Date of Award:

5-1-1996

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Biology

Committee Chair(s)

James A. Gessaman

Committee

James A. Gessaman

Committee

Kimberly A. Sullivan

Committee

Michael L. Wolfe

Abstract

There were two primary objectives of this thesis. The first was to test the validity of sampling raptors during autumn migration for the purpose of monitoring trends in populations. The second was to describe morphometric characteristics of northern harriers (Circus cyaneus) during autumn migration in coastal New Jersey and revise the key for sexing and aging harriers captured on the east coast of North America. Harriers were concurrently, but independently, counted and captured during autumn migration at Cape May Point, New Jersey, from 1976 through 1995. All data were standardized to the same 83-day annual study period and adjusted for the number of hours of sampling effort. Counts and captures showed strong significant correlation (r = 0.81, P < 0.001) over the 20-year study. Linear regression and nonparametric rank-trend analyses showed the number of harriers passing Cape May Point increased slightly, but not significantly, over the study. New Jersey migration data showed significant positive correlation (r = 0.58, P = 0.02) with breeding population indices from the New York State Breeding Bird Survey. The results of this study demonstrate that, for some species, sampling migrants with either counts or captures may be a cost-effective method of monitoring raptor population trends. Morphometric characteristics of 588 northern harriers captured during autumn migration at Cape May Point, New Jersey were described. This is the largest morphometric sample for this species in North America. Male measurements were all significantly (P < 0.001) smaller than female measurements. Juveniles of both sexes had significantly (P < 0.05) shorter exposed culmen lengths and wing chord lengths, and had less mass than adults. A linear discriminant function based on wing chord, mass, and hallux claw length correctly identified the sex of all 372 harriers tested. Wing chord length criteria currently recommended by the North American Bird Banding Techniques manual for sexing captured harriers misclassified the sex of 23% of juvenile females measured at Cape May Point. Based on the results of this study, I propose morphometric modifications to the key for sexing and ageing harriers during autumn migration on the east coast of North America.

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