Bird Wars: Brood Parasitism and the Inner Conflicts of Interfering With Nature


Writeen by Sarantia Mitsinikos, an Invasive Species Project Steward with the SCA Hudson Valley Corps. She is currently serving a 10 month position at New York’s Minnewaska State Park.

The Invasive Species Field Office at Minnewaska State Park gained a new member early this spring. An eastern phoebe (Sayornis phoebe) had begun constructing its nest right above the door to the office. Phoebe (as she shall be called) came at a good time as our team lamented the unfeasibility of having an office cat. We were delighted to have a family of birds join the Invasive Species Project Team, especially a species that our amateur ornithologist eyes and ears could identify. We became even more prideful of Phoebe when we discovered at the the New York State Office of Parks, Recreation and Historic Preservation stewardship meeting that an eastern phoebe was the first bird to be banded in North America — by John James Audubon himself!

(Eastern phoebe nest above the Invasive Species Field Office in New York.)

We excitedly awaited the arrival of eggs until one day, we checked the nest to find three eggs nestled within. There was one small white egg and two larger, brown-speckled eggs. We immediately suspected the larger eggs were the addition of a brown-headed cowbird (Molothrus ater), a known brood parasite. Rather than build its own nest for its eggs, female cowbirds lay their eggs in the nests of other bird species, neglecting all their parental duties. Oftentimes, the cowbird chicks will hatch first, growing larger and faster than the host chicks and taking resources away from them. Cowbird chicks may even knock the other eggs out of the nest entirely.

(The nest with one eastern phoebe egg and two brown-headed cowbird eggs.)

A quick search on the internet confirmed that we had trouble: cowbirds. I contemplated removing the eggs, and eating them if I’m being quite honest. But I had recently returned from a Leave No Trace training with the Student Conservation Association (SCA) during which I was responsible for teaching Principle 4, “Leave What You Find.” This was the antithesis of what I was proposing. Knowing that it’s illegal to interfere with the nesting of cowbirds on public lands (such as a state park) due to their protection under the Migratory Bird Act, I could not justifiably touch the eggs. I reminded myself that my job was not to be mama bird, but an Invasive Species Project Steward. Since the cowbirds are not invasive, I resigned to take a step back and hope for the best for the eggs.

After weeks away at various trainings, we found splattered eggs on the welcome mat and an empty nest. It’s hard to say whether it was the cowbirds or another predator. Even though I may have been able to prevent the loss of the eggs, who am I to say a cowbird’s life is any less valuable than that of the eastern phoebe, especially since phoebes are not a threatened species. As humans with brains, and thumbs, and weird gangly limbs, we have the power to decide what species of plants and animals die or thrive. It’s up to us to use this power responsibly. I’ve always said that a weed is an anthropocentric concept. In fact, a weed is just a plant growing in an “undesirable” location, as defined by humans (Homo sapiens). The distinction to be made with invasive species is that their presence is not just inconvenient to humans, in fact many of them were introduced intentionally by humans as ornamentals and escaped, but they are damaging to entire ecological communities due to their ability to create monocultures and reduce biodiversity. It is at this point, when ecosystem stability is threatened, that I invite everyone to intervene. Learn how to identify invasive species, report or remove them, plant only natives in your garden, spread the word!

For more information regarding invasive species, feel free to contact us at [email protected].