Predation by tawny owls affects the survival of the Doñana great owl population

2023-09-21 11:11:16

A team led by Carlos IbanezCSIC scientist at the Doñana Biological Station (EBD), has observed how the tawny owls (a nocturnal bird of prey) feed on the largest bat species in Europe: the large noctule.

Although these bats, one of the rarest and most endangered speciesrepresented only a very small proportion of the diet of these owls, their predation was a significant mortality factor in the small, isolated bat study colony of the Doñana Biological Reserve. These findings have been published in the open access scientific journal Royal Society Open Science.

Los nocturnal animals son difficult to observe in the dead of night, so its behavior is little known. For example, owls are known to prey on bats, but it is not entirely clear how they trap the agile bats in the dark. Previous research that has been carried out on the anti-predatory behaviors on the part of bats, such as the change of refuge, have offered equivocal results.

Noctule mortality

To carry out this study, the team analyzed more than six months of video recordings of artificial bat boxes used as day shelters by a small colony of large noctules from the Doñana Biological Reserve. In the studied colony, most of the noctules also carried passive integrated transponders (PIT-tags), which allowed the movements of bats between roosts to be recorded.

Predation by tawny owls accounted for between 30% and 40% of noctule mortality at the study site.

Analyzing the images, they discovered that the damn They tried to hunt the bats most nights. They also observed that they perched mainly in or near roosts, from where they either tried to capture approaching bats from the air, or a chase behind their prey. Despite their frequent presence near roosts, tawny owls captured very few bats, so it was estimated that bats would make up a very small proportion of these owls’ diet.

However, Contrary to the previous hypothesis and despite the regular presence of tawny owls near the shelters, the bats did not change their shelter in his response. Owl predation was estimated to represent between 30% and 40% of noctule mortality in the study location.

The lack of alternative shelters, a problem

“Although we cannot rule out the possibility that the bats were unaware of the risk of predation, it seems highly unlikely that they were not able to detect the owls perched and moving on top of their shelters,” he says. Detlev Kelmlead author of that study.

Due to the lack of large old trees with woodpecker holes, which usually serve as natural shelters, in many areas of southern Spain, large noctules depend on shelters in trees in urban parks or on bat shelter boxes.

“It is possible that the bats did not perceive the risk of predation as high enough to abandon their roost. However, we believe that the lack of alternative shelters “may also have contributed to the noctules’ unusually high fidelity to their roosts.”

In fact, due to the deforestation Yet the lack of large old trees con woodpecker holeswhich usually serve as natural refuges, in many areas of southern Spain, large noctules depend on refuges in exotic trees from urban parkslike the famous María Luisa Park in Seville, or shelter boxes for batsas occurs in the Doñana National Park.

“Our study shows that even a low intensity natural predation can have a significant impactespecially in small, local or isolated bat populations, especially taking into account the very low birth rate of these animals (one calf per year per adult female)”, reports Carlos Ibanezhead of the bat research group at the Doñana Biological Station.

“We hypothesize that low roost availability may also affect the ability of bats to escape predation by changing roosts. In such a case, natural predation could have an excessive impact on bat populations and even shape the distribution of species of bats, especially in the case of very rare species with a local presence, such as the great noctule, which are also threatened by loss of habitatdeforestation and the unsustainable development of wind energy”.

The authors of the study maintain that their findings can help understand the distribution of bats and inform its conservation. The study results suggest that even natural predation can become a threat to the conservation of rare species when they are also limited by anthropogenic habitat loss and lack of breeding sites.

Reference:

Kelm, D., Ibáñez, C. et al. “Continuous low-intensity predation by owls (Strix aluco) on bats (Nyctalus lasiopterus) in Spain and the potential effect on bat colony stability“. Royal Society Open Science (2023)

Rights: Creative Commons.