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Foraging Behavior of Gentoo and Chinstrap Penguins As Determined by New Radiotelemetry Techniques

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Foraging Behavior of Gentoo and Chinstrap Penguins As Determined by New Radiotelemetry Techniques FORAGING BEHAVIOR OF GENTOO AND CHINSTRAP PENGUINS AS DETERMINED BY NEW RADIOTELEMETRY TECHNIQUES WAYNE Z. TRIVELPIECE,JOHN L. BENGTSON,1 SUSAN G. TRIVELPIECE, AND NICHOLAS J. VOLKMAN PointReyes Bird Observatory, 4990 Shoreline Highway, Stinson Beach, California 94970 USA ASSTRACT.--Analysisof radio signalsfrom transmittersaffixed to 7 Gentoo(Pygoscelis papua) and 6 Chinstrap (P. antarctica)penguins allowed us to track penguins at sea. Signal charac- teristics allowed us to distinguish among 5 foraging behaviors: porpoising, underwater swimming, horizontal diving, vertical diving, and restingor bathing. GentooPenguins spent a significantly greater portion of their foraging trips engaged in feeding behaviors than Chinstraps,which spent significantly more time traveling. Gentooshad significantly longer feeding dives than Chinstraps(128 s vs. 91 s) and significantlyhigher dive-pauseratios (3.4 vs. 2.6). These differencesin foraging behavior suggestGentoo and Chinstrappenguins may have different diving abilities and may forage at different depths. Received3 June 1985, accepted24 April 1986. THE trophic relationships among Pygoscelis among behaviors during foraging trips. This penguins,the Ad61ie(P. adeliae),Chinstrap (P. method improved our understanding of pen- antarctica),and Gentoo (P. papua),have been a guin feeding efficiencies,ranges, and traveling major focal point of researchin recent years, speeds,and permitted preliminary compari- particularlywith respectto the ecologyof their sons of Gentoo and Chinstrap penguin forag- major prey species,krill (Euphausiasuperba). To ing behaviors. date, however, our knowledge of the birds' METHODS feeding ecologyis largely derived from stom- ach samples obtained ashore (Emison 1968; This studywas conductedat a breedingrookery at Croxall and Furse 1980; Croxall and Prince Point Thomas, King George Island, South Shetland 1980a;Volkman et al. 1980, 1986;Lishman 1985). Islands, Antarctica (62ø10'S, 58ø30'W), between 26 Diving depth is one aspectof penguin for- January and 12 February 1984. We attached radio aging behavior that has been investigated in transmitters(1.5 cm in diameter, 5 cm long, 25 g) to the backsof 7 Gentoo and 6 Chinstrap penguins rear- somedetail. Multiple depth recorders,logging ing chicks. We securedthem to back feathers with the number of dives within set depth ranges, Devconepoxy and two plastictie-wraps. A 30-cmlong have been deployed on King (Aptenodytespata- antennacurved upward from the penguin'sback to gonica;Kooyman et al. 1982), Chinstrap (Lish- assureit was well above the water when the penguin man and Croxall 1983),and Gentoo (Costapers. surfaced.We triangulated penguins' locations,at 15- comm.) penguins. Maximum diving depths min intervals, with radio receivers (164 MHz) from have been reported for Emperor (A. forsteri; two huts, 200 m above sea level and approximately Kooyman et al. 1971), Black-footed(Spheniscus 3 km apart. We used a null-peak, 4-element double demersus;Wilson and Bain 1984), and Gentoo Yagi antenna receiving system.A third receiver was (Adams and Brown 1983) penguins. Feeding coupled to a strip-chart recorder and continuously monitored a single penguin during its foraging trip. range also has been investigated, but indirect- Signalsfrom foraging penguinswere receivedonly ly, using nest relief intervals (Williams and when the bird was on the surface and the antenna Siegfried 1980,Ainley et al. 1984, Croxall et al. was not submerged.Thus, strip chartsprovided pro- 1984). files of the surface vs. underwater time during pen- We report a new method of tracking pen- guins' foraging trips. Penguins were tracked be- guins at sea that allowed us to differentiate tween 0900 and 2300, and the two species were alternatedover the studyperiod. Krill was apparent- ly plentiful in Admiralty Bay during this time as all * Present address: National Marine Mammal Labo- penguinsforaged exclusivelyin the bay, within 10 ratory, NOAA/NMFS, 7600 San Point Way N.E., Se- km of the rookery. attle, Washington 98115 USA. All data are expressedas means + standard error. 777 The Auk 103: 777-781. October 1986 778 TI•IVEI•PIECEœTAL. [Auk,Vol. 103 Statisticalanalysis was done using the Mann-Whit- ney U-test or G-test with Yates correction. •rRAC#INGNUTS MINUTE FIXœS •rOIiAG•ld G PATH RESULTS Foragingbehavior patterns.--The foraging track of Gentoo Penguin 3875 and sectionsfrom its chartrecording are illustratedin Fig. 1. We were ableto distinguishseveral types of diving pat- terns from the strip-chart records. We believe these indicate different behaviors such as rest- ing at the surface,two modesof traveling (por- poising and underwaterswimming), and two feeding behaviors(horizontal and vertical div- ing). Restingat the surfaceincluded time spent bathing. Porpoisingalways was used by penguins leaving from or returning to the immediatevi- cinity of the beach.Outward-bound porpoising often was followed by bathing, and both be- haviors were confirmed visually. Rapid por- poising, then bathing, is a constantfeature of Ad•lie Penguindeparture at Cape Crozier in the RossSea (Ainley 1972). Underwater swim- ming, the primary method of traveling usedby penguins, accountedfor 73% of all traveling time. It consistedof dives,averaging 50 s each, followed by surface pauses,averaging 12 s. Horizontal diving behavior followed under- Fig. 1. The foraging trip of Gentoo male 3875 in water swimming and precededvertical diving AdmiraltyBay. The penguin'spath wasplotted from in 5 of the 6 penguins for which we have com- compassbearings triangulated by radio and taken at plete records.Penguins that exhibit this for- 15-min intervals from the two tracking huts. Forag- aging pattern moved considerabledistances by ing behaviorswere copiedfrom a continuousstrip alternating periods of long dives with one or chart. Whenever the penguin was submerged,the two short dives. The short dives were of ap- signal was lost and the strip-chartpen returned to proximately the same duration as the dives of baseline;upon surfacing,the radio signalcaused the underwater swimming. We hypothesize that pen to deflect upward and remain there until the horizontal diving may be the primary method next dive. The raggedlook of surfaceperiods during horizontaland verticaldiving wascaused by changes of searchingbehavior used by penguins. The in the orientation of the antenna because of bird long dives of this behavior pattern may be to movement and from waves washing over the bob- explore the deeper layers of the water column bing penguin, which interfered with the signal's for krill. When no prey are located, the pen- propagation.The paper speedof the strip chart was guin moves to a new location by short "trav- 16 mm/min. Data on surface times and dive times eling dives" before diving again to searchfor were taken directly from the chartsby converting prey. Vertical diving, like underwater swim- linear distance to time. ming, was characterizedby regular intervalsof dive-to-surface pause times. The duration of dives and pauses were significantly longer, all underwaterswimming dives plus the short however, and the penguins remained in a lo- dives during horizontal diving behavior. Por- calized area during vertical diving (Fig. 1). poisingwas not consideredto be diving. For analysisof the foraging behavior of the Comparisonsof Gentoo and Chinstrap foraging be- penguins, feeding dives were defined as all haviors.--GentooPenguins spent a significantly divesduring vertical diving, plus the long dives greater portion of foraging trips engagedin during horizontal diving; traveling dives were feeding behaviors(horizontal and vertical div- October1986] PenguinForaging Behavior 779 ing) than in travelingbehaviors (porpoising and TABLE1. The percentage of foraging time spent in underwater swimming) than did Chinstrap different behaviorsby Gentoo and Chinstrap pen- Penguins (G = 5.47, P < 0.025; Table 1). Gen- guins.a toos made significantly longer vertical dives Foraging behaviorsb (%) than Chinstraps(128 + 4.5 vs. 91 _+4.9 s; U = Traveling Feeding 42.00,P < 0.005)and had significantlylonger Foraging maximum dive times (189 _+ 8.4 vs. 130 _+ 4.3 trip (h) P U H V R s; U = 12.00, P < 0.01; Table 2). Gentoos also Gentoo Penguinsc had significantlyhigher dive/pauseratios dur- 3894 F 5.7 5 12 53 21 ing vertical diving (3.4 + 0.2 vs. 2.6 + 0.2; U = UBM 7.1 3 24 6 60 6 36.50, P < 0.005; Table 2). Gentoo Penguins 3875M 5.5 6 15 34 44 1 made a mean 193 dives during 6.1 h of forag- Mean 6.1 5 17 31 44 3 ing, 90 of which (47%) were feeding dives; ChinstrapPenguins c Chinstrapsmade 182 divesduring 5.3 h, 74 of 3896M 4.8 9 18 11 57 4 which (41%)were feeding dives(Table 2). 3963 F 4.4 13 17 22 46 2 3893 F 6.8 10 47 7 32 4 We calculatedtraveling speedsfor penguins Mean 5.3 11 27 14 45 3 returning from feeding areas to the breeding rookeries.The mean (+SE) travelingspeed for aFrom analysesof strip-chart recordings of com- 3 Gentooand 3 Chinstrappenguins was 4.5 + plete foraging trips. bp = porpoising,U = underwater swimming, H = 0.4 km/h (Table 2). Penguin return trips varied horizontal diving, V = vertical diving, R = resting from 20 to 64 min. Strip-chartrecordings as- or bathing on surface. suredus penguinswere traveling (i.e. porpois- c M = male, F = female. ing or underwaterswimming) throughout their returns. tions from their histogramsshow that 445 of DISCUSSION 1,110 dives made by Chinstrap Penguinswere recordedin the shallowestdepth range(0-7 or Usingradiotelemetry to trackpenguins at sea 0-10 m). Thisrepresents 40% of all dives,many
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