High temperatures and poor habitat reduce nestling condition and survival in a tropical songbird

Climate change and habitat degradation are major threats to wildlife
worldwide. Although developing animals are particularly sensitive to their
impacts, with fitness consequences for individuals that cascade to
population persistence, their combined effect and potential interaction
are rarely considered. Here we address this in an indicator species for a
biodiverse riparian ecosystem in Australia’s tropical savanna, an
understudied region threatened by habitat loss and climate change. We
investigate the effect of habitat, temperature and rainfall on nestling
condition and subsequent survival in an individually-marked population of
the Endangered purple-crowned fairy-wren (Malurus coronatus coronatus).
Leveraging a high-quality 10-year dataset of nestling measurements, we
control for pertinent factors influencing growth (e.g. food provisioned)
and quantify short- and long-term survival with high accuracy. Higher
ambient temperatures in the week after hatching reduced nestling body
condition (mass relative to body size).
      Poor, degraded habitat
(lower density of mid-story vegetation) decreased nestling body condition,
regardless of temperature or rainfall. Lower body condition as a nestling
did not affect survival to nutritional independence (12 weeks) but
decreased survival from independence to adulthood (2 years). Poor habitat
also directly decreased survival to adulthood, compounding this effect.
Taken together, our results show that climate warming and habitat
degradation are additive threats to nestling purple-crowned fairy-wrens
that reduce survival to adulthood. Future research should address the
mechanisms underlying the protective effect of high-quality habitat and
explore how exposure to these threats during development affects fitness
in other species. Policy implications: Our study shows that improving
habitat quality is critical for riparian wildlife as the climate warms and
that supporting long-term studies is important for detecting cryptic
effects of anthropogenic threats. The Australian monsoonal savanna is
projected to warm by 3.5°C by 2090, and our models predict an associated
average 2.2% decrease in purple-crowned fairy-wren survival. This could be
offset by a 7% increase in average habitat quality, underscoring the
importance of high-density riparian habitat as a climate refuge.
Conservation strategies for climate warming should protect high-quality
habitat and improve low-quality patches, for example through effective
fire management and reduction of high-intensity grazing.