Cedarville – Warbler Capital of North America?

1-2-2019

   Spring adult Black-throated Green Warbler

Cedarville is a small waterfront town in Michigan’s Eastern Upper Peninsula (EUP), located very close to the Les Cheneaux Islands (36 small islands with numerous sheltered bays and channels).  It is named as such because many of its surrounding forests are abundant with northern white-cedar (also called eastern white cedar or swamp-cedar). This tree was given the name “arborvitae” meaning “tree of life”.  Around Cedarville, cedars are truly life-giving for warblers.

In this article, I make a case for labeling Cedarville as “Warbler Capital of North America”.  I base my opinions on 15 years of extensive study and photography of the forests’ birds where I live – east of Cedarville, as well as those in forests to the west of Cedarville and in the Les Cheneaux Islands.

There are greater numbers of warblers concentrated in the cedar dominated forests (extending in both directions along Lake Huron’s shoreline from Cedarville and within the Les Cheneaux Islands), and for a longer portion of the year, than anywhere else in North America.  Twenty-seven warbler species make extended stays during spring and late summer/early fall migration.  Eleven warbler species which nest in these forests either nest directly in or under cedar trees, so I also elaborate on (and demonstrate with photos, further below) the relationship between the warblers and the cedars.   These forests are home to a bounty of insects so more warblers (which eat insects almost exclusively on the nesting grounds and during migration within Michigan) nest per acre here than any other area further inland.

For many years I have visited warbler forests in many places in North America, and I have a friend who has done the same. We have repeatedly timed our visits to coincide with peak warbler numbers. We agree that nowhere else in North America are there such great numbers of nesting warblers per acre.

There are many other locations in North America which are migrant traps or stop-overs (both being locations of forest where warblers and other songbirds stop to feed and rest), but they do not have anywhere near the many miles of habitat that the cedar-dominated forests provide along the northern shore of Lake Huron surrounding Cedarville.

Known bird migration hot spots, such as Pt. Peelee (Ontario), Magee Marsh (Ohio), High Island (Texas), Dauphin Island (Alabama), and South Padre Island (Texas), are famous because, on the right days, they can have many songbirds and many species of warblers.  At each location, there is a large water barrier (Lake Erie or the Gulf of Mexico) which either stops migration (and birds “pile up”) or is crossed (where the nearshore habitat is the first land migrating birds find after crossing).  At each location migratory songbirds are concentrated in a relatively small area of forest because very large swaths of adjacent land are without forest.

In the EUP Lake Huron is the large water barrier but it has extensive shoreline forest, where warblers migrating south stop in late summer/early fall, and it is the large body of water that must be crossed for many warblers migrating north in spring. The forested areas surrounding Cedarville are vast, stretching out many miles, and they are pristine.

On the right days in spring the numerous peninsulas within those miles can all be loaded with migrant warblers, and so become “migrant traps”.  For example, when northbound warblers (which migrate at night, pushed by south winds) encounter a change of wind direction, a cold front, or storm over Lake Huron, a peninsula tip in the EUP is often the first land they encounter, and they will land there after such a perilous journey, and often be exhausted and in need of food and rest.  This is the same thing that can happen at Pt. Peelee, South Padre Island, or Dauphin Island – a “fallout”, and it is the main reason why these locations are famous to birders.  I have encountered “fallouts” numerous times on the EUP peninsula where I live, and adjacent peninsulas.  The warbler flocks often stayed for days on the peninsulas. The spring photos of the 25 species of warblers further below were almost all taken during numerous “fallout” conditions – mostly on my peninsula, but some are from fallouts on adjacent peninsulas.

Warbler flocks also congregate at the same EUP peninsulas on certain days with north winds in late summer/early fall, as they run out of land while migrating south.  So these areas are hotspots again at that time. And the vast forests of the peninsulas and surrounding shorelines are loaded with breeding warblers.  None of the “hot spots” above (Pt. Peelee, South Padre Island, etc) have more than a small fraction of the amount of forest habitat, anywhere near the population of breeding warblers, or the number of species nesting – 19 species of warblers nest in the nearshore forests of the EUP.  And most are a “hot spot” only in spring.

And none of them have the funneling effect of two Great Lakes in the spring. Large numbers of eastern warblers divert their northbound spring migration pathway slightly to the east of the Mississippi Flyway and up through the mitten of Michigan’s Lower Peninsula, between Lake Michigan and Lake Huron, toward the Straits of Mackinac.

The following animation demonstrates how many warblers species do this in May: https://www.allaboutbirds.org/mesmerizing-migration-map-which-species-is-which/

In my opinion, it is the tremendous midge hatches from these big lakes that have diverted the migrating warblers.

In May many warblers move northward in mixed-species flocks along Michigan’s Lower Peninsula nearshore forests of Lake Michigan and Lake Huron, and they stop in these forests when waiting for favorable winds while resting and feeding on numerous midge hatches.  These midges are non-biting and hatch from the bottom of the big lakes, and their bays or coves, to form huge clouds, which often enter the nearshore forests.

The warblers’ peak movement north typically occurs in mid-May (as seen in the link above), but some nights at this time can be very cold inland – below freezing.  So almost all insects inland could be killed.  But the midges and other insects (such as the numerous spiders that feed on midges) along the lakeshore would survive because it doesn’t freeze there. The moderation of nighttime temperatures by a large body of water (Lake Michigan or Lake Huron) prevents this.   In those circumstances, the insect-eating warblers are better off staying where the live insects are  – in the nearshore forests.

Note that on some years spring migration in Michigan for the warblers is easy.  There are no freezing nights, and the month of May is warm.  More insects hatch, develop, and survive inland.  The warbler flocks are not obligated to stay near the shoreline.  But the reassurance of reliable food there should be a big factor guiding the birds. If they make a stopover well inland and there is one night below freezing almost all insects die.  Warblers need live insects the next morning, and because they are so small and lose a lot more body heat and energy than a larger bird their need for food is critical to their survival.  Why would they risk such a stopover?  I believe evolution has minimized such a risk, and the bulk of warblers migrate near the shoreline.

A good percentage of the warblers which are funneled to the top of the mitten – the Straits of Mackinac, cross the Straits on its eastern side (some island hopping) and eventually encounter the Les Cheneaux Island area, along with migrant warblers that cross over the water to the east of the Straits.  These islands have a tremendous amount of shoreline habitat (with plenty of cedars) along protected bays, coves and channels.  They are surrounded by so much water they never have freezing nights in mid-May, and so are a reliable area of live insect food for the warblers.

Midges load the islands’ nearshore trees in many areas.  South winds bring the warblers and midges to the area, but during the warbler’s extended stay winds often change and huge clouds of midges are blown off the channels and bays between the islands into certain forests with different wind directions.  The warblers can always find an area loaded with midges and they do.  They might need to go to the opposite side of an island or around to the other side of a bay, but they find the bounty.  And they have probably done so for hundreds (perhaps thousands) of years.

In a previous article, I covered how the information above contributes to numerous reasons why this area is excellent for warbler photography: The Perfect Storm for Warbler Photography.

Cedarville is directly in the middle of the North Huron Birding Trail.  For information on birding opportunities and planning your visit see:  https://www.northhuronbirding.com/

Tremendous numbers of warblers arrive to the extensive shoreline EUP cedar forests in spring – some by crossing Lake Huron and some by “island-hopping” Bois Blanc and Mackinac Island and the Les Cheneaux Islands. Those crossing Lake Huron find an abundance of midges hatched from Lake Huron and blown into the cedar-rich forests of the Les Cheneaux Islands and nearshore cedar-rich forests of the entire area east/west of Cedarville; blown in on the same south winds that push warblers toward their northerly breeding grounds.  This is the reason why these forests provide a bounty of food to the warblers – the midges at the bottom of the food web. And the spiders just above them.

A large population of spiders resides within the nearshore cedars because of the bounty of food provided by midges. Their webs are often loaded with midges (especially in May and June) and they feed on them. The warblers feed on spiders, as well as many other insects they find in the cedars, in addition to the midges.   So the warblers take advantage of at least two levels of the food web within the cedars. And many warbler species nest in the cedars. Cedars also offer warblers the perfect combination of protection and easily accessible perches. These small birds are very comfortable maneuvering within the random open spaces within cedars, which makes it easy to evade predatory birds such as Sharp-shinned Hawks and Merlin Falcons, who specialize in hunting songbirds but cannot negotiate the interior of cedars. The warblers’ comfort level is supported by the photos further below, and known by me – after 13+ years of witnessing it.

Sometime around mid-May the large warbler flocks usually arrive from the south to the EUP.  They often stay around the northern Lake Huron shoreline cedar-rich forests and feed on midges that are stuck on the cedar leaves and branches.  They hop from branch to branch stabbing and snapping their beaks, swallowing midges instantaneously.  Some will pick a high perch and repeatedly make a short flight and return, each time snapping a midge out of mid-air from a cloud of midges near the tree.

At this time there are not nearly as many spiders and other insects in the cedars as compared to June through September.  The midges are the warbler’s prime food source before June, and there are midges everywhere.  The birds are usually very active, putting in a lot of work to receive relatively few calories from each insect.  I have images of this but the midges are so small they can never be seen in the warbler’s beak, so I am not posting them. Later in the warbler’s breeding season stone flies and May flies hatch from Lake Huron and are often blown into the cedar forests, and the warblers take advantage of the bounty, receiving a big calorie load with each capture. Moths, caterpillars and inch worms are also more abundant and on the menu, as well as mosquitoes, small insect larva and a variety of flies.

It is time for some proof – in the form of images. Below I am including some information that is pertinent to the images further below:

– All images were taken in the EUP (almost all from the peninsula where I live), and are of warblers in cedars , so I omit identifying the tree type in the caption.

– All warblers molt (grow new feathers while shedding old feathers) twice a year.  All of them molt into breeding plumage in the spring before arriving in the EUP.  Most of the adult males are in their brightest most colorful plumage at this time.  Sometime between the beginning of July and mid-September, they molt into “winter” plumage, and most of them become much duller in appearance.

– Determining the sex of certain birds at certain times of the year is difficult and determining the age can be more difficult, and sometimes sex or age cannot be determined without the bird in hand (after being captured by mist-netting; I never do this), and even if in-hand some cannot be sexed or aged.  So often I do not identify the sex or age of the birds in the captions for images.  But the species can almost always be identified based on one good image.

Magnolia Warbler with Spider in late July; an early migrant that had already molted into its non-breeding plumage.

Female American Redstart Warbler on Nest (incubating eggs) in late July; her first nesting attempt failed – this one succeeded.

Male Northern Parula Warbler feeding its fledgling a spider in July.

Female Black-throated Green Warbler with Inchworm (July); a breeding bird.

Male Yellow-rumped Warbler with moth (July): a breeding bird gathering food for young.

Male Black-throated Green Warbler near its nest and with a spider, in early July

Twelve species of warblers in the EUP are associated with cedars.  I have found six species of warblers nesting in cedars:  Black-throated Green, American Redstart, Yellow-rumped, Yellow, Blackburnian, and Common Yellowthroat (in a cedar sapling on the edge of a cattail swamp).  Black and white Warblers and Northern Waterthrush Warblers both nest on the ground in cedar dominated forests; the Waterthrush in a swampy cedar forest.  Nashville Warblers favor cedar bogs in the EUP, and Tennessee Warblers also nest there; both nesting on the ground.  I have also found Connecticut Warblers nesting in EUP cedar bogs, but they are the only species of the twelve I have not found nesting near Lake Huron’s shoreline. Northern Parula Warblers nest in forests dominated by cedars, near the northern Lake Huron shoreline.  They are found where lots of Usnea moss (old man’s beard) grows from dead (or partially dead) trees. Canada Warblers are not specifically associated with cedars but their nesting habitat is often loaded with cedar saplings in the EUP. Yellow warblers within certain areas of forest along the north shore of Lake Huron in the EUP nest in cedars.

Molting Female Black-throated Green Warbler with spider taken from its web in late July.

In late summer (and early fall) southbound warblers with breeding grounds to the north of the northern Lake Huron shoreline EUP forests “pile-up” along the shoreline, because they are reluctant to cross Lake Huron unless their energy stores are sufficient.  Peak numbers occur in mid-August to mid-September.  They can count on the midges, spiders, and other insects of the cedars to help fuel them up as they wait to cross Lake Huron. And in some areas warblers migrate along its nearshore forests in a southeasterly direction toward the Straits of Mackinac, feeding as they go.

Female Northern Parula Warbler with a dragonfly in September

Female Blackburnian Warbler with Mayfly in early August; a mayfly hatch occurred extremely late the cold year this image was taken and a migrant flock of warblers fed on them right along the northern Lake Huron shoreline. My feet were in Lake Huron while taking this image.

Female Yellow Warbler with Mayfly; same flock.

Female American Redstart Warbler with Spider in mid-August; a migrant bird along the north Lake Huron shoreline.

Magnolia Warbler with a spider,  a migrant on my peninsula in August.

A large variety of warblers (27 species) and great numbers of warblers – spring migrants, breeding birds, and southbound migrants – are attracted to the cedars surrounding Cedarville.  They are funneled there in the spring; they nest there, and their southbound migration is stopped there by Lake Huron in late summer/early fall.  At each of those periods, an abundance of food is provided within the cedars.  The title “WARBLER CAPITAL OF NORTH AMERICA” is appropriate.

But that is a lofty claim. I believe the following images of various warblers in those cedars (25 SPECIES) helps support it.  Keep scrolling down. Note the variety of plumages of the birds. Almost all of the images are of migrants and were taken on the peninsula were I live on northern Lake Huron – a great place to witness and study warbler plumages.

Adult male American Redstart Warbler in May

Adult female American Redstart Warbler in May

1st year Male American Redstart in May

Female American Redstart Warbler in September

Male American Redstart Warbler in late September

Starting in late September some of the leaves of cedars in the EUP turn orange (then brownish) as part of a normal shedding process.  This can be more extensive in drought years, in diseased trees, in trees with flooded roots, or trees with poor nutrition.

Male Black and White Warbler in May

Female Black and white Warbler in May

Male Black and White Warbler in August

Adult male Bay-breasted Warbler in May

2nd year male Bay-breasted Warbler in May

Bay-breasted Warbler in June

Bay-breasted Warbler in May

Adult female Bay-breasted Warbler in May

Male Bay-breasted Warbler in September

Bay-breasted Warbler in September

Adult male Blackburnian Warbler in May

Female Blackburnian Warbler in May

Adult male Blackburnian Warbler in May

Blackburnian Warbler in late July (near the end of molting)

Female Blackburnian Warbler in August

Adult male Blackpoll Warbler in May

Adult Female Blackpoll Warbler in May

Female Blackpoll Warbler in May

Adult Male Blackpoll Warbler in September

Blackpoll Warbler in September

Male black-throated Blue Warbler in May

Female Black-throated Blue Warbler in May

After hatch year female Black-throated Blue Warbler in May

Female Black-throated Blue Warbler in September

Male Black-throated Blue Warbler in September

Male Black-throated Green Warbler in May

Adult female Black-throated Green Warbler in May

Female Black-throated Green Warbler in May

Male Black-throated Green Warbler in May

Male Black-throated Green Warbler in May

Male Canada Warbler in May

Canada Warbler in August

Adult Male Chestnut-sided Warbler in May

Female Chestnut-sided Warbler in May

Chestnut-sided Warbler in May

Chestnut-sided Warbler in late July; already molted – note the dramatic change in appearance after molting.

Chestnut-sided Warbler in late July

Male Common Yellowthroat Warbler in May

1st year female Common Yellow-throat in May

Common Yellow-throat in August

Adult male Cape May Warbler in May

Adult male Cape May Warbler in June

Adult female Cape May Warbler in May

Cape May Warbler in August

Cape May Warbler in August

Female Golden-winged Warbler in August

Adult male Magnolia Warbler in May

Adult male Magnolia Warbler in June

Magnolia Warbler in May

Female Magnolia Warbler

Magnolia Warbler late August

Magnolia Warbler in September

Magnolia Warbler in late September

Female Mourning Warbler in August

Northern Waterthrush in August

Male Nashville Warbler in June

Nashville Warbler in September

Male Northern Parula Warbler in May

Male Northern Parula Warbler in June

Female Northern Warbler in May

Northern Parula in May

Northern Parula Warbler in August

Northern Parula in September

Northern Parula in September

Orange-crowned Warbler in May

Orange-crowned Warbler in October

Ovenbird Warbler in August

Male Palm Warbler in May

Palm Warbler in September

Adult male Pine Warbler in late April

Female Pine Warbler in May

Male Pine Warbler in May

 Tennessee Warbler in May

Tennessee Warbler in September

Adult male Wilson’s Warbler in May

 Wilson’s Warbler in September

Wilson’s Warbler in August

Adult male Yellow Warbler in May

Female Yellow Warbler in August

Hatch Year Yellow Warbler in August

Adult male Yellow-rumped Warbler in May

Female Yellow-rumped Warbler in July

Yellow-rumped Warbler in October

Yellow-rumped Warbler in October

Interested in photographing the warblers? See: Paul Rossi Workshops

For a video of the warblers surrounding Cedarville in the spring see: https://www.youtube.com/watch?v=QUHGJ91NhL4

2 species of vireos nest in the cedar-rich forests of the area: Red-eyed and Blue-headed; Philadelphia Vireo migrates through. All of them can be members of the mixed species warbler flocks migrating north in the spring or south in late summer/early fall.

Red-eyed Vireo in August

Blue-headed Vireo in May

Blue-headed Vireo in September

Philadelphia Vireo in May

Golden-crowned Kinglet in May: nests in the cedar forests, and can join the warbler flocks

Ruby-crown Kinglet in October: few nest in the cedar forests, and can join the warbler flocks

Male Pine Grosbeak in January: a late fall/winter visitor to the cedar forests

Saw-whet Owl in October – especially visits in early fall while migrating south , stopping in the cedar forests before crossing Lake Huron

Boreal Owl in January – rare visitor to the area

Barred Owl in February – a winter visitor

Red-breasted Nuthatch in September: year-round resident of the cedar forests

White-crowned Sparrow in June; nesting in a cedar sapling: a common species in the nearshore cedar dominated forests

Pine Siskins in January: they nest often when there is a good cedar cone crop

Common Redpoll in January: a late fall/winter visitor to the cedar forests

Winter Wren in July – a common nester in the cedar forests