By Megan Kasprzak and Joe Sebastiani. Photos by Shannon Modla
Megan and Shannon regularly look for birds at Ashland Nature Center, documenting what they find in eBird, and taking many great photographs. On 8 June, they witnessed a rather extraordinary ornithological event. Read on…
Notes from Megan Kasprzak at Ashland Nature Center, Monday 8 June, 2020:
I just witnessed the most bizarre bird behaviors I have ever seen. Two Blue-gray Gnatcatchers were feeding Gray Catbird nestlings!
We found a Catbird nest several weeks ago as we saw a Catbird bringing in nesting material and proceed to construct it. We monitored the nest over the last couple of weeks as a parent was on the nest incubating. Today I went to Ashland to observe the nest, and there were four nestlings in it, still with their eyes closed.
At first I saw the Catbird parents feeding the nestlings, but then I noticed two very agitated and much smaller Gnatcatchers in the same shrub. When I stopped and looked closer, I realized that the Gnatcatchers were dive-bombing the Catbirds at the nest. The Catbirds eventually left. One of the Gnatcatchers had some kind of spider or insect in its beak. I waited, and though I had a slightly obstructed view, it looked like the Gnatcatcher went to the edge of the nest and fed one of the Catbird nestlings.
To be sure, I got into a better position and waited. Next, the Catbird parents came back with food, and one of them stayed on the nest. Then a Gnatcatcher came in with food and dive-bombed the Catbird but eventually gave up because the Catbird refused to leave the nest. The Gnatcatcher ate its food and left and the Catbird eventually left as well. I watched as a Gnatcatcher then caught a green caterpillar, beat it against a branch, and flew into the unattended nest and placed the caterpillar into the mouth of one of the babies!
I ended up spending over an hour-and-a-half watching the drama at the nest. Shannon came over for the last 15-20 minutes and brought her camera. She was able to get a few photos and I took a bad cell phone video that shows a feeding. While I was there, I saw the Blue-Gray Gnatcatcher feed the Gray Catbird nestlings five times with an additional two aborted attempts because the Catbird was on the nest and refused to leave.
By Joe Sebastiani, Ashland Nature Center Manager:
Megan’s excited field notes capture the thrill of observing and documenting what is indeed a rare event! Although Megan and I searched the literature, we could not find another record of a Blue-gray Gnatcatcher feeding a nest of Gray Catbirds. However, there are plenty of other records of adults of one species feeding nestlings of another (inter-specific nestling feeding, excluding adults feeding nestlings of the brood-parasitic Brown-headed Cowbird). According to a review by Marilyn Muszalski Shy of Western Michigan University, there are 6 main circumstances or explanations for this behavior.
- Two species have laid eggs in the same nest so that both sets of parents end up feeding the young
- The nest of the feeding bird was destroyed, so they redirect their instinctive parental care into feeding chicks of a different species in a nearby nest.
- Nests of two species are so close together
,that one species ends up feeding the other species by accident.
- The sound of the young begging for food attracts, a different species which then feeds them.
- The male, whose mate is on the nest, feeds nestlings of a different species “while he waits” for his own young to hatch.
- Unmated birds carry out instinctual parental duties and feed other species nestlings.
Which of these is the most likely explanation for the Blue-gray Gnatcatchers seen feeding Gray Catbird nestlings at Ashland? Option 1 seems unlikely as all the young in the nest look Catbird-sized. Options 3 and 4 also seem unlikely since Gnatcatchers normally nest high in trees whereas the Catbird nest was in a low shrub. Since Megan observed two Gnatcatchers feedingthe Catbird nestlings, which was presumably the male and female, I don’t think it is options
4, 5, or 6 either. That leaves us with option 2 as the most likely explanation. The nest of the Blue-gray Gnatcatcher was probably destroyed, yet their parental instincts caused them to start feeding the Gray Catbird nestlings.
Shy, M. Muszalski. Interspecific Feeding among Birds: A Review. Journal of Field Ornithology, 1982, Vol. 53. No. 4 pp. 370-393.