In this article, I present evidence for the northern expansion of the Blue-winged Warbler’s range in Michigan.
Blue-winged and Golden-winged Warblers hybridize where their breeding ranges overlap. When I lived in Troy, Michigan (11-13 years ago) I visited Ohio yearly and easily found Blue-winged Warblers, but never Golden-winged Warblers. Close to home I also found Blue-winged Warblers in many places. Further north, near Port Huron, I found them alongside Golden-winged warblers as well as hybrids. That area was an active example of range overlap. When I moved to northern Michigan I often visited the Jordan River Valley, west of Gaylord, Michigan, and found many Golden-winged warblers, very few Blue-winged warblers and a few hybrids. It is another active range overlap area.
The southern limit of the Golden-winged breeding range is mapped within Michigan near its southern border; its northern limit extending to the edge of Lake Superior in the Upper Peninsula. The northern limit of the Blue-winged Warbler breeding range is mapped as an east-west line at the mid-way point of Michigan’s Lower Peninsula. So hybridization within Michigan should only occur in the southern half of the lower peninsula. But I present evidence below that suggests the northern limit of the Blue-winged Warblers’ range is most likely further north.
I have found Blue-winged’s well north of the mid-state east-west line – just east of Gaylord in the Jordan River Valley – for years and found 3 hybrid warblers (Brewster’s) in Michigan’s Eastern Upper Peninsula (EUP) in the last two years. I photographed two on consecutive years at the same location and another 15 miles away. All were breeding birds. Soon I expect to find a Blue-winged Warbler in the EUP because a Blue-winged and Golden-winged pairing is necessary to produce a Brewster’s.
Male Blue-winged Warbler in the Jordan River Valley in May
Male Golden-winged Warbler in a flowering crab apple tree, in the Jordan River Valley in May
For years the Jordan River valley proved to be reliable for Brewster’s Warblers, the more common hybrid between Golden-winged and Blue-winged warblers. For me, it is always interesting to photograph a Brewster’s because they often vary in plumage.
Male Brewster’s Warbler in the Jordan River Valley in May. Note the bright yellow “bib” on the breast.
Male Brewster’s Warbler in the Jordan River Valley in May. Note the yellow is only on the belly, extending to the lower chest.
Male Brewster’s Warbler in a flowering apple tree in the Jordan River Valley in May. Note the white and faint yellow wing bars.
This is a male Brewster’s Warblers in the EUP (where I currently live), photographed in May. Note the completely yellow wing bars on this male. And it has no yellow on its chest or belly.
Female Brewster’s Warbler found in the EUP this May. It was paired with a male Golden-winged Warbler.
This is the only Lawrence’s Warbler I have found – a male. This rare Blue-winged / Golden-winged hybrid results from a combination of recessive genes – a phenomenon that occurs infrequently. It showed up one year in a spot near Port Huron where I had consistently found Brewster’s Warblers in previous years. There is now a real possibility that this hybrid may be found in the EUP. Note that a Brewster’s Warbler results from a combination of dominant genes.
This male Blue-winged Warbler in the Jordan River Valley in May has yellow wing bars instead of the normal white wing bars. It is not classified as a hybrid, but it has some Golden-winged genes.
Some Brewster’s warblers might migrate further north than Blue-winged Warblers. It makes sense that they would do this because they have Golden-winged genes, which are from a bird with a more northerly breeding range map. This may explain why I found more Brewster’s warblers than Blue-wingeds in the Jordan River Valley, and why I am finding some Brewster’s in the EUP, but no Blue-wingeds yet.
It is well known that in recent decades Blue-winged Warblers have been expanding their breeding range northward, encroaching on the territory of the Golden-winged Warbler. Brewster’s might drive the northern expansion of the Blue-wingeds, if Blue-wingeds prefer to move into an area already occupied by Brewster’s, a bird with some Blue-winged genes.