The movements of gentoo penguins pygoscelis papua from ardley island, antarctica

ORIGINAL PAPER

R.P. Wilson · B. Alvarrez · L.Latorre · D. Adelung
B. Culik · R. Bannasch
The movements of gentoo penguins Pygoscelis papua
from Ardley Island, Antarctica
Received: 1 October 1997 /Accepted: 3 February 1998 Abstract The movements of gentoo penguins (Pygoscelis papua)
in Antarctica were studied by equipping a total of 37 birds captured
at Ardley Island, South Shetlands between December 1991 and
factors. Birds are most limited during breed when brood May 1996 with position-determining devices. Information on area constraints necessitate parents to repeatedly associate with usage was derived from 20 of' these devices and covered the the nest site to incubate the eggs or to feed young. Two incubation period (N = 3 birds), the chick-rearing period (N = 14 primary determinants of the marine areas birds can potentially birds) and the over-wintering period (N = 3 birds). During exploit are the length of time that birds can be absent from the incubation birds only ventured further than 50 km from the colony breeding site and their travelling speed (e.g. Williams and 20% of the time and no individual ranged further than 200 km from the colony. In contrast, no individuals attending chicks ranged Although penguins are the most aquatic of all birds, they are further than 16 km from the colony. During winter the maximum particularly restricted in the areas they can exploit compared to distance ranged from the colony was 268 km. Mean distances volant species because the only travel slowly (Costa 1991; between the birds and the colony were 80, 81 and 127 km. Wilson 1995). Penguins can be broadly divided into two groups Individual birds tended to associate with one spot, making short (10 depending on their capacity for movement. Some species, day) forays away before returning to nodal areas. The ranging such as the macaroni penguin Eudyptes chrysolophus, are capacity of gentoo penguins appears considerably less than that of migratory during the non-breeding season, while others, such sympatric congeners and may reflect the ability of gentoo penguins as the African penguin Spheniscus demersus, are considered to dive deeper and thus exploit prey not accessible to congeners. sedentary (Croxall and Davis, in press). Migratory species have a tendency to forage further of shore than sedentary species during the breeding season (Croxall and Davis, in press) and by so doing reduce inter-specific competition for Introduction
prey with species foraging inshore (e.g. Cooper et al. 1990; Hindell et al. 1995 ). Why gentoo penguins (Pvgoscelis papua) The extent to which seabirds can exploit various areas of the are generally thought to be sedentary during the non-breeding marine environment is dependent on a number of season (for summary see Williams 1995) while congeneric Adélie (Pygoscelis adéliae) and chinstrap (Pygoscelis antarctica) penguins are migratory is unclear (Davis et al. 1996; Wilson et. al. 1998), as is why, even during the breeding )·D. Adelung ·B. Culik
season, gentoo penguins forage much closer inshore than Institut für Meereskunde, Düsternbrooker Weg 20, either congener (cf. Lishman 1985; Trivelpiece et al. 1987; Wilson 1995). In areas of breeding simpatry the diets of the e-mail ifm@ifm.uni.kiel.de; Fax 0431-555876 three species are very similar (Trivelpiece et al. 1987 and Despite the general conclusion that gentoo penguins are Instituto Antártico Uruguayo, 8 de Octubre, sedentary for the whole year, the published data considering the movements of these birds are equivocal (see Bost and Jouventin 1990 and references therein) because, to our knowledge, no study has documented in detail distribution at Technische Universität Berlin, FG Bionik sea in birds from known breeding sites (as has been done, for und Evolutionstechnik, Ackerstraße 71-76, (see e.g. Sadleir and Lay 1990; Davis and Miller 1992; Davis et respect to sun angle. These factors are discussed in detail by al. 1996). To achieve this, foraging individuals must be fitted with Wilson et al. (1995) as well as techniques used to minimise such some sort of position-determining equipment (see e.g. Trivelpiece errors. Generally, such errors are non-systematic so that they et al. 1986). Rather, gentoo penguin area exploitation has been result in a non-biased scatter around the true position. deduced during the breeding season by consideration of foraging All positional information derived from the global location trip length and swim speeds (e.g. Adams and Wilson 1987; sensors was so treated that data derived from all birds from the Trivelpiece et al. 1987; Wilson et al. 1989) or been based on incubation period were lumped together as were data derived records of the presence or absence of the birds at breeding sites from over-wintering birds. A frequency matrix was then produced over winter (Bost and Jouventin 1990; Williams 1995). for each time period. The matrix resolution 0.25º (latitude by longitude) squared and all were converted to a percentage time We determined the movements of gentoo penguins from the per 0.25° square for graphic representation. In ord er to examine South Shetland Islands during three main phases of the year: ice-cover conditions in areas where the penguins were incubation, chick-rearing and overwintering using dead reckoning determined to have been, a search was conducted for satellite techniques (Wilson et al. 1993) and global location sensors data on the worldwide web with emphasis being placed on (Wilson et al. 1992, in press; Hill 1994) The aim of the study was to determine the space utilisation by gentoo penguins during different stages of their life-cycle and, where possible, to compare the areas used by gentoo penguins with those used by congeneric Adélie and chinstrap penguins. The vectorial loggers were based on the DK101 logger series (Driesen and Kern, Bad Bramsted, Germany) which recorded swim speed (via a paddle wheel), swim heading (using a compass whose orientation was measured using two Hall sensors) and dive depth (8 bit resolution for the range0-200 m) at intervals of 10 or 15 s. The unit had a memory of 64 bytes and was powered by two DL1/3 N lithium batteries. The electronics were potted in water-proof resin so that the whole unit was hydrodynamically styled (cf. Bannasch et al. 1994; Culik et al. Materials and methods
1994), weighed 200 g (in air) and had maximum dimensions of Field work was conducted at Ardley Island (62.22°S. 58.87°W), 140 (length) X 58 (width) X 28 mm (height). More details of this South Shetlands, Antarctica between December 1991 and system are given in Wilson et al. (1993). November 1996. Adult gentoo penguins were caught and Devices were programmed and recorded data accessed by a equipped with automatic position-determining devices to laptop computer linked to the loggers by an interface. elucidate the area utilisation of these birds during incubation, Downloaded data were treated by the programme ROUTE chick rearing and overwintering. Two types of positioning device (Jensen Software Systems, Kiel, Germany), which integrates all were used: global location sensors and vectorial (dead- speed, swim direction and depth data together in vectorial calculations so as to reconstruct the swim routes of the equipped birds (Wilson et al. 1993). Errors in vectorial calculations may vary according to drift induced by currents. Overall error in foraging tracks could be assessed by exampling the difference in calculated end point with respect to the known start point (since the point of entry into and exit from the water of the birds is known). Maximum differences were never more than 600 m so The global location sensors were based on the pillbox logger positional error from vectorial estimates is unlikely ever to have (Driesen and Kern, Bad Bramsted, Germany) and consisted of a exceeded this value. All derived foraging tracks were combined in light sensor covered by a blue filter (see Wilson et al. in press) a single matrix to derive the percentage total time spent by the set to record light intensity in a 128 kbyte memory once every birds per square kilometer within the foraging area. 128 s. Resolution was a 8 bit and the dynamic range to which the unit responded was between approximately 0.1 and 25 Ix. The global location sensors were powered by two 3 V lithium cells and all electronics were encased in transparent resin. The fully encapsulated unit was streamlined according to suggestions made by Bannasch et al. (1994), weighed 42 g and had maximum dimensions of 125 X 38 X25 mm. Recovered data Between 20 and 21 October 1995, ten gentoo penguins engaged were treated using the programme LOCATE (version 2.0 - in nest building and courtship activities were equipped with global Jensen Software Systems, Kiel, Germany), which determines the location sensors. These units were attached to the centre line of timing of dawn and dusk (considered to occur when the sun is the lower back, as recommended by Bannasch et al. (1994), so 4.9° below the horizon) as a function of Greenwich Mean Time as to minimise drag, using Tesa tape and two-component rubber and Julian date so that daylength and the timing of local midnight glue (Deutsche Schlauchbootfabrik, Eschershausen, Germany) and midday can be used to calculate geographic position (for (for details method 4 in Wilson et al.1997) The total time from bird details see Wilson et al. in press). Dawn and dusk are recognised capture to release took between 10 and 20 min. The birds were when the units record that the light intensity has passed a certain then released at their nest sites. Between 11 and 20 December threshold, this threshold corresponding to a particular sun angle 1995, a search was made for the equipped birds. When located, (nominally -4.9°). The thresholds corresponding to our specified the global location sensors were removed by cutting the ends of sun elevation angles were determined during calibrations made the feathers. At this time bird body mass was measured and the in Antarctica, Germany and Uruguay. Accuracy of these units is status of the nests of the equipped birds noted. estimated to be better than 40 km for class 1 fixes if no snow covers the sensor (Wilson et al. 1995). Snow can theoretically cover the sensor for short periods though birds tend to shake it off and, where this occurs over dawn or dusk, it can compromise the quality of fixes so that accuracy may be ± 80km. Numerous other factors compromise the quality of fixes obtained by global Between 29 December 1991 and 19 January 1992, 14 gentoo location sensors; among these are cloud cover, extensive diving penguins tending small chicks were equipped with vectorial behaviour around dawn and dusk and sensor orientation with in the case of incubating birds, the units were attached to the
centre line of the lower back, but this time were held in place
solely by Tesa tape (for details, see method 1 in Wilson et al.
1997). After return to the nest, birds were left to undertake a
minimum of one foraging trip before the units were removed.
Over-wintering
Between 6 and 7 May 1996, 13 post-moult adult gentoo penguins
were caught and restrained according to methods described in
Wilson et al. (1998) while they were equipped with global location
sensors. These units were attached in the same way as the
devices used to determine the position of birds at sea during the
incubation period. Here, however, the total time from bird capture
to release took between 20 and 65 min. the longer times being
mainly due to dry at the low temperatures experienced at that
time. The birds were then released to allow them to go to the
sea. During October and November 1996, searches were
conducted to recover device-equipped birds that had returned to
Ardley Island to breed. Recovered penguins were restrained in
the same way as before and the device removed by cutting the
ends of the feathers. Devices were then transported to Kiel,
Germany, pending analysis.
Results
Incubation
All ten device-equipped birds were recovered, the mean mass of
recovered birds being 5.69kg (SD 0.43). All birds appeared in
good condition and were breeding successfully: eight nests contained two chicks, one nest contained one chic and one nest Fig. 1a-c Frequency of occurrence of the direct distance between monitored gentoo one chick with one egg. Chick ages were determined to be penguins and their breeding colony during: a the incubation period (derived from 3 between 1 and 5 days. Only three of the ten global location birds were fixes were derived twice per 24 h for each individual giving a total of 317 fixes evenly distributed among individuals); b the chick rearing period (derived from 14 sensors produced high quality data that could be used for birds where fixes were derived once every 15 s that they were at sea); c the over- determination of bird position. This was due, in three cases, to wintering period (derived from 3 birds were fixes were derived twice per 24 h for each data corruption caused by failing batteries or, in four cases, water individual giving a total of 618 fixes evenly distributed among individuals) entering the devices. A total of 622 positional fixes was obtained. Between October and December, during the courtship and incubation period, the monitored gentoo penguins spent most 5 km (Fig. 2b). This means that no bird even ranged far enough time within 50 km of the colony (Fig. 1a). Only about 20% of time to move out of Maxwell Bay, either into the Bransfield Strait or were birds at distances in excess of 50 km and no individual ever ventured further than 200 km. Excepting the area close to the colony, the sea areas most used by the birds were the Bransfield Strait, between King George Island and the Antarctic Peninsula and the Drake Passage, immediately adjacent to King George Of the 13 gentoo penguins equipped, 6 were recovered during October and November 1996. All recovered birds appeared in good condition and were engaged in nesting behaviour. Three of the global location sensors had logged data, the other units having suffered unacceptable voltage drops so that the data were All 14 birds equipped with vectorial loggers foraged successfully corrupt. The three viable global location sensors had all logged and continued feeding their chicks. Units were covered after a data until 17 August 1996 when the memories were full. Between mean of 2.7 days (SD 1.7) and all data could be used for the May and August all three gentoo penguins had occupied an area calculation of bird position. During December and January, no west of (Fig. 2c) and ranged up to a maximum distance of 268 equipped individual foraged further than 16 km from the island km from Ardley Island (Fig 1c). Mean distances from Ardley (Fig. 1b), with the vast majority of the time being spent within Fig. 2a-c Topographic plot (from Surfer) of the positions of the tracked gentoo
penguins: a during the incubation period (the contour lines refer to the
percentage time spent per 05º2 (lat. X long) summed over the whole of the
incubation period; b during chick rearing (the contour lines refer to the
percentage time spent per km2 summed over the whole of the chick-rearing
period where the min. contour is 1 and increments are 1%); c during wintering
period (the contour lines refer to the percentage time spent per 05º2 (lat. X long)
summed over the whole of the winter period over which the birds were tracked)
et al. 1996) Device-induced detrimental effects are most likely to make themselves apparent over long intervals so that the equipment of our gentoo penguins for the winter period for 7 months must be regarded as a severe test of the acceptability of the devices by the birds. That we recovered 6 of the total of 13 equipped birds, all in apparently good condition, and all engaged in nesting behaviour, indicates that our devices are apparently well tolerated by the birds. No equipped bird was sighted in poor (SD 47, N = 206) 81 km (SD40, N = 206) and 127 km (SD53, N = condition. The failure to sight the' other eight equipped individuals 206). Each bird tended to spend most time within a particular is most likeky due to the fact that we equipped some moulting area, apparently engaging in forays away from this area lasting gentoo penguins at Ardley Island that originated from one of the
Discussion
The attachment of external devices to penguins has been shown
to affect aspects of their behaviour and energetics (see e.g.
Wilson and Culik 1992; Culik et al. 1994; Croll
numerous colonies round King George Island and that distances of up to 125 km away from the breeding sites, although consequently returned to these colonies at the onset of the the variance was high. Gentoo penguins, almost wherever they breeding season. (In support of this, we received reports that at occur, are considered to have relatively restricted foraging areas. least two gentoo penguins carrying devices had been sighted at Using distance meters, Adams and Wilson (1987) calculated a the Jubany colony, some 18 km away from Ardley, in November maximum foraging range of 35 km for gentoo penguins tending chicks at Marion Island (46º54'S, 37º45'E). These data were subsequently re-worked by Wilson et al. (1989), to correct for vertical distance acquired due to diving, to derive a foraging Area exploitation during the breeding season Why should gentoo penguins, in areas of sympatry with Adélie and chinstrap penguins, consistently be able to forage closer inshore than congeners and, in so doing, avoid incurring Earlier calculations of gentoo penguin foraging range based on travelling costs while at the same time exploiting similar prey? swim speeds and time absent from the colony ranged between 3 Trivelpiece et al. (1987) suggested that gentoo penguins might and35 km (Adams and Wilson 1987; Trivelpiece et al. 1987; habitually dive deeper than either Adélie penguins or chinstrap Wilson et al. 1989). Studies where birds were equipped with radio penguins and thus be able to exploit prey closer to their colonies transmitters showed that gentoo penguins breeding in colonies that is not available to either congener. There is a positive bordering Admiralty Bay (62.2º S, 58.8º W) rarely moved outside correlation between maximum dive depth and body mass in this area during chick rearing. Our work confirms that gentoo penguins (Wilson 1995). However, the capacity to exploit deeper penguins from King George Island during chick rearing do indeed prey not only depends on the ability of birds to reach the relevant seem to forage almost exclusively close inshore at this time. depths, but also to be able to do this consistently and to remain During incubation, these birds have a more extended foraging for extended periods at those depths in order to feed. Gentoo range, but, even so, apparently spend around 80% of their time penguins do indeed have greater diving capacities than either within 50 km of the colony. This situation contrasts with that conspecific (cf. e.g. Lishman and Croxall 1983; Whitehead 1989; found in the Adélie penguins where males take the first shift at Naito et al. 1990; Williams et al. 1991; Wilson et al. 1991A,b; incubation, which lasts some 14-17 days (Sladen 1958; Davis Bengston et al. 1993). Wilson (1995) suggested that there was and Miller, 1982), during which time the females may range up to little inter-specific difference in the frequency of maximum dive 186 km from the colony (cf Davis et al 1988; Sadleir and Lay depth of pygoscelids breeding at Ardley Island. Re-evaluation of 1990; Kerry et al. 1995). Incubation shifts by chinstrap penguins these data suggests, however, that at depths in excess of 10 m, are markedly shorter, generally varying between 6 an d10 days gentoo penguins dived more often to specific depths than either (Williams 1995) so the foraging range is likely less than that of congener in seven out of nine case, supporting Trivelpiece et al.'s Adélie penguins although to our knowledge no telemetric studies (1987) hypothesis. This does not mean, however, that the birds necessarily travel overall less far. We analysed the distributions Trivelpiece et al. (1987) calculated that gentoo penguins of maximum depth data presented by Wilson (1995) to determine tending for chicks at King George Island would have a likely the distance travelled vertically during diving (see Wilson et al. foraging range of 17 km (max. 24 km), considerably less than 1989) and found that, over 100 typical dives, Adélie penguins either sympatric Adélie penguins (likely range 43 km, max. 50 foraging from Ardley cover a vertical distance of 4.1 km, chinstrap km) or chinstrap penguins (likely range 27 km, max. 33 km). penguins 3.3 km while gentoo penguins travel 5.2 km. Thus, in Trivelpiece's values for chinstraps are somewhat higher than diving deeper, gentoo penguins travel vertically 27% more than those calculated by Bengtson et al. (1993) of 3-20 km for Seal Adélie penguins and 58% more than chinstrap penguins, which at Island. Nonetheless, Trivelpiece et al.'s (1987) contention that least partially compensates for the apparent benefits of the gentoo penguins at King George Island forage closer inshore than do either Adélies or chinstraps is supported by our results and those presented by Wilson (1995). Sympatrically brooding Adélies and chinstraps from Ardley Island may forage over 30 km away from the colony; this is something that the gentoo penguins Area exploitation during the non-breeding season The foraging ranges of pygoscelid penguins in other areas of Antarctica may vary substantially from those determined for King Absences at sea of gentoo penguins during the non-breeding George Island. For example, Lishman (1985) calculated that season become longer in the more southerly regions of the Adélie and chinstrap penguins during the chick-rearing period range, with birds from the Antarctic Peninsula being absent from from Signy Island (60º43'S, 45º36'W) have foraging ranges of 83- colonies for periods in excess of 2 months (cf. Bagshawe 1938; 119 km and 66-132 km, respectively. Kerry et al. (1995) determined, using satellite telemetry that Adélie penguins tending Our study demonstrates that gentoo penguins from King George Island apparently do not fit into the classic scheme as either truly migratory or sedentary birds. The during the austral winter of 1996 (July/August 1996; data from maximum distance between any bird and the breeding site of 268 http:llmullara.met.unimelb.edu.au). Our few results would indicate km is a fraction of that determined for chinstrap penguins from that gentoo penguins from Ardley Island during winter exploit an Ardley Island, which may move in excess of 1000 km away from environment that is, with respect to ice coverage at least, their breeding colonies during the non-breeding season (Wilson somewhat intermediate to that exploited by Adélie and chinstrap et al. 1998). Although there are no data on over-winter penguins. Should this prove to be a general phenomenon, the movements of Adélie penguins from Ardley Island, birds from exact degree to which the different ice-cover conditions other areas may move similar long distances (Davis et al. 1996). selectively favour each of the three pygoscelid penguins will be Despite this, the mean bird-island distance of around 100 km for an exciting, and difficult, topic for future research. gentoo penguins is substantial for a flightless sea bird and is certainly well outside the normal foraging radius for breeding Acknowledgements
supported
Deutsche
birds (see above). The literature on gentoo penguins sightings at Forschungsgemeinschaft with a grant to Dieter Adelung, as well as by the
Instituto Antártico Uruguayo. We are grateful to Mandy Kierspel for help with the
sea (cf. Watson et al. 1971; Enticott 1986) indicates that birds are analysis, as well as to Doris Abele for her constant, behind the lines, chivying
rarely sighted far from breeding point (cf. Voisin 1979; Enticott when things seemed intractable.
1986), demonstrating that they are capable of long-distance movements in the same way as their congeners. We conclude from this study that there are grounds for believing that gentoo penguins may undertake appreciable migrations in certain areas References
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