Introduction
The Golden-winged Warbler (GWWA) has experienced one of the steepest declines of any North American songbird in recent history (Cornell University). While the causes of the decline for many bird species can be attributed to pesticides, climate change, loss of habitat to agriculture and urbanization, perhaps the most obvious cause of the GWWA decline to the casual observer is the encroachment of the Blue-winged Warbler (BWWA) into it's breeding territory.
Hastings County is situated in a unique geographical position to observe these two species in their overlapping breeding habitat. Both species choose to nest in similar habitat, that of secondary growth of low bushes and grasses with a few taller trees for singing perches, near to forest where they will raise their young.
The two species are known to interbreed where territory overlaps, producing two main types of hybrid's known as Brewster's Warbler and Lawrence's Warbler. Both types show characteristics of both GWWA and BWWA and can sing either the GWWA or the BWWA song, or a clumsy mixture of both. Some hybrid's show a variety of characteristics but cannot always be assigned to either name. The continued interbreeding of these two species lessens the number of pure GWWA offspring, therefore causing an overall decrease in population.
The Golden-winged Warbler is well loved. So much so that it has it's own fan club, The Golden-winged Warbler Working Group - http://www.gwwa.org/
Area of Study
The GWWA territory probably begins roughly 20-30km north of the Bay of Quinte and spreads northward into the Canadian Shield.
“The southern edge of the Canadian Shield that extends along a line from Brockville west to Godfrey and northwest to Madoc provides ideal habitat for this species .” (Ron D. Weir).
I made a series of trips to the southern townships of Hastings County, south of HWY #7: Stirling-Rawdon, Centre Hastings, Tweed, Marmora and Lake, and Tyendinaga.
Species Accounts
(*All of the singing males I was able to see were coming from the correct species, but I did not see all the songsters, and some of these may have been hybrids.)
Notable were the accounts of 4 GWWA colonies. Each of the 4 colonies contained 3-4 singing GWWA males, and in 3 of those 4 colonies I saw a BWWA male singing.
One colony near the community of Read in Tyendinaga Township had 5 different males singing; 3 GWWA, 1 BWWA and a hybrid Brewster's.
In the single colony of GWWA where no BWWA's nor hybrids were seen, one of the GWWA songs may have been a Hybrid singing.
In addition to the colonies, I also encountered single males of both species singing throughout Hastings County, at a ratio of 3 GWWA seen : 5 GWWA heard : 2 BWWA seen
Summary of Species Accounts by Township
The exact locations of my sightings, with photos attached, and the sightings of other ebirders, can be found by going online to www.ebird.org. Click on “Explore Data”, then go to “Range Maps”. Zoom into Hastings county. Type in Golden-winged Warbler or Blue-winged Warbler in the Species box.
Centre Hastings:
-1 BWWA male seen
-1 GWWA heard
-1 GWWA heard
-1 GWWA male seen
Marmora and Lake:
-1 GWWA male seen
- Colony: 1 GWWA male seen, 3 GWWA heard
Stirling-Rawdon:
-1 BWWA male seen
-1 GWWA heard
-1 GWWA heard
-1 GWWA male seen
-1 GWWA heard
-Colony: First visit: 2 GWWA male seen, 1 BWWA male seen, 1 Hybrid female
Second visit: GWWA pair seen with food, 1 BWWA male seen
Tyendinaga:
-Colony: 1 GWWA male seen, 2 GWWA heard,, 1 Brewster's male seen
-Colony: 2 GWWA male seen, 1 BWWA male seen, 1 Brewster's male seen
Tweed & Thurlow:
-0 heard/ 0 seen
Conclusion
Recipe for a hybrid swarm?
Well, maybe it's not quite a hybrid swarm. Perhaps more of a gang or a posse. But I found it somewhat alarming that 75% of the GWWA colonies I encountered contained at least one male BWWA or hybrid.
The GWWA males aren't giving up their breeding territory without a fight however. On two occurrences I observed male GWWA's chase BWWA's from their singing perches.
Thanks
Thanks to area birdwatchers Terry Sprague, John Blaney, Peter Fuller, and Keith Gregoire for tips on locations and/or company in the Golden-winged Warbler Territory.
References:
Sibley, David A. Field Guide to the Birds of Eastern North America
Sprague, Terry Birds of Prince Edward County
Weir, Ron D. Birds of the Kingston Region 1984
Cornell University / ebird.com (Join for free today!)
Golden-Winged Warbler
Blue-Winged Warbler
Brewster's "hybrid" Warbler
Upland Sandpiper
Northern Mockingbird
Grasshopper Sparrow