The day after the fire: Large-scale vertebrate mortality following extreme wildfires in the Iberá Wetlands, Argentina

Although direct vertebrate mortality is one of the major impacts of extreme wildfires, it remains poorly documented. Here, we quantified vertebrate mortality through post-fire carcass surveys following severe wildfire in the Iberá Wetlands (Argentina)—a key restoration landscape—and compared outcomes with the Pantanal (Brazil) to evaluate whether extreme conditions produce consistent mortality patterns across Neotropical wetlands. We conducted post-fire line transect surveys (164.7 km) within the 2425.5 km 2 burned area, recording 194 carcasses from 42 taxa. Accounting for carcass body size, we estimated at least 641,290 carcasses in the Iberá Nature Reserve. Carcass density was highest in small reptiles (170 carcasses/km 2 ), heavily driven by semi-aquatic specialists such as Helicops leopardinus, and large mammals (32.8 carcasses/km 2 ). Among large mammals, capybara ( Hydrochoerus hydrochaeris ) carcasses were equivalent to ~63% of the minimum pre-fire population within burned areas and to ~30% of the population of the Iberá National Park. Comparatively, Iberá showed higher carcass densities of medium- and large-bodied vertebrates than Pantanal (50.08 vs. 24.18 carcasses/km 2 , respectively), whereas Pantanal fires have been reported to impact small-bodied fauna more strongly. In Iberá, carcass density did not differ significantly among vegetation types or between protection levels, although these patterns should be interpreted in terms of absolute carcass density rather than proportional mortality, given the lack of species-specific pre-fire densities. Massive losses of dominant species (capybara) could trigger cascading ecological effects and hinder restoration efforts, underscoring the need to move beyond fire suppression toward integrated fuel management and adaptive strategies under increasingly extreme fire regimes.