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24th International Ornithological Congress, Hamburg, Germany, 13-19 August 2006 Le Corre M1, Jaquemet S1, Kojadinovic J1, Bustamante P2, Cherel Y3 Geographic variation in the trophic ecology of a tropical seabird, the Sooty Tern: a multidisciplinary approach using diet analysis, stable isotope ratios and heavy metal levels
about the way animals should adjust their search effort in the two contrasted environments.
(1) Lab. ECOMAR, University of La Réunion, 15 aveneu René Cassin, BP7151, 97715 Saint Denis, Réunion, France,
[email protected],
[email protected],
[email protected] (2) LBEM, University of La Rochelle, (3) CEBC-CNRS Although tropical seabirds forage over oceanic habitats comparatively poor in food and rely on unpredictable prey patches, their populations that breed on remote oceanic islands can reach thousands or even millions of birds. This paradox suggests that tropical species have developed specific and efficient foraging strategies to cope with a paucity of resources. The pantropical Sooty Tern (Sterna fuscata) is the most abundant tropical tern and one of the most abundant seabirds in the world. Its some 80 million pairs world-wide consume 3.3 million tons of biomass annually, ranking the species fourth in a recent calculation of the annual quantity of food consumed by seabirds globally (Brooke 2004). In the western Indian Ocean, 6.2 million pairs of Sooty Terns breed on diverse islets and forage over very different marine habitats; they are thus excellent indicator populations for investigating geographic variation in trophic ecology in a top marine predator. In this paper we present results from a multidisciplinary study of Sooty Tern trophic ecology in four well-separated colonies in the western Indian Ocean, using three complementary methods: classical food sample analysis, stable isotope ratios of C and N, and bioaccumulation of heavy metals. Our results demonstrate great plasticity in trophic ecology, notably in main prey items, prey size and trophic levels, which may explain the success of this species throughout the tropics. Geographic variation in diet, dC, dN and heavy metal levels are analyzed simultaneously and discussed against geographic variation in the marine environment.
Boos M1, Carriere A1, Robin J-P1, Arnauduc J-P2, Petit O1 How is serum prolactin level linked to posthatch parental care behavior in a precocial bird, the Mallard?
Weimerskirch H1, Lecorre M.2 Foraging behavior and environmental conditions in seabirds (1) CNRS CEB, Chize, 79360 Villiers en bois, France,
[email protected] (2) Unversité de la Réunion, 97400 Saint denis, La Réunion, France Since environmental productivity and structure vary extensively among marine biomes, specific morphological and behavioral adaptations for foraging should exist among contrasted environments. We compare the morphological and foraging strategies of seabirds in two contrasted environments, tropical waters where productivity is low and the environment less structured, and sub-polar region where productivity is higher and enhanced in specific zones such as fronts or shelf edges. We use telemetry data (Argos, GPS tracking systems, accelerometers, activity recorders) to study the foraging strategy of a series of sub-Antarctic and tropical seabirds species covering petrels, albatrosses, frigatebirds, sulids, tropicbirds, penguins and terns. We also examine how seabirds respond to the environment at a range of spatial scales, and test some entrenched hypotheses
O02: Parental care
(1) CEPE-CNRS, 23 rue becquerel, 67087 Strasbourg Cedex 2, France,
[email protected],
[email protected] (2) Fédération Nationale des Chasseurs, 13 rue du Général Leclerc,92 130 Issy les Moulineaux, France Parental care is a key component of reproductive success during incubation and when risks of nestling mortality are high because of predation or need for food. It is a behavior controlled by prolactin release during incubation in precocial and altricial birds. The link between care and hormone persists in altricial parents after hatching, but has never been studied in depth in precocial species during rearing. Our study was performed from early April to mid June on the precocial Mallard (Anas platyrhynchos), using eight ducks which had hatched ducklings in outdoor closed aviaries. Food and water were provided ad libitum and ravens (Corvus corax), potential predators of young, were in evidence. Over 9 posthatch weeks, blood was sampled from the ducks every 3/4 days, and the behavior of hens and ducklings recorded daily on other days by the focal animal sampling method. Contact between ducks and their ducklings, and the leadership and creching of ducklings, decreased through time (p>0.05); and sleeping and preening by the ducks, together with aggressive and avoidance behavior toward young. increased (p>0.05). Serum prolactin concentration remained at high levels during the four first weeks posthatch (40±10 to 47±2 ng/ml), followed by a decline below 26±5 ng/ml after the 6th week. At that time, young had grown to more than 80-90% of the body mass of the ducks. From a Principal Component Analysis of 7 behaviors that changed significantly over the period of rearing, we extracted a so-called parental care variable that we then regressed against prolactin levels. The regression revealed that prolactin levels explained 80% of the variation in posthatch parental care in this precocial species. Further research should now focus on factors governing concomitant declines in prolactin and parental care, not only photoperiodic response and duckling mass, but also interactions with molt.
Müller W1, Dijkstra C2, Groothuis TGG2 Maternal yolk hormones adjust chicks to the posthatching social environment - inter-nest competition in the semi-precocial Black-headed Gull (1) University of Antwerp, Department of Biology-Ethology, Campus Drie Eiken C-127, Universiteitsplein 1, 2610 Antwerp (Wilrijk), Belgium,
[email protected] (2) Dept. of Animal Behavior, University of Groningen, The Netherlands;
[email protected],
[email protected] Avian eggs contain considerable amounts of maternal androgen which influence the physiology and behavior of the hatchling. These findings, and marked within-clutch variation in yolk androgens, have been interpreted as a mechanism for maternal
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J Ornithol 147 suppl (2006)
24th International Ornithological Congress, Hamburg, Germany, 13-19 August 2006 mediation of sibling competition within the brood. However, unlike intra-clutch variation, the adaptive significance of interclutch competitiveness, which is often variably greater, has been little studied. Here we tested whether high levels of yolk androgen, deposited across clutches as a consequence of enhanced social stimulation in breeding colonies of high density, adjusted offspring to the post-hatching social environment. Accordingly, we manipulated yolk androgen concentrations in the eggs of colonially-breeding Black-headed Gulls (Larus ridibundus) to investigate, by observations of behavior, the role of androgens in between-nest contexts. In this semi-precocial species, chicks participate in defending the natal territory and food against intruding adults and chicks from other nests soon after hatching. We found that chicks hatched from androgentreated eggs were more involved in territorial defense and tended to show more kleptoparasitic behavior. This increase in aggressive behavior in between-nest broods was not matched by an increase in sibling aggression within broods. Higher levels of yolk androgen in species that breed colonially in high density may therefore play an important role in adjusting chick behavior to levels required for territorial interaction post-hatching.
Grüebler MU1, Naef-Daenzer B2 The duration of post-fledging parental care in the Barn Swallow: Relevance to fitness (1) Zoological Institute, University of Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland;
[email protected] (2) Swiss Ornithological Institute, CH-6204 Sempach, Switzerland;
[email protected] Most passerine birds continue to care for their young after fledging, an investment that probably has an important fitness component as juvenal mortality during the first week postfledging is high. In multi-brooded species, the duration of postfledging parental care may determine the success of subsequent clutches by affecting their timing. Investigations of the postfledging stage are still rare, however, due to technical problems. Using radio-telemetry, we assessed the effect of the duration of post-fledging care on juvenal survival in Barn Swallows (Hirundo rustica) in a cross-fostering experiment that produced four groups of fledglings: those with (1) long post-fledging care, (2) short post-fledging care, (3) post-fledging care shortened compared to the brood of origin, (4) post-fledging care prolonged compared to the brood of origin. In total, 54 families with 225 fledglings were tracked for up to 50 days. Mortality peaked after family break-up, at 10-15 days post-fledging. The duration of parental care had a strong effect on juvenal survival: fledglings given long or prolonged post-fledging care were more likely to survive, and peak mortality rate decreased with increasing length of parental care. Behavioral observations revealed that postfledging parental care indirectly reduced the risk of juvenal predation. Moreover, the experiment revealed an effect of origin. In groups (2) and (3) receiving short care, fledglings with shortened care (group 3) survived better than their foster siblings. In contrast, the opposite was observed in the two groups receiving long parental care. The results show that the duration of post-fledging parental care is an important reproductive trait, accounting for a large proportion of differential post-fledging survival. In such double-brooded species as the Barn Swallow,
we assume a trade-off between prolonging the care of first brood fledglings and advancing the start of the second clutch.
Reynaud PA Red-billed Hornbills select aromatic plants to provide an insect-free environment for nidification IRD, Les Orteaux, 05700, Trescleoux, France,
[email protected] Between 1999 and 2004, we monitored the nidification of 51 pairs of Red-billed Hornbills (Tockus erythrorhynchus) in nest boxes on a reserve station in Senegal. 50% of the birds were infested by the tick (Hyalomma marginatum rufipes) when captured in the wild, but we found no infestation at all among the females and chicks in our nest boxes. To investigate the cause, we analyzed the composition of the litter in the boxes, and then removed or added some vegetal elements which were normally present. The presence of three aromatic plants - seeds of Azadiracta indica and leaves and bark of Eucalyptus calmadulensis and Prosopis chilensis - were found to be essential for optimum breeding success. All three plants constituted about 50% of the vegetal matter that the hornbills accumulated in nest boxes during breeding, the ratio between them depending on sequences of rain fall. The importance of the three plants as insect repellents is well known, but they are not native to Africa, having been introduced by man. In that short time, hornbills have learned the insect-repelling properties of these plants, and have adapted their behavior to choose them over indigenous plants as nest protection for offspring.
Ostreiher R Parental care is affected by intra-sex competition among breeders in the Arabian Babbler Hazeva Field Study Center, M. P. Arava, 86815, Israel,
[email protected] Observations over eight seasons of nestling feeding in the cooperatively breeding Arabian Babbler (Turdoides squamiceps) suggest that parental investment is affected by the social composition of the group. In simple groups comprising a breeding pair and their offspring, both parents fed at the same rate. In polyandrous groups comprising a single female breeder and two or more breeding males (with or without helpers), each breeding male fed at a higher rate than the sole breeding female. In polygynous groups, each breeding female fed at a higher rate than the sole breeding male. And in eight polygamic groups (three polygynous and five polyandrous), one of the breeders was evicted by a breeder of the same sex during the period of nestling feeding. In all cases, the feeding rates of the rivals increased significantly immediately before eviction. After eviction, the winner reduced its feeding effort instead of increasing it, in reverse to expectations if the sole purpose of feeding was to provide food, in compensation. These observations support the suggestion that nestling feeding in cooperative breeders, besides its direct role in providing food to nestlings, is also used to establish rights of possession and improve social status within the group.
