a mysterious decline

When I was a graduate student (in the 1970s), American Kestrels were one of the most common avian predators I saw in upstate New York on almost a daily basis, as they perched along roadsides hoping to spot an errant grasshopper or mouse in the grass.

The smallest and most common falcon can be prey for other, larger raptors, especially sitting exposed on a bare branch or wire.

The smallest and most common falcon can be prey for other, larger raptors, especially sitting exposed on a bare branch or wire as this one did along a road in Puerto Rico.

American kestrels, or Sparrow hawks, are easily identified by their small size, black facial stripes, spotted breast feathers, and swept back wing shape in flight.

American kestrels, or Sparrow hawks, are easily identified by their small size, black facial stripes, spotted breast feathers, and swept back wing shape in flight.  Photo credit:  Steve Hillebrand.

Kestrels can be found throughout the Americas, from the most northern Alaskan tundra to the tip of South America (except the Amazon basin), including Caribbean islands, in a wide variety of habitats.  Although still considered one of the most common raptors, their populations have declined 48% since the 1960s, as the magnitude of the red areas showing population declines in the Breeding Bird census data show.

American Kestrel population status in the U.S. from Breeding Bird census data 1966-2010.  Red = marked decline, orange = fluctuating population numbers; green = population growth

American Kestrel population status in the U.S. from Breeding Bird census data 1966-2010 (the Peregrine Fund). Red = marked decline, orange = fluctuating population numbers; green = population growth.

While I rarely see kestrels in MN these days, I was pleased to see them frequently while we were in Puerto Rico, and even on its small island neighbor, Culebra, where they seem to be fairly common.

A male kestrel took up a hunting perch above a sandy beach in western Puerto Rico.

A male kestrel took up a hunting perch above a sandy beach in western Puerto Rico.  Males have slate blue feathers on their wings and a darker slate blue head than the females.

Kestrels prospered in the late 18th and 19th centuries in the Americas, when forests were being cleared for agriculture.  The open grassy spaces made perfect hunting grounds for their insect, small bird and mammal diet, and forest borders provided the requisite number of tree holes for nesting.  So why the decline in more recent times, and especially in the last couple of decades?

A female kestrel perched on a power pole in a residential area in western Puerto Rico, unafraid of dogs, cats, and people below her.

A female kestrel perched and preened herself on a power pole in a residential area in western Puerto Rico, unbothered by dogs, cats, or people below her.

Are they vulnerable as prey of other raptors?  Cooper’s Hawk populations are increasing as Kestrel populations are shrinking — coincidence or causation?  A recent paper found no evidence for Cooper’s Hawk numbers or incidence of West Nile virus as a cause of Kestrel population decline, but suggested that nesting sites were a limiting factor.

Another explanation might be changes in farming practices in the U.S.:  clearing the fields of hedge rows and forest edges where the birds might find nest holes, pesticides that eradicate potential insect prey,  conversion of more pasture land to cropland, etc.

Progress for humans often take its toll on the wildlife, unfortunately.

13 thoughts on “a mysterious decline

  1. Beautiful photos. Kestrels are cavity nesting birds which need cavity trees specifically in open areas. Unfortunately, backyards make up an increasing portion of open habitats, where dead and dying trees are often removed. Flickers and bluebirds are in the same boat, but bluebirds have benefited from widespread provision of nesting boxes. Kestrels and flickers don’t take to them as readily, and both species are declining.

    We used to have kestrels nesting regularly in dying sugar maples lining the road I live on, but the trees were a possible hazard to the power lines, so the town cut them to the ground about 10 years ago. They could have left tall stumps, which would have been of some benefit to cavity nesters, but people think the tall stumps are ugly. Anyway, I haven’t seen a single kestrel since those trees were hacked.

    Pesticides might certainly be an issue, but I think habitat/nesting sites are probably more limiting.

    • I agree. Snags are really important habitat for a variety of birds. Nest site limitations are probably one of the key factors in their decline. Thanks for writing–interesting reflections!

    • Thanks! I think I’ll pay more attention to the nest box campaign for Kestrels, and hope that can turn the numbers around somewhat.

  2. I didn’t realize they were in decline although now that I think about it I usually don’t see Kestrels unless I’m out in the forest preserves. I think habitat may be the greater problem. Some birds adapt better than others, like the Cooper’s Hawk.

    A couple of summers ago I rescued a Kestrel that had taken refuge in my dad’s garage. It was a young bird and was being mobbed by Robins that had a nest nearby. We took him to the wildlife rehab center and they speculated that he had hit a window and was disoriented.

    • It seems there is a campaign to put up more Kestrel nest boxes in open areas where they might find good hunting. That seems to have worked well for Bluebirds.

  3. Great photos and information. So many bird species are in decline. I’m currently reading a book on the breeding birds of Maryland and DC. In it, they include data on the nesting sites across time, and whether the populations are increasing or decreasing. It’s sobering to read.

      • Sure – It’s the ‘2nd Atlas of the Breeding Birds of Maryland and the District of Columbia’, edited by Walter G. Ellison, published by The Johns Hopkins University Press in Baltimore, 2010.

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