Abstract: Despite observational evidence of carry-over effects (COEs, events occurring in one season that produce residual effects on individuals the following seasons), to our knowledge no experimental studies have been carried out to explore how COEs might affect reproductive output. We simulated an environmental perturbation affecting spring-staging migrants to investigate COEs in greater snow geese (Anser caerulescens atlanticus). During three consecutive years, 2037 females captured during spring staging (approx. 3000 km south of their Arctic breeding grounds) were maintained in captivity (with or without access to food) for 0–4 days. Duration of captivity (but not food treatment) negatively affected reproductive success, probably through stress response. Reproductive success was reduced by 45–71% in 2 years, but not in a third year with unusually favourable breeding conditions. This unprecedented manipulation indicates that COEs can have a strong effect on individual reproductive success in long-distance migrants, but that this effect can be partly compensated for by good environmental conditions on the breeding ground.
Abstract: Two frequent assumptions about the evolution of long-distance migration in birds are that they travel long distances annually to reach food-rich areas for breeding, and that they time their migratory journey to be at staging sites when the latter provide the best feeding conditions. These assumptions have rarely been properly tested, and there is no study in which a species' major food types have been measured by standardized methods throughout a flyway and over a large part of the year. We here present such data for Eurasian teal (Anas crecca), converted to a common energetic currency, and collected at wintering, spring staging and breeding sites. Teal did not time migration to maximize local food abundance; most birds left wintering and spring staging sites before a sharp increase in invertebrate food abundance occurred. On the other hand, hatching of ducklings coincided with a peak in invertebrate food abundance on boreal breeding lakes. Mean overall food abundance (invertebrates and seeds combined) did not differ between wintering sites in southern France and breeding sites in northern Sweden at the time of breeding. Our results are inconsistent with the hypothesis that long-distance migration in dabbling ducks has evolved because adult birds gain an immediate pay-off in increased food abundance by flying north in spring. However, our data confirm a selective advantage for breeding at higher latitudes, because hatching of ducklings may coincide with a peak in invertebrate emergence and because longer days may increase the duration of efficient foraging.
Abstract: Classical sampling methods often miss important components of coral reef biodiversity, notably organisms that remain sheltered within the coral matrix. Recent studies using sea kraits (sea snakes) as bio-indicators suggest that the guild of predators represented by anguilliform fish (Congridae, Muraenidae, Ophichthidae, henceforth "eels" for simplicity) were far more abundant and diverse than previously suspected. In the current study, eel diversity (similarity and species richness indices) estimated via sea snake sampling (SSS) was compared among six areas of one of the main oceanic biodiversity hotspot of the Pacific Ocean (southwest lagoon of New Caledonia). Based on the eel diversity in the snakes' diet, the results obtained in six areas, in two snake species, and using different estimates (ANOSIM, Shannon indexaEuro broken vertical bar) were consistent, suggesting that SSS provided robust information. Analyses also suggested subtle, albeit significant, differences in the eel assemblages among islets. Such spatial differences are discussed in light of local management practices. As SSS is easy to use, cost-effective, and provides the best picture of eel assemblages to date, it can be employed to monitor the eel assemblages in addition to the snakes themselves in many areas of the Indo-Pacific Ocean, thereby providing an index of the top predator biodiversity of many coral reefs.
Abstract: Understanding the processes underlying emigrating behavior is fundamental to better understand animal dispersal. Because of the difficulties involved in carrying out controlled manipulation of the proximate drivers of emigration over large spatial scales, results from laboratory or small field enclosures suitable for small-bodied species remains to be validated in natural habitats. We investigate whether emigration is driven either by intraspecific competition or resulted from hunting-risk avoidance and assessed the effect of phenotypic variation on individual decisions. We made use of a quasi-experimental situation by using hunting recoveries of mallards (Anas platyrhynchos) released as ducklings in a fragmented landscape managed for duck hunting. Our results suggest an indirect effect of hunting on emigration. Body size plays a major role in modulating individual emigrating decisions, with small-bodied individuals emigrating more to escape from high levels of predation pressure while larger bodied individuals being more vulnerable to predation.
Abstract: Despite a long historical record of radio-tracking analyses, basic home-range information is still lacking for most common waterfowl species, especially during the winter. We investigated how dabbling duck home ranges and daily foraging movements are influenced by extrinsic (site, temperature, date) and intrinsic factors (species, sex, age). We radio-tagged and monitored 125 individuals of three duck species (mallard Anas platyrhynchos, Eurasian teal A. crecca crecca and northern pintail A. acuta) in three French wetlands over four winters. Home-range sizes for a given species varied greatly among our study sites. Moreover, species differed according to home-range structure and distance traveled to reach their foraging grounds (teal had a more patchy home range and traveled farther distances than mallards). Foraging distances increased with temperature and time (over the winter season), but this effect differed among species, suggesting that they behave differently in response to food depletion and/or cold weather. The commuting behavior (i.e., the decision to leave the roost at night for foraging) differed among species and season. Teals were more risk-prone because they were more likely to leave the roost at night. In our study, ducks foraged at distances of 1 - 2 km from roosts, whereas distances of 2 - 48 km have been recorded in North America. We suggest that food supply, hunting pressure or population density may account for these inter-continental differences.
Abstract: Mate guarding by males is common in species with long-lasting pair bonds. We tested if the need to guard females affected foraging depth in male teal (Anas crecca), and if they were more vigilant than females when foraging with submerged eyes (preventing monitoring of competing males and predators). These predictions were not supported, suggesting that foraging depth selection is primarily driven by other factors, presumably food related. A likely reason why deeply foraging males did not increase vigilance is that 37.5% of the foraging time was already dedicated to it. The apparent lack of guarding costs in foraging male teal may explain why such small ducks can maintain pair bonds for up to 7 months.
Abstract: The trade-off foragers make between predation risk and feeding efficiency is readily studied in dabbling ducks, which have stereotyped feeding methods, some of which prevent predator detection while others do not. Teals forage mostly with only the bill submerged (eyes above the water surface) in winter, but use a broader foraging repertoire in summer. Given the different environments used by teals over the year, it is likely that such a shift is due to changes in diet, but it may also be caused by differences in predation risk between habitats. However, neither predation risk nor teal behaviour has been studied with consistent methods around the year or throughout any of its flyways. Covering wintering, spring-staging, breeding and moulting sites, we combined focal observations of teals and predator flyover data from seven regions ranging from southern France to northern Sweden. Although not apparent at the scale of days within sites, teals indeed relied more on shallow foraging where predation risk was higher, i.e. at wintering sites. Average foraging depth increased gradually from September to August, i.e. from wintering to breeding sites. Foraging bout length of deeply foraging teals did not decrease over the year, suggesting that it is through selection of foraging technique, rather than by the balance between foraging and interruptions, that birds adjust to predation risk. This study highlights behavioural plasticity in response to contrasting selection regimes within a flyway, in dabbling ducks as well as long-distance migrants in general. (C) 2007 The Association for the Study of Animal Behaviour Published by Elsevier Ltd. All rights reserved.
Abstract: Many dabbling ducks Anas spp. are largely granivorous, consuming a variety of seeds chiefly from aquatic plants. To assess the relative value and carrying capacity of wetlands for dabbling ducks, species-specific information about seed mass is needed, but it is still largely missing or scattered in the literature. By combining weights of seeds collected in the field with a literature review, we provide a reference table for seed mass of 200 western European plant taxa frequently encountered by foraging dabbling ducks. Seeds collected in the field were sampled in microhabitats and at depths at which ducks were observed to forage, and study sites represent wintering, staging as well as breeding areas within a flyway in western Europe. When combined with calorimetric data, the present reference table will aid managers and scientists in assessing the importance of seed food resources at different sites and during different parts of the annual cycle.
Abstract: Diet quantification has long been and still is one of the first steps undertaken when studying the basic ecology of a species. We conducted a literature review of the techniques used to study and analyse diet among waterfowl. Even though the identification of food items is the most challenging task performed when studying granivorous waterfowl diet, there is a general lack of reference collections to support the taxonomic determination of food resources. We present here a collection of indexed digital pictures of seeds from the reference collections of several French programs of research into waterfowl diet. Photographs are ranked by seed size or by taxonomic key to ease seed identification. This collection is freely accessible at the website http://www.cebc.cnrs.fr/atlasofseeds.html, and it can help wildlife researchers studying the diets of granivorous species to determine food items. A complete bibliography is also provided, including recent papers in archeobotany and useful websites.
