FEEDING BY CLAY-COLORED SPARROWS ON GRASSHOPPERS AND TOXICITY OF CARBOFURAN RESIDUES

The potential hazard of carbofuran-sprayed insects to clay-colored spa rrows (Spizella pallida) was determined by measuring consumption of gr asshoppers (Melanoplus sanguinipes) by nestlings and adults, attractiv eness of dead vs. live grasshoppers, and toxicity of sprayed grasshopp ers to adults. Hand-reared nestlings 8 to 10 and 14 to 22 d old ate me an quantities of grasshoppers per bird of 0.61 and 0.83 g, respectivel y, per bout of feeding when fed to satiety every hour from dawn to dus k. These rates of intake in the field could result in doses of 0.2 mg/ kg body mass (14% of the LD50 for adults) in brief bouts of feeding if they were fed sprayed insects containing carbofuran at 2.5 mug/g, the mean concentration found after aerial application of 134 g a.i. per h ectare. Nestlings 2 to 3 d old ingesting about 0.2 g grasshoppers in b rief periods might receive lethal doses from carbofuran residues of 2. 5 mug/g or the maximum concentration of 5.7 mug/g if they are more sen sitive than adults. There was nonetheless no evidence of reduced survi val among nestling passerines for 3 d following aerial spraying of car bofuran at 134 g/ha in a pasture. Captive adults preferred dead grassh oppers in trials in which live and dead grasshoppers were offered simu ltaneously. When six adults were provided with 24-h supplies of spraye d grasshoppers containing carbofuran at 2.6 mug/g, they showed no tast e aversion and consumed quantities 24% greater than those eaten by con trol birds. No mortality resulted from eating the contaminated grassho ppers. Mean hopping activity by treated birds increased by 80%, relati ve to controls, 5 h after receiving poisoned grasshoppers, but the dif ference was not significant. Although captive adults consumed close to their body mass in grasshoppers daily, an LD50 of carbofuran from gra sshoppers containing 2.5 mug/g would require rapid ingestion of 6.7 g, a quantity about 7 x the birds' capacity for short-term ingestion. Ou r results, combined with observations of a related field study, sugges t that adult and nestling passerines are able to tolerate the dietary exposure to carbofuran resulting from ingestion of grasshoppers spraye d at the rate of 134 g/ha. Conclusions about safety should not be draw n, however, until more field applications have been monitored.