, pelecaniforms, terns and Albatrosses shearwaters associated with predatory fishes, small nocturnal procellariiforms, Albatrosses generally feed well off shore and neuston feeding terns. These cate- by surface seizing (Ashmole 1971) (Fig. gories are somewhat artificial, and it might 14). Black-footed and Laysan albatrosses be argued that a species could more con- have similar nesting requirements with the veniently be placed in another group. exception that black-footed albatrosses nest However, we believe this characterization closer to beaches. Therefore we wished to highlights some of the more important distinguish between their feeding habits similarities and differences among the to see if or how they partition food re- diets of the seabirds within the tropical sources. Both species are very dependent and subtropical Hawaiian Archipelago. on squid (Tables 3 and 6), like other al- HAWAIIANSEABIRD FEEDING ECOLOGY-HH~~~~SO~ el al. 53

0 50

BROWN BOOBY - ___

RED-FOOTED BOOBY-

MASKED BOOBY---

RED-TAILED TROPICBIRD- - ___--

GREAT FRIGATEBIRD-

BLACK NODDY- __~

SOOTY TERN-- ___

WEDGE-TAILED SHEARWATER

CHRISTMAS SHEARWATER- ~~~ ~ ~

~ ~~~ -

BLUE - GRAY TERN- ~~ ~~ -

SOOTY STORM - PETREL- ~- ~ ~ ~~~

BULWER'S PETREL

BONIN PETREL ~ - ~

BLACK-FOOTED ALBATROS

LAYSAN ALBATROSS^^_

0 50 100 150 200 250 300 350

LENGTH (mm)

Fig 13 Cornparlson of measurable prey lengths for Hawaiian seabirds Deplcted are mean (x) 95% confldence Interval arGUnd mean (CI), and range batross species (Harris 1973, lmber and far more by black-footed albatrosses (50% Russ 1975). However, Laysan albatrosses by volume) than Laysan albatrosses (9%). consumed by volume far more squid (65%) Most of this difference came from the than black-footed albatrosses (32%). Al- large amount of flyingfish ova in the black- though it is possible that these birds fed footed albatross diet (44%) compared to on different species of squid, we could that of the Laysan albatross (4%).A com- identify to family only 2% of those found parison of optical density units (D) of rho- in black-footed albatross samples and 6% dopsin in the eyes of these species indi- of those found in the Laysan albatross cated that Laysan albatrosses are much samples and therefore cannot draw any better adapted for nocturnal vision than conclusions. Certainly, ommastrephid are black-footed albatrosses, the former squids were commonly eaten by both. h having 16 D/gram and the latter 4 reliable method of identifying the beaks D/gram (A. J. Sillman, pers. commun.). of the species in Hawaii is necessary to By comparison, pigeons had very little determine which squids are most fre- rhodopsin, barn owls had 20 D/gram, and quently consumed. Fishes were consumed great horned owls had 46 D/gram. An ad- 54 WILDLIFEMONOGRAPHS

(0v) 0

.J

I

EP w I- I- i

2 n m P i t- sm HAWAIIANSEABIRD FEEDING ECOLOGY-HU~~~SOTZ et al. 55 aptation for nocturnal feeding explains unit for discussion apart from any taxo- why Laysan albatrosses took more squid, nomic considerations. Each species occurs inasmuch as squid migrate vertically and throughout most of the study area (Table are more likely to be on the surface dur- l), but populations of brown boobies are ing darkness (Clarke 1966). Black-footed relatively small. The boobies and tropic- albatrosses, by exploiting prey that is more bird plunge (Fig. 14) to depths of several likely to be obtained during daylight meters (Ashmole 1971). Great frigatebirds hours, ate more flyingfish ova and offal are limited to snatching prey from surface from ships (Miller 1940, Palmer 1962) or waters, probably no more than 15 cm in dead birds (Table 3). Many of the prey depth, because of a structural inability to items taken by both species are capable of take off from the water if they land (R. bioluminescence, which may be impor- W. Schreiber, pen. commun.). At sea, tant to any predator that feeds at night on frigatebirds often associate with fairly vertically migrating prey (Imber 1973). large flocks of other species (Gould 1971). Such items include lanternfishes and Masked and red-footed boobies are mod- hatchetfishes, squids (Onychoteuthidae, erately social at sea, feeding in association Histioteuthidae, Octopodoteuthidae, and with small groups of birds. Brown boobies Cranchiidae), mysids (Gnathophausia and red-tailed tropicbirds feed in a soli- spp.), and tunicates (Pgrosorna spp.) (Im- tary fashion (Gould 1971). Only brown ber 1973). Most importantly, the form of boobies are thought to feed inshore, the S. oualaniensis that occurs in Hawaii has others foraging far at sea (King 1970, Dia- photophores (Young 1975). mond 1978). All species breed in Hawaii There is considerable overlap in the during spring and summer, and most de- diets of these birds, as evidenced by a pendent young are fed April-September comparison of the prey items each con- (Fig. 6). sumed, but the proportions of the major One way in which this guild partitions items are very different (Tables 2, 6). available prey is in the proportion of fish Feeding at different times of the day may and squid taken, an observation made on account for much of this difference. Both Christmas Island (Pacific) for several of species feed their young at the same time these species by Schreiber and Hensley of the year (Fig. 6), and we detected few (1976:247). Red-footed boobies took 27% differences among seasons in prey con- of their prey volume as squid, the most sumption in either species. However, Lay- for any in this group. Red-tailed tropic- san albatrosses exploited Pacific sauries birds (18%)and great frigatebirds (14%) during winter and wind-sailers during took moderate amounts whereas masked spring. boobies (3%)and brown boobies (5%)con- Black-footed albatrosses are heavier and sumed relatively small amounts. Except in hand appear to be the stronger, al- for 3 Onychoteuthidae, all identified though their bills are shorter than those of squids from these species were from the Laysan albatrosses (Table 2). The lack of surface-dwelling Ommastrephidae. Fly- reliable prey measurements and the fact ingfishes were commonly consumed by all that much of the prey of albatrosses may species, ranking first for each except for be shredded before ingestion makes at- brown boobies, in which they tied for sec- tempts to discuss differences in prey ond. Flyingfishes were especially common lengths speculative. Laysan albatrosses are in the diet of great frigatebirds, account- much more numerous, outnumbering ing for more than 60% of the prey volume black-footed albatrosses about 10 to 1 (Ta- (Table lo), a predictable result consider- ble l). ing the inability of this species to dive to exploit other fishes. Flyingfishes ranged in Pelecaniformes percent volume from 58% for masked boobies to 26% for brown boobies. Eight The 5 species of this order within the flyingfishes were identified from stomachs study area form a convenient ecological of this group (Appendix 3) with E. voli- 56 WILDLIFEMONOGRAPHS tans and Cypselurus spp. the most fre- mushkin 1965, Parin 1968, Shuntov 1968, quently identified. Had we been able to Okutani and Ih-Hsiu 1978). Resource par- identify more of the flyingfishes we may titioning among the 4 smaller species may have learned if there were species pref- occur to some extent by feeding area, e.g., erences among the different birds. Caran- brown boobies feed closer to shore than gids, chiefly adult Vecapterus spp., also the others. Feeding methods are also a were commonly eaten and ranked second factor, and the structural differences and or third for each species except brown behavior may come into play primarily boobies, where they ranked first. Half- during food shortages when competition beaks (especially Euleptorhamphus viri- would be intensified. Red-tailed tropic- dis) occurred in the diets of all pelecani- birds, which weigh much less than the forms but ranked highest in masked and other species considered here (Table 2), brown boobies. Goatfishes were preyed on take prey as large as the other birds. This by each bird in this guild but ranked high species has been reported to so seriously only in the diet of brown boobies (tied for misjudge prey length that it can harm it- second) and red-footed boobies (fifth). We self (Clancy 1974). found little geographical variation in diet, The Hawaiian Island pelecaniform but the ranking of some major prey items community eats organisms similar to those changed with season. Flyingfishes and eaten by communities at Christmas Island ommastrephid squids generally were tak- (Pacific) (Ashmole and Ashmole 1967b, en in substantial quantities throughout the Schreiber and Hensley 1976), Ascension year by each species, but Vecapterus spp. Island (Stonehouse 1962, Dorward 1963a), ranked highest during summer and ranked and Aldabra Atoll (Diamond 1974a,b, higher during fall than during spring. 1975). Percentages of flyingfishes and Goatfishes ranked highest during spring. squids consumed by each species are sim- Pacific sauries were taken only at Midway ilar at Aldabra Atoll and Hawaii. At during winter where they were common- Christmas Island, however, red-tailed ly eaten by each species except the brown tropicbirds and great frigatebirds ate much booby. Several birds, at certain seasons and larger percentages of squid than in the locations, exploited prey species that were former locations. The most striking differ- not taken by the others. Great frigatebirds ence was the prevalence of Vecapterus took juvenile sooty terns during spring and spp. and goatfishes in the diets of Hawai- summer. They ate filefish only in the Lay- ian birds. These fishes are rarely eaten san Island group during summer. Red- elsewhere, and their prevalence here un- footed boobies took anchovies only on derscores the influence that local avail- Midway during winter. Red-tailed tropic- ability of surface schooling fishes have on birds ate many truncated sun fish on the diets of seabirds in a given location. French Frigate Shoals during summer. Selection of different prey lengths is Terns and Shearwaters Associated often considered to be a means of parti- with Predatory Fishes tioning food resources in the marine en- vironment. Pelecaniforms that weigh more These 6 species are of fairly similar size, or have longer bill lengths generally take ranging from wedge-tailed shearwaters larger prey (Fig. 13). Masked boobies took (388 g) to black noddies (108 g) (Table 2). larger prey than the other 4 species during Other species are the Christmas shear- the spring-summer chick feeding period water, brown noddy, sooty tern, and white (Fig. 6) when local food resources proba- tern. Each species fed on similar prey bly are most strained. Ommastrephid items of similar size and reportedly feeds squids and flyingfishes are likely to be largely in association with predatory fish- more abundant during spring-summer es, especially tunas (Ashmole and Ash- than fall-winter (Waldron 1964, Aki- mole 1967b:97). Murphy and Ikehara HAWAIIANSEABIRD FEEDINGEc~LOGY- Harrison et a/. 57

(1955:2) found birds so frequently associ- white tern (88%) had diets that were ated with tuna schools in the Central Pa- largely fish by volume, with most of the cific that they were “virtuall?- inseparable remainder squid. Brown noddies and in our observations.” At sea these species wedge-tailed shearwaters fed on 66% fish occur in flocks, with 5 of them associated and 33% squid. Christmas shearwaters and with other birds between 67% (white tern) sooty terns took half or more of their prey and 97% (black noddy) of the time (King as squid. Except for 4 Onychoteuthidae, 1970). Gould (1971) reported that Christ- all identified squids were Ommastrephi- mas shearwaters occurred in flocks in dae. These were primarily S. oualuniensis about half of his sightings. These species but also H. pelagicus and Ommastrephes generally breed throughout the Hawaiian SPP. Archipelago, but Christmas shearwaters Juvenile goatfishes were consistently the are restricted in distribution and sooty highest ranked prey item in the diets of terns and wedge-tailed shearwaters are es- this guild, ranking first of all prey for 4 pecially abundant (Table 1). All species species and first among fishes for each. feed most heavily on resources near the Flyingfishes ranked high but not nearly as islands when young are being fed. This high as with the pelecaniforms. Flying- occurs during spring-summer for most fishes did not rank first in any diet but did species, but wedge-tailed shearwaters feed rank from second to fifth for each species young during fall and black noddies feed except wedge-tailed shearwaters. Most young during winter at some locations identified flyingfishes were E. volitans or (Fig. 13). Cypselurus spp. Decapterus spp. were This guild feeds using a variety of tech- relatively common for several birds and niques (Fig. 14). Shearwaters can pursue ranked second for wedge-tailed shear- prey under water whereas terns plunge waters and fourth or fifth for 3 other dive. Sooty terns will plunge dive only to species. Decapterus spp. was less fre- the surface and cause a splash (Gould 1974: quentiy consumed by the small, inshore 8), yet this species can rarely submerge feeding white tern and black noddy. Liz- because it lacks a substantial uropygial ardfishes occurred in the diets of each bird gland (Johnston 1979) and cannot get wet but ranked high only in black noddies without becoming waterlogged. Black (second) and brown noddies (third). noddies feed by pattering on the surface. We generally found more variation in This guild partitions prey resources in part the diet with season than with location, by selecting different feeding areas. Most and some prey items were exploited ex- of these 6 species feed well offshore, but clusively in 1 area during 1 season. Om- both black noddies and white terns can mastrephid squids were taken regularly feed inshore (Diamond 1978). One of us throughout the archipelago all year by the (CSH) observed black noddies feeding species that feed on squid. Lizardfishes and within a few meters of shore at several of flyingfishes were also taken throughout the the NWHI, often in association with jacks year, but flyingfishes ranked highest dur- Caranx spp. Sooty terns and wedge-tailed ing summer. Goatfishes, the highest ranked shearwaters can feed at night under full family of this guild, were far more prev- moon conditions (Bruyns and Voous 1965, alent during spring than other seasons but Gould 1967). Christmas shearwaters have also were common in summer. Decapte- a rhodopsin density of 3 D/g, which is not rus spp. were eaten most frequently dur- particularly adapted for nocturnal behav- ing summer but also rankcd high during ior (A. J. Sillman, pers. commun.). spring. Most of the round herrings were As with pelecaniforms, this guild par- taken during spring and summer by terns titions prey resources by consuming dif- and noddies, but black noddirs ate many ferent proportions of fish and squid. The at Midway during fall. A filefish (Perva- inshore feeding black noddy (92%) and gor spilosoma) ranked high in the diet of 58 WILDLIFEMONOGRAPHS wedge-tailed shearwaters on Laysan dur- 1955, Ashmole and Ashmole 1967b, Gould ing summer, and lanternfishes were com- 1971). monly eaten by white terns during spring on Midway. Small Nocturnal Procellariiforms Prey lengths were fairly similar, but shearwaters generally took larger prey We consider here the 3 smallest pro- than terns, and black noddies took the cellariiforms in this seabird community: smallest prey (Fig. 13).Some stratification Bonin petrels, Bulwer’s petrels, and sooty or partitioning by prey length clearly takes storm-petrels. Apparently each feeds ex- place, but for several of the most com- tensively at night. Populations of each monly eaten taxa, birds of similar size fed species occur at several locations in the on prey of the same size. Hawaiian Archipelago but do not neces- Our results are similar to those at sarily overlap (Table 1). Sooty storm-pe- Christmas Island (Ashmole and Ashmole trels and Bonin petrels breed during win- 1967b), Ascension Island (Stonehouse 1962, ter and fledge young in spring, whereas Dorward 1963b, Dorward and Ashmole Bulwer’s petrels breed during summer 1963), and Hawaii (Brown 1975). There, (Fig. 6). Bonin petrels are thought to feed ommastrephid squids, flyingfishes, half- by dipping or surface seizing (Fig. 14), beaks, and tunas are commonly eaten. but we could not locate definitive obser- Hawaiian seabirds generally consumed a vations. Bulwer’s petrels feed sitting on the smaller proportion of squid than those at water with wings spread and heads dipped Christmas Island. For example, Hawaiian below the surface (Gould 1971:56), and all Christmas shearwaters fed on 48% squid storm-petrels are strictly surface feeders compared to 71% on Christmas Island, and that feed principally by pattering (Ash- white terns fed on 12% squid compared mole 1971). Each species feeds offshore in to 50%. In addition, Hawaiian birds ate a solitary fashion, occasionally in associa- fewer flyingfishes (although flyingfishes tion with other birds. All have been re- ranked high with several species, espe- ported feeding at night (Ashmole 1971, cially the white tern) but fed instead on Gould 1971, Crossin 1974). The Bonin pe- juvenile goatfishes, juvenile lizardfishes, trel has 11 D/g of rhodopsin, which im- and Decapterus spp. Both Christmas Is- plies some adaptation for nocturnal be- land and Ascension Island birds ate many havior (A. J. Sillman, pers. commun.). blennies, which were rarely consumed in We acknowledged the difficulties pre- Hawaii. Birds at Ascension Island fed on sented by the advanced state of digestion the squid H. pelagicus, but those at of samples collected from these birds in Christmas Island and the Hawaiian Ar- the species accounts. Bonin and Bulwer’s chipelago fed on S. oualaniensis. Size petrels took substantially more fish than ranges of prey were similar in all areas for squid, whereas sooty storm-petrels took which information is available. We con- these prey in roughly equal volumes. Most clude that this group of birds is opportu- identified fishes from Bonin and Bulwer’s nistic in their feeding habits and secures petrels were lanternfishes and hatchetfish- any prey of appropriate size that is avail- es, but they also took numerous bristle- able in the surface waters near breeding mouths. These fishes inhabit midwater colonies. Prey for this guild becomes during daylight, possess photophores, and available primarily when it is driven to normally occur on the surface of the ocean the surface by predatory fishes, and in the only at night or in reduced light condi- resulting feeding flocks partitioning of tions (Clarke 1973, Imber 1973). The sin- prey probably results from differences in gle fish identified from a sooty storm-pe- feeding technique and morphology. The trel was a hatchetfish. Each bird took close association of these birds with tuna numerous sea-striders and various crusta- schools, especially for foraging, has been ceans. Bonin petrels consumed several reported frequently (Murphy and Ikehara goatfishes. Flyingfishes were rarely taken, HAWAIIANSEABIRD FEEDINGECOLOGY-Hurrison et ul. 59 although Bulwer’s petrels took enough egg ious and feed by plunging in flocks with masses from this family for it to rank sev- other species, but his data are limited (29 enth in its diet. Most of the identified sightings). The lack of sightings at sea may squids were Ommastrephidae, but indi- be due to the fact that from a distance vidual Enoploteuthidae and Histioteuthi- gray-backed terns can be mistaken for the dae were identified. These families consist more numerous sooty terns. Blue-gray largely of individuals with photophores in noddies feed by dipping and pattering at Hawaii (Imber 1973, Young 1975). the surface (Fig. 14) and seemingly are We do not have enough information to not dependent on schools of predatory draw conclusions concerning seasonal fishes to drive prey to the surface. Gray- variations in diets among these species or backed terns breed at most of the islands to discuss prey size in detail. Bulwer’s and in the Hawaiian Archipelago, but blue- Bonin petrels apparently take somewhat gray noddies are restricted to the southern larger prey than sooty storm-petrels. Bo- portion (Table 1). Blue-gray noddies feed nin and Bulwer’s petrels breed at suffi- most of their young during late winter and ciently staggered seasons that competition spring whereas gray-backed terns feed for prey in the vicinity of the breeding most chicks during spring and early sum- islands probably is avoided (Fig. 6). Bonin mer (Fig. 6). petrels ate relatively more fish than squid Neither of these species ate much squid, compared to other Pterodromz spp. (Ash- gray-backed terns taking 4% by volume mole and Ashmole 1967b, Imber 1973) but and blue-gray noddies 1.5%.The tern ate were similar in feeding on mesopelagic 92% fish whereas the noddy took only 61%, fishes and sea-striders. The taking of eating instead crustaceans (copepods and hatchetfishes, sea-striders, and by-the- stomatopods) (18%)and sea-striders (18%). wind sailors by sooty storm-petrels is con- Blue-gray noddies are the most important sistent with studies indicating that storm- avian predator on sea-striders in the petrels feed on surface organisms (Crossin NWHI (Cheng and Harrison 1983). Gray- 1974). Our conclusion that these species backed terns ate many cow fish (42%),a feed to a large extent at night does not prey item rarely taken by other birds. preclude the probability that daylight Blue-gray noddies also took some cowfish, feeding also occurs. Lanternfish occur on and gray-backed terns also ate sea-strid- the surface of the sea during daylight ers. Both birds ate juvenile flyingfishes and hours when chased there by yellowfin or goatfishes. Gray-backed terns also ate skipjack tunas (Alverson 1961). Fresh Ian- many dolphin-fishes and round herrings, ternfish were taken by one of us (CSH) whereas blue-gray noddies supplemented from a white tern chick that had just been their diet with larval lizardfishes. Hence, fed by a marked adult at 1000 and 1100 these species fed on many taxa common hours on Midway Island. The heavy reli- to those taken by other seabirds in this ance by Bonin and Bulwer’s petrels on community. The reliance of gray-backed midwater fishes makes it probable that terns on cow fish and blue-gray noddies nocturnal feeding accounts for much of on minute prey such as sea-striders, co- their diets. pepods, and stomatopods is unique. We have no information on the abso- Neuston Feeding Terns lute abundance of prey species. However, W7e treat gray-backed terns and blue- goatfishes ranked highest for both species gray noddies as a guild because their during spring. Sea-striders were con- unique feeding habits do not conveniently sumed more frequently during spring than fit elsewhere and because they have some winter, and dolphin-fishes were eaten pri- similarities in their diets. Both are thought marily during spring and summer. Gray- to feed inshore (Diamond 1978), and both backed terns are larger than blue-gray took small prey (Fig. 13). Gould (1971) noddies (Table 2) and took larger prey. stated that gray-backed terns are gregar- The diet of blue-gray noddies at Christ- 60 WILDLIFEMONOGRAPHS mas Island (Pacific) is very similar (Ash- many of its tropical bird species; Kure is mole and Ashmole 1967b). There, as in the northernmost coral atoll on earth Hawaii, they fed largely on sea-striders (Woodward 1972). Peak food availability and crustaceans, in sharp contrast to other often has been suggested as a controlling species. At both locations flyingfishes factor in the timing of seabird breeding. ranked high and prey was minute, with Pearson (1968:J27) found the breeding of fish having mean volumes of about 0.1 ml. the seabirds in Scotland to coincide “with Hawaiian birds fed heavily on lizardfishes the period of greatest abundance of the and goatfishes, which were absent in the Ammodytidae and Clupeidae in the area.” diet at Christmas Island. Christmas Island Harris (1969:151) found in the Galapagos birds fed largely on snake mackerels, tu- that unpredictable food shortages were nas, and blennies, which were present but closely related to breeding success for the did not rank very high in the diet of Audubon shearwater and concluded that Hawaiian birds. Blue-gray noddies occu- food supply is “the proximate factor con- py the same trophic level and have similar trolling breeding.” The chick feeding in- diets in each location. Differences in their terval is generally much less than the in- diets probably result primarily from dif- cubation shift with tropical marine birds ferences in prey species in waters adjacent (Diamond 1978218, Harrison and Hida to study islands. 1980:27). This phenomenon implies that during the chick feeding period (Fig. 14) Timing of Breeding Season the local waters near the breeding islands and Food Availability must provide most of this food. Ashmole (1963a:464) stated that high latitudes have It is well understood that breeding sea- an enormous flush of food in spring, but son for marine birds is related to the food in “tropical oceans seasonal fluctuations in supply in temperate and cold waters (Be- food abundance are generally much less lopol’skii 1957, Pearson 1968, Bedard extreme.” It was beyond the scope of our 1969, Croxall and Prince 1980). Breeding investigation to measure seasonal or an- seasons in tropical waters are less predict- nual levels of major prey resources, but able (Harris 1969, Schreiber and Ashmole we recognize that such information would 1970), in part because birds in moderate be useful in interpreting these data. climates do not face the ecological imper- Juvenile goatfishes were the most com- atives encountered in cold water regions. monly eaten prey item for the guild that The modal breeding season of Hawaiian associates with tunas. Goatfishes spawn seabirds is predictable (Fig. 6) even though during spring-summer in Hawaii (Miller (1) year to year variations may change 1974), and juvenile goatfishes are not egg-laying dates by many weeks, (2) abundant during fall and winter. Aki- breeding of terns and pelecaniforms is mushkin (196.5184) stated that squids generally protracted, and (3) a few indi- generally migrate with season, especially vidual birds of most species may be found shoreward to deposit eggs. The biology of in any stage of the breeding cycle for ommastrephid squids in Hawaii is insuf- much of the year (Richardson 1957). ficiently known to be sure whether they Why is the breeding season of the have predictable breeding seasons or mi- Hawaiian seabird community more pre- grations (R. E. Young, pers commun.). dictable than that of others comprising The distribution of flyingfishes indicates similar species? One consideration in de- that they vary in abundance with water termining why this community displays temperature (Parin 1963, 1968; Shuntov the spring-summer breeding season found 1968). Shuntov (1968:784) found that in more northern marine bird communi- “flyingfishes were found singly when sur- ties is its location. Much of the Hawaiian face water temperature was 19-20 C, were Archipelago is subtropical and is at the practically a common occurrence at 23- northern extent of the breeding ranges for 25 C, and were very sharply increased in HAWAIIANSEABIRD FEEDING EcoLoGY-Harrison et al. 61 numbers in areas where the water was population size with its attendant dimi- above 25 C.” The surface isotherms for nution of the risk of extinction.” the Hawaiian Archipelago (Fig. 1) indi- Five of the 18 species in this commu- cate that flyingfishes are far more com- nity feed their young during winter (Fig. mon during spring-summer than winter. 14). Laysan albatrosses, Bonin petrels, and Decapterus spp. spawn during spring- sooty storm-petrels all feed nocturnally summer (Yamaguchi 1933) as do dolphin- and thereby exploit different prey than fishes (Mito 1960). Consequently, juve- summer breeders that feed by day. The niles of these fishes would not be ability to breed during winter is enhanced abundant during fall and winter. Adult by decreased day length because this al- Decapterus spp. are resident but may be- lows more time to forage. Black-footed al- come more available during summer when batrosses exploit a unique resource, flying- chased to the surface by migratory tunas, fish eggs, that may be available only in which are usually far more numerous dur- winter-spring. In addition, both albatross- ing spring-summer than winter (Waldron es fly much further from the nesting site 1964). The presence of tunas or other than other species, especially during in- predatory fishes is apparently essential to cubation (Harrison and Hida 1980) and enable many species to obtain prey (Ash- may be less dependent on local food re- mole and Ashmole 19676:97). The biology sources because they can forage over a of sea-striders is insufficiently known to larger area. It is likely that Bonin petrels determine if or when they have a breed- and sooty storm-petrels are forced to breed ing season (Cheng 1973, 1974), but they during winter because of competition for are known to be most abundant in 24-28 nest sites by the larger wedge-tailed shear- C water (Cheng and Shulenberger 1980). waters and Bulwer’s petrels. Wedge-tailed Winter temperatures in the Hawaiian Ar- shearwaters arriving on Laysan in spring chipelago (Fig. 1) are at or below the low- kill juvenile Bonin petrels and sooty storm- er end of this range. petrels and cast them from their burrows The majority of young of most bird (M. B. Naughton, pers. commun.). Black species are fed during spring-summer noddies have the least predictable breed- (Fig. 6), and the increased availability of ing season of any Hawaiian seabird. They food resources during this time is the best feed in association with inshore predatory explanation for the observed breeding fishes (Carunx spp.) that drive prey to the season. We do not contend that prey is surface, enabling young to be raised dur- altogether unavailable in winter; indeed ing winter because these fishes are resi- we found some flyingfishes, ommastre- dent. phid squids, and lizardfishes throughout An alternative hypothesis is that breed- the year. However, the surge in available ing during winter months is inefficient be- prey during spring-summer because of cause of weather. Winter temperatures are spawning activities (e.g., goatfishes, De- much cooler than summer, and storms are cupterus spp.) and tuna migration is a frequent in the Hawaiian Archipelago. controlling factor for the regular spring- Black noddy colonies at French Frigate summer breeding seasons. Tropical birds Shoals have been decimated in winter by that feed hy daylight have less time each high winds blowing nests from heliotrope day to search for food than their northern shrubs ( Tournefortin argentea) and counterparts and need the relative cer- hundreds of black-footed albatross chicks tainty of encountering prey near the have been drowned by storm tides (R. P. breeding colonies during spring-summer Schulmeister, pers. commun.). This is to reproduce. Several bird species are mi- another relevant factor that explains why gratory, abandoning breeding colonies this seabird cornmunit). breeds during during winter months to forage else- spring-summer, hut we believe that food where, an adaptation argued by Diamond availability is much more important. The (1978222) to be “rewarded by greater fact that even small species such as sooty 62 WILDLIFE MONOGRAPHS storm-petrels and black noddies can fledge boobies; sooty and gray-backed terns; young in a winter breeding cycle is evi- brown and black noddies). These popu- dence against weather being a limiting lation differences may be merely another factor. expression of the proposition that pelagic feeders are more numerous than inshore Opportunistic Feeding and feeders (Diamond 1978). Without data on Diet Diversity the availability of prey, we cannot know whether food directly controls population Seabirds in Hawaii feed on a wide va- size. Inshore feeding species seem to have riety of shoaling fish and squid and ap- more diverse diets than offshore feeding parently take anything of appropriate size ones. It is tempting to attribute this dif- that occurs in surface waters. This diver- ference to enhanced competition in in- sity is reflected in the fact that no bird ate shore feeding areas, but inshore fauna is any 1 prey species to an extent that it much more diverse than pelagic fauna. comprised half or more of the volume of Differences in feeding zones and feed- the diet. Our analysis is confounded by ing locations are used to explain differ- prey material that could not be identified ences in diets, often without convincing to species, but even the highest ranking evidence (Ashmole and Ashmole 1967b, prey family for many birds was relatively Pearson 1968) and are based on inferences low by volume: brown booby (15%), from incubation shifts, chick feeding fre- wedge-tailed shearwater (18%),white tern quencies, or scattered observations at sea (20%), brown noddy (28%), and black in the vicinity of the colony without means noddy (31%).Diets that contain 20-40 to distinguish breeding from nonbreeding prey families are very diverse compared birds. Ashmole and Ashmole (1967b363) to those in northern latitudes (Pearson analyzed feeding zonation using percent- 1968). The most specialized diets were ages of fish that belonged to pelagic and those of gray-backed terns (42% cowfish) reef-originating families. This analysis is and black-footed albatrosses (44% flying- useful but is limited by the fact that epi- fish eggs), but the latter included more pelagic species such as flyingfishes and than 1 species. Percentage volumes are halfbeaks regularly occur in shallow water higher for unidentified flyingfishes and in the NWHI. As Diamond (1974h208) unidentified squids for Laysan albatrosses pointed out, the pelagic-feeding red-foot- and some pelecaniforms, but these cate- ed booby on Aladabra Atoll could feed gories include many prey species and it is over water 500 m deep at 1 km from the unlikely that any one accounts for as much reef, a situation common in the Hawaiian as half of the prey. In contrast, seabirds Archipelago. Future investigators must lo- in Peru feed 80-96% on a single fish (Jor- cate feeding areas of tropical seabirds to dan 1959, 1967). determine the importance of feeding zones The opportunistic character of these and to protect them from marine devel- feeding strategies is evidenced by the opment. Radiotelemetry (Harrison and many prey items that were taken only Stoneburner 1981) is a useful technique in during 1 season or at 1 location. Many this endeavor. The notion that most trop- prey taxa were taken only seasonally, ical birds feed far offshore must be chal- probably reflecting seasonal occurrence in lenged if we are to further our under- surface waters. We are limited by an in- standing of the forces that shape their ability to distinguish between relative and feeding and breeding ecology. absolute prey abundance. Much of the variation in diet occurs in the relative pro- CONCLUSlONS portions of several common prey families. The most numerous birds in this com- 1. Seabirds in Hawaii are opportunistic munity are those that eat many squid and feed on any prey of appropriate (compare Laysan and black-footed alba- size that occurs in surface waters. trosses; red-footed, masked, and brown 2. Similar to other tropical communities, HAWAIIANSEABIRD FEEDING ECOLOGY-Harrison el al. 63

Hawaiian seabirds consume many ARMSTRONG, R. W. 1973. Atlas of Hawaii. Univ. flyingfishes and ommastrephid squids. Press of Hawaii, Honolulu. 222pp. ASHMOLE,M. I., AND N. P. ASHMOLE. 1967~.Notes This community is distinguished by the on the breeding season and food of the red-foot- occurrence in the diets of many juve- ed booby (Sula sula) on Oahu, Hawaii. Ardea nile goatfishes, juvenile lizardfishes, 55:265-267. Decapterus spp., and mesopelagic fish- ASHMOLE, N. P. 1963~.The regulation of numbers es. of tropical oceanic birds. Ibis 103b:458-473. . 1963b. The biology of the wideawake or 3. Compared to Christmas Island, sea- sooty tern Sterna fuscata on Ascension Island. birds in Hawaii consume more fish than Ibis 103b:297-364. squid. 1971. Seabird ecology and the marine en- 4. Variation in diets is more correlated vironment. Pages 223-287 in D. S. Farner and with season than with location. How- J. R. King, eds. Avian biology, Vol. I. Academic Press, New York, N.Y. ever, during certain months at Mid- , AND M. J. ASHMOLE. 1967b. Comparative way, prey species such as Pacific sau- feeding ecology of sea birds on a tropical oceanic ries and round herrings are taken that island. Peabody Mus. Nat. Hist. Yale Univ. Bull. do not occur elsewhere. 24. 131 pp. The time of year during which most BAIIXY, N., AND w. R. P. BOL‘RNE. 1963. Some 5. records of petrels handled in the northern Indian young are fed (spring-summer) is cor- Ocean. J. Bombay Nat. Hist. Soc. 60:256-259. related with the maximum availability BALTZ,D. M., AND G. \’. MOREJOHN.1976. Evi- of prey. dence from seabirds of plastic particle pollution 6. Larger predators took larger prey than off central California. West. Birds 7:111-112. smaller predators, but during spring- BEARD,D. B. 1939. Man-0‘-war-birds prey on East- ern sooty terns. Auk 56:327-329. summer, similar-sized birds had few BEDARD,J. 1969. Feeding of the least, crested, and significant differences among lengths parakeet auklets around St. Lawrence Island, of common prey items. Alaska. Can. J. 2001. 47:1025-1050. 7. Diets provide circumstantial evidence BELOPOL’SKII,L. 0. 1957. Ecology of sea colony that Laysan albatrosses, Bonin petrels, birds of the Barents Sea. Izdatel’stvo Akad. Nauk SSSR, Moscow-Leningrad. Israel Prog. for Sci. Bulwer’s petrels, and sooty storm-pe- Transl., Jerusalem. 346pp. trels feed at night. BERGER,A. J. 1972. Hawaiian birdlife. Univ. Press 8. Many fundamental questions concern- of Hawaii, Honolulu. 27Opp ing the biology of tropical and subtrop- BROWN,W. Y. 1975. Parental feeding of young ical seabirds cannot be answered until sooty tern (Sterna fuscata lL.1) and brown nod- dies (Anous stolidus [L.]) -in -Hawaii. J. Anim. better methods of measuring the avail- Ecol. 44:731-742. ability of prey are developed. RRL‘YNS,W. F. J., AND K. H. VOOVS. 1965. Night- feeding by sooty tern (Sterna firscata). Ardea LITERATURE CITED 53:79. CHEM:, L. 1973. Halohates. Oceanogr. Mar. Riol. AINLE’I’, D. G., ANI) T. J. IEWIS. 1974. The history Annu. Rev. 11:223-235. of Farallon Island marine bird populations, 1854- 1974. Notes on the ecology of the oceanic 1972. Condor 76.432-446. insect Halobutes. Mar. Fish. Rev. 36:l-7. AKIhl~‘wI(IN,I I. 1965. Cephalopods of the seas of , hSD C. S. HARRISON 1983. Seabird pre- the U.S.S.R. Academy of Sciences, hloscow Is- dation on the sea-skater Halobates sericeus rael Prog. for Sci. Transl., Jerusalem. 223pp. (Heteroptera:Gerridae). Mar. Biol. 72.303-309. .4LEXAhnEH. W. B. 1954. Birds of the ocean Put- , 4!iD E. SHULENBERGER.1980. Distribu- narn, New York, N.Y. 306pp. tion and abundance of Halolmtes. Fish. Bull. 78: AL,\ ERSOR, F. G. 1961. Daylight surface occur- 579-591. rence of myctophid fishes off the coast of Central CI..ANC.I,P A. 1974. Red-tailed tropicbird inca- America. Pac. Sci. 15:483. pacitated by flyingfish. Ostrich 45.39. AMEHSOK, A. B., Jn. 1971 The natural history of CLAPP,R. B. 1972 The natural history of Gardner French Frigate Shoals, Northwestern Hawaiian Pinnacles, Northwestem Hawaiian Islands. Atoll Islands. Atoll Res. Bull. 150. 383pp Res. Bull. 163. 25pp. --, R. B. (:LAPP, ANI) I\’.0. M’IHTL. 1974 The 1976. Graybacked terns eat lizards. Wil- natural history of Pearl and Hermes Reef. son Bull. 88:354. Northwestern Hawaiian Islands. .Atoll Res. Bull. , AYD E. KHIDLER. 1977. The natural his- 174. 306pp. tory of h’ecker Island, Northwestern Hawaiian hDEHX)N, W G. 1934. Sotes on food habits of Islands. Atoll Res. Bull. 206. 102pp. sea birds of the Pacific. Elepaio 14.80-84. , A~D\V, 0. WIRTZ.1975. The natural his-

------__ _--- 64 WILDLIFEMONOGRAPHS

tory of Lisianski Island, Northwestern Hawaiian 1901. On the habits of thr Laysan alba- Islands. Atoll Res. Bull. 186 196pp. tross. Auk 21:8-20. --, AND R. R. FLEET. 1977 The nat- FIT(.H, J. E., ,+\I) R. L, BHOWSELI.,JH. 1968. Fish ural history of Nihoa Island, Northwestern otoliths in cetacean stomachs and their impor- Hawaiian Islands. Atoll Hes. Bull 207. 117pp. tance in interpreting freding habits. J. Fish. Res. CIAHKE, M. H. 1962. Thr itlent~ficationof cepha- Board Can 25:2561-2574 lopod "beaks" and the relationship betwern beak FLEET,R. R. 1974. The rrd-tailed tropicbird on size and total body weight Br hfus. (Kat. Hist.) Kure Atoll. AOV Ornithol hlonogr. 15. 64pp. ZOO^. Bull. 8:420-500. GIRSO\-€~II,I,,C. A. 1917. The normal food of trop- , 1966. A review of the s?stematics and ecol- icbirds (Phaethon spp.), Ibis 89.658-661. ogy of oceanic squids. Ad\. hlar Riol. 1:91-300 GOCHFELD,M 1975. Hazards of tail-Erst fish-swal- 1977. Beaks, nets, and numbers S?mp lowing by young terns. Condor 77.315-316. Zool. Soc. London 38.89-126. GOSLIXE,\V. A, AYLI 1'. E 131\oc:s 1960. Hand- C;I..ARKE, T. A 1973. Some aspects of the ecolog) book of Hawaiian fishes. L'ni\.. Hauaii Press, of lanternfishes (Xl>~ctophtdae)in the Pacific Honolulu. 372pp. Ocean near Hawaii Fish Bdl. 71.101-131. Go~'LD.P. J. 1967 Nocturnal ferding of Sterna CoL.i.n-rE, B. R., R Giiias, JR., :AND G. E. C:I.IPITH fuscatu and Puffinus pacificus. Condor 69:529 1969. Vprtebral numbers and identification of 1971 Interactions of seabirds over the open the t\\o species of dolphin (Coryphaena) Co- ocean Ph D Thesis. Univ of Arizona, Tucson ' peia 1969530-631. 110pp. COTT.\\~,C:., ,A\D P. K~ITE\ 1939 Food of some 197.1 Soot! tern (Sterna fitscata) Pages uncommon lorth .4mericari birds. ,Auk 56.138- 6-32 in \V E. King. rtl. Prlagic studirs of sea- 169 birds in the central and eastern Pacific Ocean CI\i\\FOf~I). H. J. 11.. :\\I) P .A. SI-IEI.TO\. 1978. Smithson (~imtrili.Zool 158 Pelagic fish and seabird interrelationships off the Gwss, hl G , J. D. ~III.I.IU\>,I 1. TI\\('~:t. JH., .A\II coasts of South \Vest and South .Africa. Riol. H. S. LADD 1969 \larine geolog! of Kure and Conserv 11:83- 109 Mid\va? Atolls, Hawaii. a prt.liminary report CKOSSI\,H S. 1971 The storm petrels (H)drohat- Pac. Sci. 23:17-25. idae). Pages 151-205 in \V. B. King, ecl Pelagic HAHRIS.hl P 1969 Fond ac a factor controlling studies of sral)irds in the central antl eastern I'a- the breeding of Prrfinirs Ihcrrninierl. Ibis 111: cific Ocran. Smithson. Contrib. Zool 158 277pp. 139- 136 CHOSALI.,J. P., 4\11 P. h PIII\(:I: 1980 Food. 1973. The hiolog! of the axed albatross feeding ecnlog: , and ecologic-al segregatiorl of nionierfra irroratn of Hood Island. Galapagos. seabirds at South Georgia 13ioI. J Linn. Soc 14. Ibis 115.183-510. 103- 131. H.\twiso\, C:. S , %\I) T S Hiri\ 1980. The status Di.szio\l), A \V 1971~. I3iolog~ and beha\,ior of of seabird research in the North\vestern Hawai- frigatebirds Frrgala spp. on Aldalm .Atoll Ibis ian Islands. Pqes 17-21 in H. \V Grigg. antl H. 117:302-32:3 T. Pfnnd. eds. Prnc of Status nf Resour. Jrirest 1974b. Thr rrd-footed boob) nn .Aldabra in .\orth\vrsterri Ila\\ aiian Islands. L.iii\ of Ha- ..itoll, Indian Ocean. .Artlea 62.196-218. \\ aii Sea Grant, Honolulu 197.5 The hiol(ig) of tropic birds at A- . 4\1) D L Yro\k.iI.L.. C; P. 197:3 The anchov) crisis Sci Am D~IIMAIII). I). F. 196:3u. of the hrmvn nntltl! .Anoirs .stolidu.y on a re\ ie\\ <:nndor 78 :3(%;-:364, .~sccnsionIsland Ibis 103b.447-437 . \\D H KL55 1973 Some fond$ of the \\an- El,\. (:. .A,, \\I> H I3 (:I,AI,I' 1973. Thr natural clering alhatrnss (Dionicdcn rrtclaris) Sotornis histor! of Laysan Islarid. \orthuesterii Hunai- "2:27-56. ian Island,. ,Atoll Res I3rill 171 36ilpp JOH\STO\, D. \I' I979 The uropygial gland of FI~IIVII,H 1 1915 I3lark-to(itetl alhatrosses rating the soot! tern <:niidor XI .1:30-492. fl?iiigfish (:oiidor 47.128-129 JOHDA~,R. 1959. El fenomeno de las regurgita- , ,\VD hl L. FIsI%E:t<1469 Thr \isits of IA>- cionrs en el guanay (Phalacrocorax hougainoillii sa11 all)atrnssec to thr \)reeding colon! \licrii- L) y tin metodo para rstimar la ingesti6n diaria. nrsica CJ Ch1I Guam) .5.17i3-221 Buletin Compania Administradora del Guano 35: FISIIIX.\Y. K 1903 Bird\ of La>sari arid tlit. Itkc- 23-40. ward islarids, lian aiiari gronp Hiill L' S Fish 1967. The predation of guano birds 011 the Cornm 23.767-807 Peru\ 1311 anchin ! (Eii,grntt/i.\ringens [Jen\ns])

66 WILDLIFEMONOGRAPHS

TY, D. L. 1952. The bird islands of the Sa- APPENDIXES hul Shelf. Ernti 32.33-39. SH[.KTO\, V, P. 1968 (hints of fl!ingfishes in the Appendix 1. Common and scientific names of birds eastern Indian Ocean. Probl of Ichth?ol. 8:784-

789. (:ornrnon iiariw Scientific riarnr S~oumro~SE, 1962. ,Ascension Island and the ~ Tyto alba British ornithologists’ union centenary expedi- Barn ou I Hark-Sootrd alhatross Dioiriedea nigripes tion Ibis 103b:107-12:3 1957-59. Black nodd! Anous niinutus STHASIX~HG,D \+’. 1964. Further notes on the iden- (tenurrostrrs) tification and biology of echeneid fishes Pac. Sci. Nrie-gray nodd) Procelsterna cerulea 1851-57. I’,nriiri petrel Pterodroma hypoleucn TISKEH,S. M‘ 1978. Fishes of Hauaii. Ha\vaiian Rniu 11 hniib\ Sula leucogaster Service, Honolulu. 392pp Brown nodd! Anous stolidus TOMB~CK,D F. 1975 .An emetic technique to in- Biiluer‘s petrrl Rulwerra Inrlwerii vestigate food preferences Auk 92 581 -383. (:hristmas shrarwatrr Pufittus nuttoitatis Gra! -hac!& tern Sterna lunata TOM’SSLEI, J 1953. .Adult and larval stomatopod S. Gra! -faced petrrl Pterodroma niacroptera crustaceans occurring in Hawaiian waters. Pac. gouldi Sci. 7:399-437. <;rr.at frigatehird Fregata niinor TI LEH, J C:. 1980 Osteolog! , ph! logen), and Crrat horned nu I Rtr bo oirgin ia n us higher classification of the fishes of the ordrr LA! SJII albatross Diomedea inini~tohlts plectognathi (Trtraodontifornies). SO.A.4 Tech Jlasked tiooh! Strln dactylatra Rep., NMFS Circ. 434 422pp. Phociiix prtrrl Pterodroma alba Sula sula , 4h1) J R. P~XTO\1979. Ne\\ genus and Rrd-S storm-prtrrl Oceanodronta tristranii 202-219. Soot! tern Sterna firscnta M+.I.uIw\, K. D. 1964 Fish schools and bird fliicks \\‘rdge-tailed shrar\\ atrr Pufinus pacif;ctrs in the central Pacific Ocran, 1930-1961 US \\‘hit? tern (fair\ trrn) Cy.@s alba Fish and \f’ilcll. Serv Spec. Sci. Rep.-Fish 464. 20PP , ,f the \Vootls Dolphin-fish Coryphaenu spp bIotiacanthiilat~ Hole region. \lassachr~setts.I. S Natl \Ius. Biil1. Filefish Fl>irig fish I-xocoetidar 158 633pp. FI! ing grirnard Dactyloptena orientah l%o. Copepods gathered by the L-nited (hathsli Jlullidae States fisheries steamer “Albatross” from 1887 to Gnh? Ptereleotris heteropterris 1909, chiefly in the Pacific Ocean L’.S. Sat1 Halflwah f leniiramphidar Mus Null. 100 44lpp Hatchetfish Sternoptychidae \VOOII\~~.~IW,I’ \V. 1972. The natural histor! of Lanternfidi \l~ctophidae Krire Atoll, Northumtern Ha\vaiiaii Islands. .Atoll 1 .izardfish Sy nndontidae 3 la n-o- u,ar fish Nonieus gronouii Res. RLlll Iti4 318pp. llarlin Istiophoridar YA\M<;L(:iii, 1933. The fisher? anti the lklog: Y. hlantis shrimp Stomatnpoda of the Hau aitan opelri, D~c’aptertcspiniiulutits Nf.edlrfisll Relonidar (E\.dour and Soulryrt) 51 S Thesis. L.tii\. HA- Pacific saw) Chlolahs saira waii. Honolulu. 123pp. Pilnt fish Notrcratea dtrctor YOL v;, R. E. 1975. .A tirid revieu of the biolog! Ihiiid herring Sprntellotdes delicotulirs of the oceanic squid Synip/Pc.totc,irthis ounlan- Hiiddrrfish Kyphosus Innpthhs iriisis (Lessonj. Comp I3iochem. Ph! si01 32H Sea-5tridrr Halolmtes sericeus 141-143 Sil\ rrsidr Prunestis instriarunt Skipjad triiia ~atsriu.onuspelaniis Sriakr ntackcd Genipylus aerpens Recaicd 1.5 June 1982. Sqriirrrlfish I iolocmtridar iicceptcd 28 June 1.983. Striped haukfish C,’heilodactylus uittatus l’runc.atrd sun fish Ranzunia /UPVIS Bv-the-wind sailor ~’clrllaurlella HAWAIIANSEABIRD FEEDING ECOLOGY-HUWZSOTI et al. 67

Appendix 3. List of Occurrence of prey items by bird species: white tern (WHTE), black noddy (BLNO), brown noddy (BRNO), blue-gray noddy (BGNO), gray-backed tern (GBTE), sooty tern (SOTE), great frigatebird (GRFR), brown booby (BRBO), red- footed booby (RFBO). masked booby (MABO), red-tailed tropicbird (RTTB), sooty storm-petrel (SSPE), Bulwer's petrel (BUPE), Bonin petrel (BOPE), Christmas shearwater (CHSH). wedge-tailed shearwater (WTSH), Laysan albatross (MAL). and black- footed albatross (BFAL). A plus (+) designates occurrence and an asterisk (*) designates an item especially important in dietary ranking.

FISHES Ammdytidae Bleekeria gillii ++ ++ ++ + ++ Atherinidae Pranesus insularum *+ ++++ Balistidae + ++ + Xan t hich t h ys men t o + Relonidae + + ++ Platybelone argulus platyura + + + Ablennes hians *+ +++ + + + +. Blenniidae ++++++ + + Plagiotremus goslinei + Bothidae +++ Rothid larvae + Bramidae Brama orcini + + Pteraclis uelifer + + ++ Cant higasteridae Canthigaster sp. + Carangidae +++ ++ ++ +++ Decapterus spp. ++* ++***** ** i D. macarellus +++ D. macrosoma +++ ++**+*+ + +* D tab1 ++ ++++ + + Selar crumenophthalmus + ++ + Naucrates ductor ++++++ + + Seriola spp + +++ ++ + Caranx spp + + Carangoides ferdau + Chaetodontidae + Chaetodon sp + Chaunacidae + Cheilodactylidae Cheilodact ylus uit ta tus +++ ++ + (:irrhitidae + + Cirrhitops fusciatus + I Clupeidae Spratelloides delicattrlus +*+ *+ Sardinella marquesensis + Congridae + 4 Coryphaenidae Coryphaena spp. ++ ++ +++++ + C. hippurus ++ +*++++++ + C. eqtriselis *++ + +++++ ++ Dactylopteridae Dactyloptena orientalis + ++++ ++ Diodontidae + ++ + + Diodon spp. + ++ + D. hystrtx + Echeneidae + + + ++ Reniora spp. + + R. remora + Remoropsis Inochypterus + + Rhonilmchirus osteochir ++ ++ Elrotridar Asterropieryx sp. i Engraultdar Stolephorus buccaneeri +++ t + 68 WILDLIFEMONOGRAPHS

Appendix 3. Continued

Exocortidae *********** +t**++ Exocoetus sp. + E. oolitans +++ +***** + + E monocrrrhus + + + Prognichthys gilberti ++ + + Cypselurus spp *+++++*+**+ + C speculiger + +++++ C. simus + c. spllolloiopterus + C. atrisignis ++ +++ C spilopterus + + + Exoc~oetidaeova + ** Fistulariidae + + Gempylidae ++++ + ++ + + ++ Gempylus serpens +**++*+++++ +++ Gobiidar + + Piereleotris heteropterus *++ + Conorhynchidae Gonorhynchus gonorhynchus +++++ + + Conostomatidar Vineiguerria spp + t + +++++ V nimbaria ++ + ++ Diplophos sp + Hemiramphidae ++++ +++++ + Euleptorhamphus oiridis ++ + +*+*+ + Hyporhamphus acutus pacificus + + t Oxyporhamphus micropierus t+ +++++ + Holocentridae ++++++ + +*+ Neoniphon sammara + Sargoceniron spp ++ + + tlolocentrid larvae + M yripristis chryseres + Hoplichthydae Hoplrchthys sp. + lstiophoridae ++++ +++ 1 Istiophorus platypierus + + Teirapferus angusiirosiris + + + Makaira nigricans +++++ lstiophorus spp + K yphosidae Kyphosus bigihhus ++ + +*+++ + Lahridae Hemipieronoius leclusei + Macrorhamphosidae Macrorhamphosus gracilis ++++++ + i ?viacrouridae + + blolidae + Ranzania lueuir ++ ++ + * + Masfurus lanceolatus + + t Monacanthidae + +++ t + ++* Peroagor spilosonin ++ +++ + Alutera scripta + Cantherhines spp + + C,’. oerecundiis + Mngilidae ++ + Mnllidae ******+**++ ***+ Myctophidae +++ ++ + + ** ++ Benthosema fihulatuni + Hygophum spp. ++ Myctophum spp ++ Lnmpanyctus spp + Dtaphus spp. + Symbolophorus sp + HAWAIIANSEABIRD FEEDING ECOLOCY- Harrison et ai. 69

Appendix 3. Continued.

+++++*+++ + + ++ ++ +++ + + + + +++ i + + +* + *

t ++++++ ++ + + + tt+ + + + + ++ ++*++ + + +++ ++++ + + + + + +++ +++++++ ++ + + ++ + + ++ + + + + + + + ++ + ++++ + + + + + +**+ + + *+ i +***++ + + +++ + + + t + + + + tt + + + + + ++++ + **+****+++******** ++ *+ + + +++ t + + ++ +

++*++**+*+******** ***++*+**** ++**** + + ++ + 70 WILDLIFEMONOGRAPHS

Appendix 3. Continued.

Symplectoteuthis spp. ++* +*++++t *++ S oualanienis +++ ++++++ ++++ S. luniinosa + +++ Hyaloteuthis pelagicus + + +++ ++ + Cranchiidar + Lepidoteuthidar + Mastigoteuthidar Mastigoteuthis sp Enoploteot hidae Thelidioteuthis nlessandrinii + Pterygioteuthis niicrolampos + On)choteuthidae + t + Onychoterr t his spp + + Oriykia spp + Histioteuthidae + + Octopoteuthidar + Octopoda + + Gastropoda Jarlthinidae Janthina spp + J. pallida + J pallida (egg masses) J. prolongatn C;a\oliriidar Cavohnta trideritata + ANNELLIDA Polyc,harta -1 ARTHROPODA (:riistacea (uriidrntified) ++* +** (histacean larvae + + ++ h1)sidacea I + ++ Lophogast ridae Gnathophausia spp + ++ G. gigas ++ C. tngens ++ hl?sidae Siriella spp. + Euphaiisiacea +++ + + +t Stoniatopoda + + i Stomatopod larvae + + Squillidar Pseudosqrilfa spp + + + Squtlla spp + + Lysiosquilla spp +++ i + Coronidu spp + t Odontodactylus spp ++ 0. Aevirostris + Amphipoda + +t + ++ Oxycrphalidae + Eurythenes gryllus Alicella sp + Isopoda ti i ++ <:? mothoidae Anrrroprrs spp + ++ A branchiatus ++ Parasitic Isopoda ++ t +++ Trbaliacra Nehaliidar Nehaliopsts typica ++ (:nprpoda t + Pmnrllidae Penella spp t + HAWAIIANSEABIRD FEEDING ECOLOGY-HUW~SOTI et al. 71

Appendix 3. Continued

Pontellidae + Pontella spp + P. atlantica *+ Calanoid copepod 2. + Parasitic copepod + Decapnda Shrimp + ++t ++++ ++ Penaeidea ++ Penacus marginatus + Crnnadus sp + Aristarinae + Caridea + + Oplophoridae ++ Nolostomus spp ++ N. japonicns + Acanthephyra sp + A fTxiniia + Srrgestidar + Lucifer spp + Pasiphaeidar ++ Crab (Brachyura) + +++ (hbmrgalopa + ** ++ + I'ortunidar + (;alatheidar + Grapsidae Planes cyaneus + ++ Insrrld + Grrridae Halobates sericeus +*+ +** +++ H niirans + Lrpidoptrra (moth) + (:atrrpillar + + Orthnptera (grasshopper) Euconocephaltrs nascrtus + Argasidat3 (tick) Ornithorlorus capensis + COLENTEHATA + Velellidae \'vlvllo veldla +++ * *+ Sryphoziia + + + 'I'UNI(:,47'A I'yros(irnatidar + ++ I3IR DS I'riict4 lariifiirmr~ Ptrfin1rs sp + P. pacifcrcus + Pirrodroino hypoleirca I I.aridae Sterna frrscata + A 1-C; A P; F11racrar Sargassuni sp + VNIDENTIFIEU REhlAINS ++++ + ++++** ti** I~NIL)ENlIFIE:I) h1EAT + +