Alain Caizergues

Population genetic structure of male black grouse (Tetrao tetrix L.) in fragmented vs. continuous landscapes

We investigated the association of habitat fragmentation with genetic structure of male black grouse Tetrao tetrix. Using 14 microsatellites, we compared the genetic differentiation of males among nine localities in continuous lowland habitats in Finland to the genetic differentiation among 14 localities in fragmented habitats in the Alps (France, Switzerland and Italy). In both areas, we found significant genetic differentiation. However, the average differentiation, measured as θ, was more than three times higher in the Alps than in Finland. The greater differentiation found in the Alps is probably due to the presence of mountain ridges rising above natural habitats of the species, which form barriers to gene flow, and to a higher influence of genetic drift resulting from lower effective sizes in highly fragmented habitats. The detection of isolation by distance in the Alps suggests that gene flow among populations does occur. The genetic variability measured as gene diversity HE and allelic richness A was lower in the Alps than in Finland. This could result from the higher fragmentation and/or from the fact that populations in the Alps are isolated from the main species range and have a lower effective size than in Finland. This study suggests that habitat fragmentation can affect genetic structure of avian species with relatively high dispersal propensities.

Survival of Black Grouse Tetrao tetrix in the French Alps

Survival rates are necessary for calculating allowable harvests and for modelling population performance. Survival rates for 93 black grouse Tetrao tetrix equipped with radio tags in two populations of the southern French Alps were estimated. Annual survival rates of hens (0.68, SE = 0.075, 0.84, SE = 0.105), but not of cocks (0.56, SE = 0.09, 0.66, SE = 0.122), tended to be higher than those of juveniles (0.52, SE = 0.071, sexes combined). The lower survival of juveniles was due to higher predation, mostly by raptors, in autumn and winter. Although both autumn and winter were seasons of peak mortality in juveniles, most adult deaths occurred either in spring (hens and cocks), or in early summer (cocks). Causes of mortality were as follows: raptors 51%, mammalian predators 27%, unidentified predators 11%, and hunting 11%. Principal raptors were golden eagltAquila chrysaetos and goshawk Accipiter gentilis. Mammalian predators included fox Vulpes vulpes, pine marten Maries maries and stone marten M. foina. Only males could be legally shot, and hunting was a minor mortality factor on our study areas. Nevertheless, the distorted adult sex ratio favouring hens that we observed on our study areas was probably due to hunting of males on and around the study areas. Sensitivity analysis showed that population growth is influenced more by adult survival than by either reproductive success or juvenile survival to one year of age. To prevent shooting from causing highly distorted spring sex ratios, which might compromise reproductive success, harvests should be reduced in years of poor reproduction, and shooting should be oriented towards juvenile males.

Population genetic structure of rock ptarmigan Lagopus mutus in Northern and Western Europe

Alpine species may be losing habitat because of global warming. Setting management priorities for such species is thus urgent and cannot be achieved without data on population structure. We studied the structure of rock ptarmigan (Lagopus mutus) populations in the Pyrenees, Alps and Norway, using six microsatellites. We found that rock ptarmigan in the Pyrenees were genetically impoverished compared with those in the Alps and Norway, and displayed a greater divergence (Pyrenees vs. Alps or Norway: θST = 0.16, Alps vs. Norway, θST = 0.04). In the Alps, despite a weak genetic differentiation between localities up to 200 km apart (θST = 0.011), a significant isolation‐by‐distance (IBD) effect was detected. When computed for each sex separately this IBD effect was significant for males but not for females, suggesting that males are highly philopatric.

Emigration rates and population turnover of teal Anas crecca in two major wetlands of western Europe

Abstract During the winter of 2003/04, we studied emigration rates of teal Anas crecca in two major wetlands: the Camargue (southern France) and the Loire estuary (western France). We derived local survival probabilities as a step in ultimately estimating emigration rates from individual mark-resighting (visual recaptures) history of birds fitted with nasal saddles. In goodness-of-fit tests of time-dependent models for local survival, we only detected the presence of transients among young females in the Loire estuary, which indicated that this category of individuals includes an ‘unstable compartment’ continuing its migratory journey further to the south. We observed low monthly local survival and high emigration rates (range: 0.01-0.81) in both areas, which suggests high turnover rates. In the Loire estuary, temporal changes in emigration rates matched the post- and pre-nuptial migration peaks (i.e. October-November and February-March). By combining local survival probabilities and count data, we derived an estimate of the ratio between the winter peak count of teals in our study areas and the minimum number of birds that actually frequented the areas over the entire wintering period (October-March). In both cases, we estimated the number of teal visiting the two wintering sites be about twice as large as the maximum number of birds counted instantaneously.

Impact of radio-tracking on black grouse Tetrao tetrix reproductive success in the French Alps

From 1991 to 1995, we tested the effects of radio-tracking, including trapping, handling and monitoring, on reproductive success of black grouse Tetrao tetrix hens in the southern French Alps. Reproductive success (total young/total hens with and without broods) was lower in hens marked with radio-collars than in unmarked hens (0.77 vs 1.66 young/hen, P = 0.02). Brood size was similar in the two groups of hens, but the proportion of hens rearing a brood was lower among marked hens (23 vs 45%, P = 0.03). Reproductive success of hens marked at the beginning of laying, or just before, was lower than that of hens marked ≥6 months before laying (0.25 vs 1.20 young/hen, P = 0.058). The success of hens marked near the time of laying was also low compared with unmarked hens in all years but 1992 (the year*time of capture interaction was significant). In contrast, reproductive success of hens marked ≥6 months before laying was not statistically different from that of unmarked hens (1.20 vs 1.66 young/hen, P = 0.28). Higher predation rates on first clutches, and to a lesser extent lower ability to renest, were responsible for the lower reproductive success of hens marked at the beginning of or just before laying. Altogether, these results suggest that initial discomfort caused by the transmitter, stress of capture, handling and monitoring following capture may temporarily alter the behaviour of hens, thereby increasing detection of their nests by predators. After a period of adjustment, radio-transmitters per se may have little or no adverse effect on reproduction. We conclude that to obtain reliable estimates of breeding parameters of black grouse in the French Alps using necklace type transmitters, hens must be equipped with these several months before laying, and nesting hens should not be approached closer than 20 m during radio-tracking.

Movements of wintering diving ducks: new insights from nasal saddled individuals

Capsule In winter diving ducks commonly move between wetlands more than 100 km apart, but short-distance daily movements dominate their activity. Aims To describe the movements of Common Pochards Aythya ferina and Tufted Ducks Aythya fuligula during the wintering season in France and to investigate intrinsic and extrinsic factors potentially affecting the direction and distance of these movement. Methods Distances, directions and patterns/strategies of winter movements were assessed from a combination of encounter data: physical recaptures at the ringing site, re-sightings of individuals fitted with nasal saddles, and ring recoveries of dead individuals. Results Patterns of movements derived from multiple locations (i.e. successive re-sightings) of individuals could be assessed, showing that several ‘strategies’ may coexist in the same species (residency, exploitation of two wintering sites with or without return journey, and exploration of several sites). Individuals may use several sites more than 100 km apart during a given winter. Interestingly, directions of movements did not fit any previously observed pattern, especially in Common Pochards, whose movements tended to be biased towards the northeast at the beginning of the wintering season (October–November) whereas south or southwest movements were expected. Weather conditions in winter affected directions of movements in Common Pochards; eastwards movements towards ice-free Alpine lakes were more frequently observed during cold spells. Conclusion Overall, our results suggest that exchanges of birds between wetlands more than 100 km apart are rather common even though short-distance movements related to daily activities are dominant. Our study provides new insights into the potential origin of ducks suspected of spreading infectious diseases.

Movement Patterns in a Partial Migrant: A Multi-Event Capture-Recapture Approach

Partial migration is a pervasive albeit poorly studied phenomenon by which some individuals of a population migrate while others are residents. It has tremendous consequences on seasonal variations of population size/structure and therefore management. Using a multi-event capture-mark-recapture/recovery (CMR) approach, we assessed seasonal site occupancy, survival and site fidelity of a partially migratory diving duck, the Common pochard (Aythya ferina), in an area potentially including both local breeders and winter visitors. The modelling exercise indeed discriminated two different categories of individuals. First, locally breeding females which had a probability of being present in our study area during winter of 0.41. Females of this category were found to be more faithful to their breeding site than males (breeding site fidelity probabilities of 1 and 0.11, respectively). The second category of birds were winter visitors, which included adults of both sexes, whose probability of being present in the study area during the breeding season was nil, and young of both sexes with a 0.11 probability of being present in the area during the breeding season. All wintering individuals, among which there was virtually no locally breeding male, displayed a high fidelity to our study area from one winter to the next (0.41–0.43). Estimated annual survival rates differed according to age (adults 0.69, young 0.56). For both age classes mortality was higher during late winter/early spring than during summer/early winter. Our study is among the first to show how and under which conditions the multi-event approach can be employed for investigating complex movement patterns encountered in partial migrants, providing a convenient tool for overcoming state uncertainty. It also shows why studying patterns of probability of individual presence/movements in partial migrants is a key towards understanding seasonal variations in numbers.

Patterns of spatial distribution and migration phenology of common pochards Aythya ferina in the Western Palearctic: a ring-recoveries analysis

We used ringed-recoveries to assess: 1) the connectivity (movements of individuals) between the three putative flyways (north–west Europe, central Europe, south–west Asia) of common pochards in the Western Palearctic, 2) possible spatio-temporal variations in the distribution of the species, and, 3) temporal evolution in spring and autumn migration dates. Based on winter counts of common pochards in the north–west European flyway, we distinguished three periods in the analyses (1960–1990, 1991–2000 and 2001–2016), which correspond to successive periods of population increase, peak and decline, respectively. Whatever the season (wintering or breeding) and period of ringing, large probabilities of ring-recoveries outside the flyway of origin (ringing) were recorded, suggesting a high connectivity between the three putative flyways. There was a significant trend towards an earlier departure from the wintering area, and an eastward shift of spring recoveries over periods. In contrast, neither autumn/winter recovery locations, nor departure dates from the breeding area in Latvia and Russia changed over periods. The latter results do not support the hypothesis that short-stopping (i.e. a reduction of fall migration distances/delaying of departure dates from the breeding area) could explain the observed decline of wintering common pochards in the north–west European flyway. Indirect recoveries support that large proportions of individuals wintering in western Europe may originate from the south–west Asia flyway and more particularly from a region in Siberia located in the Ob river catchment area. Considering trends in numbers for the three flyways together confirmed the “vulnerable” IUCN status of common pochard in the Western Palearctic as a whole, with a 35% decline over the last decade. The important connectivity between the northwest, central European and southwest Asian flyways call for considering such conservation problems at a much broader scale than the regional flyway.