Seasonal and habitat related variation in the health of tropical savanna finches

Differences in habitat quality can affect the abundance, distribution, and physiological status of wild birds. In Australia’s tropical savannas, grass finches live in habitats of varying land use and resultant habitat quality. Recent studies have documented regional declines in the abundance and distribution of small granivorous birds in areas affected by cattle grazing, urban development, and changes in fire frequency and timing. Small birds, especially semi-nomadic species of grass-finches, are extremely difficult to survey for changes in local abundance and productivity. Consequently, we are using a range of physiological measures to determine the susceptibility of populations to decline. We present the preliminary findings of a study using multiple condition indices to describe the health of five grass finch species living in a variety of savanna habitats. Our early results suggest that simple body condition measures such as bird mass, muscle contour, and fat storage, are not always sensitive enough to identify subtle differences in the health of individuals and populations. Measures of haematological health state, stress, and background nutritional status of finch populations appear to be associated with seasonal and site differences where body condition measures or abundance surveys would have failed to present a coherent picture. We are using habitat characteristics important to these species to help explain the differences in the health of finch populations across the North.