[Tweeters] 2015 Seattle Cooper's Hawk Study Summary (long)

falcophile at comcast.net falcophile at comcast.net
Thu Sep 17 09:21:18 PDT 2015

Yo Tweets,


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


The study has three main goals. First, we are trying to census within the 83.9 square mile city limits of Seattle and establish how many Cooper’s Hawk nests exist each year(a nearly hopeless task). This year we located 40 pairs engaged in courtship and nest-building. We had 3 pairs disappear after building nests, perhaps sneaking off to alternate nests we never located and 1 site fail prior to incubation due to the death of the 10 year-old banded male (tested negative for avian influenza). 36 pairs went on to incubate eggs, of which 33 pairs successfully produced fledged young. One site failed shortly after starting incubation (death of adult-window hit) and 2 sites failed after hatching (one predation and one unknown cause).


Second, we count how many fledged young they produce. This year we documented 113 young that lived long enough to fledge.


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. Our ID bands have been sighted at Freeland on Whidbey Island, Kelsey Creek in Bellevue, on the Sammamish Plateau and at SeaTac Airport, as well as numerous locations in Seattle. This season we were able to color band 22 youngsters and 7 adults.


Over the last 4 years we have color banded 148 birds. We have subsequent sightings on 36 different birds, a return rate of 25%.


The most popular choice of nest tree was Big Leaf Maple (21), followed by Douglas Fir (11), Madrona (7), W. White Pine (4), E. White Pine (1), Alder (1), W. Red Cedar (1), Deodar Cedar (1), Hemlock (1), Cottonwood (1), English Oak (1), and Unknown (3). This includes several pairs that built 2 nests and one pair that refurbished 3 old nests 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 (27), followed by private property (12) and the UW (1).


Finally, these 40 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 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. My “best guess” is that we are missing on the order of 5-10 pairs.


Special thanks are due to each of the volunteers who helped collect this information. This would have been an even more impossible task without their hard work.


We greatly appreciate any color ID band readings from Tweeterdom, especially you digiscopers!


Ed Deal

Seattle Cooper’s Hawk Project

falcophile AT comcast DOT net

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