15/05/2018
Previously thought to be relatively
ecologically harmless, invasive Ring-necked Parakeets have been seen attacking
bats in a Spanish park and ejecting them from tree-hole roosts.
At the turn of the century, the
largest colony of Greater Noctule bats in Europe occupied a park in Seville,
Spain. However, between 2003 and 2017, the number of trees used by bats in the
park fell by 81 per cent, according to a study at the DoƱana Biological Station
in the city. Conversely, the number of nests of Ring-necked Parakeets, an
introduced species native to the Indian subcontinent and East Africa, increased
by a factor of 20 over the same period.
The research team documented
parakeets nesting in tree cavities previously occupied by bats. The researchers
also observed the 120-g parakeets chasing the 50-g bats out of their nests.
Parakeets largely attacked the bats at the entrances to tree holes in the few
hours before dusk, obliging the bats to flee during daylight hours (though some
bats were able to fend them off). The researchers also found 20 dead and two
injured noctules under nest sites, and some were fresh enough to show beak cuts
on their muscle and bones.
In parallel, parakeet numbers
increased during the study period, being very scarce until 2013, but showing a
96 per cent increase in the four years thereafter. Greater Noctule bat showed a
decline of 70 per cent in the same period (and an 81 per cent fall since 2003),
almost a mirror reflection of the parakeet increase. By 2017, the number of
tree holes occupied by noctules had eroded down to 14 from 47 in 2013, while
those occupied by parakeets had increased from 159 to 311 in the same period.
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