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Changes in the Mana Island, New Zealand, bird community following mouse (Mus musculus) eradication

Notornis, 69 (4), 243-255

Miskelly, C.M., Beauchamp, A.J., Oates, K.E. (2022)

Article Type: Paper

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.

Sexing of the endangered Floreana mockingbird (Mimus trifasciatus) using morphometric measurements

Notornis, 69 (4), 256-263

Reyes, E.M.R., Smith, A.N.H., Rueda, D., Sevilla, C., Brunton, D.H., Ortiz-Catedral, L. (2022)

Article Type: Paper

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.

Post-translocation movements and ranging behaviour of roroa (great spotted kiwi, Apteryx maxima)

Notornis, 69 (3), 135-146

Jahn, P., Ross, J.G., Mander, V., Molles, L.E. (2022)

Article Type: Paper

Translocations are increasingly used in kiwi (Apteryx spp.) conservation management, and their outcome is largely influenced by post-release dispersal and survival. A translocation of roroa (great spotted kiwi, A. maxima) to the Nina Valley, near Lake Summer Forest Park, is the first reintroduction of the Arthur’s Pass roroa population. In 2015, eight wild-caught adults were translocated from Arthur’s Pass National Park, following the release of ten captive-hatched subadults during 2011–13. We monitored the translocated kiwi by radio telemetry during 2015–17. Dispersal was highly variable among the released wild birds. The straight-line distance from the release site to the last recorded location ranged 0.5–10.3 km. Seven of the wild birds remained in the Nina Valley and covered an area up to 1,700 ha (95% utilisation distribution). Releasing the wild birds had no measurable impact on the ranging behaviour of previously released subadults. The current population founder group comprises a maximum of 13 unrelated individuals, and therefore further releases are necessary for a genetically viable population. Additionally, expansion of the pest-controlled area is crucial for the long-term persistence of the reintroduced population in the Nina Valley.

Continued increase in red-billed gulls (Larus novaehollandiae scopulinus) at Otago, southern New Zealand: implications for their conservation status and the importance of citizen science

Notornis, 69 (2), 81-88

Lalas, C., Carson, S., Perriman, L. (2022)

Article Type: Paper

A published national survey of red-billed gulls (Larus novaehollandiae scopulinus) in 2015 recorded about 28,000 nests in New Zealand, a 30% decrease in 50 years. We compared nest numbers in 2020 at Otago, south-eastern South Island, with published records for 1992–2011 and 2015. In contrast to trends further north, numbers at Otago have increased but the average annual rate of increase dropped from 6–10% for 1992–2011 to 2% for 2011–2020. Citizen science provided a valuable input in 2020 with records of breeding at previously undocumented urban locations. The about 6,000 nests at Otago in 2020 probably account for 20% of the national total.