Survival and behaviour of captive Mallard broods exposed to carbofuran-sprayed vegetation: a field experiment.

: A field study was undertaken to determine the effects of exposure to vegetation sprayed with carbofuran (2,3-dihydro-2,2-dimethyl-7-benzofuranylmethyl carbamate) on the survival and behavior of Mallard (Anas platyrhynchos) ducklings. Pairs of captive hens with newly hatched broods of five to eight ducklings were released into sprayed or control 200 m long walkways leading directly to 0.1 ha pond enclosures. Carbofuran was applied at 132 and 264 g a.i. ha(-1) during five and four replicate trials, respectively. Broods were observed during the walk, and activity was recorded systematically during four 2-h periods over the following two days. Dead or abandoned ducklings were retrieved and brain acetylcholinesterase (AChE) activity was determined. Carbofuran did not affect the rate of duckling loss on the day of exposure at either spray rate compared with that of controls (3/34 versus 3/38 ducklings and 3/31 versus 0/31 ducklings, respectively). Nevertheless, one and three of the abandoned or dead ducklings in the low and high spray-rate trials, respectively, exhibited depression of brain AChE activity associated with mortality caused by anticholinesterase compounds (16 to 47% of mean control activity). Although no significant differences were detected in duckling behaviour between treated and control broods at either exposure level, treated broods tended to spend a larger proportion of time hidden in emergent vegetation. The ingestion of carbofuran by ducklings walking through sprayed vegetation appears to be the critical mode of intake, with dermal absorption being minimal.