This is the first animal that hunts flying birds during the night

Feb 14, 2007 16:36 GMT  ·  By

The darkness was thought to be a safe shield for the migrating songbirds, during their long, challenging trans-continental migrations.

But a new Spanish research revealed an unsuspected night predator for the little birds.

The unique and abundant food source represented by the billions of high-flying migrating Eurasian songbirds is exploited around the Mediterranean basin, like the Iberian Peninsula area, by a 45 cm wing-spanned mammal, possessing sharp canines and an effective radar system which is probably inaudible to birds.

Since 2001, Carlos Ib??ez's team at the Do?ana Biological Station in Seville, Spain, pointed out that the giant noctule bat (Nyctalus lasiopterus) (photo), a rare Mediterranean species, may feed largely on migrating birds.

Numerous feathers were found in their faeces, with peak occurrence in spring and autumn, during birds' seasonal migration.

All the other European bats feed exclusively on invertebrates!

But most biologists rejected such a hypothesis, believing that giant noctules accidentally ingest feathers hovering in the air, these being particularly numerous during migration or the bats mistake feathers as insects, as their echolocation system hampers fine-grained discrimination of targets; they said that swallowing feathers would cost less than spitting them away.

It was hard for the researchers to investigate feeding habits of an elusive predator that hunts its prey hundreds to thousands of meters high in the sky in total darkness.

A new complex research was led by young Romanian biologist Ana Popa-Lisseanu, under Prof. Iba?ez' supervision, was made in Do?ana Biological Station and Granada (Zaid?n Experimental Station), both locations in southern Spain.

The researchers applied the novel stable isotopes technique, which permitted them tracking species' main dietary specializations, using as tracers carbon and nitrogen isotopes.

They analyzed their concentrations in the blood of the bats, insect bodies and birds' muscular tissues throughout the year.

They found that the bats fed only on insects in summer, with some birds' flesh in their diet during spring, and a great deal of bird meat during autumn.

The higher percentage of songbirds' meat in autumn than in spring was due to the more massive bird migration in autumn, of both parents and offspring of that year, whereas in spring only birds that survived winter mortality and two migrations are available.

Moreover, young birds in autumn are inexperienced, more vulnerable prey.

The ability of giant noctules to feed on the wing upon nocturnally migrating small birds seems unique in the animal world.

In the tropics there are carnivorous bats eating small-sized vertebrates, like frogs, lizards or mice, but they collect their prey from substrates.

And the few falcon species exploiting the migratory birds resource along the Mediterranean hunts only during the day time.

Owls, too, are night predators, but they never hunt in the open space: moving prey is located from substrates by passive-listening after rustling noises.

This hunting adaptation of the giant noctule explains its biology: it occurs almost exclusively in some parts of the Mediterranean, where major migrating bird flocks congregate.

This is the largest Palaeartic (the region of temperate Eurasia) bat and the heaviest aerial-hunting bats of the world: up to 50 g for 45 cm wingspan, for subduing small birds, which can be about the same weight as other European bat species.

This amazing predatory specialization could be shared by the few other big bat species elsewhere in the world.

Photo credit: Ana Popa-Lisseanu.