Tree hollow densities reduced by frequent late dry-season wildfires in threatened Gouldian finch (

Abstract

Context. Tree hollows are a key habitat resource for hollow-nesting species, including the northern Australian Gouldian finch (Erythrura gouldiae). Certain fire and disturbance regimes limit tree hollow availability in the northern Australian savannas.Aims. This study investigated the influence of fire regime and vegetation structure on the density of tree hollows at Gouldian finch breeding sites.Methods. Fire scars were mapped across breeding sites by using LANDSAT images. Vegetation plots within sites were spatially stratified according to three fire-regime attributes, namely, fire frequency, late dry-season wildfire frequency and time since the last fire. Tree hollow and vegetation structural attributes were measured at each vegetation plot. We modelled the relationship among hollow density, fire and vegetation attributes by using general linear mixed models with site as the random factor.Key results. We found that the highest tree-hollow density was found at plots with high eucalypt tree density and cover and with the lowest frequency of late dry-season wildfires (,1 wildfire over 5 years). Tree-hollow density declined after .2 years without fire. Hollow density was not directly related to total fire frequency.Conclusions. This study adds to previous work on grass seed resources in highlighting the importance of fire in Gouldian finch ecology. This study particularly highlighted the importance of reducing the impacts of high-intensity late dry-season wildfires because of their negative impacts on tree-hollow density, which is a key resource for breeding Gouldian finches.Implications. We recommend the use of a network of interconnected annual patchy early dry-season prescribed burns for protecting Gouldian breeding habitat from threat of high-intensity wildfires. We do NOT recommend fire exclusion from Gouldian finch breeding habitats. This is because fire risks to hollow-bearing trees, and grass seed resources, increase with the long-term accumulation of savanna litter fuels in the absence of fire.

A Hollow Argument: Understory Vegetation and Disturbance Determine Abundance of Hollow-Dependent Mammals in an Australian Tropical Savanna

“…Due to the higher densities of hollow-bearing trees on Melville Island compared to the mainland (Woolley et al, 2018), we are unable to speculate as to whether the depletion of tree hollows has contributed to the broad-scale decline of arboreal mammals in northern Australia. Frequent late dry-season fires have been shown to impact the density of suitable hollows for the threatened Gouldian finch (Erythrura gouldiae) in northern Australia (Radford et al, 2021). In habitats with low hollow densities, the frequent utilization of alternative dens (e.g., hollow logs, Pandanus spiralis) may expose individuals to greater predation risk and impact breeding success, particularly after fire (Leahy et al, 2016;Penton et al, 2020b).…”

The threatened Gouldian finch preferentially forages in prescribed burnt savannas

“…Individual finches will seek to offset the energetic costs of foraging by maximising energy intake, and therefore, we would expect individuals to spend a disproportionate amount of their time foraging within areas with greater seed availability. Prescribed burning has also been shown to improve the retention of old eucalypt trees with nesting hollows used by breeding Gouldians, (Radford et al 2021), and this study provides further merit for the practice for the conservation and management of Gouldian finches.…”

“…Late dry season fires are a ubiquitous feature of savanna ecology. While these fires can negatively impact seed density (Weier et al 2016(Weier et al , 2018 and nest hollow availability (Radford et al 2021), the greatest negative influences of late dry season burning may be confined to unmanaged landscapes with a high frequency of very extensive late dry season wildfires and an absence of early fire. Whilst the space used by Gouldian finches was not influenced by late dry season fire here (either positively or negatively), it was noted that finches did not occupy areas frequently burnt by late dry season fires.…”

“…Prescribed burning was undertaken both to increase the abundance and quality of grass seeds available for Gouldian finches (Weier et al 2016(Weier et al , 2017(Weier et al , 2018(Weier et al , 2019, and also to reduce the negative impact of high intensity wildfires on tree nesting hollow density that finches rely on during breeding (Brazill-Boast et al 2011;Radford et al 2021). To achieve this, strips of inter-connected savanna vegetation were burnt early in the dry season.…”

Landscape-Scale Effects of Fire, Cats, and Feral Livestock on Threatened Savanna Mammals: Unburnt Habitat Matters More Than Pyrodiversity

“…Sorghum not only provides little cover for mammals, but it is also highly flammable once cured, leading to low patchiness and extensive fires even under milder fire weather conditions in the early dry season (Miles, 2020). Fire management which can reduce local fire frequency, will potentially also reduce Sorghum dominance (biomass, cover, seed set) and thereby benefit savanna mammals, through increasing competition from resprouting perennial grasses, shrubs and tree canopies Weier et al, 2018;Radford et al, 2021).…”