We examined the effect of habitat fragmentation, as well as breeding density and synchrony, on realized reproductive success of male Least Flycatchers (Empidonax minimus). Both breeding density and synchrony were similar in both continuous (6.75 males/ha, 3.40; respectively) and fragmented (4.04 males/ha, 2.11; respectively) habitats, and no morphological or territorial variables differed between males in either habitat. The number of nests containing extra-pair offspring was lower in fragmented habitat (11%) compared to the continuous habitat (50%). Males in fragmented habitat attracted secondary mates significantly more often than males in continuous habitat (44%, 0%; respectively) resulting in similar estimates of realized reproductive success in either habitat. Although habitat fragmentation does not appear to affect realized reproductive success of male Least Flycatchers, we suggest that males of this species demonstrate a facultative shift in reproductive tactics.
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° 34' N, 76° 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 year. Clusters of Least Flycatchers also settled in the Lake Opinicon site in 1999 and 2001, and in Sydenham in 1999 and 2000; no individuals settled at the Lake Opinicon site and only three individuals settled at the Sydenham site in 2002 (M. M. Kasumovic, unpubl. data.). Only 4% (4/98) of individuals banded as adults in a previous 4-year study returned to the QUBS area (Tarof 2001), suggesting the return rate is low.
Sampling Methods.—Study sites were surveyed daily, and arrival and pairing dates of all males and females were recorded. Least Flycatchers are an upper canopy species in eastern Ontario (Tarof et al. 2005), and we used mist nets attached to 7-m telescopingpoles (Model 2324, Mr. Longarm, Greenwood, MO, USA) raised into the canopy to capture individuals. Approximately 200 netting hours were spent at each of the two study sites, using a combination of passive netting near nests and a playback lure of conspecific song from a speaker placed below a model of a male Least Flycatcher. Birds were banded with a Canadian Wildlife Service numbered aluminum band and a single plastic colored leg band. All banded individuals were captured within 3 days of arrival and before egg laying. We measured the tarsus length of each individual. Gender of individuals was initially ascertained from tarsus length (Pyle 1997), which was later confirmed by behavior (Tarof and Ratcliffe 2000). We collected 5–30 μL of blood from the brachial vein of adults. Nestlings that survived to day 7 were banded with a single aluminum band and 5–15 μL of blood was collected from the tarsal vein. All blood samples were stored in Queen’s Lysis buffer (Seutin et al. 1991).