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Conspecific brood parasitism (CBP) has been observed in approximately half of all species of waterfowl, a philopatric group in which breeding females are frequently locally related. It has been suggested that kin selection can facilitate the evolution of CBP in waterfowl via fitness benefits for the host and parasite. One model demonstrates that discrimination of related and unrelated parasites by the host must be sufficient for kinship to promote CBP, provided that costs of brood parasitism to host fitness are sufficiently low. We parameterized the model using demographic data and behavioural observations from a population of colonial Red-breasted Mergansers (Mergus serrator Linnaeus, 1758) in which 47% of nests were parasitized by conspecifics. The costs of 1-3 foreign eggs to host hatching success were generally small (decline of 1.8% per additional egg). Nevertheless, model outputs revealed that brood parasites maximize their inclusive fitness by avoiding nests of relatives, primarily because of constraints on a host's ability to detect parasites at the nest. Indeed, hosts spent Key words: alternative reproductive strategies, conspecific brood parasitism, kin selection, relatedness, fitness, hatching success, waterfowl, Red-breasted Merganser, Mergus serrator. Le parasitisme de nids de conspécifiques (PNC) a été observé chez environ la moitié de toutes les espèces de sauvagine, un groupe philopatrique au sein duquel les femelles reproductrices sont souvent apparentées à l'échelle locale. Il a été proposé que la sélection de parentèle peut faciliter l'apparition du PNC chez les espèces de sauvagine par l'entremise d'avantages sur le plan de l'aptitude pour l'hôte et le parasite. Un modèle démontre que la discrimination de parasites apparentés et non apparentés par l'hôte doit être suffisante pour que les liens de parenté favorisent le PNC, tant que les coûts du parasitisme de nids pour l'aptitude de l'hôte sont suffisamment bas. Nous avons paramétré le modèle en utilisant des données démographiques et des observations comportementales pour une population de harles huppés (Mergus serrator Linnaeus, 1758) dans laquelle 47% des nids étaient parasités par des conspécifiques. Les coûts associés à 1-3 œufs étrangers pour le succès d'éclosion de l'hôte sont généralement faibles (baisse de 1,8% pour chaque œuf supplémentaire). Cela dit, les résultats du modèle révèlent que les parasites de nids maximisent leur aptitude inclusive en évitant les nids d'individus apparentés, principalement en raison de limites à la capacité d'un hôte de détecter des parasites au nid. En effet, les hôtes passent Mots-clés : stratégies de reproduction alternatives, parasitisme de nids de conspécifiques, sélection de parentèle, apparentement, aptitude, succès d'éclosion, sauvagine, harle huppé, Mergus serrator., Introduction Conspecific brood parasitism (hereafter referred to as CBP) is an alternative reproductive strategy wherein females (parasites) lay at least some of their eggs in the nests of other females [...]

Bird species that undertake irruptive migrations are good candidates for assessing density-dependent effects on stopover ecology because the number of birds using stopover sites varies considerably from year to year. Using morphometric data from a 9-year banding program and radiotelemetry (n  = 25 females), we found that increases in the annual density of Northern Saw-whet Owls (NSWO; Aegolius acadicus) encountered at a fall stopover site in Nova Scotia, Canada, were not linked to female body condition or minimum stopover duration. Rather, most NSWO spent no more than 1 or 2 full days at the stopover site following radio-tagging and during their return visits to the site. Body condition indices were highest for NSWO captured near the end of the migration monitoring season, possibly reflecting birds that had recently established wintering ranges and were elevating energy stores. We used breeding abundance indices derived from Birds Canada's Atlantic Nocturnal Owl Survey to help test the hypothesis that irruptive fall migrations in NSWO were driven by elevated breeding productivity and dispersal of immature birds (breeding success hypothesis). Indeed, irruptive fall migrations were characterized by elevated densities of immatures, but not adults, and mean breeding abundance indices for the Maritime provinces during years with irruptive migrations were higher than those for non-irruptive years. We hypothesize that prey abundance during years with irruptive migrations was sufficient to enable high breeding densities and minimize effects of elevated fall densities of NSWO on rates of mass gain and stopover duration. [ABSTRACT FROM AUTHOR]

American black ducks, native to eastern North America, have been the focus of significant international conservation and management programs. The combined USA and Canadian population has traditionally been managed as a single population; however black duck demographics may vary by region. To help understand potential regional differences in black ducks, we used satellite telemetry to assess migratory chronology and movements of black ducks wintering near Windsor, Nova Scotia, Canada, near the northern limits of their wintering range where numbers are increasing. Wintering black ducks from Nova Scotia did not leave the Atlantic Flyway and included both longer‐distance migrants (~ 1500 km north) and locally‐breeding individuals. None of our tracked ducks travelled south of Nova Scotia during any part of the annual cycle, indicating a population segment that never leaves Canada and is subject solely to Canadian harvest pressures. Band recovery data revealed that a small portion (2.4%) of black ducks originally banded during winter in Nova Scotia were recovered south along the east coast of the USA, indicating that some of these black ducks are subject to international harvest pressures. Our results show that there are differences in annual black duck movements even within a small part of their range, adding to the growing evidence that black duck populations show fine‐scale temporal and spatial structure. This structure will need to be considered in future interprovincial and international harvest management plans of this important species. [ABSTRACT FROM AUTHOR]

Pair formation in ducks is thought to be influenced by the acquisition of breeding plumage, the occurrence of courtship display, or both. We examined the frequency of pair formation in Mallard (Anas platyrhynchos), Green-winged Teal (Anas crecca carolinensis), and Northern Shoveler (Spatula clypeata) in the central valley of California in relation to the frequencies of male attainment of breeding plumage and courtship display. Predictions related to two hypotheses are: (1) the timing of pair formation is directly related to the attainment of breeding (definitive alternate) plumage by males, and (2) frequencies of courtship display are highest during pair formation. Most female Mallard were paired by the end of October, with >80% in pairs by early December. Of Northern Shoveler, 90% were paired by early January and 90% of female Green-winged Teal were paired by early February. The highest rates of courtship display by Mallard were observed during October through November, by Northern Shoveler in November, and by Green-winged Teal in November through January. Courtship display was, therefore, relatively frequent at the same time as pair formation for all three species. Northern Shoveler spent less time in courtship display than the other two species. Most (90%) male Mallard had acquired alternate plumage by mid-November, Northern Shoveler by early February, and Green-winged Teal by mid-December. Thus, timing of pair formation coincided with timing of attainment of breeding plumage in Mallard and Green-winged Teal but not Northern Shoveler. [ABSTRACT FROM AUTHOR]