SHORT COMMUNICATIONS 621 research and management disturbance, p. 173- NEWTON,I. 1979. Population ecologyof raptors. Bu- 182. In B. A. Giron Pendleton, B. A. Milsap, K. teo Books, Vermillion, SD. W. Cline, and D. M. Bird [eds.], Raptor manage- w, A. L. 1936. The distribution and habits of ment techniquesmanual. Natl. Wildl. Fed., Wash- Madagascarbirds. Bull. Am. Mus. Nat. Hist. 77: ington, DC. 143-499. JOLLY, A., ANDR. JOLLY. 1984. Malagasyeconomics SINCLAIR,D. F. 1985. On tests of spatial randomness and conservation: a tragedy without villains, p. usingmean nearestneighbor distance.Ecology 66: 27-54. In A. Jollv. P. Oberlt and R. Albianac 1084-1085. [eds.], Key environments-Madagascar. P&ga- STEENHOP, K. 1987. Assessinaraptor reproductive mon Press, New York. successand productivity, p. 157-170: In B. A. LACK, D. 1954. The natural regulation of animal Giron Pendleton. B. A. Milsao. K. W. Cline. and numbers. Oxford Univ. Press, London. D. M. 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The Condor98:621-629 0 The CooperOrnithological Society 1996 DIVING ABILITY OF BLUE PETRELS AND THIN-BILLED PRIONS’ OLMER CHASTELAND JOEL BRIED Centre National de la RechercheScientifique, Centre dEtudes’ Biologiquesde Chiz2 79360 Beauvoirsur Niort, France Key words: Blue Petrel; Thin-billed Prion; maxi- The Blue Petrel Halobaena caeruleaand the Thin- mum diving depths;foraging behavior;Halobaena ca- billed Prion Pachyptilabelcheri are small burrow-nest- erulea; Pachyptila belcheri. ing petrels (190 and 150 g, respectively).At Kerguelen Islands thesetwo seabirdsbreed in very large numbers Capillary depth recorders (Burger and Wilson 1988) (up to 1 million pairs, Weimerskirch et al. 1989); the are useful tools for studying the foraging ecology of prions particularly are believed to have a significant seabirds,and have been usedsuccessfully on penguins, impact on subantarcticresources (Ridoux 1994). Dur- alcids, shagsand gannets(Burger 1991, Wanless et al. ing the chick-rearingperiod (50 days, Weimerskirch et 1991, Adams and Walter 1993, Croxall et al. 1993). al. 1994),both speciesalternate long and short foraging Recent studiesof Procellariiformeshave revealed that trios over pelagic and neritic waters (Weimerskirch et diving petrels (Pelecanoidesgeorgicus and P. urinatrix) al.-1994) and prey mainly on small crustaceans(Harper are able to dive routinely down to 25-40 m (Prince and 1972. Prince 1980. Ridoux 1994). orincinallv bv sur- Jones 1992, Chaste1 1994). Furthermore, investiga- face-seizing(Harper 1987, Prince and Morgan 1987). tions on albatrosses(Prince et al. 1994), and on the This paper reports the first study on maximum dive White-chinned Petrel Procellaria aequinoctialis(Huin deothsattained bv Blue Petrelsand Thin-billed Prions. 1994),have shownthat theseseabirds can reacha depth during the chick-rearing period at Kerguelen Islands.’ of several meters, giving a new insight on the foraging techniques of albatrossesand petrels, which are gen- METHODS erally regardedas surface-seizers(Harper 1987, Prince Field work was carried out on Mayes Island, Kerguelen and Morgan 1987). Archipelago (48”28 S, 69’57 E), between 17 January and 7 February 1993. Maximum depth recorderscon- sisted of 12 cm lengths of plastic tubing (internal di- ameter, 0.8 mm.) lined with icing sugarand sealed at I Received 25 August 1995. Accepted 17 May 1996. one end. Each tube weighedapproximately 1 g (4 0.7% 628 SHORT COMMUNICATIONS TABLE 1. Maximum diving depths and gauge de- DISCUSSION ployment durations of Blue Petrels and Thin-billed Most Procellariiformes are unlikely to exhibit signifi- Prions at Kerguelen Islands. cant diving abilities, due either to low wing loading, high aspect ratios or unstreamlined tarsi (Warham 1977). Considering these morphological features, GGUge Initial $??I$Maxi- deploy- tube corn- mum shearwaters,and particularly diving petrels (the south- ment length pressed &Ptb em ecologicaland morphological analoguesof alcids, C&Y9 (mm) L h Cm) Thoresen 1969), should be the most proficient divers Blue Petrel 7 97 69.5 4.0 (Warham 1977). Anecdotal observations have re- 4 99.5 64.5 5.5 vealed that Short-tailed Shearwaters,Puffinus tenuiros- 9 106 71.5 4.9 tris (Skira 1979) and Sooty Shearwaters, P. griseus 104.5 95.5 1.0* (Brown et al. 1981) could reach 10 m down; likewise, 83 51.5 6.2* Flesh-footed (P. curneipes)and Fluttering Shearwaters 98 66 4.9 (P. guvia) were recorded to depths of about 5 m and 2-3 m, respectively (Wood 1993). Two studies using Thin-billed Prion 2 101 66.5 5.2 maximum depth gaugeshave shown that the highly 101 2: 675’2 specializeddiving petrels dove as deep as 48 m in the 5 91 South Georgia Diving Petrel (Prince and Jones 1992) 4 96 65.5 417 and 63 m in the Common Diving Petrel (Chaste11994). 1 108.5 19 3.8 However, all Procellariiformesstudied so far do dive, * Maximum depths attained by the same individual. except the Wandering Albatross, Diomedea exulans (Prince et al. 1994). Black-browed (Diomedeu melan- ophris)and Gray-headed Albatrosses(Diomedea chty- sostoma)routinely dive to 3 m, whereasLight-mantled of adult body mass)and was attachedto the back feath- Sooty Albatrosses(Phoebetria palpebruta) on average ers usingwaterproofadhesive tape. On recoveredgaug- attain 4.7 m, with a maximum depth of 12 m (Prince es the length of tube still covered with icing sugarwas et al. 1994). Furthermore, the White-chinned Petrel measuredto the nearest0.5 mm. Maximum dive depth has recently been shown to regularlydive to 6 m, with was calculatedby the equation: d_ = lO.O8(L,/Li - a maximum of 13 m (Huin 1994). 1) where d is depth (m). L. is the initial lenath (mm) Blue Petrels and Thin-billed Prions are poorly suited ofundissolved indicator and Ld its length on-recovery for diving, having low wing loading (Warham 1977), (Burger and Wilson 1988). and feeding mainly by surfaceseizing or dipping (Crox- In both species,the single chick is left alone in the all and Prince 1980, Prince 1980, Harper 1987) al- burrow within a few hours after hatching (late Decem- though aerial plunging and surface diving have been ber and early Januaryfor the Blue Petrel and the Thin- reported in the Blue Petrel (Croxall and Prince 1980) billed Prion, respectively; Weimerskirch et al. 1989) more scarcelyin the Thin-billed Prion (Harper 1987). and thereafterfed regularlyby both parents.To identify The submersion duration in the Blue Petrel did not the parent and to recover the depth gauges,traps were seemto exceedsix seconds(Bierman and Voous 1950) installed at the entranceof 13 Blue Petrel and five Thin- suggestingshallow dives. Our resultsshow that during billed Prion burrows during the course of the study. the chick-rearing period, both speciesregularly dive to The trap was fitted with a swing-doorthat let the parent 5 m, and can attain a maximum depth of 7 m. These enter the burrow when coming from the seato feed the dives are shallower than those of diving petrels, and chick, but trapped it when it tried to return to the sea. probably of shearwaters,but similar to those of alba- Birds were banded with monel rings for identification. trosses,consistent with their morphology. During the courseof the study, 19 Blue Petrel and 12 Burger and Wilson (1988) pointed out that depths Thin-billed Prion depth gaugeswere attached to adult tended to be overestimated during shallow dives (39% birds that returned to feed their chick. The traps were overestimate at 5 m). Nevertheless, even if we take inspected every hour at night and the trapped adults into account their corrections, Blue Petrels and Thin- were identified and releasedimmediately after recov- billed Prions can still dive regularly to 3 m, and oc- ery of the capillary gauge. casionally 5 m. Wanless et al. (199 1) noticed that de- vices not recovered within 24 hours could also over- RESULTS estimate values. However, we found no correlation be- tween gauge deployment time and maximum depth, Eleven capillarytubes were successfullyrecovered from suggestingthat our results are reliable. Consequently, five individuals in each snecies(Table 1). The mean Blue Petrels and Thin-billed Prions foragenot only on (+ SD) maximum depths were 4.4 -I 118 m (range: and near the sea surface,but also exploit a water col- 1.0-6.2 m) and 5.5 + 1.4 m (range:3.8-7.5 m) for the umn 5-7 m deep. Blue Petrel and the Thin-billed Prion. resnectivelv.In Studies using capillary tubes on Procellariiformes the Blue Petrel, the shallowest and the deepest dives have shown that, by diving, these seabirdsuse more were performed by the same bird. Maximum depths foraging techniquesthan previously supposed,proba- recorded and gauge deployment durations were not bly allowing them to enlarge their dietary spectrum. correlated for either species(Spearman rank correla- Capillary gaugesas maximum depth recorders, being tion: Blue Petrel: r, = 0.24, n = 6, P > 0.05; Thin- simple and efficient, should be applied to other Pro- billed Prion: r, = 0.10, n = 5, P > 0.05).