Evaluation of existing predator control programs for the benefit of the white-flippered penguin (Eudyptula minor albosignata), on Banks Peninsula, Canterbury, New Zealand

Abstract

In the early 1900's white-flippered penguins (Eudyptula minor albosignata) could be found breeding in many of the Banks Peninsula bays, but since 1980 population numbers have been declining drastically due to predation by introduced mammalian predators. Landowners in two bays (Flea Bay and Stony Bay) on Banks Peninsula have initiated their own independent predator control to protect the white-flippered penguins living in the bays. Flea Bay has a large colony (717 breeding pairs) and Stony Bay has a relatively small colony (42 pairs). Both landowners have had no external assistance in the initiating, planning and maintenance of their predator control programs. The two predator control operations were evaluated over the 2000/2001 breeding season, with a view to provide recommendations for more effective control of predators in the two bays.

A catch index was used to determine seasonal variation in predator abundance and the success of traps that had been placed in various habitats to target penguin predators. The primary predators of white-flippered penguins, ferrets and cats, were found to be present at both bays in relatively high numbers. At Flea Bay, 50% and 70% of the cats and ferrets were caught in autumn respectively. At Stony Bay 67% of the cats killed were caught in summer, and all ferrets caught at Stony Bay were killed in spring. The catch index (predators caught per 100 trap nights) at both bays for all predator catches was highest in autumn (1.87 at Flea Bay, 0.73 at Stony Bay), and lowest in winter (0.06 at Flea Bay, 0 at Stony Bay). Cats and ferrets were mainly caught in traps that had been placed on a walking track, hedgehogs in scrub and/or bush, and rats in grazed grass. Ink-tracking tunnels were also used to determine predator movement in the two bays. Cat and ferret prints were found more often in tunnels that had been placed on a walking track, hedgehogs in scrub and/or bush and rat prints were most commonly found in tunnels placed in rank grass.

Analysis of gut contents was carried out on 18 cats and 11 ferrets that were caught at the two bays to determine if they had been eating white-flippered penguins. Rabbits and hares (Lagomorpha), rats and mice (Rodentia) and invertebrates were the primary prey found in the digestive tract of both the ferrets and cats. Two cats contained a single bird (Passeriformes), but there were no white-flippered penguin remains found in any of the dissected animals.

Predation losses and breeding success was monitored over the 2000/2001 breeding season. At Flea Bay, out of 83 nests, two eggs were taken by a stoat and six adult penguins were found dead. A cat was the predator responsible for four of the adult penguins and two died of natural causes. At Stony Bay, out of 22 nests that were monitored, five white-flippered and one Fiordland Crested (Eudyptes pachyrhynchus) penguin were found dead. Ferrets were assumed responsible for the death of all six birds. There was no seasonal trend in the predation of the birds, and no particular age class of penguin found to be more at risk of predation than another.

This research confirms that cats and ferrets are the primary predators of white-flippered penguins in Flea Bay and Stony Bay. Flea Bay has a larger number of predators present in the area, and due to the large number of traps in place, a 'sink effect' is occurring. Even so, only 0.42% of the Flea Bay colony was lost to predation over the breeding season. If this years' predation rate indicates a typical year, the current Flea Bay colony will be able to withstand this level of predation. The Stony Bay colony on the other hand, lost 6% of the population to predators. If predation rates continue as they are at present, this colony will continue to decline in number. More research is required to determine whether the Flea Bay colony's success is related to other factors, such as habitat availability.