falcophile at comcast.net falcophile at comcast.net
Tue Sep 20 11:43:51 PDT 2016

Yo Tweets,

We recently completed the fifth year of our study of Seattle’s urban-nesting Cooper’s Hawks. This study builds on the 2003-2011 pioneering work of Jack Bettesworth.

The study has three main goals. First, we try to census within the 83.9 square mile city limits of Seattle and establish the number of Cooper’s Hawk nests (a nearly hopeless task). This year we located 41 pairs engaged in courtship and nest-building. We had 2 pairs disappear during nest-building, perhaps sneaking off to alternate nests we never located. 39 pairs went on to incubate eggs, of which 35 pairs successfully fledged young. One site failed during incubation and 3 sites failed after hatching (one failed after the adult male was killed by a Bald Eagle and three failed from unknown causes).

Second, we count how many fledged young they produce. This year we documented 125 young that lived long enough to fledge (plus 5 more that didn’t).

Third, myself and my study partner, Martin Muller, attempt to put unique color ID bands on as many birds as possible. This allows us to track individual birds as they move around the city and beyond. We put orange bands of the right legs of females and purple bands on the left legs of males. Each band has a unique stacked two number and/or letter combination. Over the past year our ID bands have been sighted near Freeland on Whidbey Island (two different birds), in Burlington, Skagit Co., and in King Co., in Bellevue, Kirkland, Duvall and at SeaTac Airport (trapped and relocated as part of their excellent bird-strike avoidance program), as well as numerous locations in Seattle. We had an amazing first out of state sighting, in Oakland, CA. This season we were able to color band 31 youngsters and 4 adults.

Over the last 4 years we have color banded 183 birds. We have 131 subsequent sightings on 62 different birds, a return rate of 34%.

The most popular choice of nest tree was Big Leaf Maple (20), followed by Douglas Fir (12), W. White Pine (5), Madrona (2), E. White Pine (1), Alder (1), Atlas Cedar (1), Cottonwood (1), Horse Chestnut (1), Plane (1), and Unknown (3). This includes several pairs that built 2 nests or that refurbished an old nest plus built a new nest. Three sites were belatedly detected by hearing newly fledged youngsters’ food-begging calls, thus the three “unknown” nest tree species.

Most nest sites are located in parks and greenbelts owned by the City of Seattle (29), followed by private property (11) and a private golf course (1).

These 41 courting pairs should be considered the MINIMUM number in the city. There are several potential nesting areas that are nearly impossible to search due to safety and terrain, e.g., the steep trail-less overgrown greenbelt along the railroad north and south of Golden Gardens, several parts of the extensive W. Duwamish Greenbelt, and “the jungle” homeless camp on the wooded hillside of Beacon Hill along I-5. My “best guess” is that we are missing on the order of 5-10 pairs. Our known nesting density in Seattle is one pair for every 2.05 square miles.

We recently learned our report on observations of female choice in courtship behavior was accepted for publication by the Journal of Raptor Research.

Special thanks are due to each of the volunteers who help collect this information. This would have been an even more impossible task without their hard work. Contact me if mentored volunteering to follow a nesting pair through the breeding season interests you.

We greatly appreciate any color ID band readings from Tweeterdom.

Ed Deal

Seattle Cooper’s Hawk Project

falcophile AT comcast DOT net

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