Small migratory birds were found stuffed into crevices by Eleonora's falcons so that they could not escape. Abdeljebbar Qninba

Falcons in Morocco’s Essaouira archipelago have been observed "imprisoning" other birds and holding them for several days before feeding them to their young.

The unusual behavior was observed by Abdeljebbar Qninba from Mohammed V University in Rabat, Morocco, while conducting a census of falcons on the island of Mogador in 2014, and reported in the latest edition of the journal Alauda. Among the species residing on the island is Eleonora’s falcon (Falco eleonorae), which normally eats only insects but has been known to feed on other migratory birds such as the common whitethroat, the tree pipit and others during the breeding season.

For this reason, Eleanora’s falcon colonies tend to synchronize their chick-rearing with the height of the annual migration, in order to ensure that prey is at a maximum when their young hatch.

Typically, this dietary switch from insects to other birds occurs a few days prior to laying their first eggs in late summer, as the falcons begin catching prey in anticipation for the arrival of a few extra mouths to feed. However, by killing their food so early they risk it drying out or rotting before it can be eaten.

To get around this, the birds were seen keeping their prey alive for varying periods, thereby ensuring its freshness when it came time to feed it to the chicks. This was achieved using a number of cunning tactics, such as stuffing small birds into small crevices, ensuring they were tightly wedged in and unable to escape.

The Eleonora's falcon has been found removing flight feathers from its prey in order to prevent it from escaping. Conselleria de Medi Ambient i Mobilitat, Govern des Illes Balears via Wikimedia Commons

Additionally, Qninba notes that other small migratory birds were found in holes and fissures with their flight and tail feathers removed – presumably by the falcons. Birds rely on the feathers that line their wings in order to be able to take flight, while the tail feathers act as a kind of rudder that enables them to navigate. Without these, they are incapable of flying, and could therefore not escape from the cavities into which the falcons had dropped them.

While the change in diet occurs before the eggs are even laid, Qninba and his colleagues suggest that the tactic of imprisoning birds may begin in the days leading up to the hatching of these eggs, to ensure a ready supply of food that is just the right freshness when the chicks require their first feed.