VARIATION IN THE FORAGING LOCATION OF ANTARCTIC FUR SEALS (ARCTOCEPHALUS GAZELLA) AND THE EFFECTS ON DIVING BEHAVIOR

This study investigated how female Antarctic fur seals adapt their foraging behavior, over time scales of days, to spatial unpredictability in the distribution of their food. Lactating Antarctic fur seals are central-place foragers that feed on highly patchy but spatially and temporally dynamic food. We measured the foraging distribution of 28 fur seals to test whether variation in foraging trip durations was reflected in variation in the location of foraging and the diving behavior of seals at sea. Based on the maximum distance travelled from the breeding beach, three categories of foraging trips were denned: those to the continental shelf area ( n = 12, median = 71 km), to oceanic water ( n = 11, median =164 km), and to farther offshore oceanic waters ( n = 5, median = 260 km). Trip duration and mean surface speed were positively correlated with the maximum distance travelled from the breeding beach. Seals on longer trips spent proportionally less of their time submerged, but there was no significant difference in the total number of dives or the total time spent foraging by seals in relation to trip duration. Evidence from this study and previous work investigating energy gain suggests that an animal on a longer foraging trip could potentially have a higher mean energy return per dive than a similar animal on a shorter foraging trip. Evidence presented suggests that the type of foraging trip (near or far) is not predetermined by the animal but may be a simple response to the stochastic distribution of the resources available.     

Individual foraging site fidelity in lactating New Zealand fur seals: Continental shelf vs. oceanic habitats

Wide‐ranging marine central place foragers often exhibit foraging site fidelity to oceanographic features over differing spatial scales (i.e., localized coastal upwellings and oceanic fronts). Few studies have tested how the degree of site fidelity to foraging areas varies in relation to the type of ocean features used. In order to determine how foraging site fidelity varied between continental shelf and oceanic foraging habitats, 31 lactating New Zealand fur seals (Arctocephalus australis forsteri 1 ) were satellite tracked over consecutive foraging trips (14–108 d). Thirty‐seven foraging trips were recorded from 11 females that foraged on the continental shelf, in a region associated with a coastal upwelling, while 65 foraging trips were recorded from 20 females that foraged in oceanic waters. There were no significant differences in the mean bearings (to maximum distance) of individual's consecutive foraging trips, suggesting individual fidelity to foraging areas. However, overlap in area and time spent in area varied considerably between continental shelf and oceanic foragers. Females that foraged on the continental shelf had significantly greater overlap in consecutive foraging trips when compared to females that foraged in oceanic waters (overlap in 5 × 5 km grid cells visited on consecutive trips 55.9%± 20.4% and 13.4%± 7.6%, respectively). Females that foraged on the continental shelf also spent significantly more time within the same grid cell than females that foraged in oceanic waters (maximum time spent in 5 × 5 km grid cells: 14%± 5% and 4%± 2%, respectively). This comparatively high foraging site fidelity may reflect the concentration of productivity associated with a coastal upwelling system, the Bonney Upwelling. Lower foraging site fidelity recorded by seals that foraged in oceanic waters implies a lower density/larger scale habitat, where prey are more dispersed or less predictable at fine scales, when compared to the continental shelf region.     

Foraging movements of Leach's storm‐petrels Oceanodroma leucorhoa during incubation

Knowledge of foraging movements during the breeding season is key to understanding energetic stresses faced by seabirds. Using archival light loggers (geolocators), a Bayesian state–space model, and stable isotope analysis, we compared foraging movements of Leach's storm‐petrels Oceanodroma leucorhoa during their incubation periods in 2012 and 2013. Data were collected from two colonies, Bon Portage Island and Country Island, which are 380 km apart along the coast of Nova Scotia, Canada. Based on allometry for procellariiform mass, predicted foraging ranges for Leach's storm‐petrels are 200 km; however, observed maximum distances from the colony were 3 to 5 times that. Storm‐petrels from Country Island travelled 1015 ± 238 km southeast to the Laurentian fan and south of the Grand Banks whereas storm‐petrels from Bon Portage Island travelled 613 ± 167 km southeast, beyond the continental slope, east of Georges Bank. The average distance travelled in a return trip was 2287 ± 603 km and 1303 ± 351 km for Country Island and Bon Portage Island, respectively. There were no differences between years in cumulative distances travelled within islands, but foraging trips did not last as long in 2013 (4.7 ± 1.5 d) as they did in 2012 (6.2 ± 2.1 d). Stable isotope analyses indicated that, during the incubation period, prey items from Country Island were from higher trophic levels and possibly had higher energy content than those from Bon Portage Island, perhaps explaining the more distant and longer foraging trips for Country Island birds.     

Foraging behavior of lactating northern fur seals (<Emphasis Type="Italic">Callorhinus ursinus</Emphasis>) in the Commander Islands,Russia

We characterized the foraging behavior and habitat associations of lactating female northern fur seals (Callorhinus ursinus) from two of four rookeries comprising the stable population on the Commander Islands (CI). The CI females included in the study were from Severo-Zapadnoe rookery (SZR in 2008 and 2009) and Servernoe rookery (SR in 2009) which are 16 km apart on the northern tip of Bering Island (BI). We used satellite-linked tags and time–depth recorders to track the animals at sea and record dive behavior. For SZR females, the average foraging trip duration, mean dive depth, and maximum travel distance for both years were 3.4 ± 1.42 days, 16 ± 9.8 m, and 85 ± 59.6 km, respectively. The same measures for SR females were 4.4 ± 1.90 days, 20 ± 9.7 m, and 159 ± 70.8 km, respectively. The mean duration of foraging trips, mean number of bouts per trip and trip duration, mean direction of foraging trips, and size of foraging areas were significantly different between females from SR and SZR. Foraging trips of females from neither rookery were associated with high chl-a concentration. Overall, females on the CI appeared to expend less time and energy during foraging trips than females on the Pribilof Islands, and this may explain why the latter population is declining while the CI population is stable.     

Nest attendance and foraging movements of northern fulmars rearing chicks at Bjørnøya Barents Sea

We studied several aspects of the foraging ecology of fulmars rearing young chicks on Bjørnøya. To determine precisely the duration of foraging trips during the brooding period, we used an automated logging system that recorded the presence of fulmars fitted with transponders. We also tracked, with satellite transmitters, four parent fulmars during the brooding period, and two after the chick had been left alone. When brooding the chick, fulmars appeared to alternate very rapidly on the nest, with foraging trips lasting on average 8?h. This period appeared constraining for the birds since parents lost mass. The growth of chicks was dependent on the ability of the female (and not the male) to do short foraging trips. At this time birds are foraging at an average distance of 60?km from the colony, with birds concentrating on the shelf around Bjørnøya. They did not return from one trip to the next to the same foraging area. As the season progressed and the chicks were left alone on the nest, parents increased the duration and maximum range of foraging trips as well as the distance covered. However, they still perform a succession of relatively short foraging trips to the east of the Bjørnøya shelf but they interspersed these short trips with longer foraging trips. One bird returned twice to the same site along the Norwegian coast 570?km from Bjørnøya, the other foraged at 580?km in the mid-Barents Sea. Average flight speed including time spent on the water was 28?km/h and reached 70?km/h during bouts of more than 1?h when the bird was probably continuously in flight.     

Foraging location and range of White-chinned Petrels Procellaria aequinoctialis breeding in the South Atlantic

The foraging range and principal feeding areas of White‐chinned Petrels breeding at South Georgia were determined using satellite telemetry. Foraging trips during incubation lasted 12–15 days and covered 3000–8000 km and 2–11 days and 1100–5900 km during chick‐rearing. Adults covered less distance per day during chick‐rearing (71 km) than during incubation (91 km) but the proportion covered at night (47%) was the same. Mean (31–34 km/h) and maximum (80 km/h) flight velocities were similar during both periods of the breeding season and during day and night. Between incubation shifts, White‐chinned Petrels travelled to the Patagonian shelf; during chick‐rearing they foraged more extensively. Most locations were between 30° to 55°W and 52° to 60°W around South Georgia/Shag Rocks and south to the South Orkney Islands. Diet samples from known foraging locations suggested birds fed mainly on krill and squid. They caught the squid Brachioteuthis? picta and Galiteuthis glacialis around Shag Rocks/South Georgia and also at sites close to the South Orkney Islands; Illex argentinus on the Patagonian shelf. Dispersal of adults after breeding failure was south to the South Orkney Islands then west to the Falkland Islands. This study confirms that breeding White‐chinned Petrels are amongst the widest‐ranging of seabirds; they may minimise competition with other Procellariiformes in the South Atlantic by their more extensive foraging range. The nature and extent of their range also brings substantial risk of high mortality rate in South Atlantic long‐line fisheries.     

Sex differences in Adélie penguin foraging strategies

Consistent sex differences in foraging trip duration, feeding locality and diet of breeding Adélie penguins (Pygoscelis adeliae) were demonstrated at two widely separated locations over several breeding seasons. Differences in foraging behaviour were most pronounced during the guard stage of chick rearing. Female penguins made on average longer foraging trips than males, ranged greater distances more frequently and consumed larger quantities of krill. In contrast, males made shorter journeys to closer foraging grounds during the guard period and fed more extensively on fish throughout chick rearing. Mean guard stage foraging trip durations over four seasons at Béchervaise Island, Eastern Antarctica and over two seasons at Edmonson Point, Ross Sea ranged between 31 and 73 h for females and 25 and 36 h for males. Ninety percent of males tracked from Béchervaise Island by satellite during the first 3 weeks post-hatch foraged within 20 km of the colony, while the majority (60%) of females travelled to the edge of the continental shelf (80–120 km from the colony) to feed during this period. Received: 10 December 1997 / Accepted: 10 April 1998     

Foraging strategy of the little auk Alle alle throughout breeding season – switch from unimodal to bimodal pattern

Energy and time allocation differs between incubation and chick‐rearing periods, which may lead to an adjustment in the foraging behaviour of parent birds. Here, we investigated the foraging behaviour of a small alcid, the little auk Alle alle during incubation and compared it with the chick‐rearing period in West Spitsbergen, using the miniature GPS (in Hornsund) and temperature loggers (in Magdalenefjorden). GPS‐tracking of 11 individuals revealed that during incubation little auks foraged 8–55 (median 46) km from the colony covering 19–239 (median 120) km during one foraging trip. Distance from the colony to foraging areas was similar during incubation and chick‐rearing period. During incubation 89% of foraging positions were located in the zone over shallower parts of the shelf (isobaths up to 200–300 m) with sea surface temperature below 2.5°C. Those environmental conditions are preferred by Arctic zooplankton community. Thus, little auks in the Hornsund area restrict their foraging (both during the incubation and chick‐rearing period) to the area under influence of cold, Arctic‐origin water masses where its most preferred prey, copepod Calanus glacialis is most abundant. The temperature logger data (from 4 individuals) indicate that in contrast to the chick‐rearing period, when parent birds alternated short and long trips, during the incubation they performed only long trips. Adopting such a flexible foraging strategy allows little auks to alter their foraging strategy to meet different energy and time demands during the two main stages of the breeding.     

Assemblages of necrophagous animals off Enderby Land, East Antarctica

A hyperbenthic baited trap was deployed at three sites in Lützow-Holm Bay and off Enderby Land, Antarctica, in the 1993/1994 summer to investigate the species composition, distribution, and abundance of necrophagous animals. The trap consisted of four chambers, with a length of 100 cm and a diameter of 38 cm. The sample at the abyssal site, 3,186 m deep, contained 74 individuals of 6 species, completely different from that at the other 2 sites on the continental shelf; it was dominated by the large amphipod Eurythenes gryllus, a cosmopolitan species recorded from bathyal to abyssal depths. The species composition of the continental shelf sites, 93-137 individuals of 10-12 species, was dominated by species endemic to Antarctica, such as the small amphipod Pseudorchomene coatsi and the isopod Natatolana meridionalis; in these continental shelf sites, a high degree of species diversity was observed.     

Winter diet and foraging range of gentoo penguins (<Emphasis Type="Italic">Pygoscelis papua</Emphasis>) from Kidney Cove,Falkland Islands

The winter diet and foraging range of gentoo penguins, Pygoscelis papua, were studied at Kidney Cove, Falkland Islands. The mean wet mass of the 56 stomach-content samples collected from May to October was 32.7ᇃ.4 g. The diet consisted generally of cephalopods, crustaceans and fish, as well as two other molluscs. Among the six cephalopod species identified, the commercially fished Patagonian squid, Loligo gahi, had the highest abundance and was also the main prey by reconstituted mass (53% of the total reconstituted mass). Lobster krill, Munida gregaria, one of five species of crustaceans, was the most abundant prey species by frequency of occurrence and by number (68% and 60%, respectively). Rock cod, Patagonotothen ramsayi, accounted for the majority of the fish diet with 34% of the total reconstituted mass. Most prey species identified in the winter diet were also abundant diet components during the breeding season. However, the known biology of the prey species and their rate of digestion indicated that, in winter, adults may forage further offshore than during the breeding season. This assumption was supported by the results obtained from two birds satellite-tracked during the study period. Both birds remained mainly in inshore waters and returned frequently ashore, but one penguin foraged up to 276 km from the coast. The differences in the foraging behaviour of the two birds were reflected in significant differences with regard to time spent underwater, distance travelled per day and calculated travelling speed. Furthermore, the progress of cohorts of L. gahi over the winter is consistent with results from life-cycle studies in this region and suggests that birds have been foraging in the feeding grounds of L. gahi.     

Underwater observations of foraging free-living Atlantic walruses (Odobenus rosmarus rosmarus) and estimates of their food consumption

Food consumption of Atlantic walruses (Odobenus rosmarus rosmarus L.) was quantified by combining underwater observations of feeding with satellite-telemetry data on movement and diving activity. The study was conducted between 31 July and 7 August 2001 in Young Sound (74°N-20°W) in Northeast Greenland. On ten occasions, divers were able to accompany foraging walruses to the sea floor and collect the shells of newly predated bivalves (Mya truncata, Hiatella arctica, Serripes groenlandicus) for determination of number of prey and biomass ingested per dive. Simultaneously, the activity of a 1,200-kg adult male walrus was studied by use of satellite-telemetry during an entire foraging cycle that included 74 h at sea followed by a 23-h rest on land. An average of 53.2 bivalves (SE=5.2, range: 34-89, n=10) were consumed per dive, corresponding to 149.0 g shell-free dry matter (SE=18.9, range: 62.4-253.1 g), or 2,576 kJ per dive (SE=325.2, range: 1,072-4,377 kJ). During the foraging trip, the walrus spent 57% of the time diving to depths of between 6 and 32 m, and it made a total of 412 dives that lasted between 5 and 7 min (i.e. typical foraging dives). If the entire feeding cycle is considered (97 h), the estimated daily gross energy intake was 214 kJ per kg body mass (95% CI: 153-275 kJ), corresponding to the ingestion of 57 kg (95% CI: 41-72 kg) wet weight bivalve biomass per day, or 4.7 (95% CI: 3.3-5.9%) of total walrus body mass. Due to ice cover, walrus access to the plentiful inshore bivalve banks in the area is restricted to the short summer period, where walruses rely on them for replenishing energy stores. It is hypothesised that the documented decrease in the extent and duration of Arctic sea ice may increase food availability for walruses in eastern Greenland in the future.     

Foraging a new trail with northern fur seals (Callorhinus ursinus): Lactating seals from islands with contrasting population dynamics have different foraging strategies,and forage at scales previously unrecognized by GPS interpolated dive data

We reconstructed the foraging tracks of lactating northern fur seals (Callorhinus ursinus) from two eastern Bering Sea islands (St. Paul Island and Bogoslof Island) using linear interpolation between GPS locations recorded at a maximum of four times per hour and compared it to tri‐axial accelerometer and magnetometer data collected at 16 Hz to reconstruct pseudotracks between the GPS fixes. The high‐resolution data revealed distances swum per foraging trip were much greater than the distances calculated using linearly interpolated GPS tracks (1.5 times further for St. Paul fur seals and 1.9 times further for Bogoslof fur seals). First passage time metrics calculated from the high resolution data revealed that the optimal scale at which the seals searched for prey was 500 m (radius of circle searched) for fur seals from St. Paul Island that went off‐shelf, and 50 m for fur seals from Bogoslof Island and surprisingly, 50 m for fur seals from St. Paul that foraged on‐shelf. These area‐restricted search scales were significantly smaller than those calculated from GPS data alone (12 km for St. Paul and 6 km for Bogoslof) indicating that higher resolution movement data can reveal novel information about foraging behaviors that have important ecological implications.     

Foraging areas of breeding blue-footed boobies Sula nebouxii in northern Peru, as determined by direction recorders

The association between the distribution of blue-footed boobies Sula nebouxii (BFB) and marine productivity around their breeding grounds is unclear. In Peru, they breed in a region seasonally influenced by the cold, nutrient rich Humboldt Current, and by warm, nutrient poor oceanic waters. The foraging range of BFB in Peru is unknown, although some evidence suggest that they may feed in warm offshore waters. During the austral winter 2002 and summer 2003, we tracked 26 BFBs breeding on Isla Lobos de Tierra, Peru (located approximately 15 km west of the mainland), during 59 feeding trips using small direction recorders to determine their marine habitat use. BFBs preferentially moved to the east of the island and foraged over the continental shelf in cold water masses where marine productivity and the abundance of the main prey, the Peruvian anchovy Engraulis ringens , are usually higher than in other areas. Overall, the median maximum foraging distance from the colony was 39 km (range 3–109 km), with 90% of all trips located within 30 km from the mainland, and enclosed in an area of 13,113 km². These results reveal that BFBs exploit the productive waters of the Peruvian Coastal Upwelling System, rather than open oceanic waters as previously suggested. BFBs travelled a greater distance, dispersed in a broader area, and visited more offshore waters during the winter 2002, than during the summer 2003, following the typical seasonal horizontal dispersion of the Peruvian anchovy.     

GPS tracking devices reveal foraging strategies of Black-legged Kittiwakes

The Black-legged Kittiwake Rissa tridactyla is the most abundant gull species in the world, but some populations have declined in recent years, apparently due to food shortage. Kittiwakes are surface feeders and thus can compensate for low food availability only by increasing their foraging range and/or devoting more time to foraging. The species is widely studied in many respects, but long-distance foraging and the limitations of conventional radio telemetry have kept its foraging behavior largely out of view. The development of Global Positioning System (GPS) loggers is advancing rapidly. With devices as small as 8 g now available, it is possible to use this technology for tracking relatively small species of oceanic birds like kittiwakes. Here we present the first results of GPS telemetry applied to Black-legged Kittiwakes in 2007 in the North Pacific. All but one individual foraged in the neritic zone north of the island. Three birds performed foraging trips only close to the colony (within 13 km), while six birds had foraging ranges averaging about 40 km. The maximum foraging range was 59 km, and the maximum distance traveled was 165 km. Maximum trip duration was 17 h (mean 8 h). An apparently bimodal distribution of foraging ranges affords new insight on the variable foraging behaviour of Black-legged Kittiwakes. Our successful deployment of GPS loggers on kittiwakes holds much promise for telemetry studies on many other bird species of similar size and provides an incentive for applying this new approach in future studies.     

Feeding strategies of free-ranging Adélie penguins Pygoscelis adeliae analysed by multiple data recording

The fine-scale feeding behaviour of free-ranging Adélie penguins (Pygoscelis adeliae) during a single foraging trip was investigated by monitoring three parameters simultaneously at a frequency of 1 Hz, these being depth, swim speed and oesophagus temperature. Ingestion events were detected as abrupt drops in the oesophageal temperature and related to the birds' foraging behaviour. Although a high percentage of oesophageal temperature loggers were rejected, 1 complete foraging trip was recorded for all the 3 parameters from 1 bird while 92% and 67% of the foraging trip was recorded for 2 other birds; 12.3% of the temperature drops occurred at the surface but they were mainly small, except 61 of them probably representing snow ingestion while the birds were on land. All other drops were observed during dives, 88% of them during the undulatory (and occasionally the ascent) phase of dives deeper than 40 m. The mean swim speed during non-feeding shallow and exploratory dives was relatively constant throughout the dive, around 2.1 m s^-1, whereas during feeding deep dives, swim speed during the undulatory phase was lower (1.71 m s^-1) than during the descent and ascent and was characterised by a series of rapid accelerations and decelerations; 42.6% of these accelerations were followed by one or more ingestion events and birds swam upward in 60% of the accelerations. Such multiple data recording opens new paths for the examination of the decision-making processes in foraging penguins.     

Foraging behaviour and feeding locations of Rock Shags Phalacrocorax magellanicus from a colony in Patagonia, Argentina

During 1996 and 1997, foraging Rock Shags Phalacrocorax magellanicus were studied at Punta Loma, Argentina using radio-transmitters deployed on ten adult shags during the chick-rearing period. Rock Shags undertook 2.6 ± 0.6 sd trips per day. The mean duration of a feeding trip was 2.6 ± 0.7 hours. A bird spent 36% of daylight hours away from the colony on feeding trips, diving for 92% of the foraging trip, and made a mean of 106 dives per foraging trip. Foraging trip duration was strongly correlated with the total number of dives made in one foraging trip. Rock Shags fed mainly in water less than 10m deep with a gravelly sand bottom and within 5 km of shore. Mean foraging range was 3.8 ± 2.6 km and 2.6 ± 2.3 km for 1996 and 1997, respectively. These results suggest a high foraging effort (diving time per foraging trip) for Rock Shags, presumably associated with poor food conditions close to the colony. Comparison is made with other Phalacrocorax species.     

Provisioning strategies and growth patterns of Light-mantled Sooty Albatrosses Phoebetria palpebrata on Macquarie Island

Provisioning regimes and growth of Light-mantled Sooty Albatrosses (LMSA) (Phoebetria palpebrata) were investigated on subantarctic Macquarie Island using an automatic tracking system and automatic weighing nests. The nests were deployed under five chicks in the post-brood provisioning period in 2000 and 2001. Adults typically utilised a cyclical foraging strategy consisting of a long foraging trip followed by three to four shorter trips. Chicks received an average (±SE) of 37.5±2.3 kg of food in the post-brood provisioning period and were fed every 1.6±0.1 days with a mean meal size of 520±10 g. Chicks grew at a rate of 61.3±1.0 g day^-1 to a peak mass of 4.4±0.1 kg. Mean chick fledging mass was 3.0±0.1 kg. LMSA on Macquarie Island fed their chicks more frequently and showed a lower mean trip duration than conspecifics at South Georgia, which is likely related to proximity of productive Antarctic shelf waters, differences in prey availability and competition with other Procellariiformes.     

Winter migration of rockhopper penguins (Eudyptes c. chrysocome) breeding in the Southwest Atlantic: is utilisation of different foraging areas reflected in opposing population trends?

Rockhopper penguins (Eudyptes chrysocome) breeding on Staten Island, Argentina, were satellite tracked in 2002 and 2003 during the onset of their winter migration. After their moult, the dispersal of 24 birds was monitored for a mean period of 50.0±40.3 days. Birds travelled at a mean velocity of 3.1±1.1 km/h. The mean minimum distance travelled was 1,640±1,425 km; the maximum distance to the colony was generally less than 1,000 km, although one bird travelled more than 2,000 km from the colony. The penguins dispersed over an area totalling about 1.3 million km2, ranging from 50 to 62°S and from 49°W in the Atlantic to 92°W in the Pacific, and covering polar, sub-polar and temperate waters in oceanic regions as well as shelf waters. Despite the very wide dispersal, both temporally and spatially, two important wintering grounds for rockhopper penguins from Staten Island could be identified, both located over shelf regions: one extended from Staten Island to the north along the coast of Tierra del Fuego up to the Magellan Strait; the other was located over the Burdwood Bank, an isolated extension of the Patagonian Shelf to the south of the Falkland Islands. The Drake Passage also appeared to be an important area for wintering penguins, although dispersal was far more widely spread. Comparison with data obtained during winter from rockhopper penguins originating from the Falkland Islands showed that the area off the coast of Tierra del Fuego was used more or less exclusively by birds from Staten Island, whereas the Burdwood Bank was shared with penguins coming from southern colonies in the Falkland Islands. The implications of these findings are discussed with regard to (a) opposing population trends of rockhopper penguins in the Southwest Atlantic, and (b) the urgent need to establish adequate conservation measures for species and habitat protection.     

Foraging time and dietary intake by breeding Ross's and Lesser Snow Geese

We compared foraging times of female Ross's (Chen rossii) and Lesser Snow Geese (Chen caerulescens caerulescens) breeding at Karrak Lake, NT, Canada and examined variation due to time of day and reproductive stage. We subsequently collected female geese that had foraged for known duration and we estimated mass of foods consumed during foraging bouts. Female Ross's Geese spent more time foraging (mean % - SE =28.4ǃ.3%; P=0.0002), on average, than did female Lesser Snow Geese (21.5 - 1.4%). Foraging time by female geese differed among reproductive stages, but differences were not consistent among time periods (stage-by-time block interaction, P=0.0003). Females spent considerably more time foraging during prelaying and laying than during incubation. Ross's Geese also spent a greater percent of time feeding (83.0DŽ.8%) during incubation recesses than did Lesser Snow Geese (60.9Dž.6%). Consumption of organic matter during foraging bouts was minimal; estimated consumption averaged 9.6dž.0 and 12.4dž.6 g (mean - SE) dry mass/day before incubation and 5.9DŽ.0 and 5.7DŽ.1 g dry mass/day during incubation for Lesser Snow and Ross's Geese, respectively. Diets consisted primarily of mosses (bryophytes), Chickweed (Stellaria spp.) and Sedges (Carex spp.). Before incubation, eggshell consumption was estimated as 4.3Dž.2 and 0.4ǂ.3 g dry mass/day for Lesser Snow and Ross's Geese, respectively; neither species consumed eggshell during incubation. We conclude that eggshell from nests of previous years is likely an important source of dietary calcium used to meet mineral demands of eggshell formation at Karrak Lake. Our findings of wide disparities between foraging time and food intake indicate that results from studies that do not directly measure intake rates remain equivocal. Finally, we propose four hypotheses accounting for foraging effort that evidently yields little nutritional or energetic benefit to geese nesting at Karrak Lake.     

Size variation and foraging rate in bumblebees (Bombus terrestris)

Summary: Size polymorphism is an important life history trait in bumblebees with strong impact on individual behavior and colony organization. Within a colony larger workers tend to serve as foragers, while smaller workers fulfill in-hive tasks. It is often assumed that size-dependent division of labor relates to differences in task performance. In this study we examined size-dependent interindividual variability in foraging, i.e. whether foraging behavior and foraging capability of bumblebee workers are affected by their size. We observed two freely foraging Bombus terrestris colonies and measured i) trip number, ii) trip time, iii) proportion of nectar trips, and iv) nectar foraging rate of different sized foragers. In all observation periods large foragers exhibited a significantly higher foraging rate than small foragers. None of the other three foraging parameters was affected by worker size. Thus, large foragers contributed disproportionately more to the current nectar influx of their colony. We provide a detailed discussion of the possible proximate mechanisms underlying the differences in foraging rate.