Breeding success and productivity of urban and rural Eurasian sparrowhawks Accipiter nisus in Scotland

ABSTRACT

The conversion of rural habitat into built-up areas often affects animal species negatively. However, some generalist bird species and raptors relying on avian prey have colonised urban environments. Surprisingly, no study has compared the breeding biology of urban and rural populations of a very common old-world raptor, the Eurasian sparrowhawk (Accipiter nisus). Here, we compare the territory occupancy rate, breeding success and productivity (i.e., the number of fledglings) over four years (2009–2012) of an urban and a rural sparrowhawk population in Scotland. Our results showed that urban sparrowhawk territories were occupied significantly more frequently (mean % years occupied ± se: 66.8 ± 5.9%) than rural territories (42.8 ± 4.7%). Clutch size, brood size and the number of fledglings produced did not differ between the populations. However, the breeding success was significantly higher in the urban (annual mean ± se: 97.2 ± 2.3% nests successful) than in the rural population (80.5 ± 6.6%) because of a higher nest desertion rate at the egg and chick stages in the rural population. Our study suggests that warm weather in July may have more negative effects on rural sparrowhawks compared to urban sparrowhawks. The mechanism behind the difference is unknown and requires further work.

RÉSUMÉ

La conversion d’habitats ruraux en milieux bâtis a souvent un effet négatif sur la faune. Toutefois, certaines espèces d’oiseaux généralistes et de rapaces dépendant de proies aviaires ont colonisé les environnements urbains. Étonnamment, aucune étude n’a comparé la biologie de la reproduction de populations urbaines et rurales d’un rapace commun comme l’épervier d’Europe (Accipiter nisus). Nous avons comparé le taux d’occupation du territoire, le succès de reproduction et la productivité (c.-à-d. le nombre de jeunes) durant quatre ans (2009–2012) dans des populations rurales et urbaines d’épervier d’Europe en Écosse. Nos résultats montrent que les territoires urbains étaient occupés significativement plus fréquemment (moyenne du % d’années d’occupation ± es: 66,8 ± 5,9%) que les territoires ruraux (42,8 ± 4,7%). La taille de la couvée, la taille de la nichée et le nombre de jeunes ne différaient pas entre les populations. Cependant, le succès reproducteur était significativement plus élevé en milieu urbain (moyenne annuelle de nidifications réussies ± es: 97,2 ± 2,3%) que rural (80,5 ± 6,6%) en raison d’un taux de désertion des nids plus élevé aux stades d’œuf et d’oisillon dans les populations rurales. Notre étude suggère que le climat chaud de juillet pourrait avoir un effet négatif plus marqué pour les éperviers ruraux que pour les éperviers urbains. Le mécanisme expliquant cette différence demeure inconnu et devra faire l’objet d’études ultérieures.

KEYWORDS:

• raptors
• urbanisation
• Scottish Raptor Monitoring Scheme
• climate
• Ayrshire
• Edinburgh

MOTS CLÉS:

• rapaces
• urbanisation
• Plan écossais de suivi des rapaces
• climat
• Ayrshire
• Édimbourg

Acknowledgements

We thank the many volunteers, particularly Laura and Hugh Coventry as well as Alan Leitch, who helped to collect sparrowhawk data in Edinburgh. We also thank Giles Habgood for his excellent tree climbing skills. We are grateful to the City of Edinburgh Council, Royal Botanic Gardens Edinburgh and the National Trust for Scotland for providing tree-climbing access on their land. We thank Jeremy Wilson, Patrick White and three anonymous referees in Peerage of Science for constructive criticism on a previous draft.

The ringing and handling of birds were done under the British and Irish Ringing Scheme (organised by the British Trust for Ornithology). No ethical approval was needed for this project, because no biological samples were taken from the birds. The data for this work have been archived with the Scottish Raptor Monitoring Scheme (http://raptormonitoring.org/).

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The authors did not receive any funding for this work.