American Goldfinches are strictly vegetarian. If they get any insect protein it is inadvertently when gobbling seeds. Unlike many of their cousins, this includes the nesting chicks. This has a beneficial effect on survival. While a lot of their cousins are succumbing to pressure from the brood parasitic Brown Headed Cowbirds, American Goldfinches’ all vegetation diet is a defense.
If a Brown-headed Cowbird lays an egg in a Goldfinch nest and it hatches, the nestling rarely survives more than three days. They just can’t survive on veggies alone.
There is another advantage of this approach. Brown-headed Cowbirds are revengeful. If they see a targeted host pair rolling the cowbird egg out the nest or otherwise destroying it, the cowbirds retaliate. They will return and destroy the host’s pair’s eggs. This forces the pair to try again and if the female does lay another brood the female cowbird lays another egg as well. This keeps happening until the victim pair gives up the nest or capitulates and fosters the nestling cowbird. This is known as ‘Cowbird Mafia’ behavior.
The fact that American Goldfinches’ treatment of the cowbird nestling intruder is not as covert means that they are not as bullied and not as negatively impacted as the other species with whom they often share grassland and brushland edges. This is an important difference. Cowbirds are taking advantage of the fragmentation that results from the conversion of forests to agriculture as well as intrusion of suburban development. Both create edges, often brush and shrub lined that gives the cowbirds access to new territory. Territory that holds species that are very vulnerable to the cowbird’s mafia behavior. So much so that they are considered a contributing factor in the population declines of some listed species such as Kirtland’s Warbler, Black-capped Vireo, Least Bell’s Vireos, and Southwestern Willow Flycatchers.
American Goldfinch populations, on the other hand, have been holding steady since the mid-1960s. Making them a ‘common’ uncommonly handsome bird across much of North America.
About The Shot
Taken in central Georgia, US in an area of large cotton fields and diary farms. The county and dirt roads are lined with brambles and brush that holds a number of sparrow and warbler species. Shot with Olympus OMD EM1X, Olympus 150-400 F4.5 TC1.25