Research by PhD candidate: Christina Beulow (research grant 2015)
Almost 50% of bird species found in Australia, can be found in the Wet Tropics region. It is commonly known that birds, such as the cassowary, play an important role in the ecosystem as seed dispersers. There are other complex functions that birds fulfil in relation to the Wet Tropics region. For instance, when the pied imperial pigeon (Ducula bicolor) forages on the coast and then returns to roost and breed on mangrove islands it is potentially creating connectivity between the islands and mainland. Buelow’s research “The drivers, patterns and consequences of avian connectivity in the coastal forest mosaic” investigates landscape connectivity and bird species composition; foraging patterns and connectivity; and pied imperial pigeons nutrient subsidisation of mangrove-forest productivity.
Bird composition was determined through bird surveys conducted in four coastal forest types at 10 survey locations spanning from the Wet Tropics (north-east tropical landscape) to the Central Mackay Coast (south-east tropical landscape). The connectivity of 11 categories of vegetation was measured using geographic information system software (ArcGIS). This data was combined to understand where bird species were present in relation to the connectivity of the vegetation and landscape features. The types of birds varied between wet and dry tropical landscape contexts with the most distinct species composition found in mangrove habitats. Overall, high connectivity of rainforest vegetation patches with both a high total area and total edge were higher in bird species diversity.
The foraging patterns of mangrove birds were determined through sample collection of bird blood and claw tissues. Birds were caught with mist nets to enable sampling. These samples were analysed for carbon and nitrogen isotopic signatures and compared to the isotopic signatures of basal food sources. Analysis of bird blood shows the type of foods eaten over the prior two to three weeks whilst analysis of the bird claw shows a record of food consumed over the past two to five months. This allowed reconstruction of the birds’ diets over both timeframes and it was found that granivores, insectivores, nectarivore-insectivores (birds that consume nectar and supplement with insects) and omnivores are generalist foragers and will feed on whatever is in abundance. The carnivores however are specialist foragers focusing primarily on crabs and fish.
Pied imperial pigeons were used as a case study in bird foraging connectivity. Mangrove forests provide
nesting,roosting and foraging habitats for diverse bird communities. In the Wet Tropics, the pied imperial pigeon forages along mainland rainforest habitats and nests on adjacent islands, presumably as a predator avoidance technique. This study analysed soil and leaf samples collected from nine islands which included those with no breeding colony, a medium sized colony or a large colony. Samples were collected pre and post breeding season. Results demonstrated that the islands with pied imperial pigeon colonies are being supplemented by the long-term continuation of breeding events.
Publications associated with the project can be found here:
Spatial dynamics of coastal forest bird assemblages: the influence of landscape context, forest type, and structural connectivity http://rdcu.be/po9f
