by Greg Mayer
A correspondent in Racine, Wisconsin, shares the following photos of a pair of hawks that have been perching on his fence. I say ‘pair’ with some hesitation, because although both have been in his yard, I cannot sex them, and their co-occurrence could be a coincidence. I suspect it is a pair, though, because this species has not infrequently bred in neighboring yards over the years.
I think they are adult Cooper’s Hawks (Accipter cooperii)– note the horizontal bars on the breast (with small stripes between bars). They might be a male and female, which are similar, except that females are bigger. The Sharp-shinned Hawk (Accipiter striatus) is very similar in plumage, but smaller, and the fence boards visible in the photos are 6 inches across, so I think the birds are nearer in size to a crow, which is Cooper-sized. Also, the head is a bit large looking, and the nape seems lighter than the crown. I know that many readers are more experienced North American birders than I, so feel free to weigh in with comments on identity and sex of the birds.
The last picture, of the same bird as immediately above, requires a bit of a biological digression for context. All animals produce nitrogenous wastes, and need some way to get rid of them. Among vertebrates, some fish can just get rid of the waste as ammonia, since they’re in so much water they can use large quantities of it to dilute the toxic ammonia. Mammals convert the waste to urea, a non-toxic, soluble substance, and literally piss it away. Jerry favored us with a picture of a New Zealand cow carefully raising its tail, so as to avoid soiling itself while doing so. Birds, like their reptile ancestors, largely turn their nitrogenous waste in to uric acid, which is non-soluble (and thus non-toxic). They thus eliminate not via a liquid urine, but via a slurry with just enough water to carry the uric acid solids along. Since birds (and reptiles) have only a single opening, from the cloaca, for both nitrogenous waste and the left overs of digestion to exit the body, the uric acid slurry and feces exit the body simultaneously, giving bird droppings their characteristic black and white splatter.
If relieving itself in mid air (from whence many a car windshield has been struck– as they say in Brooklyn, “the duity buid”), a bird need not be concerned with soiling itself. However, when perched, the bird could soil its tail and hinder parts, and thus, like the cow, raises its tail to noticeable heights, and ejects a stream of the uric slurry and feces mixture. It also seems to be looking back between its legs, to see where things are going.