Falcons living on Morocco's barren island of Mogador apparently like to feed their offspring the freshest of meat. In fact, biologists say it's not uncommon for Falcon parents to "imprison" smaller birds, holding them for several days before killing and feeding them to their young. 

Mogador Island lies along Morocco's Essaouira archipelago. Among the many species residing on the island are Eleonora's falcons (Falco eleonorae), which are relatively large raptors, characterized by long, narrow wings and a rounded tail. Typically, Eleonora's falcons only eat insects; however, during breeding season they are known to feed on smaller migratory birds – such as the common whitethroat and the tree pipit – that travel south through the Mediterranean islands and Atlantic coast towards their sub-Saharan wintering grounds.

After surveying the island in 2014, researcher Abdeljebbar Qninba of Mohammed V University, Rabat, and colleagues discovered a dearth of small birds – each missing flight and tail feathers – positioned in small holes or rock cavities. Many were unable to move their wings or dangling legs, reported New Scientist. Researchers suggest this storage method may be the falcon's way of preparing for "leaner times." 

Prey storage is common practice among some birds, including owls that routinely pack away dead mice for winter. And previous research indicates Eleonora's falcons have been observed hoarding catches of up to 20 dead birds during the migration season when prey is plentiful.

But storing live snacks appears to be a relatively new behavior to science.

"I haven't heard of anything like it in [non-human] vertebrates," Theodore Stankowich, evolutionary behavioral ecologist from California State University in Long Beach, told New Scientist. "Perhaps this innovation of simply immobilizing prey prior to caching has caught on and spread through the population."

"Given the right circumstances – prey availability and habitat for storing the prey – it is reasonable to see how this behavior could evolve," Michael Steele of Wilkes University in Pennsylvania added.

Furthermore, Eleonora's falcon colonies have been seen synchronizing their chick-rearing periods to the height of the annual migration. Since parents have to stay close to their nests to care for newborns, crippling and trapping prey may be the bird's way of ensuring there is enough food available for hungry chicks. Keeping them alive ensures they remain fresh before they can be eaten.

Some scientists, however, remain skeptical about this new behavior and suggest that the phenomena amounts to migratory birds using rock crevices and small holes to hiding from predators like falcons. Moreover, since raptors are known to pluck feathers from prey before killing them, the featherless birds may simply be escapees that crawled into nearby cracks because they could no longer fly. 

Further research is required to confirm whether or not the birds are actually being held prisoner by falcons. Their findings were reported in the latest edition of the journal Alauda.

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