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Habitat fragmentation and paternity in least flycatchers.

Article Excerpt
The complexity of the environment can influence extra-pair paternity (EPP) rates (Westneat and Sherman 1997) as it can alter success of which females foray off territory and the ability of males to successfully guard their mates (Mays and Ritchison 2004). Landscape fragmentation can also alter habitat complexity as it results in loss of original habitat, a decrease in patch size, and increase in distance between patches (Wilcox and Murphy 1985). These factors are thought to negatively influence forest songbird species, and are most often associated with decreases in songbird diversity (Schmiegelow et al. 1997, Drolet et al. 1999, Trzcinski et al. 1999, Hobson and Bayne 2000). Changes in species assemblages can occur quickly (Stratford and Stouffer 1999), and may be due to decreased patch size and an increase in edge habitat (Waiters 1998). Greater edge habitat has the potential to increase predation and brood parasitism rates (Hoover et al. 1995, Robinson et al. 1995), and can also result in decreased fitness due to lower pairing (Villard et al. 1993, Van Horn et al. 1995, Roberts and Norment 1999) and fledging success (Roberts and Norment 1999).

Researchers studying fragmentation have not examined its influence on the EPP rate. Rates of EPP are altered by other population dynamic factors including breeding synchrony and density (Westneat and Sherman 1997, Yezerinac et al. 1999, Richardson and Burke 2001). Habitat fragmentation could also alter EPP rates as it alters nearest neighbor distances and population density. Fragmentation decreases foray rates as individuals in fragmented habitat are less likely to cross gaps or enter open habitat (Sieving et al. 1996, Desrochers and Hannon 1997, St. Clair et al. 1998), take longer to travel through fragmented habitat (Be1isle et al. 2001), and return if they foray off territory (Norris and Stutchbury 2001). This can lead to fewer opportunities for intraspecific encounters and fewer extra-pair copulations (EPCs). Further decreases in EPP rates can result from situations in which females control EPCs or primarily foray off territory for EPCs (Mays and Ritchison 2004), because females may be less likely to leave fragmented habitats than males (Norris and Stutchbury 2002).

Least Flycatchers (Empidonax minimus) settle in clusters which are all-purpose territories with contiguous borders surrounded by unused habitat (Tarof et al. 2005). Previous research in Ontario examining males settling in continuous habitat has shown there is a high rate of EPP in clusters (37% of nestlings are extra-pair) with 62% of broods containing at least one extra-pair offspring (Tarof et al. 2005). Both males and females have been seen to foray off territory, possibly in search of EPCs, although females seem to control EPCs by either allowing or denying males the opportunity to copulate (Tarof and Ratcliffe 2000). Fragmentation could thus have a large effect on this species since males could no longer form contiguous territories, and foray opportunities for EPCs may decrease.

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We examined EPP rates among male Least Flycatchers breeding in continuous versus fragmented habitat to investigate whether variation in male realized reproductive success (RRS, total number of descendant young) is influenced by fragmentation. Our objectives were to compare the EPP rate and male RRS between continuous and fragmented habitats. We also examined whether breeding synchrony and density differed between continuous and fragmented habitat as both of these factors are known to affect EPP rates (e.g., Stutchbury and Morton 1995, Westneat et al. 1990).

METHODS

Study Site.--This study was conducted in 2000 and 2001 near the Queen's University Biology Station (QUBS) south of Chaffey's Lock, Ontario, Canada (44[degrees] 34' N, 76[degrees] 19' W). The two sites studied were at Sydenham Lake, ~22 km southwest of QUBS and Lake Opinicon, ~3.6 km southwest of QUBS. The proportion of habitat available for settlement was calculated by dividing the area covered by hardwood forests by the area of the polygon that encompassed the entire cluster. Approximately 71% of the Lake Opinicon site was covered with hardwood forest and suitable for settlement; this site was considered continuous. Only 40% of the Sydenham Lake site supported habitat available for settlement; this site was considered fragmented (Fig. 1). Both study

sites were comprised of the same primary tree species, and had similar amounts of canopy cover within forested areas (Kasumovic 2002).

The Lake Opinicon site was studied in 2000 and the Sydenham Lake site in 2001. Only a single site could be studied each year due to the intense mist netting effort required to sample the majority of birds in a cluster. However, we monitored settlement patterns at both sites each...

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