Diet and foraging effort of Adélie penguins in relation to pack-ice conditions in the southern Ross Sea

We investigated the diet and aspects of foraging effort among Adélie penguins (Pygoscelis adeliae) breeding at three colonies on Ross Island, in the southwestern Ross Sea – Capes Royds, Bird and Crozier – during the chick-provisioning period of three austral summers, 1994–1995, 1995–1996 and 1996–1997. During the study period, pack-ice cover differed in waters offshore of these colonies, by colony, seasons and year. Diet differed among colonies only slightly. The fish Pleuragramma antarcticum was the most important prey, especially during years or periods within years when little pack ice was present. With respect to krill, which composed the remainder of diet, juvenile Euphausia crystallorophias were consumed predominantly in a year of heavy pack-ice cover; more adult krill were consumed in 2 years when pack ice was sparse. Foraging trip duration differed by colony, season and year and was related directly to distance from the colony to the nearest pack ice. The amount of food brought to chicks increased as trip duration increased, to a point (2 days), but then decreased as duration increased further (up to 4 days). On the basis of data on mass of parents and of meal sizes to chicks, it appeared that on the longest trips more of the food gathered by parents was used for self maintenance; on the longest trips, parents lost body mass. Successful foraging during chick rearing, the period when adult foraging is most intense, appears to depend on the proximity of pack ice to nesting colonies for this penguin species. Received: 1 October 1997 / Accepted: 25 April 1998     

Sex and individual differences in foraging behavior of Japanese cormorants in years of different prey availability

Japanese cormorants, Phalacrocorax capillatus, are sexually dimorphic seabirds with males that are heavier and that dive deeper than females. Sex differences in prey composition and foraging behavior of those rearing chicks at Teuri Island, Hokkaido, were examined by collecting food-loads from parents in 1992–1998 and by radio-tracking ten birds each in 1997 and 1998 when prey availability was different. Males fed more on benthic and epibenthic fishes (82% mass) than did females (34%) while females fed more on epipelagic and coastal fishes (53%) than did males (18%). Males made longer dives (53 s) at feeding sites closer to the island (7 km) than females (39 s, 13 km) in 1997. In 1998 when the availability of epipelagic fish seemed to be higher, there were no sex differences in dive duration and distance to the feeding sites (35 s and 9 km for males, 36 s and 10 km for females). This sex difference in foraging behavior with a poor availability of epipelagic fish suggests that high diving ability possibly enables males to feed on demersal fish. Birds specializing in coastal shallow waters around the island made long dives; hence they were probably foraging in bottom layers. Those foraging in deeper shelf waters made short dives and they were thought to forage in surface layers. Electronic Publication     

Effects of food availability on fledging condition and post-fledging survival in king penguin chicks

Effects of summer food shortage on king penguin Aptenodytes patagonicus chicks were studied at South Georgia. Two cohorts were compared, fledging in the austral summers of 1992 (n = 32) and 1994 (n = 33) when availability of food was judged good and poor, respectively. The former cohort had a higher pre-fledging mean mass (12.78 kg vs ≤ 10.03 kg), fledged earlier (median 5 January vs 21 January), and a higher proportion was re-sighted within 2 years of fledging (28% vs 0%). Within 4 years, 47% of the former cohort had been re-sighted (i.e. post-fledge survival); in addition, one was observed at the Falkland Islands, and 22% had bred (i.e. recruitment) in their colony of origin. The re-sighted chicks of the 1992 cohort fledged earlier than those not re-sighted (median 24 December vs 10 January), but it remain unclear if they were heavier at fledging. All chicks in this study (n = 65) were marked with both transponders (subcutaneously implanted) and flipper bands (on one flipper), and no losses of any markings were found (controlled up to 4 years afterwards). Therefore, data on chick post-fledging survival and recruitment were not adjusted for losses of markings, as has been done in other studies. Received: 21 October 1996 / Accepted: 2 February 1997     

Assessment of the impacts of hydrological fluctuations and salt pans abandonment on Greater flamingos in the Camargue, South of France

Flamingos forage in both commercial salt pans and natural marshes and lagoons along the French Mediterranean coast. In order to assess the impact of changes in management of commercial salt pans and hydrological fluctuations on this flagship species, we evaluated the foraging areas of breeding flamingos using the resightings of 283 breeding flamingos marked with dye at the colony in 1987 and 1989, two years with contrasting hydrological conditions. Teams of observers searched all suitable habitats within 80 km of the colony during the four days following marking and recorded presence of off-duty flamingos. About one-third of the birds were found within 10 km of the colony, but some were seen up to 70 km away. About 24–54% of the birds were found in permanent brackish lagoons and 18–60% in the salt pans, the two most important habitats. In 1989, a dry year with lower water levels in the natural wetlands, the proportion of breeding flamingos using salt pans was twice as high [53%, range (47–60%)] as in 1987 [26%, range (18–29%)], this habitat thus acting as a refuge. Most of the feeding areas shown to be important for flamingos breeding in the Camargue are thus susceptible to variations according to rainfall and to transformations or drying out if the salt pans are abandoned. Our results provide essential benchmarks to reconsider the conservation of this flagship species when management of commercial salt pans changes.     

Raising young reduces body condition and fat stores in black-legged kittiwakes

We conducted a manipulative experiment to investigate how raising chicks affects the body condition (body mass scaled by body size) and body composition (percent fat vs. lean mass) of black-legged kittiwakes (Rissa tridactyla). For 4 consecutive years (1991–1994) we removed eggs from randomly selected nests and then compared adults raising chicks with adults that had their eggs removed. At the end of the chick-rearing period, adults raising chicks were significantly lighter for their size than adults that had their eggs removed. Adults raising chicks also had a significantly lower percent body fat (by 28%) than adults from manipulated nests. The difference in percent body fat between the two groups was apparent at all levels of condition, suggesting that adults that are raising chicks apportion their reserves differently than adults that are working only to meet their own metabolic needs. End-of-season body condition of adults from manipulated and unmanipulated nests varied significantly among 5 years of study, and appeared to reflect differences in local foraging conditions. In all years, females were in worse condition than males at the end of the breeding season. This sex-specific condition difference did not, however, appear to indicate a greater short-term reproductive cost among females. Females were lighter for their size than males in both the manipulated and unmanipulated groups. Our results suggest that adult kittiwakes compromise their body condition and body composition during chick rearing to increase the likelihood of successfully fledging young, even though such adjustments may decrease their own post-reproductive survival probabilities. Prior to estimating the body composition of the experimental birds, we evaluated the usefulness of several noninvasive techniques for predicting fat mass in kittiwakes. We used cross-validation techniques to compare multiple regression models that included total body electrical conductivity (TOBEC), total body water (TBW), and morphometric measurements as independent variables. The most parsimonious model for predicting fat mass was based on TOBEC and mass measurements. TBW and morphometrics were of little utility in predicting fat mass in kittiwakes. Previous studies that have evaluated the usefulness of TOBEC as a predictor of fat mass have shown mixed results. We suggest that the size of the experimental subject relative to the size of the TOBEC measurement chamber may affect the accuracy of this technique. Received: 30 November 1998 / Accepted: 29 April 1999     

Rates and consequences of relaying in Cassin's auklets Ptychoramphus aleuticus and rhinoceros auklets Cerorhinca monocerata breeding in a seasonal environment

We removed first eggs from early‐laying females to measure rates and consequences of relaying in Cassin's auklets Ptychoramphus aleuticus and rhinoceros auklets Cerorhinca monocerata at Triangle Island, British Columbia, Canada. Based on egg size and composition, the investment that Cassin's auklets made in first eggs was very close to that predicted from adult body mass, whereas rhinoceros auklets invested more. In both species, a high percentage of females relaid (90% of Cassin's and 87% of rhinoceros auklets). Breeding success declined weakly with later laying among control Cassin's auklet pairs, but pairs that we induced to relay bred more successfully than naturally late pairs, and similar to values predicted from laying dates of their first eggs. Their chicks also fledged heavier and younger than late control chicks, and similar to values in early control chicks, but followed the population‐wide seasonal decline in wing length at fledging. Nestling diets were dominated by Neocalanus copepods until late in the season, a sign that feeding conditions remained favourable until late. In contrast, rhinoceros auklet pairs induced to relay followed the population‐wide seasonal decline in breeding success, which was driven by a decline in hatching success. Pacific sandlance Ammodytes hexapterus, thought to be a preferred prey species, virtually disappeared from nestling diets in mid‐to‐late season, yet there was no seasonal decline in fledging mass. However, chicks from replacement eggs followed the declines among control chicks in both age and wing length at fledging. Despite the female having produced a replacement egg, and despite delayed breeding, there appeared to be little immediate consequence associated with relaying for Cassin's auklets, except for a tendency for their chicks to fledge with short wings. Consequences were more marked in rhinoceros auklets (greatly reduced hatching success, and having their chicks fledge with short wings), and this may have been due to the large investment made in eggs, and/or to delayed breeding. Results of this study show that attributes of Cassin's and rhinoceros auklets that lay at different times in the season can be important in driving seasonal declines in breeding performance, as found in studies on other Alcidae. They also show how decisions taken during the egg stage can have variable yet potentially important implications for fitness, even in relatively long‐lived species that lay single‐egg clutches.     

Chick provisioning rates and growth in Blacklbrowed Albatross Diomedea melanophris and Grey-headed Albatross D. chrysostoma at Bird Island, South Georgia

We compared the parental division of labour and the pattern and rate of parental provisioning by two sympatric species of albatross of similar mass and breeding timetable but differing in diet and in the duration of chick‐rearing. Using electronic weighing platforms inside artificial nests, we recorded chick mass of Black‐browed Albatross and Grey‐headed Albatross at Bird Island, South Georgia every 10 minutes for both species in 1993 and 1994 and for each species in two other years between 1990 and 1996. The chick mass data (nearly one million weighings) were used to calculate meal mass (over 5000 meals) and intervals between meals. Adult birds were fitted with radio‐transmitters which allowed each meal to be allocated to the appropriate parent. The combination of meal mass and foraging trip duration were used to calculate provisioning rates for chicks and individual adults. Overall, Black‐browed Albatrosses delivered significantly lighter meals (569 g) than Grey‐headed Albatrosses (616 g) but more frequently (every 2.07 days and 2.50 days respectively). Thus combining foraging trip data for both parents, Black‐browed Albatross chicks received a meal every 1.22 days compared with 1.26 days for Greyheaded Albatross. These rates did not differ significantly. The contribution of each sex of each species in chick provisioning fluctuated between years, being similar in some years or biased towards males in others. Chicks of both species that failed to fledge received smaller, less frequent meals than successful chicks. In 1990 and 1994, Black‐browed Albatross chick provisioning rates were lower than in 1992 and 1993. In 1990, both meal mass and trip duration were affected, but only in 1994 was trip duration longer. Greyheaded Albatross chick provisioning rate was lower in 1994 than in other years but trip duration was longer. In each species, significant changes in meal mass and trip duration occurred within the chick‐rearing period. Chick provisioning rates invariably declined before chicks attained their peak mass. For both species, chick growth rates and peak and fledging mass, but not fledging age, were affected by differences in provisioning rate.     

The effects of loggers on the foraging effort and chick-rearing ability of parent little auks

We studied the effects of loggers attached to chick-rearing little auks (Alle alle) on their daily time budget (proportion of time spent in the colony and at sea), foraging activity (duration and proportion of long and short foraging flights), chick provisioning rate and their growth and development on Spitsbergen. We found that experimental parent birds performed shorter but more frequent long foraging flights and reduced the frequency of short foraging flights. They spent more time at the colony and reduced chick provisioning rate compared to control birds. Nestlings reared by experimental parents weighed significantly less at their middle, peak and fledging age and departed colony later than chicks of control parents. Little auks depend on energy-rich copepods associated with cold Arctic waters and are expected to face the climate-induced worsening of the foraging conditions, which may have negative impact on their time/energy budget and survival. The study may help to determine the level of extra effort little auks need to invest to breed successfully.     

Disentangling effects of growth and nutritional status on seabird stable isotope ratios

A growing number of studies suggest that an individual’s physiology affects its carbon and nitrogen stable isotope signatures, obscuring a signal often assumed to be only a reflection of diet and foraging location. We examined effects of growth and moderate food restriction on red blood cell (RBC) and feather δ¹⁵N and δ¹³C in rhinoceros auklet chicks (Cerorhinca monocerata), a piscivorous seabird. Chicks were reared in captivity and fed either control (75 g/day; n = 7) or ~40% restricted (40 g/day; n = 6) amounts of high quality forage fish. We quantified effects of growth on isotopic fractionation by comparing δ¹⁵N and δ¹³C in control chicks to those of captive, non-growing subadult auklets (n = 11) fed the same diet. To estimate natural levels of isotopic variation, we also collected blood from a random sample of free-living rhinoceros auklet adults and chicks in the Gulf of Alaska (n = 15 for each), as well as adult feather samples (n = 13). In the captive experiment, moderate food restriction caused significant depletion in δ¹⁵N of both RBCs and feathers in treatment chicks compared to control chicks. Growth also induced depletion in RBC δ¹⁵N, with chicks exhibiting lower δ¹⁵N when they were growing the fastest. As growth slowed, δ¹⁵N increased, resulting in an overall pattern of enrichment over the course of the nestling period. Combined effects of growth and restriction depleted δ¹⁵N in chick RBCs by 0.92‰. We propose that increased nitrogen-use efficiency is responsible for ¹⁵N depletion in both growing and food-restricted chicks. δ¹⁵N values in RBCs of free-ranging auklets fell within a range of only 1.03‰, while feather δ¹⁵N varied widely. Together, our captive and field results suggest that both growth and moderate food restriction can affect stable isotope ratios in an ecologically meaningful way in RBCs although not feathers due to greater natural variability in this tissue.     

Foraging by little auks in the distant marginal sea ice zone during the chick-rearing period

During the chick-rearing period, little auks Alle alle adopt a bimodal foraging strategy, alternating long trips with several short ones. It has been postulated that they reach more remote areas during long feeding trips than during short ones. However, the range of their foraging flights has never actually been measured. The aims of this study were to find the exact location of the little auk feeding grounds and to investigate whether they reach remote areas during long foraging trips using miniature GPS and temperature loggers. The study was conducted in 2009 in Magdalenefjorden (79°34′N, 11°04′E), one of the main breeding grounds of little auks on Spitsbergen. The temperature logger records indicated that during short trips, little auks visit warmer waters (situated close to the colony) than during long ones. The tracks of two GPS-equipped birds indicated that during long trips little auks foraged in the distant, food-abundant marginal sea ice zone, at least 100 km away from the colony. During long trips, birds make several stops at sea, perhaps sampling the foraging area with respect to prey distribution. Since food conditions near the studied colony are usually suboptimal, little auks may be exploiting distant feeding areas to compensate for the poorer-quality food available at nearby foraging grounds. The extended duration of long foraging trips may enable birds to collect food for chicks on food-abundant, remote foraging grounds as well as acquire, process and excrete food needed for self-maintenance, reducing the costs of flight to the colony.     

Foraging behaviour of chick-rearing rhinoceros auklets Cerorhinca monocerata at Teuri Island, Japan, determined by acceleration-depth recording micro data loggers

Flight and diving activity of rhinoceros auklets Cerorhinca monocerata breeding on Teuri Island, Japan, were monitored during the summers 1999 and 2000 using miniaturized time-depth and acceleration recorders. Birds made 14.5 dive bouts per day of on average 15.4 min duration, which consisted of on average 16.2 dives of 12.1 m depth and 42.7 s duration. Birds made 13.8±7.3 flight bouts per day, which lasted on average 11.5±4.5 min. Daily total flight duration was 2.7±1.7 h (range 54 s–5.1 h) and the mean potential foraging range was estimated to be 87 km (maximum 164 km). Most birds stayed at the colony or rested on the water surface during the night. Rhinoceros auklets dived more actively in early morning and in late afternoon than during mid-day. Compared to results from studies of time allocation in other alcids species, rhinoceros auklets spent longer time flying (3.3 hd⁻¹) and resting on water (13.1 hd⁻¹), and less time diving (3.1 hd⁻¹) and staying at the colony (4.4 hd⁻¹). These foraging patterns are probably related to the nest attendance pattern of rhinoceros auklets, i.e. leaving the colony early in the morning, staying at sea all the day and returning to the colony in the evening to provision their chicks.     

Parental provisioning and predation risk in rhinoceros auklets (Cerorhinca monocerata): effects on nestling growth and fledging

We examined the effects of predation risk on the behavior ofrhinoceros auklets (Cerorhinca monocerata) breeding at PineIsland, British Columbia, in 1990. Provisioning parents in someareas of the colony risked predation by bald eagles (Haliacetusleucocephalus). Chicks in high and low predation risk areasof the colony hatched on approximately the same date, receivedsimilar amounts of food to 46 days of age, grew at the samerate, reached similar peak masses, and fledged at similar masses.However, chicks in high predation areas fledged at a youngerage than did chicks in low predation areas. These data are consistentwith the hypothesis that parents in high risk areas terminatedprovisioning several days before those in lower risk areas.Mass at fledging was inversely related to age at fledging inboth high and low risk areas. The regression line for the highrisk habitats lies below that from the low risk habitats, aspredicted by a model that examines optimal time of fledgingfrom the perspective of the parents. We conclude that risk ofpredation represents a significant cost of reproduction to somerhinoceros auklets and that individual auklets within the colonyvary their behavior according to predation risk.     

The heat increment of feeding in house wren chicks: magnitude, duration, and substitution for thermostatic costs

The heat increment of feeding (HIF), a transient postprandial increase in metabolic rate, is the energy cost of processing a meal. We measured HIF in house wren chicks (Troglodytes aedon) ranging in mass from 1.6 to 10.3 g. This mass range (age 2–10 days) spanned a transition from blind, naked, ectothermic chicks through alert, endothermic birds with nearly complete feathering. We fed chicks crickets (2.7–10% of chick body mass) and determined HIF from continuous measurements of oxygen consumption rate (O₂) before and after meals. At warm ambient temperatures (T _a) of 33–36 °C, the magnitude of HIF (in ml O₂ or joules) was linearly related to meal mass and was not affected by chick mass. HIF accounted for 6.3% of ingested energy, which is within the range of results for other carnivorous vertebrates. The duration of HIF was inversely related to chick mass; 10-g chicks processed a standard meal approximately twice as fast as 2-g chicks. HIF duration increased with increasing meal mass. The peak O₂ during HIF, expressed as the factorial increase above resting metabolism, was independent of body mass and meal mass. In large, endothermic chicks ( > 8 g), HIF substituted for thermoregulatory heat production at low T _a. Accepted: 11 December 1996     

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.     

Intraspecific kleptoparasitism improves chick growth and reproductive output in Common Terns Sterna hirundo

Kleptoparasitism is a well‐known foraging strategy used opportunistically by many seabirds. Here, we investigated the effect of intraspecific kleptoparasitism on chick growth and reproductive output in Common Terns Sterna hirundo. Effects were compared between two groups comprising (1) individuals using kleptoparasitism during the chick‐rearing period (kleptoparasitic group, n = 18), and (2) individuals in pairs that never performed kleptoparasitism throughout the season (‘honest’ group, n = 21). The null models best described variation in mass at day 3 and the pre‐fledging mass, indicating no significant effect of the explanatory variables. However, the best models describing the linear growth rate (days 3–13) and peak mass included the parents' foraging strategy (kleptoparasitic vs. honest parents) as an explanatory variable. These two growth parameters were higher in chicks of kleptoparasitic parents. Kleptoparasitic foraging strategy was also associated with higher pre‐fledging survival, as the reproductive performance (i.e. number of fledglings) was significantly higher in the kleptoparasitic than in the honest group. We suggest that by stealing food (and consequently feeding offspring more frequently with high‐quality prey), kleptoparasitic parents are able to produce higher quality chicks with enhanced survival.     

Intercolony variations in movement patterns and foraging behaviors among herring gulls (Larus argentatus) breeding in the eastern Wadden Sea

Herring gulls (Larus argentatus) are opportunistic predators that prefer to forage in the intertidal zone, but an increasing degree of terrestrial foraging has recently been observed. We therefore aimed to analyze the factors influencing foraging behavior and diet composition in the German Wadden Sea. Gulls from three breeding colonies on islands at different distances from the mainland were equipped with GPS data loggers during the incubation seasons in 2012–2015. Logger data were analyzed for 37 individuals, including 1,115 foraging trips. Herring gulls breeding on the island furthest from the mainland had shorter trips (mean total distance = 12.3 km; mean maximum distance = 4.2 km) and preferred to feed on the tidal flats close to the colony, mainly feeding on common cockles (Cerastoderma edule) and shore crabs (Carcinus maenas). In contrast, herring gulls breeding close to the mainland carried out trips with a mean total distance of 26.7 km (mean maximum distance = 9.2 km). These gulls fed on the neobiotic razor clams (Ensis leei) in the intertidal zone, and a larger proportion of time was spent in distant terrestrial habitats on the mainland, feeding on earthworms. δ¹³C and δ¹⁵N values were higher at the colony furthest from the mainland and confirmed a geographical gradient in foraging strategy. Analyses of logger data, pellets, and stable isotopes revealed that herring gulls preferred to forage in intertidal habitats close to the breeding colony, but shifted to terrestrial habitats on the mainland as the tide rose and during the daytime. Reduced prey availability in the vicinity of the breeding colony might force herring gulls to switch to feed on razor clams in the intertidal zone or to use distant terrestrial habitats. Herring gulls may thus act as an indicator for the state of the intertidal system close to their breeding colony.     

Sex-Specific Habitat Utilization and Differential Breeding Investments in Christmas Island Frigatebirds throughout the Breeding Cycle

In seabirds, equal bi-parental care is the rule, as it is considered crucial for raising chicks successfully because seabirds forage in an environment with unpredictable and highly variable food supply. Frigatebirds forage in poor tropical waters, yet males reduce and even stop parental care soon after chick brooding, leaving the female to provision the chick alone for an extended fledging period. Using bird-borne tracking devices, male and female Christmas Island Frigatebirds (Fregata andrewsi) were investigated during the brooding, late chick rearing and post-fledging period to examine whether sexes exhibit foraging strategies that may be linked to differential breeding investments. During brooding, males and females showed similar foraging behaviour under average marine productivity of oceanic waters close to the colony, but males shifted to more distant and more productive habitats when conditions deteriorated to continue with reduced chick provisioning. During the late chick rearing period, females progressively increased their foraging range to the more distant but productive marine areas that only males had visited during brooding. Birds spent the non-breeding period roosting in highly productive waters of the Sunda Shelf. The sex-specific utilisation of three different foraging habitats with different primary productivity (oceanic, coastal, and shelf areas) allowed for temporal and spatial segregation in the exploitation of favourable habitats which seems to enable each sex to optimise its foraging profitability. In addition, post-fledging foraging movements of females suggest a biennial breeding cycle, while limited information on males suggests the possibility of an annual breeding cycle.     

Feather corticosterone reveals stress associated with dietary changes in a breeding seabird

Changes in climate and anthropogenic pressures might affect the composition and abundance of forage fish in the world's oceans. The junk‐food hypothesis posits that dietary shifts that affect the quality (e.g., energy content) of food available to marine predators may impact their physiological state and consequently affect their fitness. Previously, we experimentally validated that deposition of the adrenocortical hormone, corticosterone, in feathers is a sensitive measure of nutritional stress in seabirds. Here, we use this method to examine how changes in diet composition and prey quality affect the nutritional status of free‐living rhinoceros auklets (Cerorhinca monocerata). Our study sites included the following: Teuri Is. Japan, Middleton Is. central Gulf of Alaska, and St. Lazaria Is. Southeast Alaska. In 2012 and 2013, we collected “bill loads” delivered by parents to feed their chicks (n = 758) to document dietary changes. We deployed time–depth–temperature recorders on breeding adults (n = 47) to evaluate whether changes in prey coincided with changes in foraging behavior. We measured concentrations of corticosterone in fledgling (n = 71) and adult breeders' (n = 82) feathers to determine how birds were affected by foraging conditions. We found that seasonal changes in diet composition occurred on each colony, adults dove deeper and engaged in longer foraging bouts when capturing larger prey and that chicks had higher concentrations of corticosterone in their feathers when adults brought back smaller and/or lower energy prey. Corticosterone levels in feathers of fledglings (grown during the breeding season) and those in feathers of adult breeders (grown during the postbreeding season) were positively correlated, indicating possible carryover effects. These results suggest that seabirds might experience increased levels of nutritional stress associated with moderate dietary changes and that physiological responses to changes in prey composition should be considered when evaluating the effect of prey quality on marine predators.     

Seasonal changes in the provisioning behaviour and mass of male and female wandering albatrosses in relation to the growth of their chick

Procellariiform seabirds have a number of extreme life-history characteristics in common, in particular low reproductive rates and slow postnatal development, which are generally assumed to reflect the difficulty in acquiring energy in the marine environment. The wandering albatross (Diomedea exulans) is a sexually dimorphic species with the longest postnatal growth found in any bird, suggesting severe constraints on provisioning and possible sex-specific strategies of provisioning. We studied the provisioning behaviour and mass changes of male and female parent wandering albatross throughout the 9-months rearing period to examine how each sex adjusts its foraging effort in relation to the needs of the chicks and the seasonal changes in food availability. The study was carried out on the Crozet Islands, using an automated system recording continuously the attendance pattern of parents between March and December 1994. During the brooding period when energy requirements are highest, parents only perform trips of short duration to sea, and their body condition deteriorates. When the chick is old enough to be left alone, the parents mix short and long foraging trips. The proportion of short trips is very high until July, allowing high rate of food delivery and rapid growth, and at the same time the body condition of adults improves. From August this proportion declines until fledging in December. As a result, the feeding rate decreases from August and adult condition declines, suggesting that feeding conditions at sea are better during the first part of the chick-rearing period, i.e. in autumn and winter. Male parents perform more short trips of shorter duration and provide larger meals than females, delivering an estimated total after brooding of 110 kg of food, compared to 70–80 kg delivered by females. Meal size is inversely related to the body condition of male chicks but not to that of female chicks, suggesting that food delivery is regulated by the adults in response to the condition of the male chick. Male chicks received larger meals and more food every month than female chicks, and overall it was estimated that they receive, after brooding, 195 kg of food compared to 180 kg for the female. As a result, male chicks have a higher growth rate, attain a higher asymptotic mass, and are larger and heavier at fledging than female chicks. However, the differences are relatively small between the chicks of each sex and suggest that energy may be used differently between the sexes to maximise fitness. The results of the study suggest that provisioning effort of wandering albatrosses is adjusted by parents in relation to the availability of food, to the energetic needs of the chick and to the sex of the chick. The adult body mass is likely to play an important role in the long term for the regulation of provisioning, deficits in body mass probably providing the buffer in high power-requirement periods. Accepted: 20 March 2000     

Using stable isotopes to study resource acquisition and allocation in procellariiform seabirds

Some procellariiform seabirds use a dual strategy for provisioning their chicks by alternating short (ST) and long (LT) foraging trips. Parent birds gain mass during LT but they lose mass while increasing the chick feeding frequency during ST. Self-feeding during LT is crucial for the success of ST because firstly most of the energy used during ST is likely to be derived from the energy stored during LT and secondly self-feeding during ST is presumed to be negligible. Self-feeding by adult procellariiforms is thus a key issue to understand allocation processes but it is still poorly known. We tested these predictions by using the stable isotope (δ¹⁵N and δ¹³C) technique on birds’ plasma and prey with the short-tailed shearwater Puffinus tenuirostris breeding at Tasmania as a model. Parent shearwaters returning to the colony after a LT have an Antarctic/subantarctic δ¹³C signature in their plasma (−23.8‰), thus indicating that they fed in cold waters, far away from their breeding colony, for their own maintenance. Parent birds returning to the colony after a ST also have a distant Antarctic/subantarctic δ¹³C signature in their plasma (−24.3‰), thus verifying that self-feeding is negligible during ST and that birds fast at that time, using energy stores built up in cold waters. Plasma δ¹⁵N values of adults (8.8‰) indicates they mainly prey upon zooplankton-eating organisms, probably mesopelagic myctophid fishes. A simple isotopic mixing model estimates that they consume by mass 87% myctophids and 13% subantarctic krill when self-feeding. Finally and as expected, the carbon isotopic signature of chick plasma (−22.2‰) was intermediate between those of high- and low-latitude marine organisms and is thus in agreement with chicks being fed with a large diversity of prey species caught by adult birds from Antarctic to Tasmanian waters. One main consequence of this system is that reproduction of a Tasmanian species is controlled by resources available at great distances from the breeding colony that drive allocation decisions of parent birds.