Male Blackburnian Warbler
The Eastern Upper Peninsula(EUP) at and just north of the Lake Huron shoreline is spectacular for northern warblers from mid-May to early June. 24 species breed in the area and 3 more migrate through at this time. Colorful beauties such as Scarlet Tanager, Indigo Bunting, Baltimore Oriole, Rose-breasted Grosbeak, and Blue-headed vireo, join them. Many of the 24 species of warblers have a breeding range extending well into Canada. That means many migrant individuals of the same species as the local birds are moving northward at that time.
Male Scarlet Tanager
Warblers and other songbirds migrate at night in mixed-species flocks. Depending on wind direction at night, many of these flocks fly over Lake Huron in order to arrive in the EUP. If they run into bad weather or find cold temperatures when approaching the northern shore all of them will stop at the first land they see along the shoreline, and even with ideal conditions, a good percentage of them will stop. There they find a bounty of food provided by superabundant midge hatches. The midges hatch from the bottom of Lake Huron and form clouds in the millions, and often coat the trees or stay in clouds near the shoreline. The midges feed the incredible population of spiders, which the warblers also love. There is so much food for warblers that their nesting territories are very often shrunken near the lakeshore and up to about 1/2 mile further inland.
Male Cape May Warbler with Spruce Budworm
There is a current outbreak of Spruce Budworm along the lakefront and in areas further inland. Periodic outbreaks of spruce budworm are part of the natural cycle in northern spruce and fir forests, and the dominant tree types of those forests are abundant just inland from the northern Lake Huron shore. The eggs of the budworm are placed in microscopic holes in the needles of these trees. The larva hatches out and feed on needles or expanding buds. As the larva grows, needles are severed at the base. After many years of defoliation, the treetop (or the entire tree) may die. The larva that escapes the mouths of birds matures to become moths that drill holes in more needles, plant eggs, and continue the cycle for the next year. Certain species such as the Cape May Warbler are known as spruce budworm specialists, and they dramatically increase their numbers near infested areas as this cycle progresses in years. They feast on the larval worms and eventually help bring the cycle to an end – that may take 8 years or more. Then most of them will likely move on to another area of North America where spruce budworm is more abundant. Many other warbler species such as Blackburnian, Magnolia, Canada and Black-throated Green have increased their numbers in response to Spruce Budworm, which will continue to be a tremendous food source for them again this year (2018). Update: the cycle has continued through 2020 and will continue in 2021.
Male Wilson’s Warbler
View this animation of migrating birds in the western hemisphere: http://www.audubon.org/news/see-millions-places-migrating-birds-have-gone-one-gif
It clearly shows that Michigan funnels migrating birds (especially northern warblers) that fly over land and are funneled up through the mitten of the lower peninsula during mid-to-late May. Many birds cross the Straits of Mackinac because it is the shortest distance over water to go north. After crossing many of these birds travel along the Upper Peninsula shoreline to the east of St Ignace, which goes north for many miles before turning to the east. They find a bounty of midges along the shoreline and move northward while they feast. Then many of them will head inland to the north. So they represent a substantial influx of warblers to the EUP.
Male Magnolia Warbler
Great numbers of warblers are concentrated in the EUP during mid-to-late May for multiple reasons. At this time the aggressive experienced males, which are in their brightest plumage, provide abundant photographic opportunity in their breeding habitat, especially because of all the migrants of the same species around. Here real estate for warblers is at a premium. And it comes with a price of constant vigilance. Males are on high alert for migrants who will try to steal their territories of bounty and they are excellent photographic subjects.
During this time period tremendous numbers of birds can migrate on a night with south warm winds if there has been many nights in a row with cold north winds. Those that cross Lake Huron can run into a life threatening thunderstorm over the lake because strong rain can force them into the water and they can drown. But sometimes they make it through. This has happened twice in the last decade. Exhausted warblers were everywhere along the northern shoreline the morning after, and they stayed for days to replenish their energy reserves on the bounty of food.
Interested in photographing these warblers and other songbirds? See: Workshop
Would you like to see a video of them? See: https://www.youtube.com/watch?v=QUHGJ91NhL4