More than 2000 birds have died on Macquarie Island since the federal government began a scheme to cull rabbits, cats, rats and mice.

The Federal Environment Department's heritage and wildlife division told a Senate estimates hearing today that 2190 birds had died since the eradication program began last year.

Department officials said the birds had died after feeding off the corpses of poisoned animals and not from eating the pellets themselves.

Tasmanian Liberal senator Eric Abetz asked if the 110 dead ducks had fed off corpses or whether it was more likely they had fed off the 305 tonnes of poison bait on the island, which lies between Tasmania and Antarctica in the Southern Ocean.

An assistant secretary for the division Theo Hooy agreed the ducks would not have fed off corpses.