Some Aspects of Grackle Feeding Behavior in Newly Planted Corn

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Observations were made of 237 common grackles (Quiscalus quiscula) in newly planted and sprouted corn to describe and quantify aspects of feeding behavior and to determine the effects of repellent-treated corn on feeding behavior. One hundred and twenty-two of the observations were of grackles that ate corn. Birds consumed sprouted seeds more rapidly than unsprouted seeds and dropped more unsprouted seeds than sprouted seeds. No differences were detected in the immediate response to repellent-treated seed (time to consume or proportion dropped). It is suggested that the birds learned to avoid completely treated seed but were not averse to entering the treated area. J. WILDL. MANAGE. 41(3):444-447 Most reports on the experimental use of repellents against birds have dealt with methods of application and measurement of reduction in damage to the crop. Few studies have dealt with the feeding behavior of the depredating species or the changes in behavior caused by contact with or ingestion of the repellent. Dyer (1967) deduced feeding behavior of blackbird flocks from damage patterns in field corn and subsequently suggested (1972, paper presented at 89th Stated Meeting of the A.O.U.) that a fright producing chemical (4-aminopyridine), which directly affects only a few members of a flock, interrupted the normal flock feeding behavior of red-winged blackbirds (Agelaius phoeniceus). He speculated on the nature of the disruption in the flock as a whole but did not report on the behavior of individual birds. The problem of blackbird damage to sprouting corn is locally serious in the Southeastern and Middle-Atlantic states (Stone and Mott 1973). Ingram et al. (1973) studied efficacy of methiocarb (3,5,dimethyl-4-methylthiophenol methylcarbamate) [Mesurol?] in reducing this damage. They suggested that their index of overall bird ac ivity in cornfields (presence of birds) did not provide a sensitive measure of the protection afforded by the repellent. These authors found that the numbers of red-winged blackbirds, brown-headed cowbirds (Molothrus ater), common crows (Corvu brachyrhynchos), and ring-necked pheasants (Phasianus colchicus) decreased in treated fields whereas the number of common grackles increased. Damage to treated fields used primarily by grackles w s significantly reduced, therefore the repellent may have caused some alteration in feeding behavior, although this was not examined. We carried out this investigation to deect, d scribe and attempt to quantify some aspects of blackbird feeding behavior in newly planted and sprouting corn, and to identify possible alterations occurring as a result of feeding on corn seed treated with the repellent methiocarb. The authors thank C. Passmore, Farm Manager, University of Delaware, for assistance with seed bed preparation and planting. We also thank G. Beauchamp and R. Doty for suggestions during the preparation of the manuscript. 1 Assigned to Pennsylvania Field Station, Denver Wildlife Research Center. 2 Assigned to Delaware Field Station, Denver Wildlife Research Center. 444 J. Wildl. Manage. 41(3):1977 This content downloaded from 207.46.13.25 on Mon, 12 Sep 2016 04:18:13 UTC All use subject to http://about.jstor.org/terms GRACKLE FEEDING BEHAVIOR Rogers and Linehan 445