Silvereye subspecies on Broughton Island, New South Wales

Three taxa of the Silvereye Zosterops lateralis were confirmed to occur on Broughton Island, New South Wales. In bird banding activities carried out in 2017-2019, we identified 404 Silvereyes to subspecies level. Subspecies cornwalli (Z. lateralis cornwalli) was present all year and some birds of that subspecies either were resident on the island or were regular visitors. The local Silvereye population on Broughton Island was swelled by two annual influxes. The migratory subspecies westernensis (from eastern Victoria and south-eastern New South Wales) and lateralis (from Tasmania) arrived in autumn and remained on the island for 4-6 months. In spring, the number of cornwalli on Broughton Island also increased substantially. The latter influx was probably in response to the abundant seasonal food supply, particularly the availability of berries of Monotoca elliptica, a native plant which is becoming widespread in parts of Broughton Island now that feral animals have been removed. In autumn and winter c. 15% of the trapped Silvereyes examined were of subspecies lateralis and there were 40-45% each of cornwalli and westernensis. The ratio of the migratory subspecies, westernensis and lateralis, was around 3:1 in every autumn and winter field trip. This suggests a regular migration pattern for both subspecies. We recorded biometric data for all three subspecies. On average, the tails of westernensis birds were longer than those of cornwalli and lateralis, but there were no other statistically significant biometric differences.    It would be difficult to differentiate the three subspecies based on measurement, although lateralis and westernensis potentially could be differentiated on tail length.  

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