Tuesday, February 5, 2019

Eurasian Tree Sparrow: historical report

NOTE: In anticipation of publishing a new Dearborn bird checklist, I am posting information on some of the city's more interesting sightings. 


On 21 October 1999, a Eurasian Tree Sparrow (Passer montanus) was reported at a residential feeder in west Dearborn, about a block from Snow Woods near Snow Avenue and Rotunda. The bird was seen over several days, but due to an email glitch I did not get the original report until about a week had passed. The observers were well known to me, and frequent participants in Christmas Bird Counts and breeding bird surveys in Michigan. Here is their original description, written the first day they saw this bird:
At 8 AM this morning, my wife and I observed a different sort of sparrow for about 5 minutes off and on at our feeder. The feeder is about 7 feet from our kitchen window so we had lots of good hard looks at it. There is no doubt in our mind that it is a a Eurasian Tree Sparrow after consulting Petersons Field Guide ( page 263), Golden Field Guide Birds of North America (page 279) and Audubon Master Guide to Birding Book 3 (page 351).  The bird had a black patch on the ear covert as well as around the eye, a small black chin patch (smaller than the regular house sparrow), rich brown crown, faint white ring around the collar, was slimmer than the house sparrow and immediately left the feeder whenever the regular sparrows came in. It was more fidgity than the other sparrows--quite nervous. 
Eurasian Tree Sparrow in Europe. From a photo by Jan Rose, used under
a Creative Commons license.
Prior to the 1970s or so, a report of a Eurasian Tree Sparrow would be highly suspect. It is not native to North America, as the name indicates, but since 1870 a population has been established near St. Louis, MO. Twenty birds were imported from Germany and released there, and for decades did not expand much from this area. By the 1940s, the colonization extended only about 80 miles from their original point of establishment, mostly in a north and northwest direction. A more rapid expansion began in the 1960s, with birds showing up in northern Illinois and southern Wisconsin. In the 1990s, multiple reports came from Wisconsin, Minnesota, Indiana, Iowa, and Ontario.

Good data on early records of introduced species can be difficult to dig up because these species are dismissed as "uncountable" by birders, and it's the birding community that usually documents these occurances. At some point, reports begin to get archived, and Michigan's first "official" record of Eurasian Tree Sparrow occurred in Cass Co. in 2005. Since then, there have been around 30 or more Michigan reports, including those of multiple birds.

The flurry of reports from Michigan beginning in 2005 and mostly in the Upper Peninsula coincides with a surge of reports of other European birds in this region. Between 2004-2006, Common Chaffinch, Eurasian Siskin, and European Greenfinch were all reported from the U.P. These birds were likely the result of releases from the same source that founded the population of European Goldfinches in the Chicago area. The same importer thought to be responsible for these birds also imported and sold Eurasian Tree Sparrows. From what I've been able to ascertain, the releases began sometime after 2000, likely around 2002. Thus, I would not be surprised if Michigan records after 2002 or so were derived at least in part from the Chicago-area releases. Earlier records (if there are any others besides the Dearborn bird) in Michigan and elsewhere would be attributable to expansion of the core Illinois/Missouri population. (You can read much more about European birds in the Midwest on my page regarding this research here.)

Back to Deaborn. Living in an urban area, the observers of the Dearborn bird were, of course, extremely familiar with the House Sparrows that were ubiquitous at their feeders. In another rare bird report they completed, they noted the bird at the feeder was so close to their kitchen window that they couldn't use binoculars, so it was seen well. Their description seems wholly adequate, including their observations (also shared with me from subsequent sightings) that the Eurasian Tree Sparrow seemed skittish around House Sparrows -- a number of researchers have indicated that Eurasian Tree Sparrows do not compete well and are subordinate to House Sparrows. These facts, coupled with the expansion into the Upper Midwest in the 1990s, leads me to conclude that this is a reasonable, valid record for Dearborn.

A lot of interesting work has been done comparing the North American population of Eurasian Tree Sparrows with the German ancestral birds. Here are just a few papers on the history of the North American birds as well as their evolution and differentiation:

Barlow, J.C. 1973. Status of the North American population of.the European tree sparrow. Ornithol Monogr 14:10–23.

Barlow, J.C., and A.L. Lang. 1997. Cultural evolution in the Eurasian Tree Sparrow: Divergence between introduced and ancestral populations. The Condor: 99: 413-423.

Burnett, J.L., Roberts, C.P., C.R. Allen, M.B. Brown, and M.P. Moulton. 2017. Range expansion by Passer montanus in North America. Biol Invasions (2017) 19: 5-9.

Graham, J., C. Harnevich, N. Young, G. Newman, and G. Stohlgren. 2011. How will climate change affect the potential distribution of Eurasian tree sparrows Passer montanus in North America? Curr Zool 57:648–654.

St. Louis, V. L. and J. C. Barlow. 1988. Genetic differentiation among ancestral and introduced populations of the Eurasian Tree Sparrow (Passer montanus). Evolution 42:266-276. 

St. Louis, V. L. and J. C. Barlow. 1991. Morphometric analyses of introduced and ancestral populations of the Eurasian Tree Sparrow. Wilson Bull. 103:1-12.

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