Olive-sided Flycatchers breed throughout much of North America. Some of the highest densities have been reported in coniferous forests of California (Robbins et al 1986). But, populations in the western region are exhibiting sharp declines. However, densities appear to respond positively to management techniques including timber harvest and fire.
Breeding Bird Survey data indicate Olive-sided Flycatchers are declining throughout their range (Robbins et al 1986, Peterjohn et al 1996). Apparently this process is becoming more rapid (Peterjohn and Sauer 1994). Peterjohn et al (1996) reported an average decline of 4.1% per year. These trends are statistically more significant in western North America (DeSante and George 1994).
Robbins et al (1986) analysis of BBS data found that while Olive-sided Flycatchers were declining in general, populations in the Sierra, Trinity and Los Angeles ranges remained stable. A study from San Benito mountain region in western Fresno and San Benito counties also reports an increase in Olive-sided Flycatcher abundance over approximately 50 years. A comparison of several days of observation in 1983-84 to field notes from 1936 and 1944 results in an estimate of increased Olive-sided Flycatcher abundance. The authors suggest the difference is due to climate change, although the forest had undergone significant changes (fire suppression and decreased tree removal) in that period of time (Johnson and Cicero 1985). Raphael et al (1988) propose that Olive-sided Flycatchers reached high population levels due to timber management. They suggest that the immediate response of birds to clearcutting is increased population density. However, post-harvest habitats quickly become dense and unsuitable until the forest reaches a multi-layered stage (See Habitat Use).
Marshall (1988) compared presence of birds in a Sequoia forest to his own field notes 50 years prior. He reported a lack of Olive-sided Flycatchers in locations occupied 50 years prior. He attributed this difference to problems in the wintering habitat due to a lack of obvious vegetational changes.
A nearctic-neotropical migrant the Olive-sided Flycatcher winters in mountainous areas throughout South America. First migrants arrive in southern California in mid-April and in northern California in early May. Some transients are still moving through the state in June and rarely birds have been known to winter in southern California (Gaines 1990).
Olive-sided Flycatchers are sustained nearly entirely on flying insects. Otvos and Stark (1985) found birds in California to be feeding primarily on Coleoptera (39.8% of their diet). The largest group represented among the beetles were the Scolytidae (bark beetles) at 50% (or 20% of the total diet). Beal (1912) found Olive-sided Flycatchers to be feeding largely on Hymenoptera (82.6%).
The species is apparently monogamous. Usually three eggs are laid in an open cup nest placed far out on a limb at varying heights. June is the peak of egg laying with nests being noted as early as mid-May and as late as July. Incubation lasts 14 to 17 days. Nestlings are cared for by both parents and typically fledge in 15-19 days (Gaines 1990).
Reported to frequently nest near water, but no other specific requirements have been found (Gaines 1990).
Trends regarding Olive-sided Flycatcher habitat use include association with old growth forests, post-fire habitats, and several timber management techniques. Multiple authors have noted the bird’s affinity for high, open perches. Many of the habitats in which they are found have abundant perches.
Carey et al (1991) report an increased abundance with increasing stand age in the Oregon coast range. Importantly, the youngest stands surveyed in this study were 40-72 years old and the old growth had a structurally diverse canopy layer.
In the Rocky Mountains, Hutto (1995) found that Olive-sided Flycatchers responded positively immediately after a high intensity fire. After conducting point counts for two years following the burns Hutto concluded that Olive-sided Flycatchers in the northern Rockys are relatively restricted to post-fire habitat.
Hagar (1960) was one of the first to note the Olive-sided Flycatchers increased abundance after harvesting. He records the bird as common in "brush cutover" stands. Also working in northwestern California, Raphael et al (1988) found similar densities in sapling stages as in mature stands. Decreased abundances were noted in the sawtimber stage. Finally, McGarigal and McComb (1995) showed that Olive-sided Flycatchers were affected by habitat configuration. They were more common in areas of fragmentation as compared to the average condition in their study area. They suggest an association between Olive-sided Flycatchers and the juxtaposition of late-seral stage forest and early-seral staged, open canopies.
The common condition throughout these studies is an increase in Olive-sided Flycatchers as canopy cover decreases. Several methods appear to cause an immediate increase in population levels including clearcuts, stand replacement fires and selective logging.
Response to Management
The Olive-sided Flycatcher’s association with decreased canopy cover allows it to respond positively to timber management. As mentioned previously, Hagar (1960) noted an increased abundance after clearcutting. Evans and Finch (1993) noted a similar response in Idaho. Medin and Booth (1989) and Medin (1985) report increased densities after selective logging removed large trees. These removal operations left mature trees in stream buffers and unit buffers. Finally, in a mixed-coniferous forest study in Arizona Olive-sided Flycatchers were more abundant on logged plots with residual aspen and snags than on unlogged plots (Franzreb and Ohmart 1978).
In the above analysis relating bird densities to seral stage Raphael et al (1988) suggest Olive-sided Flycatchers may be severely affected by timber practices. Despite the immediate benefits of clearcuts the primary affect of even aged timber management is an increasing proportion of the environment in the sawtimber stage. As a result of the large area of unsuitable habitat they estimate that Olive-sided Flycatchers may decline by as much as 37%.
Using fire as a management tool also benefits the Olive-sided Flycatcher. Raphael et al (1987) subjected stands to low-intensity fires that resulted in decreased tree density in the Sierra Nevada. This more open habitat supported a slightly higher density of Olive-sided Flycatchers than unburned stands.
Timber management may significantly benefit Olive-sided Flycatcher populations. First, configuration is important. Small clearcuts adjacent to mature forests would be ideal. Retention of snags, stream buffers and small clumps of residual trees is preferred. Second, within sawtimber and mature aged stands selective cutting should be practiced to open the canopy.
Finally, management should incorporate fire. Frequent low intensity burns would decrease canopy density. Infrequent, high intensity burns seem to be strongly attractive to Olive-sided Flycatchers. Allowing fires to burn and refraining from salvage logging is suggested.
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