Abundance patterns across months and locations, and their differences between migrant and resident landbirds in lowland subtropical eucalypt forest

Abstract

Many migrant landbird species are winter visitors to lowland eucalypt forests of the south-east Queensland region within subtropical eastern Australia. However, neither the specific patterns of habitat use by these migrant species, nor the extent to which the temporal and spatial patterns of migration are synchronised among different species, are well understood. This paper examines the pattern and synchrony of monthly change in bird species over a nine-month period (March–November), based on counts at seven survey sites within each of three large (>600 ha) lowland eucalypt forest remnants. These were surrounded by a mostly urban matrix, and widely separated within a total area of ~1000 km². Species were analysed with respect to both their individual abundances and collective patterns within four a priori groups: winter migrants, summer migrants, complex wanderers and residents/local movers. Collectively, the numbers of winter migrants were highest from May to August, but species' broad arrival times varied from April to June, departures from July to October, and times of peak abundance also varied. Seven of eight winter migrant species that were individually analysed (Rose Robin, Yellow-faced and Scarlet Honeyeaters, Striated and Spotted Pardalotes, Grey Fantail and Golden Whistler, but not Rufous Whistler) showed large changes in abundance over the period. The abundance of these seven species did not vary among the three locations, and also showed concordant patterns of temporal change across locations. Some showed partial migration. The resident/local mover species showed little or no change in abundance over time, and eight of the 16 species analysed showed substantial abundance differences among locations. The difference in location effects between migrant and resident species may occur because the winter migrants are non-breeding visitors to the region, whilst the resident species are year-round inhabitants and are hence more selective since they are more likely to occupy long-term home ranges that must provide habitat suitable for nesting.