Thursday, January 22, 2015

Alpine bat diet

Credit: © A Alberdi
The alpine long-eared bat, Plecotus macrobullaris was discovered 2002. It is considered the only bat to feed above the tree line, but it uses its foraging ability at lower altitude too. Not long after its discovery it was found far away around the Mediterranean coasts, where the climate is pretty different from any at high alpine altitude.

So how alpine is this bat? In summer, they can be found between 1,500 and 2,500 m. The bats take advantage of meadows in flower that provide insects with shelter and food. This enables the bats to exploit a different food source compared with their cousins hunting at lower altitudes. Earlier survey showed that this species specializes on moths while other long-ear bats (genus Plecotus) feed on greater varieties of insects. The limited diet of Plecotus macrobullaris is probably the result of the limited high-mountain environment.

A study that was published a while back used DNA Barcodes to pin-point prey species of the alpine long-eared bat. I came across this paper during my research on high-altitude specialists for yesterday's post. The researchers were able to identify a number of moth species found in feces from bats trapped using mist nets. 

One of the advantages of the study was the fact that the order Lepidoptera is one of those taxa with an extensive amount of available DNA Barcodes (more than 80,000 species, almost 100,000 BINs). Such comprehensive reference libraries allow for very specific analyses.

Consequently the colleagues were able to identify 44 moth species in the bat's diet. Most of them were owlet moths (Noctuidae) but they also found individuals of the small elephant hawk moth (Deilephila porcellus). 

Rather than indicating any selective behaviour, these results likely reflect the actual prey availability at high elevation, because noctuids and geometrids are almost the only lepidopteran taxa present in alpine environments, the former eight times more abundant than the latter. 

Prey species also occurred at many different altitudes, indicating a broad range of hunting grounds. Most of the moths occur in subalpine meadows and the habitats bordering those, all of them are rather open. 

In our study, results show that the Mountain Long-eared Bat P. macrobullaris is a moth specialist that forages in high mountain meadows and rocky areas during summer. However, our data are restricted to summer and we should not dismiss the possibility that P. macrobullaris forages at lower elevations and in different habitats during other seasons, especially spring, when alpine habitats are moth-impoverished.

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