braided rivers

Strategies for defending large tracts of land from mammalian pest incursion are urgently needed. We report on a study investigating whether brushtail possum (Trichosurus vulpecula) range expansion into a controlled area was restricted by a watercourse. The true left of the Orongorongo River valley was treated with 1080 poison baits, and a 250 ha area bordering the river on the true right was excluded from treatment. Nontoxic cereal bait containing pyranine biomarker was sown repeatedly over half of the excluded area for nine weeks after poisoning.

We evaluated willow removal as a technique for enhancing habitat for birds of braided rivers by monitoring five bird species at three sites in the Mackenzie Basin, New Zealand, from 1991 to 1994 Four species—banded dotterel (Charadrius bicinctus), pied stilt (Himantopus novaezelandiae), black- fronted tern (Sterna albostriata) and South Island pied oystercatcher (Haematopus ostralegus) used the areas of riverbed cleared of willows for nesting and foraging, at the same or greater density than other areas of riverbed already free from willows.

Egg and chick loss at banded dotterel (Charadrius bicinctus) nests was studied over the 1992/93 season on the Tekapo, Ohau and Ahuriri Rivers in the Central South Island. Egg loss at nests was higher on the Ohau and Tekapo Rivers than on the Ahuriri River, especially early in the season. Only 11% and 12% of nests fledged one or more chicks on the Tekapo and Ohau Rivers respectively, compared to 42% of nests on the Ahuriri River. Nests on islands within the braided riverbeds were more successful than nests on the mainland.