Mortality among birds and bats during an extreme heat event in eastern South Africa

Abstract

Heat‐related mortality events involving birds and bats are projected to occur more frequently as a result of anthropogenic global heating. Reports of mass mortalities associated with extreme heat have, over the last decade, mostly involved Australian birds and pteropodid flying‐foxes. Here, we report a mortality event involving ~110 birds and fruit bats in eastern South Africa in early November 2020 when maximum air temperatures (Tmax) reached 43–45°C and relative humidities were 21–23%. The mortalities included 47 birds of 14 species, all but three of which were passerines, and ~60 Wahlberg’s epauletted fruit bats (Epomophorus wahlbergi). This mortality event occurred on a single very hot day preceded by several cooler days (Tmax = 37–39°C at one location) and involved weather conditions similar to those associated with at least one recent flying‐fox die‐off in Australia. The disproportionately high representation of passerines among the avian mortalities supports recent predictions that songbirds are more vulnerable to lethal hyperthermia on account of the relative inefficiency of panting as an avenue of evaporative heat dissipation. As far as we are aware, this is the first documented heat‐related mortality event involving wild birds and bats in southern Africa.

Global heating poses a serious threat to Australia’s birds: reply to Pacheco-Fuentes et al.

“…In our discussion ( Conradie et al, 2020 ), we pointed out that lethal hyperthermia, rather than dehydration, appeared to be the major cause of mortality during historical and recent heat-related mortality events in Australia, a point also noted by Davies (1982 ). More recent events also support the view that a lack of water availability is often not the primary driver of mortality: during southern Africa’s first documented avian mortality event associated with extreme heat in November 2020, birds died in large numbers despite many being within a few hundred metres of the shore of the 133-km 2 Pongolapoort Dam ( McKechnie et al , 2021b ).…”

Caves, crevices and cooling capacity: Roost microclimate predicts heat tolerance in bats

“…The urgency of better understanding constraints on bats' capacities to tolerate very hot conditions is underscored by the increasing frequency of heat-related mortality events among pteropodids in Australia (Ratnayake et al, 2019;Welbergen et al, 2008) and elsewhere (e.g. McKechnie, Rushworth, et al, 2021).…”

In the Hot Seat: Behavioral Change and Old-Growth Trees Underpin an Australian Songbird’s Response to Extreme Heat

“…As a consequence, they succumb to lethal heat stress at air temperatures > 42 • C, and 45,500 (in 600 colonies in SE Queensland) died on a single day in 2014 (Welbergen et al, 2014). This vulnerability to extreme heat may be much more widespread than we recognize, particularly among small endotherms (McKechnie et al, 2021) because few species are as readily observable as flying foxes, which roost in large, noisy colonies, and attempts to quantify individual responses to extreme heat are rare (Buchholz et al, 2019).…”

“…Anthropogenic climate change has led to an increase in the frequency and intensity of extreme weather events, particularly heat waves (Stillman, 2019). Record-breaking temperatures are having severe consequences for biodiversity, with mass mortality events (Welbergen et al, 2008;McKechnie and Wolf, 2010;McKechnie et al, 2021), the loss of arid-zone communities (Riddell et al, 2019) and reduced population viability (Thomas et al, 2006;Ruthrof et al, 2018;Stillman, 2019).…”