June 27, 2013
Peregrine Falcon aerie
Peregrine Falcon aerie
Because we’ve raised two sons, one biological, the other adopted, the nature/nurture debate has always been intensely fascinating to me.  And if you’ve watched birds long enough, you have to wonder how human activity has impacted them—nature/nurture from avian perspective as it were.  These two thoughts recently coalesced for me as I observed a Peregrine Falcon aerie along a well-traveled human corridor.

For over a decade, off and on with no purpose more formal then the awe of watching and learning how revered avian predators at the top of the food chain lived their lives, I’ve been visiting a Peregrine breeding area near Phoenix during nesting season.  This spring, trail work in the area precluded these visits, but I tracked down a rumor to discover a different pair of Peregrines nesting at a different location.  You might assume that if you’ve seen one, you’ve seen them all but, as with human families, this is certainly not the case.

The pair with which I had become familiar over the years used the same two or three cliff face grottoes, sometimes alternating yearly.  Though given the derivation of the word “peregrine” it seems a little odd to call this pair “stable,” that indeed is what they seemed to be.  Although a nest monitor told me the female had years ago taken up with a new male after her original mate had disappeared, the same two adults have been together since I became aware of the territory.  In the bird world experience breeds success, pun intended.

With that pair I routinely observed the same daily routine.  The female stayed in the aerie while the male always perched on one of a handful of nearby, but higher, favored perches from which he would go off hunting or stoop on encroaching neighborhood Red-tails or ravens.  If he returned silently, the prey he had caught was his, but if he came back calling, it was breakfast time for his mate or the young.  Occasionally he would deliver directly to the nest, but usually she would answer, rise from the aerie to meet him, tip upside down for a talon to talon exchange, then flip over and pluck the luckless avian prey as she returned to the nest.

I have probably spent over thirty mornings near this aerie since 2000.  Without exception the male was always somewhere in close attendance.  This pair has successfully raised at least two young every year, and in 2012 they fledged four, this in an area of very high human activity, albeit activity that takes place far below the falcons and with little noise disturbance.  The pair I discovered this year should be so lucky.  Or more discriminating in their choice of nesting sites.

Their chosen site is also in a cliff face, near the top and inaccessible from the top, but the cliff is small and isolated, perhaps less than an eighth of a mile in length compared to the two mile long virtual mountain with hundreds of cliffs and crannies where the first aerie is located.  Though the human activity below this second nest is much more seasonal, the nest is not nearly as high above that activity, and the noise level is much greater.

On my first visit I found the female incubating and the male on a roost.  On my second visit the female and two fuzzball chicks, eyes still unopened, were in the grotto, but the male was nowhere around and never showed up.  The following week there were still two young, but the female herself went out to hunt and I never saw her mate until a quick flyby after I had watched for three hours.  Two weeks later I found the female in the aerie with but one surviving chick, much larger with flight feathers growing in, again no sign of the male.

Here are two speculative conclusions:  this is a young, inexperienced female with a young, inexperienced male; the proximity of raucous, drunken humans has spooked the male and precluded a viable breeding strategy.  I’m guessing the lack of proper nurturing, directly related to human noise and activity, has trumped the species’ survival instincts of one of nature’s top predators.

And yeah, welcome to the Salt River tubing season!