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Effect of Radio Transmitters on Survival, Harvest Rate, and Body Condition of Northern Bobwhite

Lori Corteville, L. Wes Burger, Department of Wildlife and Fisheries, P.O. Drawer 9690, Mississippi State University, Mississippi State, MS 39762 USA, and Leonard A. Brennan, Tall Timbers Research Station, P.O. Box 670, Tallahassee, FL 32312 USA

Radio telemetry is an important tool in wildlife research. It is the best available method for estimating home range, quantifying habitat selection, estimating survival, and monitoring reproductive success of wild, free-ranging animals. Radio telemetry studies assume that the attachment of radio packages does not affect the behavior or survival of the animal. However, transmitters could affect animals either directly (e.g., inhibiting movement) or indirectly (e.g., increasing stress or energetic costs). If the effect is large, it could bias measurements of home range, habitat selection, survival, and reproductive success.

With respect to game birds, a number of previous studies focusing on grouse, pheasant, wild turkey, and woodcock have differed with regard to the magnitude of transmitter effects. Several researchers have reported that radios altered courtship behavior, reproductive success, flushing behavior, and survival of adults and/or chicks. Other researchers have observed minimal effects that occur only during an adjustment period shortly after being radio-marked. Several factors could affect the occurrence and magnitude of radio effects. It is important to consider the method of transmitter attachment (back-mounted vs. neck-mounted), the ratio of transmitter weight to body weight, and the color, size and visibility of the transmitter. A factor often overlooked in telemetry studies is the subtle, sub-lethal effects of transmitters on the health of the bird. Stress from wearing a radio package has resulted in weight loss or less weight gained for some species of game birds.

The effect of radio transmitters on bobwhite has not been rigorously tested. However, numerous recent studies have used radio telemetry to study bobwhite reproduction and survival. The magnitude of bias in these studies is unknown. The objective of this study was to evaluate the effects of radio transmitters on bobwhite harvest rate, annual survival, and body condition.

During 1994-96, we banded 317 and radio-marked 260 bobwhite (Colinus virginianus) on the Divide Section Wildlife Management Area in Mississippi. During 1994-96 we banded 221 and radio-marked 259 bobwhite at Tall Timbers Research Station (TTRS) in Florida. Harvest and survival rate were estimated using data from both live recaptures and dead recoveries in a multinomial capture-recapture-harvest model. The computer program MARK was used to compute these estimates and construct hypotheses tests. We used 1-way z-tests to test for effects of radio-marking on survival and harvest rate. We used 2-way ANOVA to compare weight at harvest between banded and radio-marked birds.

Harvest rate did not differ (X2 = 5.377, df = 4, P = 0.2508) between radio-marked and banded birds in Mississippi (1994 r = 0.34, 1995 r = 0.34, 1996 r = 0.20). However, in Florida, radio-marked bobwhite (r = 0.27) were harvested at a higher rate than banded birds (r = 0.15) (X2 = 9.139, df = 1, P = 0.0025). Annual survival did not differ (X2 = 0.354, df = 6, P = 0.9992) between banded (11%) and radio-marked (7%) birds in Mississippi or in Florida (banded S = 0.07, radio-marked S = 0.05; X2 = 0.287, df = 6, P = 0.9996). Change in body mass between banding and harvest recovery did not differ between treatments in Mississippi (F = 0.749, df = 31, P = 0.393) or in Florida (F = 0.353, df = 59, P = 0.555). Higher harvest rates of radio-marked quail on one area suggest that radio transmitters may bias estimates of harvest. However, we were not able to detect bias in annual survival estimates. Development of smaller, less conspicuous radio-packages would further reduce the potential radio effects on bobwhite.

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