Carolina Wrens are our most familiar garden friends. They are joyful, energetic, curious, adventurous, and sing almost non-stop. This year we have seen so many Carolina Wren fledglings in our backyard garden. We smile every time when we see these little birds taking a bath and paying among our potted plants on the deck. They often come as a big group with all the siblings and the parents.
One day, we saw one adult Carolina Wren feeding a strange-looking fledgling that is at least double of the wren's size. This chick was constantly demanding food, while the parent wren kept looking for new food in the grass and frequently taking mealworms from our feeder to feed into the seemingly endless belly of the baby bird. I could almost feel the tiresome spirit mixed with content from this little Carolina Wren. That's what takes to be a parent, maybe that's what it is thinking.
I remembered reading that Cowbirds are one of the "brood parasitism" bird species. We have seen a few Cowbirds around earlier this year. So I looked up online and confirmed that this little giant baby bird was indeed a cowbird fledgling. The unaware parents are spending all their time and energy taking care of the "parasite" baby bird, while their own nestlings have been out-competed and starved to death. What's worse is that the female Cowbird, birth mother of this fledgling, is very likely hidden around to monitor everything. She will use her characteristic rattle call to "unlock" the self-identity in the baby cowbird's brain to prevent it from misimprinting its foster parent. What's more eye-opening is that the cowbird babies would "sneak" out of their foster nest after sunset and roost overnight with the other cowbirds in the fields where the species lives. And they will return to their foster families the next day.
Reading all the information makes us sad (but also fascinated). I tried to stay neutral and objective and tell myself that this is just nature. Nature has its own way and rules to maintain the balance. Also note that it is illegal to remove Cowbird eggs from a birdnest in the United States. But witnessing the cruel scene happening in our garden makes me feel heartbroken. We did nothing and only hoped that the foster Carolina Wrens have better luck for the second brood of this year.
Updated on 8/30/21: We have another Carolina couple settled at the strawberry basket in our greenhouse. Currently, there are two wren nestlings still with eyes closed in the nest. We keep the greenhouse door closed and the parents access through the window. This weatherproof and hidden nest seems very ideal to these little birds who are not afraid of people. I guess we have to reserve the strawberry basket as a permanent Carolina Wren nest site!
Helpful Information:
How does Cowbird learn to be cowbird: https://www.audubon.org/news/how-does-cowbird-learn-be-cowbird
General introduction and how to deter Cowbirds: https://nestwatch.org/learn/general-bird-nest-info/brown-headed-cowbirds/
Fascinating studies about how Cowbirds recognize their own identity: https://www.allaboutbirds.org/news/if-brown-headed-cowbirds-are-reared-by-other-species-how-do-they-know-they-are-cowbirds-when-they-grow-up/
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