Matthieu Guillemain

Ecology of spring-migrating Anatidae: a review

Spring migration is generally considered as a crucial period of the year for many birds, not the least due to its supposed importance for subsequent breeding success. By reviewing the existing literature for Anatidae (ducks, geese, and swans), we show that little is known about their ecology in spring, although some goose species are exceptions. Another general pattern is that the ecology of Anatidae at staging sites is particularly neglected. Existing studies tend to focus on questions dealing with acquisition of nutrient reserves, whereas almost nothing has been published about stopover habitats, time use, microhabitat use, foraging behaviour, food availability, food limitation, diet selection, and interspecific relationships. Besides summarising present knowledge, we identify taxonomic groups and topics for which gaps of knowledge appear the most evident, thereby also highlighting research needs for the future.

The importance of protected areas as nocturnal feeding grounds for dabbling ducks wintering in western France

We studied the diurnal and nocturnal habitat use of wintering dabbling ducks (Anas spp.) in two protected areas of an internationally important winter quarter in western France. The waterbodies of the reserves are heavily used by ducks during daylight hours, and 3–55% of these birds used the reserves at night: >50% of shoveler (A. clypeata), 20% of granivorous ducks (mallard A. platyrhynchos, teal A. crecca and pintail A. acuta), and lower numbers of herbivores (wigeon A. penelope and gadwall A. strepera). Radio-tracking showed that some ducks used the reserves by day and by night, and that some of them may switch from one protected site to another: radio-tagged birds were located in one of the two protected areas for 76% of the days and 81% of the nights they were sought, with granivores switching from waterbodies to wet grasslands within a reserve between the two periods. Such resident individuals may be ‘experienced’ wintering ducks, avoiding surrounding unprotected feeding habitats at night, while birds that leave the reserves at night may be subdominants and/or ‘naive’ individuals from a transient migratory sub-population. This study suggests that management of nature reserves should combine day-roosts with significant areas of nocturnal feeding grounds, since in protected areas both habitats may be successively used by wintering dabbling ducks across the 24-h cycle.

Spread of Avian Influenza Viruses by Common Teal (Anas crecca) in Europe

Since the recent spread of highly pathogenic (HP) H5N1 subtypes, avian influenza virus (AIV) dispersal has become an increasing focus of research. As for any other bird-borne pathogen, dispersal of these viruses is related to local and migratory movements of their hosts. In this study, we investigated potential AIV spread by Common Teal (Anas crecca) from the Camargue area, in the South of France, across Europe. Based on bird-ring recoveries, local duck population sizes and prevalence of infection with these viruses, we built an individual-based spatially explicit model describing bird movements, both locally (between wintering areas) and at the flyway scale. We investigated the effects of viral excretion duration and inactivation rate in water by simulating AIV spread with varying values for these two parameters. The results indicate that an efficient AIV dispersal in space is possible only for excretion durations longer than 7 days. Virus inactivation rate in the environment appears as a key parameter in the model because it allows local persistence of AIV over several months, the interval between two migratory periods. Virus persistence in water thus represents an important component of contamination risk as ducks migrate along their flyway. Based on the present modelling exercise, we also argue that HP H5N1 AIV is unlikely to be efficiently spread by Common Teal dispersal only.

The scientific basis for a new and sustainable management of migratory European ducks

Abstract It is an axiom in ecology that knowing the sheer number of individuals in a population is of very little help if the objective is to understand future and past changes in population size. Yet, this is exactly how migratory European ducks are monitored, many of which are important quarry species in several countries. We argue that present monitoring is insufficient to address objectives of wise use andsustainabilitysuchasthoseemphasisedinrecentmanagementdirectivesand multilateral international agreements. The two main problems are the almost total lack of reliable data on recruitment and mortality. We advocate a pan-European monitoring system based on undisputed scientific principles; i.e. a long-term, coordinated and standardised scheme that produces data about vital rates of duck populations as well as about harvest size. Data from such a scheme can be used by game biologists to produce predictive tools, thus providing a functional basis for management decisions for adaptive harvesting and conservation alike.

Foraging methods can affect patch choice: an experimental study in Mallard (Anas platyrhynchos)

Animals can adapt to changes in feeding conditions by switching between foraging methods. Dabbling ducks use different foraging methods, including dabbling in deep water with the head and neck submerged, and grubbing in the mud (or shallow water) where the eyes are above the surface, so the bird can visually monitor its environment while foraging. Deep foraging is considered to provide lower intake rates and to have high associated costs, such as predation risk, compared to shallow foraging. Ducks should thus prefer shallow foraging and switch to deeper methods when feeding conditions deteriorate. We conducted a set of experiments with Mallard to assess the importance of intake rate as a cue to choose between patches associated with different foraging methods, and evaluate the influence of food depletion on the decision to switch between methods. When 50 g of wheat were presented in two patches, one at a depth of 5 cm and one at 35 cm, most of the foraging was in the shallow area. Reducing food abundance to 10 g in the shallow area led to an increase in deep foraging, although the birds still preferred the shallow area at the beginning of the tests despite the fact that it did not provide a higher intake rate. This area was used until complete depletion, and birds did not turn to deep foraging before ensuring that the shallow patch was empty. These results show that food depletion affects the choice between feeding patches hence foraging method. However the value of intake rate is not the main cue for decision, rather the birds appear to choose between patches with different methods on account of their respective costs.

The cost of vigilance for intake rate in the mallard (Anas platyrhynchos): an approach through foraging experiments

Vigilance while foraging incurs costs such as a reduction of the time available for feeding or a reduction in instantaneous intake rate. Vigilance has two major components: scan rate and scan duration. We investigated the cost of these components for the instantaneous intake rate in Mallard. We first modelled the relationship between food availability and instantaneous intake rate (i.e. the functional response), and looked at the relationship between the residuals of this relationship and scan rate and scan duration. Both scan rate and scan duration were negatively correlated with the residuals, but the cost associated with an increase in each component of vigilance differed. The average time spent in vigilance by ducks was 5 sec per minute: 5 scans of 1 sec decreased the maximum instantaneous intake rate by 2.4% whereas one scan of 5 sec decreased the maximum intake rate by 6%. This shows that an increase in the duration of scans has a greater effect than an increase in their frequency and confirms that vigilance not only affects the time spent feeding but also feeding efficiency through instantaneous intake rate. We explored the potential consequences of such costs in the time spent foraging on a daily basis.

Effects of climate change on European ducks: what do we know and what do we need to know?

The consequences of climate change for bird populations have received much attention in recent decades, especially amongst cavity-nesting songbirds, yet little has been written on ducks (Anatidae) despite these being major elements of wetland diversity and important quarry species. This paper reviews the major known consequences of climate change for birds in general, and relates these to the limited information available specifically for ducks. Climate change can influence migration distance and phenology, potentially affecting patterns of mortality, as well as distribution and reproductive success in ducks. Studies addressing effects of climate change are, however, restricted to very few duck species, including mallard Anas platyrhynchos and common eider Somateria mollissima. Shifts in winter duck distributions have been observed, whereas the mismatch hypothesis (mistiming between the periods of peak energy requirements for young and the peak of seasonal food availability) has received limited support with regard to ducks. We propose a range of monitoring initiatives, including population surveys, breeding success monitoring schemes and individual duck marking, which should later be integrated through population modelling and adaptive management to fill these gaps.

Low survival after release into the wild : assessing “the burden of captivity” on Mallard physiology and behaviour

Captive-reared animals used in reinforcement programs are generally less likely to survive than wild conspecifics. Digestion efficiency and naive behaviour are two likely reasons for this pattern. The Mallard is a species with high adaptability to its environment and in which massive reinforcement programs are carried out. We studied physiological and behavioural factors potentially affecting body condition and survival of captive-reared Mallards after being released. Digestive system morphology and an index of body condition were compared among three groups: captive-reared birds remaining in a farm (control), captive-reared birds released into the wild as juveniles (released) and wild-born birds (wild). We also compared behaviour and diet of released vs. wild Mallards. Finally, we conducted a 1-year survival analysis of captive-reared birds after release in a hunting-free area. Gizzard weight was lower in control Mallards, but the size of other organs did not differ between controls and wild birds. The difference in gizzard weight between released and wild birds disappeared after some time in the wild. Diet analyses suggest that released Mallards show a greater preference than wild for anthropogenic food (waste grain, bait). Despite similar time-budgets, released Mallards never attained the body condition of wild birds. As a consequence, survival probability in released Mallards was low, especially when food provisioning was stopped and during harsh winter periods. We argue that the low survival of released Mallards likely has a physiological rather than a behavioural (foraging) origin. In any case, extremely few released birds live long enough to potentially enter the breeding population, even without hunting. In the context of massive releases presently carried out for hunting purposes, our study indicates a low likelihood for genetic introgression by captive-reared birds into the wild population.

A flyway perspective on food resource abundance in a long-distance migrant, the Eurasian teal (Anas crecca)

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.

Ecotourism disturbance to wildfowl in protected areas: historical, empirical and experimental approaches in the Camargue, Southern France

Ecotourism is becoming very popular, especially in protected areas where wildlife concentrate and is easier to observe, but the consequences of associated disturbance have seldom be quantified other than in the short-term, making the sustainability of this activity untested. We combined a historical, an empirical and an experimental approach to assess the long-, medium- and short-term consequences of disturbance to wintering wildfowl (Anatidae) in a wetland of international importance in the Camargue, Southern France. In the short-term, disturbance made teal (Anas crecca) move away temporarily from observation blinds without leaving the waterbody. Wildfowl fed more after disturbance, disrupting their normal resting activities. In the medium-term, waterbodies with more tourists did not host fewer birds: conversely the most heavily disturbed one hosted the highest wildfowl density. In the long term, wildfowl numbers were not related with the number of visitors. When practiced with appropriate guiding of people, and where appropriate facilities are provided to limit human disturbance as done here, ecotourism may not affect wintering wildfowl other than reversibly in the very short term. The legitimate demand of the public for access, even in fragile protected areas, may therefore be sustainable under some conditions.