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.     

Indicators of seabird reproductive performance demonstrate the impact of commercial fisheries on seabird populations in the North Sea

In a world of growing anthropogenic pressures on biodiversity, effective indicators need to be specific and sensitive to the pressures in the ecosystem concerned, yet be simple enough to be interpreted by non-experts and straightforward enough to facilitate routine monitoring. Globally, seabirds are under increasing pressure as a result of anthropogenic activities and environmental variation. Traditionally, seabird indicators have been based on abundance at breeding colonies. However, as many species do not reach sexual maturity for several years, and may not attend the colony over this time period, such indicators may fail to capture the ecological complexity of the system concerned.We constructed two indicators of the state of nine seabird species that breed along the UK coast of the North Sea: (i) abundance of seabirds at breeding colonies, and (ii) probability of seabird breeding failure. The indicators were significantly and strongly correlated with each other for eight out of nine species, but the abundance indicator typically lagged the indicator on seabird breeding failure by two to three years. We then considered a third indicator which compared kittiwake (Rissa tridactyla) breeding success to the levels expected given the underlying environmental conditions; changes in the abundance indicator also lagged this by three years. We investigate how sensitive each of these indicators was to the impacts of fishing. We found that the species which had seen the greatest increases in breeding failure rate over the study period were those species which were most sensitive to fisheries pressure.By focussing on demographic parameters, and correcting for the underlying environmental conditions, we can detect potentially important population level changes at an earlier stage than by focussing on abundance alone. These indicators are able to more accurately capture the complexity of the ecosystem concerned and can be readily interpreted by policy-makers.     

Are corticosterone levels a good indicator of food availability and reproductive performance in a kittiwake colony?

We evaluated the use of corticosterone to gauge forage availability and predict reproductive performance in black-legged kittiwakes (Rissa tridactyla) breeding in Alaska during 1999 and 2000. We modeled the relationship between baseline levels of corticosterone and a suite of individual and temporal characteristics of the sampled birds. We also provided supplemental food to a sample of pairs and compared their corticosterone levels with that of pairs that were not fed. Corticosterone levels were a good predictor of forage availability in some situations, although inconsistencies between corticosterone levels and reproductive performance of fed and unfed kittiwakes suggested that this was not always the case. In general, higher corticosterone levels were found in birds that lacked breeding experience and in birds sampled shortly after arriving from their wintering grounds. All parameters investigated, however, explained only a small proportion of the variance in corticosterone levels. We also investigated whether corticosterone, supplemental feeding, year of the study, breeding experience, body weight, and sex of a bird were able to predict laying, hatching, and fledging success in kittiwakes. Here, breeding experience, year of the study, and body weight were the best predictors of a bird's performance. Corticosterone level and supplemental feeding were good predictors of kittiwake reproductive performance in some cases. For example, corticosterone levels of birds sampled during the arrival stage reliably predicted laying success, but were less reliable at predicting hatching and fledging success. Counts of active nests with eggs or chicks may be more reliable estimates of the actual productivity of the colony. Supplemental feeding had strong effects on kittiwake productivity when natural forage was poor, but had little effect when natural forage was plentiful.     

Metabolic adjustments in breeding female kittiwakes (<Emphasis Type="Italic">Rissa tridactyla</Emphasis>) include changes in kidney metabolic intensity

Black-legged kittiwakes (BLKIs) reduce self-maintenance cost through reductions in mass-specific basal metabolic rate (BMR), body mass and the size of visceral organs during the chick-rearing period. In the present study, we measured kidney in vitro oxygen consumption and plasma 3,3',5-triiodo-L: -thyronine (T3) levels of incubating and chick-rearing female BLKIs, to test whether the decrease in BMR is caused mainly by decreased metabolic intensity or simply by reductions in the size of organs with high metabolic intensity. Body mass and body condition were lower in chick-rearing birds compared with the incubating birds. In contrast to the previous findings, however, the kidney mass did not differ between the two breeding stages. Plasma T3 levels decreased substantially during the breeding season, indicating a reduction in BMR. Over the same period, kidney mass-specific oxygen consumption decreased (by 17.2%) from the incubating to the chick-rearing stage. Thus, the reduction in BMR found in breeding BLKIs seems partly explained by adjustments in metabolic intensity of visceral organs. Lowered metabolic intensity of visceral organs would permit increased allocation of energy to offspring at the expense of their own self-maintenance.     

The role of parent–offspring interactions during and after fledging in the Black-legged Kittiwake

Most bird species endure a high mortality at fledging, and selection should favour parental behaviour diminishing these costs. Post-fledging parental care varies greatly among species and is often linked to parent–offspring recognition. In the Black-legged Kittiwake (Rissa tridactyla), fledglings need to return to the natal nest to be fed by their parents until independence. Rejections of fledglings by non-parent adults may be fairly violent, and parents are expected to recognize and help their chicks at the time of first return. However, previous cross-fostering experiments pointed out that parents are not able to recognize their chicks up to 15 days before fledging. In this paper, we study the behaviour of both parents and juveniles at fledging. We found that parents answered significantly more to their fledgling's calls than to those of others. Compared to silent juveniles, juveniles that called before landing were more likely to be accepted by their parents. No such pattern was observed with foreign juveniles, indicating that fledglings’ voice may carry individual identity. Furthermore, fledglings found their way back to the natal nest faster when parents attended the natal nest and reacted to their offspring's calls than when they were absent or inactive. Such interactions may therefore diminish juvenile mortality at fledging.     

Are simple environmental indicators of food web dynamics reliable: Exploring the kittiwake–temperature relationship

This study examined the inter-relationships between kittiwake breeding success and sandeel abundance, Calanus copepods, chlorophyll and temperature. The validity of past proxies of sandeel prey (Calanus and temperature) suggested in the literature was also examined. Winter temperature was not found to be a reliable indicator of the abundance of sandeel or lower trophic levels, although the present study did support past evidence for a dependence of kittiwake breeding success on local sandeel abundance as, with the exception of two years, there was a linear relationship with log age-0 sandeel abundance. The abundance of sandeel was positively linked to the dates of predicted peak egg abundance in C. finmarchicus and C. helgolandicus. This supported earlier evidence that the match with prey timing is important to sandeel recruitment. Neither Calanus species was associated with temperature in the February to March period nor in the April–May period, which may explain the lack of a temperature effect that propagates through the trophic levels. Consequently, although kittiwake breeding success appears to show some sensitivity and specificity to changes in their prey, this responsiveness was not found to extend to the lowest trophic level (Calanus abundance) or to temperature. As such kittiwake breeding success was not a reliable indicator of climate-driven changes in the local food web.     

Polymorphic microsatellites in the black‐legged kittiwake Rissa tridactyla

We isolated seven microsatellite sequences from a library of recombinant clones in Rissa tridactyla (Laridae). We investigated their polymorphism in one population from France. Preliminary results indicate that these markers should prove valuable tools for the study of mating systems, population genetic structure and dispersal abilities in this seabird species. We present the results of cross‐species amplification for two seabird species: Uria aalge (Alcidae) and Stercorarius parasiticus (Stercorariidae). Some of the microsatellites isolated in R. tridactyla might be useful for studies on other seabird species.     

Corticosterone and time-activity budget: an experiment with Black-legged kittiwakes

In vertebrates, the well established increase in plasma corticosterone in response to food shortage is thought to mediate adjustments of foraging behavior and energy allocation to environmental conditions. However, investigating the functional role of corticosterone is often constrained by the difficulty to track time-activity budget of free-ranging animals. To examine how an experimental increase in corticosterone affects the activity budget of male Black-legged kittiwakes (Rissa tridactyla), we used miniaturized activity loggers to record flying/foraging, presence on the sea surface and nest attendance. To investigate how corticosterone affects allocation processes between self-foraging and foraging devoted to the brood, we monitored body mass change of males from capture (day 0) to recapture (day 3). Among control birds, males in poor condition at day 0 spent significantly more time flying/foraging and less time attending the nest site than did males in good condition. Corticosterone treatment affected time spent flying/foraging in interaction with body condition at day 0: corticosterone-implanted males in good condition spent more time flying/foraging than control ones; this was not observed in poor condition males. In control birds, change in body mass was negatively correlated with body condition at day 0. This was reinforced by corticosterone treatment and, on average, corticosterone-implanted males gained much more mass than controls. These results suggest that in Black-legged kittiwakes, body condition and corticosterone levels can interact to mediate foraging decisions and possibly energy allocation: when facing stressful environmental conditions, birds in good body condition may afford to increase the time spent foraging probably to maintain brood provisioning, whereas poor body condition birds seemed rather to redirect available energy from reproduction to self-maintenance.     

Measuring immigration and philopatry in seabirds; recruitment to Black-legged Kittiwake colonies

The degree of philopatry in two new Black-legged Kittiwake Rissa tridactyla colonies in northeast England was studied for 36 and 16 successive years, respectively. There was a tendency in both colonies for the number of recruits to the breeding group to increase with the age (and size) of the colony, but by an average of only one additional recruit each year. In the two new colonies, it was 7 and 9 years respectively before the first young birds bred in their natal colony. By that time, over 100 immigrants had recruited and bred in each colony. Thereafter, new philopatric birds were recorded annually. But these formed only an average of 23% of the recruits during 36 years (1955–90) at North Shields, and 4.2% over 16 years (1991–2006) at Coquet Island. In every year at both colonies the number of new immigrants exceeded the number of philopatric recruits. Males formed 82% of philopatric birds. The low degree of philopatry in the Kittiwake will result in appreciable gene flow between colonies and this is consistent with little geographic variation in the species. Each immigrant has to make a choice of which colony to enter, but the criteria for this selection are not understood. It is argued that many measures of philopatry in birds are biased towards high values because of the greater ease in identifying philopatric individuals. The generalization that there is a high degree of philopatry in colonial seabird species is not justified, as there is considerable variation between species, and possibly between colonies. More estimates based on unbiased data are needed.