Hawk nest hunt

Every spring and summer, Red-shouldered Hawks make their presence known in the backyard.  They soar over the cottonwood trees in the wetland just beyond the backyard and occasionally stop to perch on the trees in the backyard to see if there is anything worth eating in my yard.

One of a pair of Red-shouldered Hawks that were mobbing an owl (that I couldn’t find) last summer.

They have been particularly noisy this spring soaring overhead, calling to each other with plaintive cries, and mating in full view in the cottonwoods in the wetland (far away and behind many sticks).  So, this week while I have been walking out in the wetland photographing woodpeckers and wood ducks, I’ve been searching the tops of the trees for the Red-shouldered Hawk nest, and finally found it yesterday with the help of a neighbor.

It was across the wetland high up in a tree, probably much more visible from the street in front of the houses.

I could just see the top of the hawk’s head (and eye) with my binoculars and the zoom of the camera lens.

Trekking through the muddy wetland and across to the other side, another neighbor told me that this was a new nest this year, and that their former nest in his yard had fallen down with a heavy snowfall this past winter.  Eureka! — this might the pair that have been soaring and screeching over the wetlands in previous years.

One of the effects of this pandemic “stay home” restriction is that neighbors are outside socializing from driveway to driveway in the middle of the afternoon, and are happy to point out the wildlife they have seen in their backyard.  And the neighbor in whose tree the hawks built their nest kindly opened his backyard gate and let me to photograph the nest.

I got there just as there was a nest exchange and the sitting hawk flew off when its partner arrived and sat on the edge of the nest.  The nest doesn’t look particularly well-built, with loose sticks woven into the fork of the tree where four branches come together.  But perhaps they will add on if they are successful rearing chicks here.

A better view of the Red-shouldered Hawk adult with its obvious red shoulder patch, lightly barred rusty-colored breast feathers, and black tail with narrow white stripes.  The tail (along with the red shoulder patch and rusty barred breast feathers) helps distinguish this bird from its similar-sized, but more open country inhabitant, the Red-tailed Hawk. (Note I edited out the branches in front of the bird for a better look.)

The fact that one of the hawks was sitting down in the nest cup probably means there are some eggs there already, and I hope this pair successfully rears a couple of chicks so that I can return to photograph this spring and summer.

What’s all the commotion?

I could hear two Red-shouldered hawks screeching at each other in the backyard, so I went out to investigate (with camera, of course).  As they flew back and forth between the tall oak trees, still vocalizing quite noisily, I caught a glimpse every now and then.

Red-shouldered Hawks have a distinctive call, more of a shrill scream, actually, “kee-yeear” uttered repeatedly with a downward inflection.

This commotion went on for about 15 minutes, and I have no idea what it was about, whether they were fighting over territory or a prey item or mobbing something I couldn’t see.

Both were adult birds, perhaps a breeding pair that used the way backyard forest and ponds to raise their young this summer.

Red-shouldered Hawks are a forest bird in eastern North America, and eastern-most Minnesota seems to be the western limit of their breeding range.  But they are not permanent residents here, where snow-cover limits their ability to find their favorite food — voles, chipmunks, frogs, toads, and crayfish, which are all dormant in the winter.

It’s easy to see why the scientific name of this bird is Buteo lineatus, with its finely striped, rusty-colored breast stripes.

One last pose among the branches before taking off…

the morning mob

A quiet Sunday morning reading the newspaper was interrupted with loud and raucous crow calls from the backyard.  Suddenly a swarm of them appeared and landed in a neighbor’s tree, still calling, so I knew there must be a hawk or an owl out there somewhere.

At first glance, all I saw was a mob of crows.

Looking a little lower in the tree, it was obvious the crows were quite upset about the presence of a Red-shouldered Hawk in their territory.

Another hawk called from the top of a tree nearby, so perhaps this was a mated pair of hawks is investigating the backyard for nest sites.

The crows finally chased one of the hawks out of its tree perch.

The pair met up briefly in another tree before the crows finally chased them both off into the wetland behind the backyard.

Red-shouldered Hawks are forest birds, like Crows, and search out wooded areas near water for nest sites.  Three (as yet unfrozen) ponds in the woods behind the backyard might look like a good spot for a nest, but not with those pesky crows around to harass them continually.

These hawks prey primarily on small rodents, but I suppose they wouldn’t pass up a nestling crow if they had a chance of success, so Crows, like other smaller birds, mount a successful defense against predation by ganging up at first sight of a predator in the area.  Warning calls bring more crows into the area, and some will be daring enough to fly right at the predator, using their feet and wings to strike at them.

Crows successfully mobbed a Red-tailed Hawk in the backyard last summer as it flew overhead. Having to watch numerous small bodies coming at you is usually enough to drive a hawk away.

Cold weather and one-legged birds

Do you find that ice cubes sometimes stick to your warm fingers as that slight moisture in your fingertips instantly freezes on contact with the ice surface?  So then, why don’t the webbed feet of ducks, geese, swans, gulls, etc. freeze to the ice?

Standing with her bare webbed feet on snow and ice doesn’t faze this mallard hen. Why not?

A wonderful adaptation of the circulatory system in the legs, called a counter-current heat exchanger, warms the cold venous blood returning from the foot while it cools the arterial blood flowing to that site.  The “exchanger” is actually a network (rete) of arterial blood vessels wrapped around a central vein, and the counterflow between the two sets of blood vessels allows a steep gradient of temperature to be created between the body core and the webbed foot.

With no heat exchange (left), the foot stays warm and loses heat to the ice. A warm web would also stick to the ice! With heat exchange (right), arterial blood going to the foot is gradually cooled by giving up its heat to the vein bringing blood back from the foot. Thus, with heat exchange, foot temperature is about the same temperature as the ice it is resting on. Voila! Less heat loss! [Figures from (Ask a Naturalist)]

This anatomical adaptation for reducing foot temperature has important implications for staying warm in cold weather.  Even with reduced blood flow to the legs, the bare areas of the foot and leg are potential sites of great heat loss in extreme cold weather.  So, the less leg and foot surface area exposed, the better.

Birds have perfected the one-legged stance of the yoga “tree pose” and adopt it frequently when temperatures dip, placing their center of mass directly over one leg and tucking exposed limbs into their plumage.

Trumpeter Swans maintain perfect balance, with their head tucked under a wing for additional protection from heat loss.

On first glance, you might think this was simply an unfortunate, one-legged Ring-billed Gull, But the “tree pose” is used in all activities — whether resting or eating.

At rest, long-legged herons and egrets often tuck one leg up into their belly plumage to reduce heat loss while standing in cold water.  Even shorter-legged Black-crowned Night Herons take advantage of this behavioral strategy.

A Broad-winged Hawk sat on a cold steel pole in my backyard one fall morning, and fluffed its belly feathers over its legs as it perched on just one foot (right photo).  A few minutes later, when the sun had reached that spot, the bird let the sun do a little warming of its bare legs and feet (left).

Would the one-legged, yoga tree pose work for us, while we wait at a cold bus stop?

Humans posing like trees.
It’s unlikely this would promote heat conservation for humans in cold weather, though.

 

In the spotlight

Sitting in the sun to digest its mouse meal, this Red-shouldered Hawk is a stark contrast against the dark forest background.

I saw this Red-shouldered Hawk fly up to the perch (top of the swing set in the backyard) after catching something small on the ground.  The bird quickly devoured whatever it was with its back to me, and then turned around to bask in the sunlight just hitting the edge of the forest.

Without really meaning to, I captured the perfect sort of photo backdrop for this hawk, which is a bird of the forest.  Focusing on just the lighter shades of the bird’s breast feathers made the dim light of the forest behind it even darker.

This is a distinct and colorful hawk with its reddish barred breast feathers and black and white mottled wings.  Like its close relative the Red-tailed Hawk, it feasts on a variety of rodent species (mice, chipmunks, even squirrels), as well as small snakes, lizards, and amphibians.

Fall migrants sometimes hang around bird feeders, hoping to catch the unwary songbird or two.  But unlike the Red-tailed Hawk, this bird has mastered the art of silent flight through the forest, and is often not heard before it pounces by gliding low through openings in the vegetation.  I never heard it flap as it left the perch and took off about 3 feet off the ground toward the neighbor’s backyard.

Crow – Hawk face-off

Crows seem to detest hawk and owls.  The other day they mobbed the Great Horned Owl in the backyard before I could get a good photo of him.  The owl was hooting in the middle of the day and it would have made a great picture, but the crows chased him off.

Yesterday, the local crow family went after a pair of Red-shouldered Hawks that had landed in the big oak trees in the backyard.  What a handsome pair they were as they screeched at each other (or the crows, perhaps).

The hawk took refuge in the center of the oak, so it was surrounded by branches and not highly visible.

At least four crows surrounded an individual hawk, flying at it from all angles, one after the other.

This was about as close as the crows would approach before flying right at the hawk and then taking off to perch in a different place. The hawk continually turned its head to look at each crow, perhaps trying to intimidate.

Eventually, the hawks had enough of this harassment and left the area, still making their distinctive “kee-raah” call.

Such a handsome hawk, with its striped red breast feathers and striped tail.

Despite their long soaring wings, Red-shouldered Hawks are birds of the forest, and I suspect their long tail provides the maneuverability they need to fly in and out of trees.  They hunt much like a Red-tailed Hawk does, perching high and waiting for some prey animal to move before pouncing on them, but Red-shouldered Hawks station themselves more at the forest edge, and Red-tailed Hawks tend to hunt in more open, exposed areas.

Photo by Matthew Townsend from Wikimedia Commons

We have both Great Horned Owls and Red-shouldered Hawk nesting in the backyard, judging by calls I’ve heard from these birds over past summers.  The hawks occasionally may actually join forces with the crows to chase Great Horned Owls out of hawk breeding territory.  Interestingly, both the hawks and the owls will steal each other’s young out of the nest and eat them.  That’s a different sort of population control.