March 21, 2016
Thanks to Elizabeth Kennedy for this guest student blog post. Elizabeth explains how birds who have supplemental food from your feeders sing more than birds who are left to fend for themselves.
Many birders relish the experience of waking to a chorus of birds. In fact, birdsong can be an effective alarm clock for dawn bird-watching! Once you wipe the sleep from your eyes, you can enjoy the concert while the sun rises. Birds sing throughout the day, but they are especially vigorous in the morning. You probably realize this is not their morning choir practice, but have you ever wondered why so many birds join this group activity?
Researchers have two different ideas about why birds participate in the “dawn chorus,” the term for a network of birds singing at the same time. The first idea is the “condition-dependent hypothesis.” In this explanation, a bird’s song depends on its environment, especially how much food is available. If this is the case, singing is a status update to neighbors, “I’ve got food!” A male can signal to females that he has the resources to be a good mate. Because all the birds are singing together in the morning, females are listening for an appealing male.
The other explanation is the “social-dynamic hypothesis,” which theorizes that a bird’s song is related to its interactions with neighboring birds. Rather than an announcement, this would mean that singing is a conversation, or sometimes an argument, between birds. As they sing together, some males may be using their song to intimidate and assert dominance over others.
Researchers Thibault Grava, Angélique Grava, and Ken Otter ran an experiment to test which of these hypotheses better explains the dawn chorus. They recorded and compared the singing of two groups of Black-capped Chickadees; one group had received supplemental feeding in the form of mealworms every other day and the other had received no additional food. The researchers found that well-fed birds sang more than the birds left to fend for themselves. This suggests that singing is an announcement or a “badge of status” based on the conditions the bird finds itself in. The dawn chorus is a social network, the bird’s version of Facebook, where they update their neighbors and potential mates about what is happening in their lives.
Dominant and subordinate birds both increased their singing when they got extra food, indicating that song is not an attempt to intimidate others. Dominant birds do sing more as a whole, but this could simply be because they have more access to food and therefore more energy to invest in singing.
Many birders consider morning the ideal time to view birds since that is when they are most active—and full of song. By filling your bird feeder, you are strengthening the local chorus; enjoy the concert!
Grava T, Grava A, Otter KA. 2009. Supplemental Feeding and Dawn Singing in Black-Capped Chickadees. Condor, 111(3): 560-64.