Quick Dips

The Birds and the Weeds

Introduced birds could be spreading weeds to bush reserves and reducing the food supply for native birds, according to Landcare Research biologist Peter Williams. He believes the spread of weeds by introduced birds could have implications for native bird populations.

"Introduced and native birds have different diets, so the spread of weeds could reduce the amount of food that native birds can eat."

Williams, with fellow researcher Brian Karl, has been studying two kahikatea and totara forest reserves near Nelson, using mist nets suspended across the forest canopy to capture birds.

"We are using a technique where we literally scare the shit out of small birds. Birds are the main carriers of seeds from woody weeds and we are looking at the droppings to see what weeds they are bringing in."

Williams says they hope to identify which birds are spreading weeds.

"So far we have found that birds have a varied diet according to the season, what is in fruit, and what they prefer. It seems that native birds such as bellbirds don't like most fruity weeds, but that introduced birds feed on such weeds as barbary and privet."

This summer Williams is looking at how the dispersal of weeds affects the food available. He says past research of New Zealand scenic reserves has shown that if a bush reserve is close to an urban area, it is more likely to have weeds spread by introduced birds.

There are still many unanswered questions, such as what happens once weeds are established and whether birds change their diets or decline. Williams says the information will assist in identifying which weeds need controlling.