An estimate of the water budget for the endangered night parrot of Australia under recent and future climates

Abstract

Background: Endangered species management must now incorporate the potential effects of climate change, but this is often in the context of limited data. The endangered night parrot was recently rediscovered in the Australian arid zone and a major effort is underway to ensure its survival. A key question is to what extent it is dependent on standing water under current and future climates, as this has major implications for understanding and managing its habitat requirements. However, very little is known about its ecology and physiology, and its conservation status precludes invasive ecophysiological studies. Method: Here we show how the methods of biophysical ecology permit strong inferences about this problem with minimal data. We developed a biophysical model of both the parrot and its habitat at the site of its rediscovery. We used allometrically-adjusted observations of the known physiology of a closely related desertadapted Australian parrot, the budgerigar, to infer unknown aspects of the night parrot's physiological responses, together with plumage measurements from museum specimens. We tested the microclimate model against empirical data on microhabitat temperatures and compared the endotherm model predictions against an infra-red thermograph of the bird itself. We then used the model to predict the frequency with which the parrot would need to find standing water under current and future climates depending on the water content of its food. Results: Our field data show that air temperature in night parrot roosts during high summer typically exceeds the inferred resting core temperature (38°C) and can exceed 45°C. Our calculations imply that night parrots can persist on dry seed during winter conditions without exceeding dangerous levels of dehydration, but would need access to water or succulent (55% water) food during summer. Air temperature at the site is projected to increase 3°C by 2070, which would lead to likely lethal (22% of body mass) levels of daily dehydration in some years even on succulent food, and would dramatically increase its dependence on standing water. Conclusion: Our findings have significant implications for the conservation management of the night parrot and provide guidance for future research priorities.

Does metabolism constrain bird and mammal ranges and predict shifts in response to climate change?

“…At warm range boundaries, the capacity for evaporative cooling may be more limiting than the associated metabolic costs and minimal endogenous heating is favored (McKechnie, Whitfield, et al, 2016;Tieleman & Williams, 2000). Evaporative cooling poses a risk of dehydration in response to short term heat stress (McKechnie, Hockey, & Wolf, 2012) and presents a challenge for longer term water balances (Kearney et al, 2016). Additionally, other biotic factors such as species interactions and resource or habitat constraints often constrain warm range boundaries (Sexton, McIntyre, Angert, & Rice, 2009).…”

“…Mitchell et al (2018) review misconceptions of thermal physiology that plague predictive models of mammalian responses to climate change. Several recent examples employ biophysical models to estimate metabolic constraints, activity limitations, and water balance for focal endotherms (Kearney, Porter, & Murphy, 2016;Mathewson et al, 2017), but can these approaches be generalized?…”

Reflection of near-infrared light confers thermal protection in birds

“…Briefly, the microclimate model takes daily weather and terrain data to compute hourly radiation (long and short wave), air temperature, wind speed and humidity at organism height for a particular location and solves a heat and water budget, taking into account biophysical attributes of an organism and its physiological and behavioural responses. Ultimately, it calculates the metabolic and EWL rates required to maintain a given core temperature for each hour, allowing the bird to vary its posture, skin thermal conductivity, body temperature, respiratory water loss and cutaneous water loss, in that order, under heat stress 38 .…”

Seasonal physiological responses to heat in an alpine range-restricted bird: the Cape Rockjumper

“…If these physiological responses result in a seasonal water bottleneck our findings may partially explain declining populations in species with a restricted and well-defined climatic niche. However, to fully understand the effects on water budgets resulting from elevated EWL demands will require a more mechanistic approach such as was attempted for Sparrow-weavers and Night Parrots (Pexoporus occidentalis; (Kearney et al 2016). Indeed, for Rockjumpers a modeling approach using closely related, more common species, may be the only alternative.…”