[Tweeters] 2018 Seattle Cooper's Hawk Project Summary (long)

ED DEAL falcophile at comcast.net
Sat Oct 6 19:10:35 PDT 2018

Yo Tweets,

We recently completed the seventh year of our long-term 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 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 46 pairs engaged in courtship and nest-building. A record 5 pairs disappeared during nest-building, perhaps sneaking off to alternate nests we never located. 41 pairs went on to incubate eggs, of which 40 pairs successfully produced fledged young.

Second, we count how many fledged young they produce. This year we documented a record 145 young that lived long enough to fledge, an excellent 3.63 young per successful nest.

Third, colleague Martin Muller and I 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 on the right legs of females and purple bands on the left legs of males. Each band has a unique combination of stacked two number and/or letter. Over the past year our ID bands have been sighted near Clinton on Whidbey Island, in Kent, on Mercer Island, as well as in numerous locations in Seattle. This season we color banded a record low 17 youngsters and 2 adults. We attribute the low numbers to “fat and happy” juveniles with little interest in hunting.

Over the last 7 years we have color banded 228 birds. We have 197 subsequent sightings on 88 different birds, a return rate of 38.5%.

The most popular choice of nest tree was Big Leaf Maple (12), followed by Douglas Fir (10), White Pine (8), Alder (5), Sycamore (3), Madrona (1), Atlas Cedar (1), Deodar Cedar (1), Norway Spruce (1), Hemlock (1), Oak (1), and Unknown (6). This count includes several pairs that built 2 nests or that refurbished an old nest plus built a new nest. Six sites were belatedly detected by hearing newly fledged youngsters’ food-begging calls, thus the six “unknown” nest tree species.

Most nest sites are in parks and greenbelts owned by the City of Seattle (30), followed by private property (14), and one each in a cemetery and the UW.

These 46 nest-building pairs should be considered the MINIMUM number in the city. Several potential nesting areas are nearly impossible to search because of 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 homeless camps 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 1.82 square miles.

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, especially you digiscopers!

Ed Deal

Seattle Cooper’s Hawk Project

falcophile AT comcast DOT net
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