Evening Grosbeak (Coccothraustes vespertinus) Zach Gayk
Iron Co., MI 6/14/2009 © Elizabeth Rogers (Click to view a comparison of Atlas I to II)
An irruptive denizen of boreal and montane probably present as a scattered breeder. Currently, it is a widespread but irruptive conifer forests across North America, this thick- resident, with variable seasonal and annual billed finch breeds from southern detectability. In MBBA I, the Evening Newfoundland to northern British Columbia, Grosbeak was recorded as at least possibly extending south into the U.S. along the Rocky breeding in 57.5% of UP townships and 15.4% Mountain chain in the west and along the of northern LP townships. In MBBA II, it was Canadian border states in the east. In Michigan, recorded as at least possibly breeding in 36.8 % the Evening Grosbeak breeds in the UP and of UP townships and 4.54 % of northern LP locally in the northern LP. In winter it may townships. This decline equates to a 20.6% and range southward into the southern LP and across 10.8 % decrease in townships in the UP, and the central U.S. Evening Grosbeak is the only northern LP, respectively. Michigan species in which the type specimen was distribution in MBBA II remains similar to that collected in Michigan. Henry Schoolcraft in MBBA I at the county scale. Wide-scale collected the first known Evening Grosbeak distribution remains the same, but individual near Sault Ste. Marie, Michigan in April 1823 breeding birds are becoming more localized (Barrows 1912). It also appears that this species within that region. In the UP, there appears to was localized and rare east of the Mississippi have been a decrease in township detections in River prior to the 1850s, when a massive western Houghton and Ontonagon Counties eastward range expansion from the west from MBBA I to MBBA II and an increase in occurred, with the Atlantic states being reached township detections in Marquette County. in the 1930’s (Gillihan and Byers 2001). Menominee and south-central Delta Counties Currently it appears Evening Grosbeaks may be had minimal breeding evidence in both atlases. undergoing a significant range contraction Notable also is the northward contraction of (Butcher and Niven 2007). township detections in the northern LP between
MBBA I and MBBA II. In MBBA I, a possible Distribution record from Lake County and a confirmation Historical distribution in Michigan prior to the from Arenac County comprised the southern presumed eastward range expansion is largely terminus of the breeding range; in MBBA II, unknown, but the Evening Grosbeak was
© 2011 Kalamazoo Nature Center Evening Grosbeak (Coccothraustes vespertinus) Zach Gayk northern Iosco and Ogemaw Counties had the rather a decline in range as a function of a southernmost breeding evidence found. presumed decline in abundance.
In the UP, breeding habitat is comprised of Bonter and Harvey (2008) analyzed Project mesic mixed forests and open boreal forests of Feederwatch data from the U.S. and Canada spruce, balsam fir, and aspen (pers. obs.). between 1988 and 2006 and indicated a massive Payne (1983), citing N.E. Sloan, observed that contraction in both range and abundance for Evening Grosbeak was found in deciduous Evening Grosbeak during those years. For the forests adjacent to jack pines, which were used western UP, mean abundance at feeders during spruce budworm outbreaks. In Quebec, decreased from 8-16 individuals from 1989- Evening Grosbeak breeds in second-growth and 1994 to less than one individual per feeder from mature conifer woodland of balsam fir and 2001-2006 (Bonter and Harvey, 2008). spruce, with deciduous woodland secondarily Similarly, much of the northern LP had a mean occupied (Vincent 1996). abundance of four to eight individuals per feeder from 1989-1994, while in the years 2001- Breeding Biology 2006, the mean abundance has decreased to less In the eastern U.S., pair bond formation than one individual per feeder (Bonter and typically occurs in May (Shaub 1954), with nest Harvey, 2008). construction occurring from mid-May through mid-June (Gillihan and Byers 2001). Christy Several explanations have been proposed for the (1930) reported a nest under construction in widespread decrease in abundance of Evening eastern Baraga County on 19 June. Loose Grosbeak in Michigan and the Great Lakes platform nests of twigs lined with mosses are region. While Bolgiano (2004) suggested that typically placed at 5-35 meters, or 60-80 % of this decline is tied to significant decreases in the tree’s height (Bekoff et al. 1989); white pine abundance of spruce budworms, it seems and sugar maple have been used as nest trees in uncertain how important a role budworms play Michigan (Christy 1930). Little information on in the summer diet of Evening Grosbeak. fledging dates in Michigan exists, but an Further research is needed tracking frequency of unattended pre-juvenile in Houghton County on budworm consumption to determine that results 17 June and a juvenile being fed on 14 July in as obtained by Mitchell (1952) [one Maine Houghton County give some indication (Binford specimen from area of budworm outbreak with 2006). stomach contents comprised of 80 % budworm larvae and pupae] are not simply the result of Abundance and Population Trends exploitative feeding on a nearby resource rather (Click to view trends from the BBS) than adaptation. Deforestation of Canadian PIF Landbird Population Estimates Database boreal forests, where more than one million (2007) lists the Michigan Evening Grosbeak hectares were cut in 2006 alone (Bonter and population to be 50,000 individuals of a Harvey 2008), may be influencing Michigan 5,700,000 worldwide population, or 0.9 %. In declines due to decreased connectivity between MBBA I, there were 351 and 91 total township the two populations. detections in the UP and NLP, respectively. In MBBA II, there were 229 and 27 total township Conservation Needs detections in the UP and NLP, respectively. Evening Grosbeak may be an immediate Thus, MBBA data do not show a decline in conservation concern in Michigan; the Evening Grosbeak abundance directly, but widescale range reduction that has occurred since at least the late 1980s may also be a
© 2011 Kalamazoo Nature Center Evening Grosbeak (Coccothraustes vespertinus) Zach Gayk natural process mirroring the eastward Christy, B.H. 1930. The Evening Grosbeak expansion of Evening Grosbeak during the 19th nesting in northern Michigan. Wilson century. More research must be done to better Bulletin 32: 217-218. determine the causes of the decline in this Gillihan, S.W., and B. Byers. 2001. Evening enigmatic species. Large scale habitat alteration Grosbeak (Coccothraustes vespertinus). In (deforestation) in the boreal forests, and the The Birds of North America, No. 599 (A. resultant spruce budworm decline, along with Poole and F. Gill eds.). The Birds of North increased avian disease (such as conjunctivitis America, Inc., Philadelphia, PA. caused by Mycoplasma gallisepticum) (Bonter Mitchell, R. T. 1952. Consumption of spruce and Harvey 2008), have all been proposed as budworms by birds in a Maine spruce-fir factors contributing to Evening Grosbeak forest. Journal of Forestry 50: 387-389. decline. Currently the American Bird Partners in Flight (PIF). 2007. PIF Landbird Conservancy and National Audubon Society do Population Estimates Database [web not recognize Evening Grosbeak as a watchlist application]. Version 2004. Rocky species; MBBA II authors would propose its Mountain Bird Observatory.
© 2011 Kalamazoo Nature Center