American Kestrel

by Stan Tekiela
© NatureSmart
August 31, 2007

It is nearly raptor photography season again and I can hardly contain myself. For a wildlife photographer there are few species of bird that are as exciting to photograph as the raptors. Raptors as a group are also known as the birds of prey. They include hawks, eagles, falcons, owls and kites. The word raptor is a general term to describe any of these birds. In fact the word raptor is Latin and means “one who seizes” or “grabs”. I would say that is a good translation because raptors catch their dinner by grabbing their prey with their powerful feet.

A recent report on one of the raptors—the American Kestrel was recently published. These are the kinds of issues I like to follow closely so I thought I would summarize a few of the highlights from the report for this week’s column.

First a little background about the kestrel. It is the smallest species of falcon in North America, measuring only 9 inches from head to tip of tail. Compare that to the American Robin which is 10 inches and you can get an idea of how small this falcon really is.

The American Kestrel is by far our most common falcon and can be found all across the U.S. and Canada from coast to coast. In Canada and the northern states, it is a migratory bird with most but not all the kestrels migrating to the southern states for winter. In the states where winter is mild it is non-migratory.

In summer much of its diet consists of large insects such as grasshoppers. It hunts in open fields and prairies by perching on prominent objects such as posts or trees. It will also hover in flight over a field looking for its next meal.

Raptors such as the kestrel have been monitored and counted during migration at several locations throughout the country for the past 50 or more years. This has produced a large set of data that gives researchers a glimpse into the population trends of these birds.

Recently the data from seven raptor monitoring sites in the eastern half of the United States was examined to reveal some interesting population trends concerning the American Kestrel. Over the past 30 years from 1974 to 2004 the population of the kestrel has been declining. Upon further examination the sharpest declines have been over the past 10 years. For example at Cape May, New Jersey there has been a 4.5 percent drop in just the past 10 years. Hawk Mountain Pennsylvania reports a similar drop. Hawk Ridge in Minnesota is the exception with less than 1 percent drop.

Analyzing the Christmas Bird Count data, which is another long term study of the population trends of birds, confirms a similar decline in numbers in the same states where the hawk watch data was collected.

The same trends are observed in the western half of the country leading researchers to conclude the decline is widespread across the U.S.

So what might be causing this decline? It is important to understand that there is no “one” reason for these kinds of declines. So with that in mind here are some possible explanations. The use of chemical pesticide used to kill insects could be a problem. During the summer Kestrels feed heavily on large insects such as grasshoppers. Eating dozens if not hundreds of contaminated grasshoppers would accumulate large amounts of pesticide in the bird. We saw this same problem with DDT about 40 years ago.

Changing habitat may also be a problem. Kestrels require open habitat. All across the eastern half of the country the forests are expanding and maturing. Combined with fire suppresnnnnsion any open habitat is quickly changing to forest habitat.

Increased predation from the larger Cooper’s Hawk may be contributing to the kestrels declines. The Cooper’s Hawk is a forest dwelling species that is benefiting from the reforestation and feeds upon smaller birds such as the kestrel.

Lastly is West Nile Virus which has had an impact on many species of bird including the kestrel. Only time will tell what will happen with this species. Until next time...

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