TY - JOUR
AU - Burger, Alan, E.
AB - Abstract Maximum diving depths were measured for shearwaters breeding on Cousin Island, Seychelles. Eighty-three percent of 23 Wedge-tailed Shearwaters (Puffinus pacificus) dived, and their mean maximum depth was 14 m (SD = 23 m, range 1–66 m, N = 19). All Audubon's Shearwaters (P. lherminieri) dived, and their mean maximum depth was 15 m (SD = 12 m, range 6–35 m, N = 7). These data contradict the hypothesis that tropical shearwaters should not specialize in underwater foraging. They are capable of exploiting deep prey unavailable to most other tropical seabirds. Five Puffinus species (temperate and tropical) attained allometrically scaled maximum depths comparable to those of penguins and alcids. It has long been known that shearwaters dive beneath the ocean to forage, using their feet and wings for propulsion (Brown et al. 1978, 1981), and show anatomical adaptations for this mode of foraging (Kuroda 1954, Warham 1990). Simple depth gauges measuring the maximum depths indicate some remarkably deep dives attained by shearwaters (Weimerskirch and Sagar 1996, Weimerskirch and Cherel 1998, Keitt et al. 2000). More sophisticated time-depth-recorders (TDRs), which indicate time spent at various depths and trace individual dives, have revealed much of the underwater foraging behavior of penguins, alcids, and cormorants (Kooyman 1989, Croll et al. 1992, Wilson 1995, Watanuki et al. 1996), but have not been applied to shearwaters. I report maximum depths attained by two tropical shearwaters, Wedge-tailed (Puffinus pacificus) and Audubon's (P. lherminieri) shearwaters, breeding on Cousin Island, Seychelles (4°20′S; 55°40′E), and review data on diving depths of other shearwaters. I examine the hypothesis that tropical shearwaters should not specialize in underwater foraging (Brown et al. 1978), and discuss the role of diving in tropical shearwaters. Methods Maximum-depth gauges were made from flexible plastic tubing with internal diameter 0.8 mm, lined with a thin layer of icing sugar and sealed at one end. Gauges were 70–120 mm long on Wedge-tailed Shearwaters, and 70–90 mm long on Audubon's Shearwaters. As the gauge is submerged, the increasing pressure forces water into the tube, dissolving the sugar and leaving a record of the deepest dive (Kooyman et al. 1971, Burger and Wilson 1988, Hedd et al. 1997). The equation provided by Burger and Wilson (1988) was used to calculate maximum dive depths. Cousin Island supports breeding populations of ∼13,000 pairs of Wedge-tailed and 5,000–10,000 pairs of Audubon's shearwaters (Burger and Lawrence in press). At the time of this study (7–17 June 1999), Wedge-tailed Shearwaters were returning nightly to nest cavities for courtship, but did not have eggs or chicks. Audubon's Shearwaters breed all year round on Cousin Island and the status of those used in the study was not known. Adult shearwaters sitting in or near nest cavities were caught and banded at night. Each gauge was firmly tied to the base of a single tail feather with a thread (dental floss). Once attached the gauges were surrounded by feathers and created no impediments to the birds. Handling time was 10–15 min. Gauges not recovered would eventually work loose or be lost when the birds molted. Each bird was sampled once. I made no attempt to collect food samples, and none of the captured birds regurgitated food. Prolonged deployment increases errors in these devices (Burger and Wilson 1988). I included gauges recovered within two days of deployment, and all except two (one for each species) were recovered after one day. I encountered an unusual problem in the form of tiny ants that crawled inside the tubes and removed the sugar. Ants removed sugar unevenly, in contrast to the sharp boundary created by water, and so with careful inspection I was able to reject gauges affected by ants. Results Out of 23 undamaged gauges recovered from Wedge-tailed Shearwaters, 19 (83%) indicated some diving activity (Fig. 1) and their mean maximum depth was 14 m (SD = 23 m, range 1–66 m). All 7 gauges recovered from Audubon's Shearwaters indicated diving, and the mean maximum depth was 15 m (SD = 12 m, range 6–35 m). Most Wedge-tailed Shearwaters remained within 20 m and most Audubon's Shearwaters within 10 m of the surface (Fig. 1). Fig. 1. Open in new tabDownload slide Frequency distribution of maximum depths attained by Wedge-tailed and Audubon's shearwaters on Cousin Island, Seychelles. X-axis labels indicate the upper limit of each 5 m depth category Fig. 1. Open in new tabDownload slide Frequency distribution of maximum depths attained by Wedge-tailed and Audubon's shearwaters on Cousin Island, Seychelles. X-axis labels indicate the upper limit of each 5 m depth category Discussion Many procellariiform species dive to capture prey, but most species remain within 1–5 m of the surface (Warham 1990, Prince et al. 1994, Hedd et al. 1997), with the exception of the specialised diving petrels, Pelecanoididae (Prince and Jones 1992, Chastel 1994, Zavalaga and Jahncke 1997). Some shearwaters of the genus Puffinus regularly use pursuit diving for foraging (Brown et al. 1978, 1981; Warham 1990). They show adaptations for underwater swimming, including flattened tarsi and humeri, and shorter wings and higher wing-loading than most other petrels (Kuroda 1954, Warham 1977, 1990). Maximum diving depths have been measured using gauges in five species of Puffinus (Table 1). Some published depth records unavoidably came from prolonged foraging trips. There is a greater chance that those gauges overestimate maximum depths with repeated submersion and prolonged deployment, although the error with dives >20 m was likely to be <10% (Burger and Wilson 1988). There is also a greater probability of recording an exceptionally deep dive during a long trip. Those data are compared with depths measured in Cory's Shearwater (Calonectris diomedea) and White-chinned Petrel (Procellaria aequinoctialis), which share many similarities with Puffinus but seem less morphologically adapted to diving (Warham 1977, 1990). Table 1. Maximum diving depths in shearwaters and petrels measured with depth gauges Open in new tab Table 1. Maximum diving depths in shearwaters and petrels measured with depth gauges Open in new tab All five Puffinus shearwaters demonstrated remarkable diving abilities (Fig. 2). Their maximum diving depths clustered close to the allometric equation derived from maximum diving depths of penguins and alcids (maximum depth (meters) = 75.905 M0.316, where M is body mass in kilograms; Burger 1991). Maximum depths of Calonectris and Procellaria fell well below that regression. The diving abilities of Puffinus shearwaters require more detailed study, using TDR and activity data-loggers, to confirm whether deep diving forms a significant part of their foraging routine. It will be fascinating to discover whether they show convergent anatomical, physiological, and behavioral adaptations for prolonged diving to those being revealed for penguins, alcids, and cormorants. Fig. 2. Open in new tabDownload slide Puffinus shearwaters had maximum diving depths similar to those of alcids and penguins. This log-log plot of maximum diving depths against body mass compares five species of Puffinus shearwaters (squares), including Audubon's (AU), Black-vented (BV), Sooty (SO), Short-tailed (ST), and Wedge-tailed (WT) shearwaters, with Cory's Shearwater (triangle) and White-chinned Petrel (diamond), and the allometric regression of maximum depths predicted for penguins and alcids (Burger 1991) Fig. 2. Open in new tabDownload slide Puffinus shearwaters had maximum diving depths similar to those of alcids and penguins. This log-log plot of maximum diving depths against body mass compares five species of Puffinus shearwaters (squares), including Audubon's (AU), Black-vented (BV), Sooty (SO), Short-tailed (ST), and Wedge-tailed (WT) shearwaters, with Cory's Shearwater (triangle) and White-chinned Petrel (diamond), and the allometric regression of maximum depths predicted for penguins and alcids (Burger 1991) Kuroda (1954) regarded smaller species of Puffinus as morphologically more specialized for diving than most other shearwaters. Visual observations of small shearwaters (Brown et al. 1978), including Audubon's Shearwater (Harris 1969), confirmed that they dived, but this study is the first to confirm that diving occurs regularly (in all foraging trips made in my small sample), and that they are proficient, deep divers. Keitt et al. (2000) speculated that shearwaters might be most efficient at diving during wing molt, when the reduced wing area would produce sufficient propulsion but less drag. None of the shearwaters in my sample showed any sign of primary wing molt and all appeared to have recently replaced primaries. Maximum diving depths are generally determined by allometrically scaled physiological limits (Kooyman 1989), whereas the depths of most foraging dives are determined by distribution of prey. Typical foraging dives are much shallower than maximum limits (Kooyman 1989, Burger 1991, Wilson 1995). That applies to the Puffinus shearwaters; their mean maximum dives were generally far shallower than the overall maximum (Table 1). More accurate depth profiles will emerge with deployment of TDRs that show the depth distribution of all underwater activities, and not just the deepest dive per foraging trip. Brown et al. (1978) speculated that shearwater species specialized for diving should be restricted to richer, cold, or cool-temperate seas. The sparse distribution of prey and presence of predatory fish in the tropics was believed to favor shearwaters with more efficient gliding flight rather than specialist divers. Shearwaters specialized for diving tend to have somewhat shorter wings and higher wing loading and hence rely more on flapping flight (Warham 1977, 1990), which is normally associated with highly productive temperate and polar seas. My data do not support the hypothesis that tropical shearwaters avoid diving in preference for surface foraging. Both Wedge-tailed and Audubon's shearwaters were proficient, deep divers, and most (83%) Wedge-tailed and all Audubon's shearwaters employed diving on foraging trips. Diets of those species in Seychelles have not been recorded, but Pacific Wedge-tailed Shearwaters primarily take small schooling fish and squid (Harrison et al. 1983), and Audubon's Shearwaters take planktonic fish larvae and crustaceans (Harris 1969). Depth distribution of likely prey in Seychelles is not known, nor is it known whether shearwaters were restricting their foraging to concentrated prey patches. Neither species was restricted to the most productive water masses in the tropical Indian Ocean (Bailey 1968, Pocklington 1979). Both Wedge-tailed and Audubon's shearwaters regularly feed at the surface (Harris 1969, Harrison et al. 1983, Warham 1990), as do most tropical seabirds (Ashmole and Ashmole 1967, Harrison 1990, Ballance et al. 1997). The shearwaters' diving abilities give them access to additional, deeper prey inaccessible to most other tropical seabirds. Even plunge-diving boobies and tropicbirds seem restricted to the upper 13 m (Le Corre 1997). More intensive research is needed to elucidate foraging behavior of tropical shearwaters, to confirm whether they fill a similar pursuit-diving niche to that occupied by penguins, alcids, and cormorants in cool-temperate and polar seas. Acknowledgments This study was funded by a grant from the Second Dutch Trust Fund to BirdLife Seychelles. Additional support came from National Sciences and Engineering Research Council Canada and the University of Victoria. I thank Andrea Lawrence and Ahtee Labonté for field assistance, Nirmal Jivan Shah and Steve Parr for support and discussion, and Harry Carter, David Lee, and Yutaka Watanuki for helpful comments. Literature Cited Ashmole , N. P. , and M. J. Ashmole . 1967 . Comparative feeding ecology of sea birds of a tropical oceanic island. Bulletin of the Peabody Museum of Natural History 24 : 1 – 131 . WorldCat Bailey , R. S. 1968 . The pelagic distribution of sea-birds in the western Indian Ocean. Ibis 110 : 493 – 519 . Google Scholar Crossref Search ADS WorldCat Ballance , L. T. , R. T. Pitman , and S. B. Reilly . 1997 . Seabird community structure along a productivity gradient: Importance of competition and energetic constraint. Ecology 78 : 1502 – 1518 . Google Scholar Crossref Search ADS WorldCat Brown , R. G B. , W. R P. Bourne , and T. R. Wahl . 1978 . Diving by shearwaters. Condor 80 : 123 – 125 . Google Scholar Crossref Search ADS WorldCat Brown , R. G B. , S. P. Barker , D. E. Gaskin , and M. R. Sandeman . 1981 . The foods of Great and Sooty shearwaters Puffinus gravis and P. griseus in eastern Canadian waters. Ibis 123 : 19 – 30 . Google Scholar Crossref Search ADS WorldCat Burger , A. E. 1991 . Maximum diving depths and underwater foraging in alcids and penguins. Pages 9–15 in Studies of High-latitude Seabirds. 1. Behavioural, Energetic and Oceanographic Aspects of Seabird Feeding Ecology (W. A. Montevecchi and A. J. Gaston, Eds.). Canadian Wildlife Service Occasional Paper 68 . WorldCat Burger , A. E. , and A. D. Lawrence . 2001 . Census of Wedge-tailed and Audubon's shearwaters on Cousin Island, Seychelles using call playback. Marine Ornithology 29 . in press . WorldCat Burger , A. E. , and R. P. Wilson . 1988 . Capillary-tube depth gauges for diving animals: A review of their accuracy and applicability. Journal of Field Ornithology 59 : 345 – 354 . WorldCat Chastel , O. 1994 . Maximum diving depths of Common Diving Petrels Pelecanoides urinatrix at Kerguelen Island. Polar Biology 14 : 211 – 213 . Google Scholar Crossref Search ADS WorldCat Croll , D. A. , A. J. Gaston , A. E. Burger , and D. Konnoff . 1992 . Foraging behavior and physiological adaptation for diving in Thick-billed Murres. Ecology 73 : 344 – 356 . Google Scholar Crossref Search ADS WorldCat Harris , M. P. 1969 . Food as a factor controlling the breeding of Puffinus lherminieri. Ibis 111 : 139 – 156 . Google Scholar Crossref Search ADS WorldCat Harrison , C. S. 1990 . Seabirds of Hawaii: Natural History and Conservation. Cornell University Press, Ithaca, New York . WorldCat Harrison , C. S. , T. S. Hida , and M. P. Seki . 1983 . Hawaiian seabird feeding ecology. Wildlife Monographs, no. 85 . WorldCat Hedd , A. , R. Gales , N. Brothers , and G. Robertson . 1997 . Diving behaviour of the Shy Albatross Diomedea cauta in Tasmania: Initial findings and diver recorder assessment. Ibis 139 : 452 – 460 . Google Scholar Crossref Search ADS WorldCat Huin , N. 1994 . Diving depths of White-chinned Petrels. Condor 96 : 1111 – 1113 . Google Scholar Crossref Search ADS WorldCat Keitt , B. S. , D. A. Croll , and B. R. Tershy . 2000 . Dive depth and diet of the Black-vented Shearwater (Puffinus opisthomelas). Auk 117 : 507 – 510 . Google Scholar Crossref Search ADS WorldCat Kooyman , G. L. 1989 . Diverse Divers: Physiology and Behavior. Springer-Verlag, Berlin . WorldCat Kooyman , G. L. , C. M. Drabeck , R. Elsner , and W. B. Campbell . 1971 . Diving behavior of the Emperor Penguin, Aptenodytes forsteri. Auk 88 : 775 – 795 . Google Scholar Crossref Search ADS WorldCat Kuroda , N. 1954 . On the classification and phylogeny of the order Tubinares, particularly the shearwaters (Puffinus). Published by the author, Tokyo . WorldCat Le Corre M. L. 1997 . Diving depths of two tropical Pelecaniformes: The Red-tailed Tropicbird and the Red-footed Booby. Condor 99 : 1004 – 1007 . Google Scholar Crossref Search ADS WorldCat Monteiro , L. R. , J. A. Ramos , R. W. Furness , and A. J. del Nevo . 1996 . Movements, morphology, breeding, molt, diet and feeding of seabirds in the Azores. Colonial Waterbirds 19 : 82 – 97 . Google Scholar Crossref Search ADS WorldCat Pocklington , R. 1979 . An oceanographic interpretation of seabird distributions in the Indian Ocean. Marine Biology 51 : 9 – 21 . Google Scholar Crossref Search ADS WorldCat Prince , P. A. , N. Huin , and H. Weimerskirch . 1994 . Diving depths of albatrosses. Antarctic Science 6 : 353 – 354 . Google Scholar Crossref Search ADS WorldCat Prince , P. A. , and M. Jones . 1992 . Maximum dive depths attained by South Georgia Diving Petrel Pelecanoides georgicus at Bird Island, South Georgia. Antarctic Science 4 : 433 – 434 . Google Scholar Crossref Search ADS WorldCat Warham , J. 1977 . Wing loadings, wing shapes, and flight capabilities of Procellariiformes. New Zealand Journal of Zoology 4 : 73 – 83 . Google Scholar Crossref Search ADS WorldCat Warham , J. 1990 . The Petrels: Their Ecology and Breeding Systems. Academic Press, London . WorldCat Watanuki , Y. , A. Kato , and Y. Naito . 1996 . Diving performance of male and female Japanese Cormorants. Canadian Journal of Zoology 74 : 1098 – 1109 . Google Scholar Crossref Search ADS WorldCat Weimerskirch , H. , and Y. Cherel . 1998 . Feeding ecology of Short-tailed Shearwaters: Breeding in Tasmania and foraging in the Antarctic? Marine Ecology Progress Series 167 : 261 – 274 . Google Scholar Crossref Search ADS WorldCat Weimerskirch , H. , and P. M. Sagar . 1996 . Diving depths of Sooty Shearwaters Puffinus griseus. Ibis 138 : 786 – 794 . Google Scholar Crossref Search ADS WorldCat Wilson , R. P. 1995 . Foraging ecology. Pages 81–106 in The Penguins Spheniscidae (T. D. Williams, Ed.). Oxford University Press, Oxford . WorldCat Zavalaga , C. B. , and J. Jahncke . 1997 . Maximum dive depths of the Peruvian Diving-petrel. Condor 99 : 1002 – 1004 . Google Scholar Crossref Search ADS WorldCat © The American Ornithologists' Union, 2001
TI - Diving Depths of Shearwaters
JF - Auk: Ornithological Advances
DO - 10.1093/auk/118.3.755
DA - 2001-07-01
UR - https://www.deepdyve.com/lp/oxford-university-press/diving-depths-of-shearwaters-ImBe2QyZGo
SP - 755
VL - 118
IS - 3
DP - DeepDyve
ER -