Paul P. Woronecki

COMPENSATORY RESPONSE OF MATURING CORN KERNELS FOLLOWING SIMULATED DAMAGE BY BIRDS

(1) A study was made to measure compensatory growth responses and to estimate losses associated with bird damage to maturing corn. (2) Corn kernels contain 20-40%. of their final biomass at the time they are usually consumed by blackbirds. (3) Very slight compensation of kernel weight occurred following simulated bird damage to tip kernels. (4) Heavy bird damage, early in kernel development, increased fungal, sprouting, and insect damage before harvest. (5) Estimates of bird damage, subsequent secondary damage, and compensation were affected by the amount of damage, maturity of the kernels at the time of damage, and environmental factors before, during, and after damage. (6) Visual estimates of weight change were closely correlated with actual loss of the total kernel weight. (7) Studies of food habits and bioenergetics that have used feeding rates and numbers of birds to estimate the impact of blackbirds on corn crops may have underestimated reductions in corn yields.

Taste preferences of male red-winged blackbirds among dried samples of ten corn hybrids

Damage by red-winged blackbirds (Agelaius phoeniceus) to maturing corn results in the loss of about 1% of the United States crop (Stone et al. 1972; Dolbeer 1980, 1981). In some localities, especially near marshes, economic losses can be severe for individual farmers (Wakely and Mitchell 1981). For example, in Ohio, 1.3% of the cornfields receive losses of greater than 5% (Dolbeer 1981). A number of management schemes are used to reduce bird damage. Such schemes sometimes include the use of chemical toxicants (e.g., 4-aminopyridine [Woronecki et al. 1979]), propane exploders, shell crackers and electronic systems to frighten birds from fields, or chemical sprays to reduce roosting populations in corn growing areas (Weatherhead et al. 1980). Unfortunately, because of the difficulties in accurately predicting bird damage and properly timing control, and because of the limited effectiveness and often high cost of such methods, a net benefit is not often achieved (Dolbeer 1981). The use of hybrid corn resistant to bird attack has received little attention; however, findings from the few studies done to date suggest varietal resistance as a promising approach for reducing bird damage. Thompson (1963) evaluated four inbred lines of corn and their single crosses and concluded that bird damage was related to husk extension in the different phenotypes. More recently, Caccamise (1975) and Linehan (1977) documented that bird damage varies widely among hybrids grown in experimental station plantings, and Dolbeer et al. (1982) reported that husk extension beyond the cob tip and husk thickness are significantly and negatively correlated with bird damage. Our preliminary work has suggested that taste properties might also contribute to hybrid resistance. The objectives of the experiment reported in this paper were to investigate taste preferences that male redwinged blackbirds might exhibit among hybrids as well as correlates between preferences and chemical differences among the hybrids.

Red-winged blackbird (Agelaius phoeniceus L). feeding response to oil and anthocyanin levels in sunflower meal

Abstract Bird damage to sunflowers might be reduced by the development of resistant cultivars. Neagra de Cluj may be one such cultivar, with high levels of anthocyanin (a possibly aversive flavour) in achene hulls, but low oil yield. Four experiments were designed to assess the importance of oil content and anthocyanin concentration in feeding preferences expressed by red-winged blackbirds (Agelaius phoeniceus L.). Differences in oil concentration of 15% (w/w) were reliably discriminated in two-choice tests: higher concentrations were preferred. Conversely, all anthocyanin concentrations (0·5, 1·0, 2·5 and 5·0% [w/w]) were avoided, and two-choice tests suggested that higher concentrations (2·5 and 5·0%) were relatively more aversive. Both anthocyanin concentration and oil content could influence Neagra de Cluj resistance to bird depredation. Of these two characteristics, oil may be relatively more important.

Ranking and evaluation of field corn hybrids for resistance to blackbird damage

We measured husk characteristics for a sample of ears from each of 229 hybrids grown in a performance test in Ohio in 1987 and ranked these hybrids for potential resistance to bird damage. Hybrids predicted to be resistant (i.e. with heavier husks) tended to mature later and have lower yields in the 1987 performance test than did the lighter-husked hybrids. We selected three hybrids from the 10 predicted to be most resistant, three from the 10 predicted to be least resistant and two intermediate hybrids to be evaluated in a free-choice aviary test with red-winged blackbirds (Agelaius phoeniceus L.) in 1988. The three resistant hybrids averaged 2.5% corn loss, significantly (P < 0.01) less than the 26.1% loss for the three susceptible hybrids. The two intermediate hybrids had intermediate damage levels. In a 1989 field evaluation in New York, damage was substantial in all hybrids although the three predicted-resistant hybrids still averaged significantly (P < 0.05) less loss (20.5 bu/ac) than did the predicted-susceptible hybrids (27.4 bu/ac). Final yield was not significantly different between the two hybrid groups. The ranking system accurately predicted resistance but additional evaluation is recommended regarding within-hybrid variation in husk characteristics among planting sites and years.

Visual Cue Fails to Enhance Bird Repellency of Methiocarb in Ripening Sorghum

Methiocarb (Mesurol®) produces a conditioned aversion which birds associate with a particular treated food and then avoid (Rogers 1974). Numerous field tests have shown that methiocarb is generally effective in reducing bird damage to ripening fruits when applied at rates of 1 to 2 kg/ha. Methiocarb was registered in the United States by the Environmental Protection Agency for use in cherries and blueberries during the 1980’s (Dolbeer et al. 1988). These registrations were withdrawn by the proprietary company in 1989 because of additional studies required by EPA related to methiocarb residues and environmental effects.