[CT Birds] Red-tailed Hawks and Red-shouldered Hawks, Part I

Stephen Broker ls.broker at cox.net
Mon Jan 19 11:31:48 EST 2015

Intrigued by yesterday’s comments about the relative occurrences of Red-tailed Hawks and Red-shouldered Hawks in Connecticut, and aided greatly by a wretched, sleep-depriving cold, I thought I’d try to see what light, if any, is shed on this discussion by Christmas Bird Count results.  I’ve used the last 30 years of CBC results (1984-85 through 2013-14) from our 18 statewide early winter counts for these two hawk species and sliced and diced the state CBCs in several ways to calculate the ratios of Red-tails to Red-shoulders around the state.  I would expect that proportions of Red-tails and Red-shoulders are influenced greatly by such considerations as overall geographic distribution, habitat preferences and available habitats, and, perhaps, elevational factors.  There also is the time factor.  Over the 30-year period, each hawk species has increased in numbers significantly, but Red-shouldered Hawks have seen the greater growth in numbers.  These comments get somewhat lengthy, so I’ve also sliced and diced them into a few smaller ctbirds posts - 6-part harmony.

On a statewide basis (all 18 CBCs lumped together), we have recorded 23,488 Red-tailed Hawks and 1,931 Red-shouldered Hawks in the last 30 years.  That’s a ratio of 12.2 Red-tails for every Red-shoulder.  Clearly, Red-tailed Hawks greatly outnumber Red-shouldered Hawks on Connecticut CBCs.  In building the annual statewide CBC spreadsheet, I tabulate results for the 6 Northern counts (LS, LH, BA, HA, ST, EW), the 5 Mid-State counts (PA, WR, OX, QV, SR), and the 7 Coastal counts (GS, WE, SM, NH, OL, NL, NA).  The 30-year regional ratios for Red-tails to Red-shoulders are:  Northern, 22.3 (8,924/400); Mid-State, 10.5 (6,830/651); Coastal, 8.8 (7,749/885).  These numbers, indicating a clinal increase of Red-shoulders to Red-tails from north to south, would seem to contradict the views of Northeastern Connecticut observers such as Mark Szantyr.  To be continued.

Steve Broker

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