Date: 9/6/17 6:13 pm
From: Tim Freiday <tim.freiday777...>
Subject: [de-birds] Middle Run Bird Walk 9/5/17 -Results
Hello Fellow DE Birders,

Yesterday was the first Tuesday Morning Bird Walk at Middle Run of the season, and we started strong. 58 species were recorded by 16 observers in about 4 hours of birding. We tallied 9 species of warbler, 10 if you include the Lawrence's backcross that was seen by the participants of the pre-walk and some of the participants of the regular walk.

I had to do some research to figure out what this bird was, as it was the first time almost everybody had ever seen one. I find some great information on vermivora hybrids from ABA and Cornell. These hybrids challenge our concept of a species, as the parent species produce fertile offspring.



The Lawrence's warbler is a rare hybrid between Blue-winged and Golden-winged warbler in which the bird inherits recessive genes from both parents. The Brewster's Warbler, which we saw on the BioBlitz, is the dominant hybrid of the two species. Pure hybrids of the two species are F1 or first generation hybrids.

The Lawrence's backcross we saw however is an F2 or second generation hybrid, in which an F1 Lawrence's Warbler bred with a parent species, most likely a Blue-winged Warbler. The Lawrence's backcross differs from the F1 Lawrence's Warbler by lacking the white above and below the dark triangular mark on the eyes is less pronounced. The F2 Lawrence's backcross basically looks like a Blue-winged Warbler with a dark triangular throat patch.

Other highlights on our walk include a Yellow-bellied Flycatcher which was seen well by all in the remains of the tree of heaven. On the identification of Empidonax flycatchers I came across a great piece from the American Birding Association about using structural features to aid in the identification of empids. You can see the notes I put about the empids IDed in the field in the checklist for the morning.

ABA Empidonax Identification:

A Tennessee Warbler was seen during the pre-walk but not during the walk itself. We did get nice looks at a Bay-breasted warbler during the walk, and a Yellow-breasted Chat popped up for some of the participants. There were a number of American Redstarts and Magnolia Warblers around, as well as some Wood Thrush and a couple Veery. Complete checklist for the day here:

There will be another Tuesday morning bird walk next week and every week until the end of October. These walks are free and open to the public, sponsored by New Castle County Parks and led by Delaware Nature Society staff. Next week there will be an official pre-walk from 7-8 AM as that is when a lot of the action has been. We will then meet with people at the parking lot for the 8 AM walk which continues until 10-11, depending on how birdy it is. September is the best time to bird in my opinion, so get out as much as possible!

Happy birding,
Tim Freiday
Middle Run Project Coordinator

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