A NEST PREDATOR'S VIEW OF A MANAGED FOREST: GRAY JAY (PERISOREUS CANADENSIS) MOVEMENT PATTERNS IN RESPONSE TO FOREST EDGES

Auk, The, Jan 2004 by Ibarzabal, Jacques, Desrochers, Andre

ABSTRACT.-High nest-predation risk is often associated with forest edges. Most nest predators in boreal coniferous forests of North America are forest specialists living in mature stands. Nest predators have been studied mainly through use of artificial nests; knowledge of their behavior remains limited. We used radiotelemetry to examine movement patterns, relative to forest edge, of a forest nest predator, the Gray Jay (Perisoreus canadensis), in boreal coniferous forest. Each of 11 family groups of Gray Jays monitored in early summer exhibited a marked association with forest edges. Jays were found within 30 m of the forest edges more often than expected from random use of mature forest. Furthermore, jays traveled more slowly near forest edges than in the forest interior. Because forest edges apparently represent prime foraging habitat for Gray Jays, narrow forest strips left by logging could act as ecological traps for mature-stand songbirds before stands regenerate in adjacent clearcuts. Received 19 March 2003, accepted 5 October 2003.

RESUME. - Un risque eleve de predation est souvent associe aux lisieres des forets. La plupart des predateurs de nids des forets coniferiennes boreales de l'Amerique du Nord sont essentiellement des especes du milieu forestier mature. Les predateurs de nids ont surtout ete etudies a l'aide de nids artificiels et la connaissance de leur comportement reste limitee. Nous avons utilise la telemetrie conventionnelle pour examiner les patrons de mouvement relatifs aux lisieres des forets par un predateur de nid forestier, Perisoreus canadensis, dans une foret coniferienne boreale. Chacun des 11 groupes familiaux de Perisoreus canadensis suivis au debut de l'ete montraient une association marquee avec les lisieres. Les mesangeais ont ete trouves plus souvent a moins de 30 m d'une lisiere forestiere que l'aurait suggeree une repartition aleatoire de leurs activites dans la foret mature. De plus, les mesangeais se deplacaient plus lentement pres des lisieres qu'a l'interieur de la foret. Etant donne que les lisieres representent apparemment un habitat privilegiee pour la quete de nourriture chez Perisoreus canadensis, les bandes etroites de forets laissees apres les coupes forestieres pourraient constituer des pieges ecologiques pour les passereaux de la foret mature, avant que les peuplements se regenerent dans les coupes adjacentes.

NEST PREDATION is one of the most important factors affecting nesting success (Ricklefs 1969). The risk of nest predation varies according to the predatory community involved, nest location (e.g. on the ground or in trees), and bird species (Nteller 1989, Nour et al. 1993, Tewksbury et al. 1998, Yahner and Piergallini 1998). Many studies have shown that forest edges in agricultural landscapes (Andren 1995, Henske et al. 1999) and occasionally in managed forests (Angelstam 1986, Andren 1995, Bayne and Hobson 1997) are associated with high nest-predation risk.

The high risk of nest predation near forest edges is usually attributed to opportunistic species invading forests from other nearby habitats (DeGraaf 1995). However, forest-dwelling nest predators can also have a significant effect on nests near forest edges (Andren 1995). In fact, nest predators of managed boreal forests seem mainly to be forest specialists rather than species occurring in agricultural fields or urban fringes (Andren 1995, Bayne and Hobson 1997, Darveau et al. 1997). Although risk of nest predation near forest edges is well documented, knowledge of the underlying processes-predator behavior in particular-remains limited for both temperate and boreal regions.

Logging in coniferous boreal forests typically creates landscapes that are dominated by clearcuts and regeneration. In Quebec, Canada, ~300,000 ha of boreal forest are logged annually (Parent 1999). Forest remnants are generally linear and appear mostly as riverine bands (20 m) and forest strips of 60 or 100 m between clearcuts (Ministere des Ressources Naturelles du Quebec 1996). The resulting landscape structure may affect songbirds, nest predators, and their relationships, particularly if nest predators prefer to forage near edges.

We examined movement patterns of the Gray Jay (Perisoreus canadensis), a species commonly found in boreal coniferous forests (Strickland and Quellet 1993). Like many other members of the Corvidae (Andren 1995), Gray Jays are nest predators (Bayne and Hobson 1997, Sieving and Willson 1998, Boulet and Darveau 2000, Boulet et al. 2000) and use eggs and nestlings as main food items (Strickland and Quellet 1993). Gray Jays have been observed preying on eggs or nestlings of many bird species (Spruce Grouse [Dendragapus canadensis], Ruby-crowned Kinglet [Regulus calendula], Swainson's Thrush [Catharus ustulatus], Hermit Thrush [C. guttatus], American Robin [Turdus migratorius], Magnolia Warbler [Dendroica magnolia], Lincoln's Sparrow \Melospiza lincolnii], Fox Sparrow [Passerella iliaca], White-crowned Sparrow [Zonotrichia leucophrys], White-throated Sparrow [Z. albicollis]; Bent 1946, Quellet 1970). Given that higher nest predation rates by Gray Jay were recorded near forest edges (Bayne and Hobson 1997, Sieving and Willson 1998), we tested the prediction that foraging Gray Jays are associated with forest edges during the nesting season.