Breeding Biology of the Rhinoceros Auklet in Washington’
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TheCondor88:143-155 0 The Cooper Ornithological Society 1986 BREEDING BIOLOGY OF THE RHINOCEROS AUKLET IN WASHINGTON’ ULRICH W. WILSON U.S. Fish and Wildlife Service,Nisqually National Wildrif Refuge, 100 Brown Farm Rd., Olympia, WA 98506 DAVID A. MANUWAL Wildrife ScienceGroup, Collegeof Forest Resources,University of Washington,Seattle, WA 98195 Abstract. During 1914 through 1983, we investigated the breeding biology of the Rhinoceros Auklet (Cerorhincamonocerata) at three main colony siteson the coastof Washington:Destruction Island (offshore) and Protection and Smith islands (inland islands of the Strait of Juan de Fuca). Averageburrow densitieswere higher offshore,where the aukletsnested on shrub-coveredslopes; inland aukletsnested on grassyslopes and level areas. Egg-layingpatterns varied among years and populations,although initiation dates on all islandswere similar. The incubation periods averaged 45 days and ranged from 39 to 52 days. Chicks were brooded, on average,for 3.9 days (rangezero to 9 days). On Protection Island, early-hatched young grew more rapidly than chicks hatched at a later date. Chicks on offshore islands were fed a variety of fish, whereas those on inland islands were fed primarily two species.The inland chicks were fed heavier fish loads, reachedheavier peak body weights, and were heavier when they fledgedthan were offshore chicks. Breeding successwas higher on the inland colony sites. Key words: RhinocerosAuklet; Cerorhinca monocerata; Washington(state); breeding biology; pujins. INTRODUCTION DESCRIPTION OF STUDY SITES Among the Pacific alcids, the puffins show Destruction Island (47”40’N, 124”24’W) is lo- strong structural (Storer 1945) and ecological cated 4.8 km west of the Olympic Peninsula similarities that provide an opportunity to ex- and 29 km south-southeastof La Push, Wash- amine the species’ responsesto their environ- ington (Fig. 1). The 0. 15-km2 island, part of ment. Most published accounts of these birds an extensive sandstone reef, forms a nearly reflect studiesat single colony sites.We report level terrace approximately 30 m high, with here a comparative study of the breeding bi- abrupt cliffs and steep slopeson all sides. Ex- ology of one of these puffins, the Rhinoceros tensive rocky outcroppings entirely surround Auklet (Cerorhinca monoceruta), at three dif- the island. The vegetation on the top of the ferent major colony sites in Washington State. island consistsmostly of salmonberry (Rubus Marine birds that nest on islands differing spectabilis)and salal (Gaultheriashallon), and in physiography and marine environment can is devoid of much understory. The surround- be expectedto differ among colonies in aspects ing slopesand cliffs have interspersedpatches of their biology. The breeding distribution of of salal and salmonberry, coast willow (Mix the Rhinoceros Auklet in Washington is ide- hookeriana),dune wildrye (Elymusmollis) and ally suited for comparisonsof colonies because grassassociations dominated by common vel- approximately half of the state’s auklets nest vetgrass(Holcus lunatus), orchardgrass (Dac- off the outer coast of the Olympic Peninsula, tylis glomerata),and red fescue (FestucaYU- while the remainder nest in the inshore waters bra).Mean annual precipitation for the area is of the eastern Strait of Juan de Fuca. The two 267 cm. Destruction Island is jointly admin- populations may thus experience different en- istered by the U.S. Coast Guard, which main- vironmental influencesthat are not masked by tains a lighthouse and other navigational aids latitudinal effects. on the island, and the U.S. Fish and Wildlife Our specific objectives were (1) to gain new Service. information on the major aspectsof the breed- Protection Island (48”08’N, 122”55’W) lies ing biology of the Rhinoceros Auklet, (2) to 3.2 km off the mouth of Discovery Bay at the document the responsesof individual colonies southeasternend of the Strait of Juan de Fuca to terrestrial and marine components of their (Fig. 1). About 80% of the island’s 1.59 km* environment, and (3) to compare the breeding area consistsof a plateau bounded by precip- biology of the Rhinoceros Auklet with that of itous cliffs 35 to 76 m high. At the southeastern the other two Pacific puffins. and southwesternends, extensive grassyslopes terminate in sand and gravel spits. The vege- tation of this plateau area consists of mixed 1Received 30 January 1984. Final acceptance4 Decem- coniferous woods and thickets of flowering ber 1985. shrubs, grassy areas, alfalfa fields, and sand 11431 144 ULRICH W. WILSON AND DAVID A. MANUWAL ner (1976) on Destruction Island in 1974 and 1975, and by Wilson on Protection Island in 1975 and 1976. Food habits, growth of chicks, and habitat preferences were further investi- gated by Wilson during short visits to Destruc- tion and Protection islands during 1979 through 1981 andin 1983. The distributions and densities of auklet burrows were determined either by counting all burrows or by obtaining average burrow densities for specific habitat types using ran- domly spacedquadrats that varied in size from WASHINGTON 3 x 3 m to 10 x 10 m. On Protection Island, the slope was measured by placing an Abney level on the top of a two-by-four that was laid acrossthe center of each quadrat; burrow oc- cupancy patterns were determined by placing toothpicks on the entrancesof auklet burrows. Becausewe saw no evidence that small mam- FIGURE 1. Locations of Rhinoceros Auklet study sites mals inhabited the nesting areas, we assumed in Washington. that a pushed-over toothpick indicated that an auklet had entered the burrow. There is some evidence, however, that sub-adults may visit dunes. The vegetation of the grassyslopes and colony sites,although they do so generally after the more level, adjacent, peripheral areas con- the main breeding is over (pers. observ.; Ver- sistsprimarily of annual grasses,with Bromus meer, in litt.). rigidis dominating other Bromusand Aspris We investigated activity patterns by record- grasses(Richardson 196 1). Protection Island ing the daily arrival time of the first auklet that lies in the rain shadow of the Olympic Moun- we observed flying to the colony site. Fur- tains and, consequently,has an annual precip- thermore, we attempted to quantify arrival and itation of only about 41 cm. Approximately departure flights throughout the 1976 breeding 85% of the island was privately owned at the seasonby erectinga blind in a major flight path time of our study. In recent years, numerous below approximately 500 burrows that were recreational homes have been built on the pri- located on a gradual slope at the southern end vate portion of the island. Under recent leg- of Protection Island. Since Rhinoceros Auklets islation, the private portion of the island will make a characteristicwhistling sound with their be acquired by the U.S. Fish and Wildlife Ser- wings when they fly, we could count the num- vice and will become part of the refuge system. ber of arrivals and departures every 15 min The remaining 15% comprisesthe Zella Schultz throughout the night at approximately two- Seabird Sanctuary, administered by the Wash- week intervals. Becausehigh winds, rain, and ington Department of Game. pounding surf drown out the soundsof flying Smith Island (48”19’N, 122”5 1’W) is situ- auklets, this part of the study was limited to ated 16.5 km northeast of Protection Island, relatively calm nights. in the Strait of Juan de Fuca (Fig. 1). With the We determined egg-layingdates, incubation exception of several denseshrub thickets, most periods, and dates of hatching and fledging in of the approximately 0.25-km2 island is cov- the following manner: a sample of burrows was ered by beachgrassand various exotic grasses. staked, numbered, and excavated before the The island has a somewhat triangular shape onset of egg laying. Excavation was done in with a rapidly eroding cliff about 15 m in height the manner described by Manuwal (1974). on the western and southern sides. The top During the spring, the sample burrows were slopes gradually toward the east and termi- checked daily for the presence of auklets and nates in a sandy point. Annual precipitation is eggs.When an incubating bird was found, the approximately the same as at Protection Is- eggdate was recorded and the burrow was left land. Smith Island is also administered by both undisturbed for 45 days, after which time the the U.S. Coast Guard and the U.S. Fish and burrow wassearched for the presenceof a chick. Wildlife Service. If incubation was still in progress,the burrow was not checked again for another five days. METHODS Observations of chick developmental patterns Rhinoceros Auklets were studied by Manuwal were made daily throughout the nestling pe- and Wilson on Smith Island in 1974, by Lesch- riod during 1974 to 1976. Chicks were con- RHINOCEROS AUIUET IN WASHINGTON 145 TABLE 1. Use of nestinghabitat by Rhinoceros Auklets on Destruction, Protection, and Smith islands, Washington. Mean burrow density Number of burrows Perwn; of Sampled area Habitat type (burrows/m’) on island WI Destruction Island (23,621 burrows) Cliffs/steep slopes 0.13 1,167 4.9 1,200 Grass-coveredslopes 0.47 3,938 16.7 768 Shrub-covered slopes 0.99 10,290 43.6 167 Willow-covered slopes 0.59 2,395 10.1 167 Dunegrass-coveredslopes 0.74 5,023 21.3 180 Shrub-coveredlevel edge 0.06 808 3.4 177 Protection Island (27,549 burrows) Cliffs/steep slopes 0.04 1,076 3.9 direct count Grass-coveredslopes 0.50 23,356 84.8 540 Grass-coveredlevel edge 0.15 3,117 11.3 direct count Smith Island (1,194 burrows) Cliffs/steep slopes 0.04 320 26.8 direct count Grass-coveredlevel edge 0.12 874 73.2 direct count sideredto have fledgedwhen they disappeared ing and again 12 to 14 days later. From these from their burrows. data, composite growth curves were construct- We collected food samples at night from ed accordingto Ricklefs and White (1975) and adult auklets returning to feed their chicks by k values were computed following Ricklefs’ scaringthe birds as they approached the bur- (1967) method.