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In many tropical bird species, partners combine their songs to form precise duets, of which the function is imperfectly understood. Duet structure and sex differences in vocal strategies may be important indicators of different selective pressures that have led to the evolution and maintenance of these complex acoustic displays. This study examines the singing behaviour of a population of the eastern whipbird, a bird that forms antiphonal duets initiated exclusively by the male. In all, 7% of duets recorded were between a paired female and a male other than her social partner. Males sang more often than females, their songs were longer and moved through a wider frequency range, and they had a larger song repertoire. Females sang two types of song: response songs, used primarily in a duet context, and structurally distinct solo songs, typically used during interactions with other females. Eastern whipbirds lacked unique song types among the repertoires of individual males and females. Males and females combined songs non-randomly to produce specific duets that were shared across the population. Results suggested that song and duet type matching might play an important role in intrasex interactions, such as defence of a territory, or a partner, from same-sex intruders.

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ABSTRACT. Land managers often respond to declining numbers of target species by creating additional areas of habitat. If these habitats are also subject to human disturbance, then their efforts may be wasted. The European Nightjar (Caprimulgus europaeus) is a ground-nesting bird that is listed as a species of European Conservation Concern. It appears to be susceptible to human disturbance during the breeding season. We examined habitat use and reproductive success over 10 years in a breeding population on 1335 ha of managed land in Nottinghamshire, England. The study site was divided into a heavily disturbed section and a less disturbed section of equal habitat availability, forming a natural long-term experiment.The site is open to the public, and visitor numbers approximately doubled during the study. We found that overall Nightjar density was significantly lower and there were significantly fewer breeding pairs in the heavily disturbed habitat compared with the less disturbed habitat. However, average breeding success per pair, in terms of eggs and fledglings produced, was not significantly different between the two sections across years. Our findings suggest that human recreational disturbance may drastically alter settlement patterns and nest site selection of arriving females in some migratory groundnesting species and may reduce the utility of apparently suitable patches of remnant and created habitat. Land managers should bear this in mind when creating new areas of habitat that will also be accessible to the public. Our study also highlights the value of longterm population monitoring, which can detect trends that short-term studies may miss. Effet des perturbations d'origine anthropique sur l'utilisation de l'habitat et le succès de reproduction à long terme de l'Engoulevent d'Europe, Caprimulgus europaeusRÉSUMÉ. Afin de contrer le déclin d'espèces prioritaires, les gestionnaires de territoires ont souvent recours à la création de nouveaux habitats. Si ces milieux créés font l'objet de perturbations d'origine anthropique, les mesures de conservation entreprises par les gestionnaires peuvent alors être vouées à l'échec. L'Engoulevent d'Europe (Caprimulgus europaeus), un oiseau qui niche au sol, a été désigné « préoccupant » en Europe. On pense que cette espèce est sensible à la perturbation humaine au moment de la nidification. Nous avons examiné l'utilisation de l'habitat et le succès de reproduction d'une population nicheuse durant dix ans sur un territoire aménagé de 1335 ha dans le Nottinghamshire, en Angleterre. Le site d'étude présentait deux sections dans lesquelles la disponibilité de l'habitat était égale, l'une qui était fortement perturbée, l'autre moins perturbée, l'ensemble formant un contexte d'expérimentation naturelle à long terme. Ce site est ouvert au public et le nombre de visiteurs a pratiquement doublé au cours de l'étude. Nous avons trouvé que la densité d'engoulevents était significativement plus faible et qu'il y avait significativement moins de couples nicheurs dans les milieux ...

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