An Evaluation of 4-aminopyridine for Dispersing Winter Blackbird Roosts in Colorado

INTRODUCTION Blackbirds and starlings (Sturnus vulgaris) often establish large winter roosts in areas where their presence is objectionable because of economic, public health, and nuisance reasons. Several techniques are available for alleviating roost problems, including habitat manipulation, roost dispersal with mechanical and pyrotechnic devices (Mott et al 1978), and, where necessary, direct population reduction (DeGrazio 1964). These techniques, however, have limitations due to weather, roost accessibility, logistics, and adverse public reaction. In the past, 4-aminopyridine (4-AP) has been used effectively as a bird-frightening agent in agricultural crops (Besser 1976), but until now has not been adequately tested for its effectiveness as a roost dispersal agent. Two earlier small-scale tests conducted on two Colorado roosts of 10,000 and 160,000 blackbirds indicated that 4-AP-treated cracked corn baits had a potential as a roost dispersal tool (DeCino et al 1965, Schafer 1966). In January and February 1979, I conducted additional tests to assess the potential of using 4-AP for dispersing roosts, to develop techniques for bait delivery, and to determine hazards to nontarget birds. METHODS Study Areas Two cattail (Typha spp.) marsh roost sites were selected in Colorado to test roost dispersal techniques utilizing 4-AP during January and February 1979. The first was 1.4 miles southeast of Longmont in Boulder County, and contained an estimated 49,000 red-winged blackbirds (Agelaius phoeniceus) and 1,000 starlings (Sturnus vulgaris) that roosted in two acres of a 15-acre marsh (Table 1). The second roost, in which birds were concentrated in eight of 26 acres, was eight miles east of Las Animas in Bent County, Initial roost estimates were 300,000 blackbirds (95% redwings, 4% starlings, and 1% Brewer's blackbirds (Euphagus cyanocephalus)). Dosing In January at the Longmont roost, 100 male redwings were individually dosed with one 3% 4-aminopyridine corn tablet (Garrison et al. 1979) each of three consecutive evenings and released into the roost as flights of blackbirds entered the roost at sunset. All dosed blackbirds had been captured locally and were held for 14 days in aviary cages before treatment. The actual dosing took about 30 minutes to complete each evening. At the 3% level, treated birds were expected to become affected within 20 minutes (DeGrazio et al. 1971, Garrison et al. 1979). DeGrazio et al. (1972) reported good dispersal results from cornfields when less than 1% of the flocks of birds in the fields were affected by 4-AP treated baits. 249 Bait Trays In February at the …