Chick Provisioning Research Articles

Breeding performance of Common Terns (Sterna hirundo) does not decline among older age classes

Abstract Declines in reproductive performance among older age classes have been reported in many bird and mammal species, and are commonly presented as demonstrating reproductive senescence. However, no declines in performance could be demonstrated in studies of several bird species. We measured reproductive performance in Common Terns (Sterna hirundo) of known age (2–28 yr) during a 19-yr period at a site in Buzzards Bay, Massachusetts, USA. We measured 6 components of reproductive performance and used generalized additive mixed models (GAMMs) in a Bayesian framework to analyze dependence of each measure on parental age, while controlling for variations among years and indices of individual quality. Four measures of performance improved (earlier laying date, higher values of clutch size, fledging success, and productivity) with age, most rapidly between ages 2 and 10 yr; egg mass and hatching success varied only slightly with age. No measure of performance showed reversals among the older age classes; fledging success and productivity continued to increase through at least age 22 yr. These findings are consistent with results from an earlier study of the same species. Continued increase in reproductive performance through the oldest age classes is not incompatible with “reproductive senescence” (decline in physiological or other functions required for successful reproduction) if either reproductive effort or efficiency continue to increase. Studies within our population have yielded no evidence for age-related increase in reproductive effort, but 3 studies have suggested that older Common Terns can raise chicks more successfully than younger birds without increasing reproductive effort, probably by more efficient foraging and chick provisioning. Our findings suggest that Common Terns offset reproductive senescence by continuing to improve efficiency through at least age 22 yr. Age-related changes in efficiency should be investigated in other species with similar life-history traits.

A method for capturing and GPS tracking breeding White-backed Woodpeckers Dendrocopos leucotos

ABSTRACT Capsule: The use of mist nets placed at more than 9 m high and small GPS tags fitted with a pelvic harness, and equipped to download remotely, allows the capture and tracking of breeding White-backed Woodpeckers Dendrocopos leucotos. Aims: To describe and test a method for capturing, ringing and GPS-marking medium-sized woodpeckers. Methods: Birds were captured using an overlapping mist net system located between two poles with a minimum height of 9.25 m and a maximum of 12.95 m, previously designed for catching bats. Once captured, the birds were ringed and fitted them with a remote download GPS tag, weighing 3.4 g. Results: Twenty individuals (17 adults and 3 juveniles) from 14 territories were captured during the 28 sampling days. All marked breeders continued with chick provisioning and in 12 of the territories were successful in fledging young. We found no significant difference in the number of fledglings between nests where the breeders were captured and tagged with devices (1.71 ± 0.19 se) and nests where the breeders were not captured (1.71 ± 0.29 se). The GPS tags allowed us to obtain a mean of 102.6 (±15.91 se) locations for each bird during a tracking period averaging 57.8 (±10.4 se) days. Despite the steep slope and the high forest canopy in the hábitat, 77.09% of GPS locations were accurate to within 20 m. Conclusion: Our results showed that this method allows us to obtain important information about the habitat use of this species during the breeding period without any apparent effect on reproductive success.

No change in Atlantic Yellow-nosed Albatross (Thalassarche chlororhynchos) egg size over 160 years

ABSTRACT Biotic and abiotic conditions in the world’s oceans have changed considerably in the last two centuries as a result of anthropogenic factors, including whaling, sealing, fishing, and climate change. For species that have limited variation in life-history traits, life-history characteristics may impede the ability to adapt to changing environmental conditions. Albatrosses are one such group, where breeding investment is limited to a single egg every one or two years. At a coarse level, individuals may decide whether to breed or not, or whether to incubate an egg or not, but one of the only finer-scale adjustment in parental investment involves altering egg size, along with parental foraging and chick provisioning. We investigated changes in egg size in Atlantic Yellow-nosed Albatrosses (Thalassarche chlororhynchos) breeding at Tristan da Cunha, South Atlantic Ocean, from 1856 to 2015. We found no change in egg length, or breadth, which may suggest that with regards to this life-history parameter, Atlantic Yellow-nosed Albatrosses appear to have been able to buffer the effects of the trophic, climatic and oceanographic changes in the South Atlantic Ocean.

From trips to bouts to dives: temporal patterns in the diving behaviour of chick-rearing Adélie penguins, East Antarctica

Breeding Adélie penguins forage at sea and return to land to provision their chicks, adjusting their foraging behaviour in response to environmental fluctuations over time. At Béchervaise Island, a nesting site in an East Antarctic population, Adélie penguin diving behaviour remains undocumented. This represents a key area of uncertainty in efforts to understand and predict foraging success at this colony. We compiled a multi-year telemetry dataset from time-depth recorders deployed from 1992 to 2004 on 64 birds at Béchervaise Island. We examined diving activity at multiple scales, ranging from foraging trips (n = 125) to dive bouts (n = 3461) to individual dives (n = 84521), and then characterised the stage- and sex-specific variation in diving behaviour of chick-rearing Adélie penguins using linear mixed effect models. Total foraging trip effort (trip duration, number of dives, vertical distance travelled and number of wiggles [a proxy for prey ingestion]) substantially increased as the chick-rearing period progressed (guard through crèche), consistent with increasing chick provisioning and self-maintenance requirements over time. Foraging activity was predominantly structured in periods of sustained diving bouts, indicating sustained foraging effort over the course of the foraging trip. Diving behaviour (dive-level depth, duration, bottom time and attempts of catch per unit effort) varied in relation to sex and chick-rearing stage. Dives were performed more frequently during high and low levels of solar light, which is likely linked to visual predation strategies or prey activity. Our findings advance our understanding of this population’s foraging behaviour, which is ultimately required to underpin the conservation and management of this breeding colony.

Parental Coordination of Chick Provisioning in a Planktivorous Arctic Seabird Under Divergent Conditions on Foraging Grounds

An increasing number of studies report coordinated chick provisioning by avian parents. Although the pattern of parental coordination varies across species, broad occurrence of this coordination suggests that it has an adaptive value: it may increase individual fitness via higher offspring survival, faster offspring growth rate and/or higher body reserves of the parents. However, to what extent the pattern of coordinated provisioning in a species represents a flexible response to current foraging conditions remains an open question. Here, we examined coordination of chick provisioning in the Little Auk (Alle alle), a planktivorous seabird species that breeds in the Arctic. Harsh environmental conditions impose bi-parental care on this species, and high variability within and across breeding seasons promotes flexibility in parental involvement to secure breeding success. During the chick rearing period, parents exhibit a dual-foraging strategy (i.e. alternating long foraging trips, serving to maintain the adults’ body reserves, with several short trips aimed to provision the chick). We examined coordination of parental provisioning across five breeding seasons varying in terms of environmental conditions and found that the parents indeed coordinate their provisioning, avoiding performing long trips simultaneously and thus enabling a more even distribution of feeding through time. We also examined chick body condition in relation to the level of parental coordination to test the potential adaptive value of coordination, but we found no significant relationship between these two parameters. We found high variability in the level of the coordination between pairs, and this variability was similar across all study seasons, which represented a wide range of experienced environmental conditions. Nevertheless, we found that the energy density of food loads delivered to chicks was associated with the level of parental coordination: when conditions were characterised by the delivery of higher-energy food loads, the level of coordination exhibited by the studied population was higher. These findings suggest that environmental conditions somehow affect parental coordination, but the range of the environmental variation could be still below a critical threshold of extreme conditions that would trigger more pronounced modifications of parental foraging patterns and coordination.

Forage fish to growing chicks: shared food resources between two closely related tern species

The assessment of the relevance of forage fish in seabird diet and how different species partition food resources is fundamental to understand predator–prey relationships. We assessed the importance of forage fish in the diet of Royal (Thalasseus maximus maximus) and Cayenne (T. sandvicensis eurygnathus) terns and their partitioning of food resources during the early and late chick stages of 2013 and 2014 at a colony in Argentina. Direct observation of prey deliveries during chick provisioning showed that diet composition of Royal and Cayenne terns comprised at least 16 and 9 prey species, respectively. In both tern species, Argentine Anchovy (Engraulis anchoita) and five species of silversides (Odontesthes spp.) were the main prey fed to chicks (over 90% contribution, anchovy and silversides pooled). Both tern species fed their chicks with similar prey species, but Royal terns delivered, in general, larger prey than Cayenne terns. Based on carbon and nitrogen isotopic values from chick whole blood samples, Bayesian mixing models showed that anchovies and silversides contributed similarly to the diet of both tern species’ chicks. Both conventional and stable isotope methods showed a high overlap in their trophic niches. Prey sizes delivered to chicks were larger in the late chick stage and the second study season. Wind speed did not have a significant effect on the frequency of the different prey species and sizes delivered to chicks by both tern species. As anchovies and silversides are fishery targets, tern trophic requirements should be considered when planning future fisheries development and management.

Fine-scale foraging behaviour of southern Buller’s albatross, the only Thalassarche that provisions chicks through winter

Predators generally time their reproductive events to match the peak in prey resource availability in order to sustain the elevated energy requirement of offspring provisioning. Consequently, most temperate/polar seabirds breed in spring/summer, including the majority of small albatross species that have short breeding cycles. In contrast, the southern Buller’s albatross Thalassarche bulleri bulleri has a delayed breeding schedule, with chick-rearing extending throughout the entire austral winter. In the present study, the fine-scale at-sea movements and trophic niche of chick-rearing southern Buller’s albatross were determined at Hautere/Solander Island (New Zealand, 46° 35’ S, 166° 54’ E) during the 2016 and 2017 chick-rearing periods to investigate the winter foraging strategy used during this nominally challenging period. The tracks recorded by 15 males (n = 43) and 11 females (n = 21) revealed that foraging behaviour accounted for only a small proportion of time at sea, primarily influenced by the time of day. Foraging occurred mainly in the neritic waters of New Zealand’s South Island shelf, with individuals undertaking consistent short trips (£ 230 km from the colony) or alternating short and long trips up to 1500 km from the colony. Fine-scale tracking data revealed that males spent more time foraging, during shorter trips than females. Their isotopic niches were small, with overlap between sexes, but with males having higher dN values than females. Time spent foraging was influenced by both static and dynamic oceanographic variables. These findings suggest that southern Buller’s albatross foraging behaviour, despite having to sustain chick provisioning in winter, is similar to that of summer-breeding congeners.

Habitat utilization of a mesopredator linked to lower sea-surface temperatures & prey abundance in a region of rapid warming

Central place foragers rely on areas within a small range of their breeding grounds for chick provisioning. Therefore there exists a tight coupling between their breeding success and local bio-physical conditions. The effects of fine-scale variability in environmental parameters and resource distribution on the foraging behaviour of marine predators is studied in a region of rapid environmental change. Here we use little penguin habitat preference during two years of varying environmental conditions, to investigate the interactions between environmental variables, resource distribution and penguin habitat preference. Penguins were tagged with GPS devices during a marine heatwave event in 2016 and again in 2018 during comparatively cooler conditions. We found the distribution of penguins to be highly correlated with a fine-scale horizontal SST gradient feature, which appeared on the shelf in 2016 as a result of tropical water from the East Australian Current (EAC) interacting with cooler temperate water from southern Tasmania. Spatially, warmer SST anomalies corresponded to a lower probability of little penguins utilizing an area in both years. This was despite the much more uniform SSTs which were present during 2018. By modelling little penguin habitat preferences using two biological predictors, zooplankton community abundance as an indication of general resource distribution, and krill abundance - a prey species of little penguins - we show habitat preference to be only slightly more strongly driven by prey type, than by general resource distribution. The correlation between little penguin habitat preference and both zooplankton and krill abundance could indicate a plasticity in foraging behaviour which might be beneficial if lower-trophic level structure continues to change due to warming. In light of the continued warming predicted for this region, and the preference shown for cooler SSTs, this plasticity might be important under future resource climates.

What’s for dinner mom? Selective provisioning in southern rockhopper penguins (Eudyptes chrysocome)

Breeding seabirds must balance self-care and reproduction, especially once offspring have hatched and have to be fed regularly. Seabirds may selectively provision chicks with higher quality food than they consume themselves. In contrast, adults may prioritize their survival rather than their progeny by feeding chicks with lower quality prey items than they feed themselves. We examined the parental provisioning strategies of southern rockhopper penguins at Isla de los Estados in 2012 using nitrogen (δ15N) and carbon (δ13C) stable isotope analysis to determine if selective provisioning and foraging habitat differences exist between parents and their offspring. We found that chicks had higher δ15N values compared to both male and female penguins, and female had slightly higher δ15N values compared to male penguins. There was also a strong positive relationship in δ15N values between female penguins and their offspring, indicating that chicks’ diet resembles the female parent more than the male parent. Our results support the hypothesis of selective provisioning of chicks with higher trophic level (i.e., δ15N value) prey and the observation that females exclusively feed chicks during the guard stage. We did not find differences in δ13C values between adult and chicks suggesting no differences in the areas or habitats used to forage for self-provisioning and chick-provisioning. These findings likely have broader significance as provisioning rates and quality of food consumed by chicks is often strongly related to chick growth and survival.

Boldness at the nest predicts foraging and diving behaviour of female but not male African penguins

Optimal foraging theory suggests that the environment (e.g. distribution of resource patches) will shape an individual's decision to exploit the resource available or explore other locations. Together with the environment and the social context, individual characteristics such as personality have been recently discovered to affect behaviour, offering new insights in the field of behavioural ecology. In many species, personality types differ in breeding success, and foraging behaviour could potentially mediate the influence of personality on reproductive output. A recent study conducted on African penguins, Spheniscus demersus, revealed that bold and shy individuals raised chicks with different growth rates. Here we investigated whether strategies of resource acquisition vary with personality, that is, boldness degree, which may explain the differences in breeding success previously observed in this endangered species. Over 3 years, we deployed GPS loggers, sometimes in conjunction with time–depth recorders, on chick-rearing penguins on Bird Island, Algoa Bay, South Africa, and recorded their boldness degree using a standard human approach protocol. Bolder females, but not males, foraged following a more sinuous path than shyer ones. Similarly, wiggle frequency and the total vertical distance travelled underwater increased with female boldness degree. These results suggest different resource acquisition strategies between personality types in female African penguins. However, none of the foraging or diving behaviour characteristics influenced breeding success. These findings suggest that personality may influence breeding success through other mechanisms (e.g. chick provisioning). Our study indicates that, in this species, some nest behaviours (i.e. proxy of personality) may link with foraging and diving behaviours more than others. Nevertheless, the sex-specific adaptation observed in foraging and diving behaviour may result from a differential investment in the breeding season and reduce intraspecific competition for food in this species.

Short-term tracking tag attachment disrupts chick provisioning by Atlantic Puffins Fratercula arctica and Razorbills Alca torda

ABSTRACTCapsuleAtlantic Puffins Fratercula arctica and Razorbills Alca torda alter their chick provisioning behaviour when equipped with tracking loggers.AimsTo test whether feeding data from global positioning system (GPS) tags in a companion project represented normal behaviour, we examined the effect of externally mounted GPS loggers on parental effort of Atlantic Puffins and Razorbills through chick measurements and video recordings to determine individual responses to tagging.MethodsWe compared chick growth, nest attendance and provisioning between breeding pairs with and without tagged birds (nest-level), as well as between tagged and untagged mates (mate-level) with the aim of revealing responses of untagged partners to the tagging of their mate.ResultsWe found all measures of parental effort compared at the nest-level to be similar between nests with one tagged adult and nests without tagged birds. However, video recordings revealed differences in individual behaviour in both species, in which untagged partners spent more time provisioning the chick and also delivered significantly more food to chicks than their tagged partners, though partners shared nest attendance.ConclusionBehaviours revealed through video recordings showed that the GPS tags introduced bias against detecting where adults forage for their chicks. Future tracking studies should consider measures of tag effect at both the mate- and nest-level as well as the potential bias in the movement data when making biological inferences.

Conflicts between touristic recreational activities and breeding shearwaters: short-term effect of artificial light and sound on chick weight

Human disturbances are increasingly becoming a conservation concern for many populations of colonial seabirds. Colonially reproducing species are particularly vulnerable to localised disturbances because detrimental elements can simultaneously affect the entire population. Studies of petrels and shearwaters have shown that light pollution, in particular, can be harmful for both fledglings and adults, but little is known of the way such anthropogenic elements affect the quality of parental care at the nest. Chick provisioning in petrels and shearwaters occurs exclusively at night and is also negatively correlated with the amount of moonlight. We tested the hypothesis that high-intensity light and sound disturbances will disrupt nest attendance and thus affect weight gain in chicks but that the magnitude of such effects would be modulated by moonlight conditions. We measured the effect of two outdoor disco events on overnight weight gain in 26 chicks of Scopoli’s shearwaters (Calonectris diomedea) from a breeding colony on Linosa Island. The two disco events occurred under contrasting moonlight conditions (moonless vs moonlight). Chicks situated closer to the disturbance gained significantly less weight compared to conspecifics from nests further away but the effect was only evident on the moonless night.Our results suggest that light and sound disturbances can have a negative effect on parental care in C. diomedea but moonlight might moderate the bird’s perception and thus the magnitude of the disturbance. However, while occasional disturbances may impact short-term weight gain in C. diomedea chicks, such effects are not perceivable at fledging when measured as differences in the weight or the date at which they left the nest.

Male and female Black terns choose different prey types for chick provisioning

Male and female Black terns choose different prey types for chick provisioning

Development of the Visual System in a Burrow-Nesting Seabird: Leach's Storm Petrel

Little is known about the development of vision in wild birds. It is unknown, for example, whether the ability to see can be predicted by the level of prenatal growth or whether the eyes are open at hatching in a particular species. In this study, we investigated the growth of eyes, the formation of retinal ganglion cell topography, and the appearance of simple, visually guided behaviours in chicks of a small procellariiform seabird, Leach's storm petrel (Oceanodroma leucorhoa). This semi-precocial species, which has a well-developed sense of smell, nests in underground burrows where adults provision chicks for 6-8 weeks in the dark before fledging. Retinal ganglion cell topographic maps revealed that fine-tuning of cell distribution does not happen early in development, but rather that the ganglion cell layer continues to mature throughout provisioning and probably even after fledging. While the olfactory bulbs reached adult size around 7 weeks after hatching, the eyes and telencephalon continued to grow. Optokinetic head response and artificial burrow finding experiments indicated that chicks in the 2nd week after hatching lack even the most basic visually guided behaviours and are probably blind. Thus, vision in Leach's storm petrel chicks starts to function sometime around the 3rd week after hatching, well after the eyes have opened and the olfactory system is functional.

Variation in zooplankton prey distribution determines marine foraging distributions of breeding Cassin's Auklet

To investigate the causal basis for patterns of seabird foraging distributions during breeding we integrated data from ship-board seabird and zooplankton surveys, aerial radio telemetry, and colony-based research programs. We examined the marine distributions of Cassin's Auklet (Ptychoramphus aleuticus) breeding on Triangle Island, in the Northeast Pacific off the coast of B.C., Canada using surveys conducted in 1999, 2000, and 2001. Concurrently, we sampled zooplankton at 16 stations along a cross shelf transect in the vicinity of Triangle Island. In 1999 and 2000, when populations of the preferred copepod prey Neocalanus cristatus were available at deep-water stations (1000–2000m), the majority of the auklets were concentrated SW of the colony 40–75km offshore and parallel to, but 35 −50km beyond the shelf break in deep water (1200–2000m). Birds did not fly farther out to sea to where prey was five times more abundant when N. cristatus could be found at lower abundance levels, closer to the colony. In 2001, N. cristatus were virtually absent at the deep-water stations, likely as a result of massive salp (family Salpidae) aggregations which may have consumed and displaced the seabirds’ preferred prey. We demonstrate that while birds were still able to locate and provision chicks with N. cristatus in 2001, they had to forage farther away from the colony in order to do so. Our telemetry results are generally consistent with analyses of at-sea distributions of Cassin's Auklets derived from ship-board surveys (1990–2010) both of which have contributed to the design of the proposed Scott Islands marine National Wildlife Area, the first of its kind in Canada.

Diet specialization in a colonial seabird studied using three complementary dietary techniques: effects of intrinsic and extrinsic factors

The breeding period has a critical influence on the trophic ecology of seabirds because of the energetic costs of egg production for females, the need to return regularly to the nest to provision chicks, the combined energetic demands of adults and chicks, and potential intraspecific competition if resources around the colony are scarce. The present study combined three dietary methods to investigate if and how these intrinsic and extrinsic factors influenced diet specialization in a colonially breeding seabird, the Cape gannet Morus capensis. The diet of this species was studied from November 2009 to October 2010 at the species’ largest colony at Bird Island, Algoa Bay (33°50′S, 026°17′E; South Africa). Potential prey species were sampled concurrently and dietary tracers (stable isotopes and fatty acids) were analysed. Stomach content and carbon and nitrogen stable isotope analyses indicated that adults relied heavily all year round on small pelagic fish (anchovy and sardine), with prey species composition and individual prey size changing with season, probably reflecting prey biology. Dietary tracers did not show any differences between adult and chick diets. Subtle differences were found between stable isotope values of adult males and females but these were not supported by a Bayesian mixing model. In contrast, differences between the sexes were highlighted in blood fatty acids. The combined results suggest that these were probably related to the cost of egg production rather than to inter-sex differences in diet. Individual diet specialization was observed using stable isotopes in adults. Altogether this dataset indicates the importance of combining complementary methods to understand multiple facets of seabirds’ trophic ecology, and highlights interactions with fisheries that require future monitoring.

Light oiling of feathers increases flight energy expenditure in a migratory shorebird.

Flying birds depend on their feathers to undertake most activities, and maintain them in peak condition through periodic molt and frequent preening. Even small exposures to crude oil reduce the integrity of feathers, and could impair flight performance. We trained wild western sandpipers (Calidris mauri) to perform endurance flights in a wind tunnel, and used magnetic resonance body composition analysis to measure energy expenditure after birds were exposed to weathered MC252 crude oil from the Deepwater Horizon oil spill. The cost of transport was 0.26±0.04 kJ km-1 in controls, and increased by 22% when the trailing edges of the wing and tail were oiled (<20% of body surface; considered light oiling). Additional crude oil on breast and back feathers (∼30% total surface; moderate oiling) increased the cost of transport by 45% above controls. Oiling tended to decrease flight control, and only half of moderately oiled birds completed the flight test. We then flew birds at a range of speeds to estimate basic kinematic parameters. At low speeds, light and moderately oiled birds had larger wingbeat amplitudes than controls, while moderately oiled birds showed greater wingbeat frequencies across all speeds, and a shift in optimal flight speed towards higher wind speeds. We suggest these changes reflect poorer lift production and increased drag on the wings and body. Oiling will increase the difficulty and energy costs of locomotion for daily and seasonal activities such as foraging, predator evasion, territory defense, courtship, chick provisioning, commuting and long-distance migration. These sub-lethal effects must be considered in oil spill impact assessments.

Artificial Light at Night Reduces Daily Energy Expenditure in Breeding Great Tits (Parus major)

The impact of artificial light at night (ALAN) on ecological and behavioural processes is increasingly recognized but we have limited knowledge on the impact of ALAN on wild species, and on the potential to mitigate any negative effects by using different light sources and colors. In birds, effects of ALAN on activity levels are reported for several species and, hence, their daily energy expenditure (DEE) may be affected. DEE is a potent mediator of life-history trade-offs and fitness and thus an important aspect to consider when examining the potential long-term ecological effects of ALAN. Previous work has suggested that birds exposed to ALAN show higher levels of provisioning and nocturnal activity, suggesting that white ALAN increases DEE. Other factors regulating DEE, such as provisioning behavior and food availability, might also respond to ALAN and thus indirectly affect DEE. We tested the hypothesis that ALAN increases DEE using an experimental setup where four previously unlit transects were illuminated with either white, green, or red LED light, or left dark as a control treatment. This setup was replicated in eight locations across the Netherlands. We measured DEE of our focal species, the great tit (Parus major), using a novel doubly labelled water technique that uses breath rather than blood samples. Contrary to our expectations, birds feeding their offspring under white and green ALAN showed lower DEE compared to birds in the control dark treatment. Differences in chick provisioning activity did not explain this result, as neither visit rates nor daily activity timing was affected by light treatment. However, food availability under white and green light was much higher compared to red light and the dark control. This difference strongly suggests that the lower DEE under white and green ALAN sites is a consequence of higher food availability in these treatments. This result shows that there can be positive, indirect effects of ALAN for breeding song birds which may balance against the negative direct effects shown in previous studies.

Hematological indicators of habitat quality: Erythrocyte parameters reflect greater parental effort of Red-necked Grebes under ecological trap conditions

ABSTRACT Knowledge about interactions between habitat quality and individual condition is vital for understanding ecological processes. We examined variation in commonly used hematological indices and body mass in incubating and chick-rearing Red-necked Grebes (Podiceps grisegena) in Poland breeding under contrasting foraging conditions in ponds used for aquaculture. Grebes used either ponds with low prey availability in the early breeding period and abundant food in the brood-rearing stage (high-quality habitat), or ponds stocked with fish attractive as prey to spring-arriving adults yet later unavailable to chicks due to size constraints (low-quality habitat acting as an ecological trap). Parental effort, measured as the proportion of time allocated to food acquisition and provisioning of chicks, was greater in the low-quality habitat, although adult grebes spent less time foraging there than in the high-quality habitat early in the season. Scaled body mass was higher in incubating grebes than in brood-...

A novel foraging strategy in gentoo penguins breeding at sub-Antarctic Marion Island

To help meet the high energy demands of raising the young, some seabirds alternate between short, frequent foraging trips to maximize food delivery to the young, and infrequent, long foraging trips that serve towards self-maintenance. Our study is the first to investigate the foraging behaviour of gentoo penguins at Marion Island, which we did through a combined use of GPS loggers and time-depth recorders. The shallow shelf between Marion and Prince Edward Islands proved to be an important foraging area, and penguins exploited this area using a novel foraging strategy. Penguins undertook alternating trips of relatively short and long durations. Short trips, performed in the afternoon, were likely associated with self-maintenance as they were followed by roosting on the beach overnight and not returning to the colony. They were followed by longer and more distant foraging trips, after which birds returned to the colony to provision chicks. To our knowledge, this is the first study to demonstrate alternating trip lengths in gentoo penguins and the first to associate short trips with self-maintenance in seabirds. We suggest that due to the close proximity of a predictable foraging area for these penguins at Marion Island, there is minimal energetic cost to return to land after self-provisioning. Hence, unlike other seabirds that feed at greater distances from their breeding colonies, gentoo penguins are afforded the opportunity for short self-maintenance trips. Finally, we argue that these birds may be using this novel strategy due to sub-optimal feeding conditions resulting from environmental change.