Philadelphia Vireo (Vireo philadelphicus) Skye Christopher G. Haas & Ryne D. Rutherford
Magee Marsh Wildlife Area, Ottawa Co., OH 5/14/2009 © Darlene Friedman
(Click to view a comparison of Atlas I to II)
One of the most poorly understood breeding species was “not certainly known to nest within our limits, but it is not improbable that it may do species in Michigan, the Philadelphia Vireo is so in the northern part of the State.” Breeding found in deciduous forests in the central and was not confirmed in Michigan until 1966, western Upper Peninsula. Their breeding range when a fledgling bird was found in Charlevoix extends from the Canadian Maritime Provinces County, and a second confirmation was gained west through Alberta and eastern British in 1970 with the collection of a fledgling at Columbia, barely reaching south into the Grand Sable Falls, Alger County (Binford northern Great Lakes states and New England 1991). Owing to the dearth of subsequent (Moskoff and Robinson 1996). A subtle and observations, atlas observers during MBBA I likely under-reported bird, its voice is incredibly were surprised to record the species in 48 similar to the abundant Red-eyed Vireo; even townships spread over 15 counties, including the most experienced birders are wise to hesitate three in the NLP. Shortly after the completion to call this species without getting a visual of MBBA I, Dr. Laurence Binford discovered confirmation of the bird. This emulation the first nest for Michigan in Hubbell, Houghton represents an excellent example of adaptive County on 27 June 1990 (Binford et. al. 1991). interspecific territoriality: the Philadelphia The distribution of Philadelphia Vireos in Vireo can frequently defend territory from the Michigan seems to have contracted between larger Red-eyed without risking physical atlases. MBBA II located only one bird in the confrontation. (Rice 1978). NLP, a possible breeder from Wilderness State
Park in Emmet County, while formerly Distribution occupied areas of the eastern and south-central Authors have been offering the same assessment UP revealed few to no individuals. Consistent concerning the status of Philadelphia Vireos in with MBBA I, Philadelphia Vireos were again Michigan for nearly a hundred years: an found along the base of the Keweenaw uncommon species, but probably under-reported Peninsula, particularly in central and southern as a breeder in the northern reaches of the state. Houghton County, and in northwestern Barrows (1912) wrote “This is one of our rarest Ontonagon County, but expanded into extreme vireos, though probably more numerous than western Gogebic County as well. Among UP our observations would show” and that the
© 2011 Kalamazoo Nature Center Philadelphia Vireo (Vireo philadelphicus) Skye Christopher G. Haas & Ryne D. Rutherford areas of apparent expansion – Isle Royale, found within 10 km of Lake Superior and western Gogebic County and the Central frequently in hilly undisturbed regions. Another Superior region between Marquette and Pictured confirmed breeding site was on the outskirts of Rocks National Lakeshore – some of these gains the City of Marquette in a mature maple forest may be an artifact of better atlas coverage by with scattered mature aspen and yellow birch. experienced observers during MBBA II. In At all three sites, the habitat was bisected by a total, Michigan observations declined from dirt or small paved road. Still, many sites in 7.4% of all UP townships in MBBA I to 5.3% in Ontonagon, Houghton, Marquette and Alger MBBA II. counties were primarily aspen, birch or ash forest (S. Haas and R. Rutherford pers. obs.). Breeding Biology Nests are typically placed high, and there is only As with a few other boreal region species at the one brood per year (Moskoff et al. 1996). southern edge of their breeding ranges (e.g. Connecticut Warbler, Boreal Chickadee), the Abundance and Population Trends presence of seemingly suitable habitat did not Partners in Flight have an optimistic estimate of often lead to the discovery of Philadelphia 1,600 Philadelphia Vireos breeding in Michigan Vireos on territory. The species seems to have a (PIF 2007). While this number seems high preference for softwoods like aspen and birch relative to Atlas findings, it is well recognized (particularly big-tooth aspen), usually in second- that this is a cryptic species and many may go growth to early mature age classes. Both undetected during the breeding season. published literature and MBBA II observers have noted a tendency to find nesting sites near Second atlas efforts in Ontario and New York small openings in the forest, typically a dirt two- both noted an increase in the number of track, paved road, select logging, creek valley or Philadelphia Vireos compared to their downfalls (Moskoff et al. 1996, Binford 2006, respective first atlases (James 2007, McGowan S. Haas and R. Rutherford pers. obs). 2008). BBS data show a slight decrease in the number of birds found on U.S. routes, and a In Michigan, big-toothed aspen groves are often slight increase on Canadian routes; neither trend selected by Philadelphia Vireos for breeding was considered significant due to the small (Binford 2006). However, there were some sites sample size (Moskoff et al. 1996). The where Philadelphia Vireos were found in Wisconsin atlas expanded the distribution of this MBBA II that were dominated by maples rather species’ range with the discovery of a small than aspens. In two locations where breeding population found on the Bayfield Peninsula was confirmed in MBBA II, (Gogebic and Alger (Frank 2006). Geographically close to the counties), mature sugar maple was the primary western UP, the Bayfield peninsula shares many tree present. At the Alger site on Grand Island ecological and habitat-management similarities there was a notable understory of sapling with Gogebic and Ontonagon Counties, and maples and ironwood (Rutherford pers. obs.). may be a natural extension of that population. Rutherford also noted that many areas where Philadelphia Vireos were located were Conservation Needs regenerated forest from select cuttings, with the Establishing specific conservation parameters Gogebic confirmed breeding site having only for such an irregularly occurring species can be been logged in the previous few years, though complex, and likely any benefits to be had for maintaining a continual coverage of forest Philadelphia Vireo would be shared by other canopy. In many cases, in Gogebic, Ontonagon species using a shared habitat. As with most and Alger Counties, Philadelphia Vireos were forest-dwelling insectivores, controlled logging
© 2011 Kalamazoo Nature Center Philadelphia Vireo (Vireo philadelphicus) Skye Christopher G. Haas & Ryne D. Rutherford practices are required to guard against negative Breeding Birds in New York State. Cornell fragmentation effects such as nest parasitism by University Press, Ithaca, NY. Brown-headed Cowbirds. Rice (1978) found Moskoff, W., and S.K. Robinson. 1996. that yellow birch was strongly preferred by leaf- Philadelphia Vireo (Vireo philadelphicus). gleaning songbirds, including the Philadelphia In The Birds of North America, No. 214 (A. Vireo, even when it was a minor component in Poole and F. Gill, eds.). The Birds of North beech-sugar maple forest; consequently it can be America, Inc., Philadelphia, PA. assumed that selective logging of yellow birch Partners in Flight (PIF). 2007. PIF Landbird may have a strong negative effect on the Population Estimates Database [web species. Similarly, the early harvest of aspen in application]. Version 2004. Rocky a 15-year cycle may not provide enough time to Mountain Bird Observatory. allow for forest maturation to be useful to
© 2011 Kalamazoo Nature Center