Regulation of foraging trips and costs of incubation shifts in the Antarctic petrel (Thalassoica antarctica)

In species where incubation is shared by both parents, the mate'sability to fast on the nest may constrain the time availablefor foraging. The decision to return to the nest should thereforebe a compromise between an animal's own foraging success andits mate's ability to fast on the nest. To examine how the bodyconditions of incubating Antarctic petrels, Thalassoica antarctica,influence both the length of foraging trips and incubation shifts,we experimentally handicapped females by increasing their flightcosts during a foraging trip by adding lead weights to theirlegs. Handicapped females spent more time at sea and had lowerbody conditions at arrival to the colony than controls, and,moreover, females in poor body condition at arrival to the colonyspent generally more time at sea than those with higher bodycondition. The prolonged time period spent at sea by handicappedfemales was associated with higher desertion rates than amongcontrols. The time the incubating mates fasted increased withtheir body condition at arrival to the colony, suggesting thata high body condition of the incubating bird may reduce theprobability of nest desertion. Accordingly, our results suggestthat the time spent foraging is adjusted to the body conditionsof both the foraging and incubating mate.     

Reversed sexual size dimorphism and parental care in the Red-footed Booby Sula sula

The 'division-of-labour' hypothesis predicts that males and females perform different roles in parental care and that natural selection acts differently on each sex so as to produce different body size optima suited to their particular roles. Reversed sexual size dimorphism in avian species (females larger than males) may therefore be an adaptive consequence of different roles of males and females in parental care. We investigated patterns of nest attendance, brooding, foraging and provisioning rate in a tropical seabird, the Red-footed Booby Sula sula , a species showing a reversed sexual size dimorphism. During incubation, females attended the nest more often than males, and spent more time brooding the small chick than did males during daytime. Males and females did not differ in the average duration of their foraging trips. During incubation, there was a positive relationship between nest attendance and the duration of foraging trips in males, but not in females. During the small-chick stage, for the same time spent at the nest, males spent significantly more time than females at sea. On average, females fed the chick more often than did males. In males, there was a significant and positive relationship between the probability of feeding the chick and the duration of the foraging trip, whereas in females, this probability was much less dependent on the duration of the foraging trip. Overall, female Red-footed Boobies achieved slightly, but significantly, more parental commitment than did males. However, these sexual differences in parental participation were small, suggesting a minimal division of labour in the Red-footed Booby. Our results suggest that the division of labour hypothesis is unlikely to explain fully the adult size dimorphism in Red-footed Boobies.     

Relationship between reversed sexual dimorphism,breeding investment and foraging ecology in a pelagic seabird,the masked booby

Reversed sexual dimorphism (RSD) may be related to different roles in breeding investment and/or foraging, but little information is available on foraging ecology. We studied the foraging behaviour and parental investment by male and female masked boobies, a species with RSD, by combining studies of foraging ecology using miniaturised activity and GPS data loggers of nest attendance, with an experimental study where flight costs were increased. Males attended the chick more often than females, but females provided more food to the chick than males. Males and females foraged during similar periods of the day, had similar prey types and sizes, diving depths, durations of foraging trips, foraging zones and ranges. Females spent a smaller proportion of the foraging trip sitting on the water and had higher diving rate than males, suggesting higher foraging effort by females. In females, trip duration correlated with mass at departure, suggesting a flexible investment through control by body mass. The experimental study showed that handicapped females and female partners of handicapped males lost mass compared to control birds, whereas there was no difference for males. These results indicate that the larger female is the main provisioner of the chick in the pair, and regulates breeding effort in relation to its own body mass, whereas males have a fixed investment. The different breeding investment between the sexes is associated with contrasting foraging strategies, but no clear niche differentiation was observed. The larger size of the females may be advantageous for provisioning the chick with large quantities of energy and for flexible breeding effort, while the smaller male invests in territory defence and nest guarding, a crucial task when breeding at high densities. In masked boobies, division of labour appears to be maximal during chick rearing—the most energy-demanding period—and may be related to evolution of RSD.     

Is Mate Provisioning Predicted by Ornamentation? A Test with Northern Cardinals (Cardinalis cardinalis)

Male birds of many species feed their mates during courtship and incubation. The amount of food provided can be substantial and even essential for successful reproduction in some species, and can influence female nest attentiveness in many others. Additionally, mate provisioning may predict later nestling feeding rates. Females may thus benefit from being able to determine male provisioning effort. We assessed the expression of several ornaments, known to indicate condition in male northern cardinals (Cardinalis cardinalis), and compared these with mate provisioning rates, nestling feeding rates, and nest attentiveness. We found that male ornamentation may not be indicative of mate provisioning rates. Mate provisioning rate did not co‐vary with reproductive success, male feedings to nestlings, or nest attentiveness of females. However, females which were fed more often during incubation tended to provision nestlings less. Reduced female parental effort following extensive incubation feeding may be indicative of females using incubation feeding to assess future male parental effort. Male hormonal condition that favors high rates of nestling provisioning may be a proximate cause of mate provisioning during incubation, even in the absence of selection, favoring high rates of mate provisioning. Both sexes may have capitalized on this unselected behavior.     

Evolution of passerine incubation behavior: influence of food, temperature, and nest predation

Abstract.— Incubation behavior is one component of reproductive effort and thus influences the evolution of life-history strategies. We examined the relative importance of body mass, frequency of mate feeding, food, nest predation, and ambient temperature to explain interspecific variation in incubation behavior (nest attentiveness, on- and off-bout durations, and nest trips per hour) using comparative analyses for North American passerines in which only females incubate. Body mass and frequency of mate feeding explained little variation in incubation behavior. We were also unable to detect any influence of food; diet and foraging strategy explained little interspecific variation in incubation behavior. However, the typical temperature encountered during reproduction explained significant variation in incubation behavior: Species breeding in colder environments take shorter bouts off the nest, which prevents eggs from cooling to temperatures below the physiological zero temperature. These species must compensate for shorter off-bouts by taking more of them (thus shorter on-bouts) to obtain needed energy for incubation. Nest predation also explains significant variation in incubation behavior among passerines: Species that endure high nest predation have evolved an incubation strategy (long on- and off-bouts) that minimizes activity that could attract predators. Nest substrate explained additional variation in incubation behavior (cavity-nesting birds have shorter on-bouts and make more frequent nest trips), presumably because nest predation and/or temperature varies among nest substrates. Thus, nest predation can influence reproductive effort in a way previously not demonstrated–by placing a constraint on parental activity at the nest. Incubating birds face an ecological cost associated with reproductive effort (predation of entire brood) that should be considered in future attempts to explain avian life-history evolution.     

Foraging trip decisions by the streaked shearwater Calonectris leucomelas depend on both parental and chick state

Parents of albatross and shearwater species employ a dual foraging strategy, feeding their chicks quickly in repeated short trips and then restoring their own fuel reserves during longer trips. A decline in parental body condition is believed to trigger longer trips, but chick body condition and age may also play a role. To investigate these factors in the little-studied streaked shearwater Calonectris leucomelas, we monitored the nest attendance of 17 pairs on Mikura Island in 2005 using an automated identification system. We also monitored body mass changes and meal masses of 5 of the 17 pairs using an automated weighing system. Although the birds did not show a clear dual foraging pattern, trip duration varied widely from 1 to 15 days. On average, the birds fed chicks 67.6 g during nighttime meals at 2.74-day intervals. Since meal mass did not depend on trip duration, feeding efficiency (meal mass delivered per unit trip duration) decreased as trip duration increased. Parents accumulated more energy reserves when they took longer trips. Parents appeared likely to initiate longer trips when their body condition declined or chick body condition recovered.     

Incubation and brooding rhythm of the Cape Petrel Daption capense at Nelson Island, South Shetland Islands, Antarctica

Incubation and brooding performance of the Cape Petrel Daption capense at Nelson Island, South Shetland Islands, Antarctica, in the 1991 -1992 austral summer is reported in detail and compared with data from two other areas. There was an inverse relationship between the mean foraging trip length and mean peak weight of chicks. Variation in shift length throughout incubation resulted from a combination of seasonal effects (food supply) and behavioural adjustment to hatching. The length of the last incubation shift was independent of its number but decreased with date of initiation. The average weight of nestattending birds increased steadily during the incubation period and at the same rate in both sexes. Females attained seasonal peak body-weight before the egg hatched, whereas males just recovered their pre-breeding weight. Males took on a slightly larger share of incubation (52%, range 40–63%) and invested more time in mutual nest attendance. Length of foraging trips varied consistently in pairs and individuals, its repeatability being twice as high in females as in males. The incubation performance of individual females (length of the first and an average foraging trip) was correlated with the size of the egg they had laid and also to subsequent chick growth and fledging success. There was a tendency in successful pairs to spend more time together at the nest and to have shorter foraging trips. I suggest that variation in breeding performance among pairs was mainly a result of individual variation in female quality, with pairs where the female contributed more to incubation being more successful. There is little evidence that egg losses were caused by parental errors.     

Interactive vocal communication at the nest by parent Great Tits Parus major

Although most bird species show monogamous pair bonds and bi‐parental care, little is known of how mated birds coordinate their activities. Whether or not partners communicate with each other to adjust their behaviour remains an open question. During incubation and the first days after hatching, one parent – generally the female – stays in the nest for extended periods, and might depend on acoustic communication to exchange information with its mate outside. The Great Tit Parus major is an interesting study system to investigate intra‐pair communication at the nest because males address songs to their mate while she is in the nest cavity, and females answer the male from the cavity with calls. However, the function of this communication remains unknown. In this study, we recorded the vocalizations and observed the resulting behaviour of Great Tit pairs around the nest at different breeding stages (laying, incubation and chick‐rearing). We observed vocal exchanges (vocalization bouts, alternated on the same tempo, between the female inside the nest and her male outside) in three contexts with different outcomes: (1) the female left the nest, (2) the male entered the box with food, and the female then used specific call types, (3) mates stopped calling but did not leave or enter the nest. The structure of vocal exchanges was globally stable between contexts, but females used calls with an up‐shifted spectrum during exchanges, at the end of which they left the nest or the male entered the nest. Birds vocalized more and at higher tempo during exchanges that ended up in feeding inside the nest. Birds also vocalized more during exchanges taking place during laying – a period of active mate guarding – than during incubation. We conclude that vocal exchanges could signal the females’ need for food and the males’ mate guarding behaviour, and discuss other possible functions of this communication.     

Regulation of foraging trips and incubation routine in male and female wandering albatrosses

The resolution of the conflict between eggcare and foraging was studied in male and female wandering albatrosses. The foraging zone and range, duration of incubation shifts and foraging trips, and associated changes in body mass were studied. Costs during incubation, expressed as the time spent incubating and the proportional loss of body mass, were similar for both sexes. The mass gained at sea was related to the duration of foraging trips, but the relationship was much less significant in males, where foraging ranges, though similar on average to those of females, were very variable. Males foraged in more southerly waters than females, and gained mass more rapidly. Only females appeared to regulate the duration of foraging trips, and this compensated for the mass lost during the incubation fast. Previous breeding experience had no influence on foraging efficiency. Egg desertion because of depletion of body reserves was very rare because birds have a wide safety margin, i.e. the difference between the average body mass when relieved and that at nest desertion. This safety margin enables the birds to compensate for the high variability in the duration of foraging trips, and is probably a reason for the high breeding success of wandering albatrosses. Decisions to return from the sea to the nest or to desert the nest are probably related to the status of body reserves, and have been selected in the large wandering albatross so that both present and future reproductive success are maximised.     

Incubation routines and foraging-trip regulation in the Grey-faced Petrel Pterodroma macroptera gouldi

In Grey-faced Petrels Pterodroma macroptera gouldi parental care during the 55-day incubation period is mainly achieved by three long shifts (two by the male) when one partner is ashore while the other forages at sea. This situation would seem to carry high risks of parental desertion and failure of the hatching chick to receive a meal before its yolk sac is exhausted. We examined incubation routines of 51 pairs of Grey-faced Petrels to investigate factors implicated in parental desertion and in the duration of the final foraging trip before hatching. The duration of the final long foraging trip (by the female) during incubation is not predicted by the time spent fasting on the nest but by the time elapsed since laying. Desertions accounted for 6.5% of egg losses. Eggs were deserted not after the delay of the foraging bird to return to the nest, but when the incubating bird departed early in the incubation spell. Desertions were not a response to critically depleted energy reserves.     

Stage-dependent foraging in breeding black-legged kittiwakes Rissa tridactyla: distinguishing behavioural responses to intrinsic and extrinsic factors

Different phases of the annual cycle in birds and mammals are often associated with characteristic and recurrent foraging behaviours. The extent to which stage‐dependent changes in foraging behaviour are caused by intrinsic or extrinsic factors is unclear. We controlled for the effects of extrinsic factors by synchronising groups of incubating and chick‐rearing black‐legged kittiwakes Rissa tridactyla. Synchrony amongst incubators and rearers was achieved experimentally by switching eggs between nests. Behavioural responses to the treatment varied between the sexes. Male kittiwakes with prolonged‐incubation made fewer foraging trips but of greater duration compared to those rearing chicks resulting in no change in the time spent on trips between the two groups. Females with prolonged‐incubation carried out fewer trips than those rearing chicks but trip duration did not differ between the two stages which resulted in prolonged‐incubating birds spending a lower percentage time on trips. In contrast, foraging ranges did not differ between prolonged‐incubation and chick‐rearing birds for either sex. This suggests that extrinsic factors, such as food availability and distribution determine kittiwake foraging locations and ranges, whereas intrinsic factors, reflected in parental duties, constrain nest attendance. Female prolonged‐incubators invested lower levels of parental effort, in terms of daily energy expenditure, compared to chick‐rearers whereas males did not show stage‐related differences in energy expenditure. This provides evidence that incubation could be an energetically cheaper stage although under normal conditions this difference may be masked by temporal variation in environmental factors. We conclude that while conditions differ between the incubation and chick rearing stages for kittiwakes at this colony, they are not the main factors prompting changes in stage‐related foraging patterns. Intrinsic factors such as sex differences, or behaviours required for each stage of the annual cycle, rather than extrinsic factors related to seasonal environments, are likely to be the main proximate cause of recurring changes in behaviour between breeding stages.     

Energy expenditure, body-weight and foraging performance of Storm Petrels Hydrobates pelagicus breeding in artificial nesting chambers

Many avian species, such as Storm Petrels Hydrobates pelagicus, are intolerant of disturbance at the nest, which complicates the collection of data relating to metabolic rate and the use of body reserves during incubation. I describe the design of an artificial nest chamber, which is simple and inexpensive to construct and facilitates the collection of such data. Eighty-one nest chambers situated in a large colony of breeding Storm Petrels had high occupancy rates (29/81 in each of 2 years), and the breeding success of birds nesting in boxes was similar to that of pairs nesting in natural crevices. Direct measurement of carbon dioxide production using standard respirometry techniques and estimations of metabolic rate based on the rates of mass loss during incubation indicated close agreement between the two methods of estimating energy consumption. Assuming the metabolic requirements during incubation are furnished entirely from stomach oil, 76% of the daily mass lost represented stomach oil catabolism. The duration of incubation shifts was unrelated to the body mass, and presumably to body reserves, of Storm Petrels on arrival at the nest. Shifts were usually terminated by the return of the foraging partner. The body mass of birds returning from foraging was relatively constant and was unrelated to the amount of time spent foraging at sea, indicating that the decision rule to return from foraging was the acquisition of a threshold level of body mass (about 31 g). There was a negative relationship between the duration of foraging trips and the body mass of Storm Petrels at departure from the nest and a positive relationship between trip duration and the net mass gain at sea. The use of nestboxes based on the design described here would have a wide variety of applications in facilitating data collection for many cavity-or burrow-nesting species which are sensitive to disturbance.     

Corticosterone alone does not trigger a short term behavioural shift in incubating female common eiders Somateria mollissima, but does modify long term reproductive success

The trade-off between reproductive effort and adult survival in birds is modulated by several factors. Corticosterone and prolactin have additive effects on reproductive behaviour by stimulating foraging and parental behaviours, respectively. When incubation is associated with fasting, nest desertion is supposed to be activated by an unknown refeeding signal when body condition becomes critically deteriorated. The concomitant rise in corticosterone levels has been suggested to be the triggering factor. We tested the role of corticosterone on reproductive success by observing the effect of corticosterone implants on reproductive success and on plasma prolactin concentration in female common eiders Somateria mollissima . Implanted females showed a significant increase in corticosterone and a decrease in prolactin levels. Despite their enhanced daily body mass loss, females did not abandon incubation nor did they start to refeed in the four days following implantation. These data show that the experimentally induced rise in plasma corticosterone concentration alone does not trigger nest desertion. However, after 25 days of incubation, implanted females displayed a higher rate of egg loss, suggesting lower nest attentiveness towards the end of incubation. We suggest that the short-term effects of corticosterone may be dependent on the energy state of the bird. However, the late-induced change in reproductive success is indirectly linked to corticosterone, and we suggest that either a prolactin decrease, or a depletion in protein body reserves, may participate in the long-term adjustment of incubation behaviour in female eiders.     

Vocal negotiation over parental care? Acoustic communication at the nest predicts partners' incubation share

In species with biparental care, individuals adjust their workload to that of their partner to either compensate or match its investment. Communication within a pair might be crucial for achieving this adjustment. Zebra finches, Taeniopygia guttata, form life‐long monogamous pair bonds, in which partners are highly coordinated and both incubate the eggs. When relieving each other during incubation, partners perform a structured call duet at the nest. If this duet functions to coordinate incubation workload, disrupting the pair's usual nest‐relief pattern by delaying the male's return to the nest should affect the structure of the duet. Using domesticated birds breeding in a large aviary, we found that delaying the male's return induced shorter duets with higher call rates. In addition, we tracked the location of individuals with a transponder at the nest and the feeder, and showed that these accelerated duets were associated with an increased haste of the partners to take turns incubating and foraging. Females also spent less time incubating during their subsequent shift, and females' time off‐nest was best predicted by their mate's calling behaviour in the previous duet. Taken together, these results suggest that duets may function as ‘vocal negotiation’ over parental care.     

Incubation feeding by male Scarlet Tanagers: a mate removal experiment

ABSTRACT Incubation feeding, where males feed their mates, is a common behavior in birds and may improve female condition, nest attentiveness, and nesting success. We used behavioral observations and a temporary mate removal experiment to test the female nutrition hypothesis for incubation feeding by male Scarlet Tanagers (Piranga olivacea). All males (N= 20) were observed incubation feeding and fed females both at the nest (x? 1.36 trips/h) and away from the nest (x? 20.1 trips/h). Male feeding rate off‐nest was negatively correlated with the duration of female foraging bouts and positively correlated with the total time females spent incubating per hour. Eggs were predated at seven of 19 (37%) nests, but nest survival during incubation was not related to either female incubation behavior or male feeding rate. During temporary removal experiments (N= 12), female Scarlet Tanagers remained on the nest significantly longer and did not have longer foraging bouts. An unexpected outcome of the removal experiments was a dramatic change in female vocal behavior. All 12 experimental females gave chik‐burr calls during the male‐removal experiments (x? bout length = 11.7 min), but during normal observation periods only six of 20 females at the incubation stage gave chik‐burr calls (x? bout length = 0.7 min, N= 20). Our results suggest that female tanagers likely gain nutritional benefits from incubation feeding, but male feeding may not improve immediate reproductive success. Nine of 54 (17%) nestlings in five of 17 broods (29%) were extra‐pair young (EPY), indicating that males could potentially benefit from incubation feeding via mate retention and fidelity as well as, or instead of, through immediate gains in reproductive success. Our study indicates that females benefit from incubation feeding and do not simply passively accept food from their mates, but instead may influence male feeding rates through direct (e.g., mate following and vocalizing) and indirect (the threat of mate abandonment or cuckoldry) means.     

Luxury in freshwater and stress at sea? The foraging of the Common Tern Sterna hirundo

We compared the foraging strategies of Common Terns Sterna hirundo in freshwater (Lake Jeziorsko, Brzeg, Poland) and marine environments (Minsener Oldeoog, German Wadden Sea). Body mass changes, nest relief and duration and number of feeding trips per day were studied by automatically weighing the adults, using electronic balances under the nests. At the freshwater site, adults were lighter both before and after feeding and gained less mass during a trip. in the Wadden Sea, single feeding trips lasted longer than at the freshwater site and the terns made fewer trips per day. To achieve the same mass gain per day as in birds in freshwater, trips at sea had to be longer and food intake per trip was higher. The daily duration of absence for feeding and the daily mass gain were about the same in both areas. The limnetic feeders finished foraging earlier in the evening than the terns foraging at sea. These differences are consistent with the hypothesis that limnetic prey availability was consistent, whereas the tides limited the availability of marine prey. In consequence, foraging over freshwater presents several advantages, such as higher colony attendance, better mate coordination and better parental care.     

Avian growth and development rates and age-specific mortality: the roles of nest predation and adult mortality

Previous studies have shown that avian growth and development covary with juvenile mortality. Juveniles of birds under strong nest predation pressure grow rapidly, have short incubation and nestling periods, and leave the nest at low body mass. Life-history theory predicts that parental investment increases with adult mortality rate. Thus, developmental traits that depend on the parental effort exerted (pre- and postnatal growth rate) should scale positively with adult mortality, in contrast to those that do not have a direct relationship with parental investment (timing of developmental events, e.g. nest leaving). I tested this prediction on a sample of 84 North American songbirds. Nestling growth rate scaled positively and incubation period duration negatively with annual adult mortality rates even when controlled for nest predation and other covariates, including phylogeny. On the contrary, neither the duration of the nestling period nor body mass at fledging showed any relationship. Proximate mechanisms generating the relationship of pre- and postnatal growth rates to adult mortality may include increased feeding, nest attentiveness during incubation and/or allocation of hormones, and deserve further attention.     

Incubation routine, body mass regulation and egg neglect in the Blue Petrel Halobaena caerulea

The incubation routine and mass changes of male and female Blue Petrel Halobaena caerulea were studied at the Kerguelen Islands to investigate factors influencing the durations of incubation stints and foraging trips at sea and the factors determining nest desertion and return to the nest.
The body mass at the start of an incubation shift and also when the bird was relieved varied throughout the incubation period, whereas the mass when birds deserted the nest was stable. Birds deserted the nest when their mass decreased to threshold, independent of the duration of the fast. Temporary egg neglect was observed in successful as well as in unsuccessful breeding attempts, but it increased the risk of breeding failure. The net and daily massgained at sea during the second part of the incubation period were higher than during the first part, suggesting an increase in food availability. During the first part, the mass gained at sea and time spent foraging were inversely related to the mass of the bird before it left the burrow, whereas a similar relationship did not occur thereafter.
The results suggest the occurrence of a fixed mass threshold when birds decide to leave the nest if not relieved by their partner. The mass when a bird left its nest inffuenced the time spent foraging or mass gained when food was scarce. Although decision rules to leave the nest or return from the sea are related to body condition. the possibility of neglecting the eggs temporarily enables Blue Petrels to regulate the trade-off between risks of breeding failure and risks of an increase in adult mortality. A model for behavioural decision to stop incubating or stop feeding, based on a variable set point, is proposed.     

Modulation of prolactin but not corticosterone responses to stress in relation to parental effort in a long-lived bird

We tested the hypothesis that parental effort modulates the magnitude of corticosterone and prolactin responses to stress in a long-lived bird, the Black-legged kittiwake (Rissa tridactyla). To do so, we compared corticosterone and prolactin responses to capture/restraint stress between chick-rearing birds and failed breeders (no parental effort). We predicted that (1) the increase in plasma corticosterone levels in response to stress should be lower in chick-rearing birds, (2) the decrease in plasma prolactin levels in response to stress should be lower in chick-rearing birds, and (3) as both sexes care for the chick, there should be no sex difference in the hormonal response to stress. Baseline plasma corticosterone and prolactin levels were higher in chick-rearing birds and were not influenced by body condition. Failed breeders were in better condition than chick-rearing individuals. Corticosterone response to stress was unaffected by parental effort as both chick-rearing and failed birds exhibited a robust corticosterone increase. Prolactin response to stress was however clearly influenced by parental effort: chick-rearing birds showed a modest 9% prolactin decrease whereas in failed birds prolactin concentrations fell by 41%. Body condition did not influence hormonal responses to stress. When facing stressful condition, breeding kittiwakes attenuate their prolactin response to stress while enhancing their secretion of corticosterone. Increasing corticosterone secretion triggers foraging efforts and diminishes nest attendance whereas an attenuation of prolactin response to stress maintains parental behavior. We suggest that this hormonal mechanism facilitates a flexible time-budget that has been interpreted as a buffer against environmental variability.     

Should I stay or should I go? Hormonal control of nest abandonment in a long-lived bird, the Adélie penguin

According to life-history theory, long-lived birds should favor their survival over the current reproductive attempt, when breeding becomes too costly. In seabirds, incubation is often associated with spontaneous long-term fasting. Below a threshold in body reserves, hormonal and metabolic shift characteristics of a switch from lipid to protein utilization (phase III, PIII) occur. These metabolic changes are paralleled by nest abandonment and stimulation of refeeding behavior. Parental behavior is then under control of two hormones with opposite effects: corticosterone (CORT) and prolactin which stimulate foraging and incubation behavior, respectively.The aim of this study was to determine the respective role of these two hormones in nest abandonment by Adélie penguins. To this end, plasma hormone levels were measured before egg-laying and at departure from the colony (i.e. when birds were relieved by their partner or abandoned their nest), and related to nutritional state and incubation success.We found that males abandoning their nest in PIII presented high CORT levels and low prolactin levels. Interestingly, males which presented high plasma levels of prolactin in PIII did not abandon. We show that although CORT is the first hormone to be affected by prolonged energy constraints, the combined effects of high CORT and low prolactin levels are necessary for parents to favor self-maintenance and abandon the nest. We provide insights into time-course changes of the endocrine profile as PIII proceeds and report that reaching proteolytic late fasting is not sufficient to induce nest abandonment in a long-lived bird.