Interacting impacts of drought and fire on bird populations—insights from a long-term study in the Warrumbungles

The interacting effects of drought and fire on ecological communities are poorly understood. Long-term studies in the Warrumbungle Mountains, central-west New South Wales, subject to drought and fire during the past 21 years, enabled their separate and combined effects to be quantified for individual species and functional groups. Insectivores (especially ground-foragers) dominated previous lists of declining species in this region of NSW and were also prominent in the present work. Insectivores were more likely to be drought- than fire-affected, with seven species declining due to drought, three to drought plus fire, and three to fire alone. Our analyses also revealed declines in a suite of honeyeaters (Meliphagidae), previously not reported as declining. Honeyeaters are major pollinators of eucalypts, so the loss of nectarivores and insectivores has far-reaching implications for pollination, recruitment, successional dynamics, and forest health. Four honeyeater species were adversely affected by drought, five by fire, and one by a combination of drought and fire. Drought and fire, alone or in combination, were implicated in declines of granivores, including the Crimson Rosella Platycercus elegans, and frugivores, especially the Mistletoebird Dicaeum hirundinaceum, the latter reflecting the loss of mistletoes in fire-affected landscapes, and foreshadowing additional losses due to the reliance on mistletoe by many species. Another group not previously identified as threatened, but declining due to drought were two omnivores, the Pied Currawong Strepera graculina and Australian Raven Corvus coronoides. Hollow-nesting birds including two species of treecreeper and the Laughing Kookaburra Dacelo novaeguineae fared badly. Several common Australian species were among the decliners, including Laughing Kookaburra, Willie Wagtail Rhipidura leucophrys and Australian Magpie Cracticus tibicen. We conclude that no suite of birds is exempt from these environmental stressors, and predict that, as droughts reduce populations at regional scales and fires diminish carrying capacity of critical habitats at landscape scales, rarer species will decline to local extinction while more commonly observed species will be reduced in abundance.