U.S. Department of Agriculture: Animal and Plant Health Inspection Service


Date of this Version

January 1980


Journal of Applied Ecology (1980) 17,737-746. Permission to use.


(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.