Publications Archive

Abstract: Bird abundances on a small island (150 ha) near the mainland of northern North Island New Zealand were studied using a standardised, longitudinal survey through 38 years (1988–2020), a period during which habitat restoration, reintroductions of five native bird species, and control of rats (Rattus spp.) and stoats (Mustela ermina) occurred. We estimated time-series abundances of 33 bird species and found substantial population shifts shared by many taxa. The unique data set from this restoration project showed that: (1) more species and more individual birds were present at the end of the study than at the beginning; (2) rat control made an immediate and lasting difference, increasing population growth of the typical species 6% per year; (3) boosting ecological succession by habitat conversion and habitat enrichment resulted in a long term population growth of many native bird species; (4) shifts in species composition are still ongoing 20 years after predator control, with both gradual, long-term increases, and declines. In particular, two endemic species, and pōpokotea (whitehead, Mohoua albicilla) proved robust competitors in a predator- free environment, increasing in abundance, while most non-native and many native species declined. These gradual, longer-term shifts became clear during “maturation”, a period beginning about 13 years after predator control started.

Abstract: The species composition of moa assemblages reflected the local vegetation. These assemblages have been used as indicators of the geological age – glacial or Holocene – of the fauna. Within the assemblages, some species of moa have been associated with specific vegetation types, including Anomalopteryx didiformis with lowland rain forest, and Euryapteryx curtus, with dry shrubland. The sequence of radiocarbon ages for A. didiformis and E. curtus in the Waitomo karst, in the west central North Island, New Zealand, records changes in the distributions of their habitats over the past 28,000 years. The presence of A. didiformis shows that, contrary to current reconstructions, there was lowland rain forest in the karst during the Last Glacial Maximum. An abrupt change to E. curtus and hence of its shrubland habitat coincided with the Oruanui super eruption of Taupo volcano 25,400 years ago. Anomalopteryx didiformis and its rain forest habitat did not return to the karst until c. 13,000 years ago. E. curtus disappeared from the karst some time before that, during the gradual post-glacial warming, but remained elsewhere on the Volcanic Plateau, probably in the seral vegetation that followed the continual eruptions. Moa distributions were not always altered just by climate change. Major eruptions such as the Oruanui could change their habitat and hence their distribution over much of both main islands.

Abstract: House mice (Mus musculus) have proven to be the most difficult introduced mammal to eradicate from (and keep out of) New Zealand reserves and sanctuaries. Partly as a consequence of this, little is known about how bird communities respond to mouse eradication. Mice were successfully eradicated from 217 ha Mana Island Scientific Reserve, near Wellington, in 1989–90. Five-minute bird count surveys undertaken in spring and autumn before and after mouse eradication revealed that 13 of 22 species were recorded significantly more often after mouse eradication, and just two species were recorded significantly less often following the eradication (and each of these in one only of the two seasons that were compared). Four species had no significant change, and three species showed mixed responses between the two seasons. While the overall pattern was of increased relative bird abundance after mouse eradication, there is limited information on why individual bird species increased during the study period, and whether this was a consequence of mouse eradication. Bird count data revealed that insectivorous passerines may have benefited the most from mouse eradication on Mana Island, suggesting that competition for invertebrate prey was the main impact that mice had on the birds of the island. The use of anticoagulant rodenticides to eradicate mice from Mana Island had little detectable impact on populations of the island’s birds.

Abstract: Male and female adult Floreana mockingbird (Mimus trifasciatus) have monomorphic plumage features that make them impossible to sex in the field. In this study, we use discriminant function analysis (DFA), a widely used technique, to assess the best measures to determine sex. We measured six morphological characteristics (mass, beak depth, beak width, tarsus length, wing length, and head-beak length) for birds of known sex (determined by molecular techniques) from the two extant populations of M. trifasciatus on Champion and Gardner islets, within the Galápagos archipelago. Using a coefficient of sexual dimorphism, we found that males are significantly larger than females in three of the variables. Discriminant functions using wing length and a combination of wing length + mass, and wing length + tarsus length could classify birds with a 98% level of accuracy. Furthermore, we were able to estimate a robust cut-off point to determine the sex of individuals in the field through a decision tree, using only wing length as morphological variable. Fast and accurate sexing of the bird based on one variable will reduce handling times and minimise stress for captured birds.