Monday, December 03, 2012

The Hawk and the Dove

My wife and I were enjoying the afternoon on our front porch when we noticed a Cooper’s hawk (Accipiter cooperi) glide into in a large water oak in my neighbor’s yard across the street.  I wandered over to find that it had a white-winged dove in the taut grip of its talons. I eased off to retrieve my camera and returned to a blizzard of dove feathers drifting in the air around the tree.  Looking up I watched as the hawk’s head moved up and down, its hooked bill cleaving through the dove’s sinew like a well-oiled machine.
 White-winged doves have increased in numbers in this area over the last decade.  I can remember in years past observing only a few, but nowadays, they’re everywhere, to the point of becoming a nuisance.  This increase in their populace I’m sure has filled these local avian predators with glee. White-winged doves are robust, meaty birds and most likely rank high on the hawk’s menu.
They come to roost in droves late in the evening in several trees in the neighborhood and during these times, on occasion, a Cooper’s will be trolling the skies overhead.   The maze work of the tree’s branches gives the doves sanctuary, but the vision acuity of a hawk is exemplary.  Once its unwary target is chosen it drops abruptly like a weighty stone, busting into the branches causing doves to flee like a blast of shot.  The hawk most times coming away with a hearty meal.
In Arthur Cleveland Bent’s Life Histories of North American Birds of Prey (Part One, pg.118) he states- “It surprises its prey by a sudden, swift, dash, pouncing upon it before it has a chance to escape.  Its short wings and long tail give it such control of its movements that it can dart in and out among the branches of the forest trees with impunity, or dodge through the intricacies of thickets where its victims are hiding.”
Many years ago farmers considered this particular hawk as pests due to their taste for chickens.  In the book “Birds of America” published in 1917, a contributing author R.I. Brasher is quoted as saying- “Cooper’s Hawk is preeminently a “chicken Hawk”, and is by far the most destructive species we have to contend with, not because it is individually worse than the Goshawk, but because it is so much more numerous that the aggregate damage done far exceeds that of all other birds of prey.”  He goes on to say- “It will dash into the farmyard like a bolt, passing within a few feet of individuals and carrying off a young chicken with incredible swiftness.  The attack is accomplished so suddenly that, unless the gun is in hand, the robber always escapes.”

Bent adds- “Cooper’s hawk does more damage in the poultry yard than all other hawks put together.  It is very destructive to domestic pigeons, of which it is very fond, and, if not killed, will clean out a colony.”
Its sharp eyes picked up on my movement below and paused several times to glare down at me, but my presence didn't seem to hinder its feeding in the least.  Apparently it came to the conclusion that I was not a threat and decided it would not be worth the precious energy to haul the chunk of meat to a more private spot.

While positioning myself for a better camera angle, I heard something thump atop the roof of my neighbor’s house, which was directly below the hawk’s perch.  At first I had assumed the accipiter had decapitated the dove and tossed the head, but as I searched the ground alongside the house what I discovered was the dove’s gizzard.
When a bird swallows food it first travels down the esophagus and into the “crop”, which is just a ballooned area of the esophagus where food is stored until it’s ready for digestion.  From the crop it travels into the bird’s “true stomach” known as the proventriculus.  This is where acid and digestive enzymes are added to help break down the food.  From here it then goes into the gizzard, which acts by all accounts as the bird’s teeth.  Birds at times consume “grit” in the form of small stones, which remain in the gizzard and aid in the crushing of hard foodstuffs. 
I took the gizzard and dissected it down the center, spreading it in half to see what the bird had eaten recently.    As you can see the seeds of a tallow tree were taking up most of the space along with and two small yellowish-orange "gizzard" stones that had been deliberately swallowed by the dove to act as grit.  Note the shards of tallow seed shell that had already been ground into pieces by the powerful muscles of the gizzard.
 The hawk continued to tug at the bird’s flesh until much of nothing was left.  It then sat relaxed on its perch at times glaring down at me. It then began to preen and wipe its bill along the branch it sat on satiated from its meal.
Click on these to read my other posts on this hawk: (1) (2) (3) (4).


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