Time and landscape context shape insular bat responses to wildfire

Wildfire is a powerful force that reshapes the world, stripping away vegetation and leaving behind a landscape of ash and open space. For many animals, this sudden change is a crisis, but for others, it can temporarily create new opportunities. Bats, the only mammals capable of true flight, rely heavily on the structure of their surroundings. They navigate and hunt using sound, sending out high-pitched calls that bounce off objects to reveal the location of insects. How they use these calls depends on their body shape and hunting style: some are built for speed in wide-open spaces, others for weaving through the edges of trees, and some for maneuvering tightly within dense foliage. When a fire sweeps through an island, it alters this physical world instantly, and the question remains: do these changes help or hurt the local bat populations in the years that follow?

In the southern part of Madeira, an island in the Atlantic Ocean, a severe wildfire in 2016 burned through forests and plantations, leaving a scarred landscape. Five years later, researchers returned to the same spots to listen to the bats. They wanted to know if the fire had created a lasting haven for some species while driving others away, or if the effects had faded as the land began to recover. By recording the sounds of three different bat species at sites that had burned and sites that had not, the team discovered that the story of the fire was not a simple tale of destruction or renewal. Instead, the impact depended entirely on the specific type of bat and the surrounding landscape, revealing a complex dynamic where the burned sites did not necessarily become better for everyone, but simply remained stable while the unburned areas grew quieter.

The study focused on three distinct species that call Madeira home. The first is the Madeiran pipistrelle, a small bat that hunts along the edges of forests and in open areas like farms and towns. The second is the Madeira noctule, a larger bat built for fast, efficient flight in wide-open spaces. The third is the grey long-eared bat, a specialist that prefers to hunt in tight, cluttered spaces close to dense vegetation. The researchers set up acoustic recorders at 58 locations across the southern part of the island. They had originally visited these spots in 2016, just one month after the fire, and returned in 2021, five years later. At each location, they counted how many times bats flew past the microphone, a measure of how active the bats were in that area. They also looked at the landscape around each spot, noting how much of it was forest, farmland, or open ground.

The results showed a striking difference in how the bats responded over time. In the unburned areas, the activity of all three bat species dropped significantly between 2016 and 2021. The bats simply became less active in these places. In contrast, at the sites that had burned in 2016, the activity levels of the Madeiran pipistrelle and the Madeira noctule did not change much over the five years; they stayed at the same level they had been in 2016. Because the unburned sites got quieter while the burned sites stayed steady, the burned areas ended up looking much more attractive to these bats by 2021. In fact, the total number of bat movements recorded at the burned sites was about six and a half times higher than at the unburned sites in 2021. This did not mean the fire had suddenly made the burned land a paradise that drew more bats in; rather, it meant the bats that were already there had stayed, while their neighbors in the unburned forests had moved away or become less active.

The grey long-eared bat told a different story. This species, which prefers dense vegetation, was found to be more active at burned sites than at unburned sites in both 2016 and 2021. However, unlike the other two species, its activity declined at both burned and unburned locations over the five years. The gap between the burned and unburned sites remained roughly the same, suggesting that this bat's preference for the burned areas was established early on and did not change as the landscape evolved. The researchers noted that this species is harder to detect because it flies quietly and close to vegetation, so its overall numbers were much lower than the other two species, making its patterns harder to track.

The landscape surrounding the bats also played a crucial role in shaping these behaviors. For the Madeiran pipistrelle and the Madeira noctule, the type of land next to the burned sites mattered greatly. At the burned locations, having more farmland nearby was actually linked to fewer bats, whereas at the unburned sites, farmland did not seem to have a strong negative effect. This suggests that the way fire interacts with agricultural land might create conditions that are less suitable for these bats than other open areas. Conversely, the presence of forests and woodlands was linked to higher activity for the Madeira noctule in unburned areas, but this link disappeared at the burned sites. This indicates that the value of a forest to a bat depends on whether that forest has been burned; a pre-fire forest might provide resources that are lost or altered once the fire passes.

Perhaps the most revealing finding came from listening specifically for "feeding buzzes." These are rapid, high-frequency calls that bats make when they are actively chasing and catching an insect, a sound that confirms they are not just flying through but are actually hunting. In 2021, the researchers found that feeding buzzes were about three times more common at the burned sites than at the unburned ones. This confirmed that the bats were not just commuting through the burned areas; they were actively feeding there. The frequency of these hunting calls also increased with the amount of forest and woodland nearby, suggesting that even in a burned landscape, the presence of nearby trees helps concentrate the insects that the bats eat.

The study concludes that the aftermath of a wildfire is not a single story of recovery or ruin. For the Madeiran pipistrelle and the Madeira noctule, the burned sites remained a stable resource while the unburned sites declined, creating a situation where the fire-damaged land became the primary hunting ground five years later. For the grey long-eared bat, the burned sites were always preferred, but the overall population activity dropped everywhere. The research suggests that managing these landscapes requires a nuanced approach. Simply letting a forest burn or trying to restore it to a single state is not the answer. Instead, maintaining a mix of unburned refuges, along with a variety of open spaces, edges, and woody habitats, is essential. This diversity ensures that different types of bats, with their different hunting styles, have places to live and feed, regardless of how the fire changes the land around them. The fire did not just destroy; it reshaped the map of opportunity, and the bats adapted to the new map in ways that were specific to their own needs and the specific patch of land they called home.