1004 SHORT COMMUNICATIONS BURGER,A. E. 1991. Maximum diving depths and un- Zecanoides georgicus at Bird Island, South Geor- derwater foraging in alcids and penguins. Can. gia. Antarct. Sci. 4:433-434. Wildl. Serv., Occas. Pap. 68:9-15. SAMEOTO,D. 1981. Distribution and abundanceof six BURGER,A. E., AND R. P WUON. 1988. Capillary- speciesof fish larvae in Peruvian waters and their tube depth gauges for diving animals: an assess- relationship with the physical and biological en- ment of their accuracy and applicability. J. Field vironment: Boletin Inst&uto de1 Mar de1 Peru. Omithol. 59:345-354. Volumen Extraordinario:164-170. CHASTEL,0. 1994. Maximum diving depths of Com- SANTANDER,H., G. LUYO,S. CARRASCO,M. V~LU, AND mon Diving Petrels Pelecanoides urinatrix at Ker- 0. S. DE CASTILLO.1981. Catalog0 de zooplanc- guelen Islands. Polar Biol. 14:211-213. ton en el mar peruano.Primera parte: area Pisco- HARRIS,M. P, H. TOWLL,A. E RUSSELL,AND S. WAN- San Juan. Boletfn Instituto de1Mar de1Peru 6:1- LESS. 1990. Maximum dive depths attained by 75. THORESEN,A. C. 1969. Observationson the breeding auks feeding young on the Isle of May, Scotland. behaviourof the Diving Petrel Pelecanoides u. ur- Scottish Birds 16:25-28. inatrix (Gmelin). Notomis 16:241-260. HAYS, C. 1989. The Peruvian Diving-petrel in Peru. WATANUKI,Y., A. KATO,AND Y. NAI~O. 1996. Diving Oryx 23:102-105. performance of male and female JapaneseCor- LISHMAN,G. S., AND J. F! CROXALL. 1983. Diving morants. Can. J. Zool. 74: 1098-l 109: depths of the Chinstrap Penguin, Pygoscelis ant- WECE D. C.. AND A. J. LONG. 1995. Kev areas for arcticu. Br. Antarct. Surv. Bull. 61:21-25. threatenedbirds in the Neotropics. BGdlife Con- MURPHY,R. C. 1936. Oceanic birds of South Amer- servation Series No. 5. Smithson. Inst. Press, ica. Vol. 2. Macmillan, New York. Washington,DC. PIAT~,J. E, AND N. NETIZESHIP.1985. Diving depths WILSON,R. l?, AND M. T. Wnso~. 1990. Foraging of four alcids. Auk 102:293-297. ecology of breeding Spheniscus penguins,p. 18l- PRINCE, P A., AND M. JONES.1992. Maximum dive 206. In L. S. Davis and J. T Darby [eds.], Penguin depthsattained by South Georgia diving petrel Pe- biology. Academic Press, San Diego. The Condor 99:lOCb1007 0 The CooperOrnithological Society 1997 DIVING DEPTHS OF TWO TROPICAL PELECANIFORMES: THE RED-TAILED TROPICBTRD AND THE RED-FOOTED BOOBY’ MAITHIEU LE CORRE CEBC-CNRS Villiers en Bois-79360 Beauvoir sur Niort, France Abstract. The diving ability of two tropical Pele- Most boobies (tropical Szdidae) and all tropicbirds caniformes, the Red-footed Booby (Sulu sulu) and the (Phaethontidue) a& pelagic plunge diving seabirds Red-tailed Tropicbird (Phaethon rubricauda) was (Ashmole 1971, Nelson 1978, Schreiber and Clapp studiedon EuropaIsland, southernMozambique Chan- 1987), foraging solitarily (tropicbirds,Masked Booby) nel, using capillary depth recorders fitted on breeding or collectively-(most boobies), and feeding mainly on adults. Both speciesmainly exploited the first 4 m of flying fishes and squid (Ashmole and Ashmole 1967, the water column. Although such a depth can be Diamond 1974, 1975, Harrison et al. 1983). Plunge reached solely by passive plunge diving, the range of divers supposedlyhave limited diving capacities, the depths reached by the two species suggeststhat they depth they reach depending mainly on the momentum may, at least sometimes, use their feet and wings to gained during the plunge (Ashmole 1971). However, perform active underwater pursuit swimming. Intra- at least Cape Gannets (S&I cupensis) can use their specific comparisonof the depth reachedby Red-tailed wings and feet to gain additional depth (Adams and Tropicbirdsalso suggeststhat this speciesmay change Walter 1993). Here I report diving performances of its diving behavior seasonally. two tropical plunge divers, the Red-tailed Tropicbird (Phaethon rubricaudu, 0.8 kg) and the Red-footed Key words: diving depth, feeding ecology, Red- Booby (Sula sula, 0.9 kg). tailed Tropicbird, Red-footed Booby, Phaethon rubri- cauda, Sula sula, Europa Island. METHODS The study was conductedon Europa Island (22”2O’S, 40”22’E) in the southernMozambique Channel. About 1Received 8 May 1997. Accepted 31 July 1997. 3,000 pairs of Red-footed Boobies and about 3,500 SHORT COMMUNICATIONS be related to changesin diving behavior of Red-tailed _ Tropicbirds.During incubation,the main prey items (n = iO1 preys items-identified) were squid*(48.5%), fly- ing-fishes (26.7%) and unidentified fishes (19.8%). Thvre were‘very few dolphin-fish (0.9%). Althbugh we 1 lack data on the behavior of Red-tailed Tropicbird at sea, it is of interest to note that seasonalchanges in diet is related to changesin diving depths recorded. My data on the diving depthsof Red-footed Boobies and Red-tailed Tropicbirds show that both speciesex- ploit mainly the first meters of the water column, per- forming mainly passive plunge diving. However, the : range of depthi r&ordedsuggest that both speciescan occasionallv(Red-footed Boobies) or seasonallv(Red- tailed Tropicbirds) perform activk pursuit swi&&ng, depending upon the prey available to foraging birds. This work was supportedby the Direction Rtgionale de 1’Environnement (DIREN) of Reunion Island. Visits I / 1 I 7 to the island were authorizedby the Prefect of Rtunion 0 2 4 6 0 10 Island, and organized with the help of the Direction Gaugedeployment duratmn (days) Rtgionale de M&Co France, and I would like to thank its Director, G. Le Goff, and his team on the island. FIGURE 1. Relationship between gauge deployment Transportationto Europa was facilitated by the Forces durations (days) and the maximum depth recorded in Armtes de la Zone Sud de I’OcCan Indien (FAZSOI). incubating (black circles) and chick-rearing (open cir- I thank S. Ribes and I? Jouventin for encouragement, cles) Red-tailed Tropicbirds (9 = 0.32, P < 0.001 J. Bried and J. M. Probst for help in the field, J. Bried, when plotting all the data together; 9 = 0.01, P > A. E. Burger, D. Capdeville, 0. Chastel, H. LormCe, 0.05 for incubatingbirds only, r2 = 0.04, P > 0.05 for and an anonymous reviewer for their constructive chick-rearing birds only). comments on earlier drafts of the manuscript, and J. Thompson for help with the English. ed (9.6 m) could hardly be reached solely by passive LITERATURE CITED plunge diving, and this suggeststhat Red-footed Boo- bies can occasionally use their feet and/or wings to ADAMS, N. J., AND C. B. WALTER. 1993. Maximum perform active underwaterpursuit swimming, as found diving depths of Cape Gannets. Condor 95:734- by Adams and Walter (1993) on Cape Gannets. 736. More than 90% of the chick-rearing Red-tailed ASHMOLE,N. I? 1971. Seabird ecology and the marine Tropicbirdsdived between 1 and 4 m, suggestingthat environment. D. 223-286. In D. S. Farner. J. R. during the chick-rearing period, this speciesperforms King, and K: 6. Parkes reds.], Avian biology, Vol. mainly passive plunge diving to catch prey at or very 1. Academic Press, New York. close to the surface.Preliminary data on diet show that ASHMOLE,N. F!, AND M. J. ASHMOLE.1967. Compar- these prey (n = 282 prey items identified during the ative feeding ecology of seabirdsof a tropical oce- chick-rearingperiod) are squid (5 lS%), dolphin-fishes anic island. Peabody Mus. Nat. Hist. Yale Univ. (Coryphoenidue, 14.9%), and flying-fishes (Exoceti- Bull. 24:1-131. dae, 14.5%). Remaining prey are needlefishes(Belon- BARR&N., AND J. SERVAN.1988. L’avifaune des Iles i&e), juvenile tuna (Scombridue), and unidentified Eparses.ICBP, Monographie- 5:209-224. fishes. BURGER,A. E., ANDM. SIMPSON.1986. Diving depths During incubation, the depths recorded were much of Atlantic Puffins and Common Murres. Auk deeper (about 60% of the incubating Red-tailed Trop- 104:218-224. icbirds dived between 4 and 8 m), suggestingthat this BURGER,A. E., AND R. I? WILSON. 1988. Capillary- species may change its diving behavior seasonally. tube depth gauges for diving animals: an assess- However, foraging trips were five times longer during ment of their accuracy and applicability. J. Field incubation than during the chick-rearing period (Table Ornithol. 59:345-354. 1). As mentionedin the Methods section,long duration CHASTEL,O., AND J. BRIED. 1996. Diving ability of of gauge deployment can lead to overestimationof the Blue Petrels and Thin-billed Prions. Condor 98: depth recorded (Burger and Wilson 1988). 627-629. Although I fitted the gauges in order to minimize DIAMOND,A. W. 1974. The Red-footed Booby on Al- this cause of error, the deeper depths found during in- dabra Atoll, Indian Ocean. Ardea 62: 196-218. cubation may in part be due to overestimation.How- DIAMOND,A. W. 1975. The biology of tropicbirds at ever, there was no correlationbetween deploymentdu- Aldabra Atoll. Indian Ocean. Auk 92: 16-39. rations of the gaugesand diving depthsrecorded when HARRISON,C. S., i S. HIDA, AND M. l? SEKI. 1983. consideringincubation only, suggestingthat my results Hawaiian seabird feeding ecology. Wild. Monogr. are reliable. Thus, the difference in diving depths re- 85:1-71. corded during incubationand chick-rearingperiod may LE CORRE,M., AND l? JOUVENTIN.In press. Ecological SHORT COMMUNICATIONS 1007 significanceand conservationpriorities on Europa Croxall [ed.], Seabirds: feeding ecology and Island (western Indian Ocean), with special ref- role in marine ecosystems. Cambridge Univ. erence to seabirds.Terre & Vie. Press, Cambridge. NELSON,J. B. 1978. The Sulidae: gannets and boo- WILSON,R. I?, AND M. l? WILSON. 1990. Foraging bies. Oxford Univ. Press, Oxford. ecology of Spheniscuspenguins, p. 181-206. In SCHREIBER,R. W., AND R. B. CLAPP. 1987. Pelecan- L. S. Davis, and J. T Darby [eds.], Penguin bi- iform feeding ecology, p.