Saturday, March 19, 2005

Water Consumption by Hawks

Do you have any idea how much water Savanna drinks per day?
Would that be comparable to a wild Red-tails water consumption?

And as I'm asking about what goes in one end, what
about the other? I rarely see these birds defecate so
have no idea of how many times a day this occurs.
Could you hazard a bsllpark figure?

Donna Browne


How much water does my falconry red-tail Savanna drink each day? In the cooler months, none. In summer, when it's in the high 80s she will drink several times a day. The provision of water to captive red-tails is a continuing matter of contention for falconers and raptor rehabilitators, both of whom keep red-tails in captivity. Falconers fly and hunt their birds. Raptor rehabilitators often keep disabled (wingless or flight-crippled) red-tails as so-called "program birds" that are used in educational programs on raptor conservation.

On one side of the issue are those who are certain that red-tails need to drink copiously each day. For them, water must be continuously available to the bird at all times of the day and year. These people are certain that red-tails would soon dehydrate from a lack of drinking water. They point out that Cooper's hawks and peregrine falcons are famous for taking daily baths (even in winter!) and drinking frequently. They presume that red-tails would do this, too, if given an opportunity.

On the other end of the scale (where I tend to lean), are those who note that red-tails only infrequently bathe in the wild, not every day as many accipiters and falcons do. It is also noted that red-tails successfully occupy territories in desert areas where there is no available water. In my area of northern Ohio, we have ample winter populations of red-tails that have no available drinking water often for several weeks during frozen winter periods. It is very clear that red-tails can live very successfully without available drinking water. They do this over large expanses of their continental range, both in arid regions and cold winter periods.

If you will remember back to chemical physiology classes, you will recall that all of the oxygen breathed in for aerobic respiration is used to take up de-energized hydrogens at the end of the Krebs cycle, which forms simple H-2-Os. The red-tail, like all other animals, is forming water with each breath. A good portion of the birds' metabolized lipids and proteins end up as respiratory water. So it's not just a matter of determining how often wild red-tails land on a stream-side rock and gulp down a mouthful of water. In 40 years of field observations of Ohio red-tails, I've never once seen one drinking or bathing in the wild. I'm sure they do, but it's infrequent.

The more cogent questions are how often and in what volumes do the birds defecate. Frankly, I've just never counted these events, but I'm guessing defecation occurs every hour or two. We falconers are aware that after the bird has gorged on a big kill, such as a rabbit or squirrel (a pigeon in Central Park), copious quantities of "hawk chalk," the white uric acid remnants of the prey's proteins will be propulsively excreted in eight to sixteen hours.

Hawk watchers might wish to adopt the ancient terminology of falconers on the matter. Falcons are unable to eject their feces with any great force. Falcons, then, are said to "mute," which means that they merely lift their tails and squirt the feces (properly called "mutes") not far. Hawks and eagles, however, have much stronger anal muscles and as most Central Park hawk watchers have noted, they are able to eject the feces (the mutes) some good horizontal distance. This powerful ejection is called "slicing." When defecating, a falcon mutes her mutes. A hawk slices hers.

The slicings of bald eagles can be downright dramatic. A few hours after a full crop of Lake Erie fish, I've watched a bald eagle slice a 6-ft strand of mutes across the marsh below. Quite impressive.

And while on the subject, here's something to watch for as the red-tail eyasses begin to stand on their feet in the second week. The little eyasses begin to respond to a developing genetic urge to defecate by backing their tails right to the edge of the nest where they can slice hygenically over the edge. Sadly, some eyasses are lethally too attentive in this and back themselves too close to the nest edge. Many an eyass has sliced itself literally over the edge, falling to oblivion on the forest floor below. Yes, take a deep breath and hold it firmly when you watch the eyasses start to take their first slices over the nest edge. One wrong thrust and they will fall out. Mutes happen, sometimes with disasterous ends.

This is not so likely, however, in the 927 nest, as the metal support structure extends around the nest proper on all sides. I think our elevated eyasses up there will be safe from the incidental hazards of learning to properly and safely slice over the nest edge.

Sorry for being so mute on these matters.


John A. Blakeman