The Hunters and the Hunted

12-16-2018

Michigan’s Eastern Upper Peninsula (EUP) is a great place to witness the relationship between hawks (the hunters) and their prey (the hunted). Here migrant hawks and smaller birds they prey upon are abundant in spring and fall.  And the abundant national and state forest land provides plenty of pristine habitat for a variety of breeding hawks and a greater variety of songbirds.

Whitefish Point, located on the southern shore of Lake Superior in the EUP, is a tremendous hawk migration spot in early spring, especially good when south winds drive the hawks. The northern shoreline of Lake Huron is also a lesser know southbound hawk migration corridor in September and October, especially good with north winds. At both locations, hawks fly along shorelines (or just inland from them) because they are reluctant to cross a large body of water.  Some hawks stop to hunt small birds that are migrating at the same time.

A female adult Merlin hunting

Merlin Falcons hunt both locations extensively, and they nest along both shorelines.  They target small songbirds often (especially warblers).

Above is a photo of a male Yellow-rumped Warbler in early May.

A Merlin made an attack flight that passed over it and the bird flattened out as if to become less noticed (above) but kept an eye upward.  When a hawk (or falcon) makes an attack like this the warbler is usually a member of a much larger community of birds occupying a forest – a migrant flock, breeding birds or a mix of both.  As the hawk flies through and is first noticed one of the warblers will make a sharp distinctive call note that has a specific meaning – warning of an imminent attack.  This call note is heard by another member further ahead and repeated from member to member with a speed that is quicker than the hawk can fly.  The whole community is put on alert in this manner just before the hawk can strike, and many of them take this pose, looking upward.  Male birds can be fighting for territory at that time, but their fighting will stop and this cooperative behavior takes over as a survival tactic.

A Sharp-shinned Hawk eats mainly small birds in a similar manner as a Merlin but it is more adept at maneuvering in thicker forests.  When it migrates past Whitefish Point in spring it often has a bulging crop, after having recently captured a small songbird.  This hawk is a prime reason why warblers must be constantly vigilant.

Sharp-shinned Hawk with full crop at Whitefish Point

Migrating warblers seem to be constantly moving their heads.  They often glance toward the sky when any larger bird flies overhead.  Pine Warblers and Yellow-rumped Warblers arrive in the EUP in late April and Early May – earlier than most warblers.   There are more Sharp-shinned Hawks migrating at that time as compared to later in May – when the bulk of the warblers arrive, so these 2 warbler species are exposed to more danger, and surely must glance upward more often.

Male Pine Warbler in early May looking up for hawks

Cape May Warblers (and many other warbler species) arrive later in May but often glance upward to identify potential predatory birds, even if fewer hawks are around.  By then migrant hawks have almost all passed by and the nesting Merlin Falcons and Sharp-shined Hawks, which are abundant, are more interested in mating and nesting.  But if a Seagull, Crow or Raven passes overhead it will be identified as not being much of a threat.

Migrant female adult Cape May Warbler looking upward in late May

Northern Goshawks nest in the EUP in small numbers and usually only a few migrate past Whitefish Point in early spring. They prefer to hunt birds larger than warblers, such as grouse.  But they will take smaller songbirds as well.

Immature Northern Goshawk just above the dunes at Whitefish Point

The immature Northern Goshawk above stayed around the tip of Whitefish Point for hours on a day with strong south winds in early May. It was obviously a successful hunter.  Look at that bulging crop!

When Kestrels arrive in the EUP, usually in April (some in early April when nights can be very cold), they will sometimes hunt the bushy ditches bordering inland farmer’s fields, especially on colder mornings.  They are a small falcon and lose more heat (and energy) than larger Hawks on a cold night, so they are more pressed to make a successful kill.  There are often migrating sparrows in those bushes, which are certainly on the menu.

Male Kestrel hover hunting over ditch bushes

Broad-winged Hawks do not target songbirds often but in the spring and again in late summer, at times when migrant songbird flocks are abundant and very active in the morning, I often find this hawk perched at a forest edge, as if mesmerized by all of the surrounding activity.

This Broad-winged Hawk allowed a close approach with my van as it concentrated on migrant sparrows in the grasses below.

In the last half of August and the beginning of September, the forests along the north shore of Lake Huron can be full of warbler flocks migrating south for the winter. The best days, with many flocks, are after cold nights with north winds.   The warblers which migrate through in August typically avoid the many hawks that will eventually target them.  At that time the hawks are usually in the last stages of assuring the independence of their broods.  After that, the warblers are confronted with constant attack and their behavior changes drastically, and they vocalize softer and less often. Two species, Sharp-shinned Hawks and Merlin Falcons are especially numerous along the northern Lake Huron shoreline, and especially on peninsulas that trap the migrant flocks as they try to head south and find nothing but water, which they are reluctant to cross. Often these migrant flocks will move into the peninsula during the day, be subject to many attacks, and then move back northward to escape the peninsula.

The adult female Black-throated Green Warbler above was photographed in late August at a time when she could be much less wary as compared to September. A glance upward to identify any potential predatory bird can still be life-saving.  A Merlin or Sharp-shinned Hawk that was a failed breeder (and have no brood to educate) could be around.

But the adult male Northern Parula above was photographed in September, at a time when many hawks were migrating overhead.  Fortunately for this warbler, they had a perfect migration day with steady north winds and good thermal lift, so we’re not interested in hunting.  This bird and his flock seemed to know this. At other times the ideal winds shut down mid-morning and the hawks and warbler flocks stop migration.  Then the hunt is on, and flock behavior changes drastically.

The north shore of Lake Huron in the EUP has an extensive pristine marsh habitat that holds nesting American Bitterns during the breeding season and offers migrating bitterns excellent stopover habitat.  Those that migrate south in the early fall experience many hawks migrating overhead on some north wind days.  Migrating Northern Harriers will often stop for a day or more to hunt a marsh from a few feet above the vegetation.

In September the American Bittern above glanced up from a grassy section of a marsh along the northern Lake Huron shore.  A Harrier passed by but was no threat.  The bittern was too big to handle.  But if a Bald Eagle, Northern Goshawk, or Red-tailed Hawk was overhead the threat was very real.  Any of them could have been around at that time.

The adult female Northern Harrier above dove on a lone sparrow in marsh grasses which was busy feeding on mature grass seeds.  The sparrow evaded capture. Harriers are often unsuccessful in their capture attempts but have a greater chance when attacking a lone individual.

Black-bellied (front) and American Golden Plover

The plovers above stopped at Pt. LaBarb on the northern side of the Mackinac Straits in September.  They fed and rested for a few days before migrating southward.  Northern Harriers often cruised the shoreline above them, and the plovers were on the menu, but only if a Harrier could somehow make a surprise attack.  One female Northern Harrier passed by many times, each time seeing that the plovers noticed her, so she acted as if she didn’t even see them.  But she could have switched to attack mode at any instant.

Some Northern Harriers stay well into October in the EUP before migrating south, and some can be found hunting the inland hay fields – mainly for voles.  The adult male in the 2 images above hunted in late October without concern for my presence in my van, coming right at me in the last image.  It had not rained for many days and then a big rain occurred.  The vole tunnels just below the field’s surface were flooded and the voles were forced out into the open. This bird knew to take advantage of the opportunity to feed well, fueling up for migration southward.

The immature Northern Goshawk above was migrating at Whitefish Point at the beginning of May, looking down at me confident and menacingly, as if I might be prey.