Eurasian Tree Sparrows; A St. Louis Specialty

St. Louis is home to an Old World Sparrow that normally resides in Europe, the UK as well as China, and Japan. I'm talking about the Eurasian Tree Sparrow (Passer montanus). On April 25^th 1870, Carl Daenzer and a Mr. Kleinschmidt released 20 Eurasian Tree Sparrows and a variety of other non-native finches in Lafayette Park.  German immigrants largely comprised this part of St. Louis and it was popular during this time period to release European birds in the hopes the introduced birds would control the existing insect population and give the immigrants a little taste of home in their new city. The Eurasian Tree Sparrows were the only birds that survived the release and quickly established a breeding population concentrated near the breweries in south St. Louis. 

It is speculated that the initial success of the Eurasian Tree Sparrow was due to the absence of their aggressive cousin the House Sparrow, which did not arrive in St. Louis until 1878. Once the House Sparrow reached St. Louis, the Eurasian Tree Sparrow population boom slowed but the species extended their range to the Illinois cities of East St. Louis, Alton, Grafton and Belleville, all within about 20 miles of their original point of release.

Today small colonies can be found in the City of St. Louis, Ladue, North St. Louis, Florissant, and east St. Charles County. There are now Eurasian Tree Sparrow colonies in Iowa as well. The first sighting of a pair of Eurasian Tree Sparrows was at West Branch in Cedar County Iowa in March 1987. There were no records for 2 more years, and then 10 birds were found in Des Moines County in December 1989.  A pair of Sparrows nesting was confirmed in Burlington in 1993. The Eurasian Tree Sparrow currently has breeding populations in Lee, Des Moines, Louisa and Muscatine counties

Adult Eurasian Tree Sparrow

A several years ago, I assisted UMSL on a study of Eurasian Tree Sparrows and their cousins the House Sparrows. Their findings suggested that Eurasian Tree Sparrows are homebodies and rarely migrate more than a mile from where they hatched. This could explain why their population has not spread across North America in the same manner as House Sparrows and European Starlings. But there are always the intrepid explorers among the colonies who do wander outside their point of origin and it appears they are following the path of the Mississippi River.

 Eurasian Tree Sparrows are social birds that prefer open fields with shrubby vegetation, especially agricultural areas. These ground feeding birds primarily live on a diet of weed, corn, millet, wheat and sunflower seeds, grass seed and seed shoots but feed their offspring a diet of insects and arachnids during the spring and summer months.

Breeding season begins in April for the Eurasian Tree Sparrow and ends in July (Baicich and Harrison 1997). These birds are cavity nesters, using tree holes, nest boxes or other man-made structures to build their nests.

These birds create an orb-shaped nest with the outer layer composed of coarse grass material and the inner portion lined with down and finer vegetative matter. Eurasian Tree Sparrows can have up to 4 broods per year, though 2-3 broods is the average. Each clutch consists of 1-8 oval eggs (but the average is closer to 4-5 eggs) and incubation lasts 11-14 days. The young fledge around 12-14 days.
 

Eurasian Tree Sparrow chick I banded last summer.

The House Sparrow (Passer domesticus), is an aggressive nest competitor with the Eurasian Tree Sparrow and will displace the latter species from a given habitat. Though both birds are able to adapt to many habitats, the House Sparrow appears to prefer urban areas while the Eurasian Tree Sparrow will occupy more rural, agricultural areas.  However, the Tree Sparrow will move into parks and suburban areas when pushed out of their preferred habitat by their House Sparrow cousins.           

I do know from personal experience that Eurasian Tree Sparrows do visit bird feeders and inhabit backyard nest boxes. Be on the lookout for that little sparrow with the black dot on its cheek.