[LUM#23] Chickadees Everywhere
This little ball of yellow and blue feathers fills the skies above our forests and cities alike, punctuating the sounds of our surroundings with its distinctive song. The chickadee has been the subject of a monitoring program for over 50 years at the Center for Functional and Evolutionary Ecology , and the good news is: it is adapting well to climate change, as shown by the work of doctoral student Jérémy Defrance.
The great tit is one of those species that thrives in urban areas. But this adaptation hasn’t come without a cost: “The great tit lays its eggs four days earlier in the city and lays an average of 7.5 eggs, which is 1.5 fewer than its forest-dwelling counterpart. We also observe that fewer chicks reach fledging age, with 3.5 chicks for the former, compared to 5 for the latter, ” notes Jérémy Defrance. This doctoral student is studying the link between food resources and reproductive traits in this small passerine, which has been monitored for 50 years by the teamof Anne Charmantier (Portrait: Digging into Titmice), a researcher at the Center for Functional and Evolutionary Ecology, where he is completing his thesis.
In an attempt to explain these differences, the young man is focusing on the quantity and quality of the food source. And using a large net, he searches through the bird’s pantry. “We call this ‘tree tapping.’ Every week between mid-March and late June, I collected samples of the insects found on white and green oaks, as well as on Aleppo pines and stone pines.” And what did he find on the menu? Mainly “spiders, lepidopteran larvae, and other arthropods.” All of these are delicacies for our chickadee.
The question remains: which ones actually make it to the chicks? To find out, Jérémy Defrance installed video cameras in 40 nest boxes in the city and 40 in the forest. The goal: to capture images of the parents bringing prey back to their young. While the frequency of trips is the same in the city and in the forest—on average every 1 to 2 minutes—the type of prey differs depending on the season. “Urban chickadees bring back more caterpillars during the first clutch (40% of prey) than forest chickadees (20%), which consume far more spiders (55% of prey) before switching to caterpillars for the second clutch (80%).”
To take things a step further, the doctoral student collected chick droppings to subject them to metabarcoding analyses —“a DNA analysis method that uses droppings to determine which insects were eaten.” While we await his conclusions, Jérémy Defrance, who won over the jury of *My Thesis in 180 Seconds* by rambling like no one else (Science at UM: 3 Years of a Thesis Summarized in 3 Minutes, April 2025), shares his photos in a yellow-and-blue portfolio. Warning: “Chickadees are so fast that, even when filming at 120 frames per second, I can’t always make out what they’re holding in their beaks.”
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