Permissive Adoptive Mothers

Porthidium porrasi juvenile head, White-Tailed Hognosed Pitviper, snake

A bronzed cow-bird chick and a black-striped sparrow

A few weeks ago, while cooking, I heard in the garden a sharp, loud, demanding, and continuous "peep" that seemed to ask for constant attention. Without hesitation, I went out with my camera and captured a curious scene: A bronzed cowbird chick, also known as Pius, was continually chasing and claiming food from a black-striped sparrow, a different kind of bird. It was very evident that this dark and screaming pigeon was not the son of that discreet and shy sparrow, whom he had already seen on occasion in the garden.

The poor sparrow was stressed with such incessant chanting, enough to reach a little piece of banana and feed her black pursuer from beak to beak. Typically, these finches are not easily seen. They feed on the ground and among twigs of low bushes, looking for seeds, small insects, and sometimes wild berries. It is rare to see them eating a banana in an open area.

This strategy of reproduction by the bronzed cowbird is called “parasitism of interspecific laying.” Instead of investing in a nest and devoting a few weeks to tend to their chicks, the females of this species lay their eggs in the nests of other, usually smaller birds.

Thus when the sparrow incubates the eggs, and these hatch, a pigeon turns out to be much larger than the others. It begins to throw them out of the nest and get all the food that its adoptive mother" can bring to satisfy its hunger and continue growing. When it already has its flight plumage, the pigeon eats a lot and is big.  It chases its host progenitor in search of more food until it becomes independent.

Some people will think that the cowboys play dirty, leaving their offspring in charge of other bird species and allowing them to have a hard time.  Nature does not know about moral judgments. Do we humans not raise cows to eat their calves?



~by Biol. Susana García

The Sparrow, Permissive Adoptive Mothers 1

a hungry chicken with his foster mother




The mystic mountains, only 20 km away from the bustling shopping oasis of San Isidro, nestled in the Talamanca mountain range, lays the Cloudbridge Reserve. It extends up to 2600m along the foot of the Chirripo, the highest mountain in Costa Rica.

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