A Comparison

We are currently witnessing a good example of one of the behavioral differences between North American races or subspecies of peregrine.

On the one hand, we are observing the resident pair of adult anatum peregrines at the Washington Mutual Tower in Seattle (this website). At this point in their breeding cycle, having remained at their nest site year round and already completed their courtship, they are just starting to incubate their brand new eggs. They should have completed their four egg clutch today, 12 April. So incubation is just beginning for them here at 47 degrees 36 minutes north latitude, a little over halfway from the equator to the North Pole.

In contrast, we are also watching three tundra peregrines in South America. One of them, Sparrow King, has just started his migration north to the Arctic to nest. Based on our past satellite data, we know this migration will likely take him approximately 7 weeks to reach Baffin Island from Antofagasta, Chile. So the onset of his migration coincides with egglaying in our local peregrines.

When Sparrow King finally arrives at his northern nest site at about 62 degrees north latitude, the Seattle peregrines should be about three weeks old. When Sparrow King is less than halfway through his incubation period, the Seattle young should be flying.

Of course, this disparity is based on the climatic conditions found in the arctic. If Sparrow King arrives too early, there will be too much snow and too few prey birds for him to survive. But if he arrives too late, he risks not getting his young off the nest before the harsh fall weather arrives in the north or being usurped by another adult male at his nest site.

In addition, our two other tagged adult females, Elizabetha and Island Girl, have not even left their wintering grounds in Chile as yet and they are much further south.

These two examples illustrate the effects of latitude on peregrines and hint at the long evolution that must have been involved in the northern birds developing their tendency to travel so far south at such a great cost and great danger to themselves.