Influence of nest-site vegetation and predator community on the success of artificial songbird nests

Abstract

Vegetation characteristics are commonly invoked to explain differential nesting success, but few studies have identified how habitat attributes may be associated with specific predator groups responsible for nest losses. We measured vegetation characteristics at artificial songbird nests deployed on and above the ground in mixedwood forest in west-central Alberta, to discriminate characteristics of successful nests from those of nests destroyed by mice and voles, squirrels, and birds. Successful nests, and those depredated by mice and voles, tended to be on the ground and were well concealed by dense shrubs. Squirrels and birds usually raided aboveground nests at sites with few shrubs and high tree densities. These results suggest that nest visibility is a major factor influencing risk of predation, but the relative importance of concealment varies according to the types of predators and their behavior. The characteristics of nests from which eggs were removed, leaving no egg remains to identify predators, closely resembled those of nests visited by squirrels and birds. Our findings have implications for how individual songbird species cope with selection pressures imposed by nest predators associated with vegetation characteristics of birds' nest patches and, ultimately, how predators may shape the structure of avian communities.Résumé : Les caractéristiques de la végétation sont souvent évoquées pour expliquer les fluctuations du succès de la nidification, mais peu d'études ont tenté de déterminer comment les attributs d'un habitat peuvent être associés à des groupes spécifiques de prédateurs responsables des pertes au nid. Nous avons mesuré les caractéistiques de la végétation près de nids artificiels de passereaux installés sur le sol et au-dessus du sol dans une forêt mixte du centreouest de l'Alberta, afin de déterminer lesquelles de ces caractéistiques sont reliées aux nids réussis par opposition aux nids détruits par les souris et campagnols, les écureuils et les oiseaux. Les nids réussis et ceux pillés par les souris et campagnols sont des nids au sol, bien camouflés par des buissons denses. Les écureuils et les oiseaux pillent généralement les nids au-dessus du sol à des sites où il y a peu de végétation et où les arbres sont denses. Ces résultats semblent indiquer que la visibilité du nid est un facteur très important de risque de prédation, mais l'importance relative du camouflage varie selon le type de prédateur et selon son comportement. Les caractéistiques des nids pillés où il n'est resté aucun débris permettant d'identifier le prédateur ressemblaient fortement à celles des nids pillés par les écureuils et les oiseaux. Nos résultats soulèvent le problème de l'adaptation des passereaux aux pressions de sélection qui sont créées par les prédateurs de nids et qui sont associées aux caractéristiques de la végétation dans l'entourage des nids et, ultimement, nous amènent à nous demander comment les prédateurs peuvent influencer la structure des communautés d'oiseaux.[Traduit par la Rédaction] Rangen et...

Use of sensory cues by fish crows Corvus ossifragus preying on artificial bird nests

“…We provide experimental evidence that the predatory behavior of fish crows in an aviary was principally influenced by the visibility of artificial nests. Our results are consistent with opportunistic observations and inferences derived from field studies, which suggest that visibility is a frequent correlate of nest discovery by corvids in communities where they are known to be active nest predators (Harriman and Berger 1986, Sugden and Beyersbergen 1986, 1987, Yahner and Cypher 1987, Major 1990, Rangen et al 1999). For example, Sugden and Beyersbergen (1987) demonstrated that American crows Corvus brachyrhynchos were less likely to prey on concealed (<20% visible) simulated duck nests than more visible nests, and that nest survival increased with cover height and density.…”

Habitat selection by the Superb Lyrebird (Menura novaehollandiae), an iconic ecosystem engineer in forests of south‐eastern Australia

“…Lyrebird nests are highly vulnerable to native predatory birds (Lill ; Dalziell & Welbergen ) and, by selecting sites with greater vegetative concealment, reproductive output should be greater (Møller ; Rangen et al . ; Colombelli‐Négrel & Kleindorfer ). The concealment hypothesis is supported by a strong positive influence of structural complexity of understorey vegetation (high strata) on nest site location in the local‐scale model.…”

The potential for interactions between predation and habitat change to cause population declines of farmland birds

“…This may occur when predators use non‐visual stimuli for nest detection (e.g. Rangen et al . 1999 obs) and/or because a trade‐off exists between nest crypsis and the ability of parents at the nest to detect predators and thus take mitigating action (Gotmark et al .…”