Olive-sided flycatcher (Contopus cooperi) COSEWIC assessment and status report: chapter 6

Biology

Little information is available on the breeding ecology and survivorship of the Olive-sided Flycatcher; most current knowledge has been gained from studies in Alaska (Wright 1997) and Oregon (Altman 1999). Information provided here has been primarily summarized from these sources andAltman and Sallabanks (2000).

Reproduction

Olive-sided Flycatchers are monogamous, with nesting pairs generally well-spaced. In Alaska, 16 territories ranged in size from 10.5-26.4 ha, with a mean size of 18.4 ha. In the Sierra Nevada, larger territories are reported (up to 45 ha). Territory borders in Alaska were frequently associated with drainage features, rather than having a common territorial border with another territory.

Pair bonds are formed when females arrive on the breeding grounds. There are two records of the same pair together in consecutive years, so inter-seasonal pair bonds may be possible. Females choose the nest site, construct the nest from twigs and rootlets, and lay one egg per day for an average clutch size of 3 (range 2-5). This is a rather low clutch size for a songbird; the Olive-sided Flycatcher and its congeners apparently have the lowest reproductive rate of all passerine genera in North America (Altman and Sallabanks 2000).

Incubation is performed solely by the female, with males providing food to the female during this period. The incubation period ranges from 15-19 days. The female broods the nestlings for the first week, with both parents feeding the young. The nestling period lasts from 17-23 days, and fledglings depend on parents for food for up to one week post-fledging. If an early season nesting attempt fails, the pair may attempt to re-nest; up to 3 nesting attempts have been reported. However, there is no evidence of re-nesting after successfully rearing one brood.

Olive-sided Flycatchers apparently breed on their first return to the breeding grounds (i.e. in their second year). The proportion of birds breeding in any given year is unknown, but the presence of unpaired males may indicate that females may not breed every year.

There is no information on hatchling or fledgling success. It is therefore not possible to measure fecundity for this species. However, there is some information on nest success. In central Alaska, 8 of 13 pairs (62%) fledged young, and in northwest Oregon 82 of 126 pairs (65%) fledged young. In Montana, Robertson and Hutton (2007) found 61% nest success in naturally burned habitats but only 30% success in harvested habitats.

Survival

Lifespan and survivorship of adults is unknown. Two birds that survived at least 7 years after first capture have been recovered during banding studies (one in California and one in Ontario) (Altman and Sallabanks 2000).

Dispersal/migration

Olive-sided Flycatchers arrive in Canada between April and June, but predominantly in mid- to late May. They begin fall migration in late July to early August. Olive-sided Flycatchers travel over 8,000 km between their wintering and breeding grounds, with migration and wintering periods accounting for over half the annual cycle. The availability of resources, changes to habitat and inclement weather can all reduce survivorship of migrants during winter and migration periods (Moore et al. 1995). In addition, Neotropical migrants generally do not deposit enough fat to travel non-stop between the breeding and wintering grounds, and so must make frequent stops to feed. Migration pathways and wintering locations of Canadian breeding populations are unknown as Olive-sided Flycatchers are rarely recorded in mist nets at migration monitoring stations.

Olive-sided Flycatchers may have strong breeding site fidelity, although data are scarce. From banding recapture data there is also evidence to indicate wintering ground site fidelity (Altman and Sallabanks 2000).

Interspecific interactions

There have been no reported predation attempts on Olive-sided Flycatchers. However, Olive-sided Flycatcher remains have been found at a Peregrine Falcon (Falco peregrinus) eyrie in Alaska (Cade et al. 1968). The sallying foraging behaviuor of adults is expected to make them easy targets for raptors. Squirrels and jays are suspected to be important nest predators, although there are no reports for Canada. In Oregon, a Gray Jay (Perisoreus canadensis) was observed taking 2 Olive-sided Flycatcher eggs (Altman and Sallabanks 2000). Both sexes aggressively defend the nest area, attacking both potential predators and human intruders. Robertson and Hutto (2007) suspect that increased predation was the primary cause for significantly reduced breeding success in harvested habitats versus those in naturally burned areas; red squirrels (Tamiasciurus hudsonicus), Gray Jays and Common Ravens (Corvus corax) were all more than twice as common on their harvested plots.

Behaviour/Adaptability

The Olive-sided Flycatcher is a passive sit-and-wait predator that remains perched until flying insects are sighted. They then actively pursue prey until capture and then return to the perch. Hymenopterans (bees, wasps, ants, etc.) form the largest percentage of the diet in the breeding season, accounting for up to 83% of stomach contents in 63 stomachs examined (Beal 1912, cited in Altman and Sallabanks 2000). Hymenoptera also formed a large component of the diet in the wintering grounds in Costa Rica (Sherry 1984). Meehan and George (2003) found that beetle remains formed a large part of Olive-sided Flycatcher feces in California.

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