The breeding biology of the little blue penguin Eudyptula minor on Somes/Matiu Island

Abstract

A decline in the numbers of Little Blue Penguins (Eudyptula minor) have been recorded at both Australian and New Zealand colonies (Dann, 1992, 1994; Hodgson, 1975). These decreases have been attributed largely to disturbances caused by humans and introduced predators (Dann, 1994; Hodgson, 1975). The opening of Somes/Matiu Island to the public has increased the vulnerability of its E. minor colony to such disturbances. The goal of this study was to assess the management of the Somes/Matiu Island E. minor colony, and provide the information required to assist its future management under the island's new regime of open access to the public. This was achieved by using recovery data dating back to 1968 to assess the population status of this colony since that time. The nesting habits and breeding biology of E. minor were documented over the 1995 and 1996 breeding seasons. This information was compared with Kinsky's (1960) study on the island. Over the 1995 and 1996 breeding seasons a total of 87 clutches were laid in the study area. Of the total clutches laid, 87% were two-egg clutches and 13% were one-egg clutches. Of the 163 eggs laid, 93 hatched (hatching success = 0.57). Of the 93 chicks, 77 survived to fledge (fledging success = 0.83). The overall reproductive success of the colony was 0.47, representing the proportion of chicks that survived to fledge out of the total number of eggs laid. Between the two seasons monitored there was no significant difference (X2 = 1.29, α = 0.05. 2 df, p = 0.53) found between the proportion of eggs laid, hatched and chicks fledged. Replacement clutches were found in both seasons, but only in 1996 were they successful. Of the losses suffered in the nests, the majority occurred during the egg stage. The type of nest used (i.e., soil burrow, rock crevice, under boulder etc.) was found to influence the fate of E. minor eggs on Somes/Matiu Island. A case of adoption was noted in the 1996 season, something not recorded in other E. minor colonies in New Zealand. E. minor were found to exhibit the tendency for mate and nest site fidelity between seasons, with breeding success influencing nest retention. Kinsky (1960) guessed that there were approximately 300 breeding pairs on the island. The population estimates that I calculated for the E. minor colony on Somes/Matiu Island from 1968 to 1996 ranged from 0.2 to 261 birds. The mean annual survival rate of adult E. minor breeding on Somes/Matiu Island was calculated as being 0.57 and the average life expectancy as 1.8 years. The estimates obtained using the recovery data are not reliable, largely due to limited recover data and inadequate sampling over this time period. Measures of reproductive success, pair productivity and total offspring losses from three other E. minor colonies showed much variation. Between the sites reproductive success ranged from 0.16 to 0.50, pair productivity from 0.32 to 1.22, and total offspring losses from 50% to 83%. Over the two seasons monitored the Somes/Matiu Island colony had a reproductive success of 0.47, pair productivity of 0.94 and total offspring losses of 53%.