Saturday, January 8, 2022

Pondering Sparrow Distribution

 


Looking out into my backyard on the south side of town, I peer through binoculars to quickly count the dozens of sparrows that dropped down onto the snow to grab the scattered sunflower hearts, before a flitting shadow sent them all fluttering into a neighbor's tree. Before they went, I noted two Eurasian Tree Sparrows among all the House Sparrows, their round black cheek patch making them easy to pick out.

They are uncommon visitors to the yard, usually only stopping by when there are a few inches of snow on the ground. I often, however, spot a few of them along the wooded northern end of the Greenway trail (and occasionally south by the wetlands as well). I've also seen them near the McCollister bridge and vicinity, a little to the west. I wonder, how widespread are these little sparrows throughout the city?

House Sparrow
Eurasian Tree Sparrow
I turn to eBird, with its extensive data about bird observations, and compare the local maps for Eurasian Tree Sparrows with those of House Sparrows, showing (as expected) the House Sparrows are extremely common throughout town. Eurasian Tree Sparrows, though not rare, had more sporadic spottings, with a cluster around TTRA.  

Eurasian Tree Sparrows are a fairly recent settler in our area; most of the records on eBird are from the past ten years, with only two sightings recording between 2001 and 2011 (although I am unsure how comprehensive data submitted to eBird for that timeframe is, compared to more recent observations). Perhaps they are just getting started in Iowa City, as the species continues its slow expansion from St. Louis, where just a dozen or so birds were released in 1870. 

Will they continue their expansion through town, with more numbers appearing along the brushy margins near the river and other waterways, where they can find shelter and cavities for nesting away from their more urban, and more aggressive, cousins? Or have they already established themselves in those areas that are suitable, to remain in smaller numbers than the House Sparrows?

Either way, I feel fortunate to have these thus-far well-mannered sparrows as neighbors in the South District, and will watch their movements with interest.