January 12, 2016
Thank to Gates Dupont for this guest student blog post. Gates describes how male-female winter pair-bonds produces hierarchies in flocks of Black-capped Chickadees and the resulting drama at your feeders.
The springtime song of the Yellow Warbler searching for love proclaims, “Sweet, sweet, sweet, I’m so sweet.” That sweetness stretches into the winter season for a common feeder bird, the Black-capped Chickadee. While watching chickadees through frosty window panes, it seems impossibly cold outside for these little lovebirds, yet their hearts are warm with winter romance.
Not all birds have strong bonds outside of the breeding season, so why do chickadees? Winter pair-bonding in chickadees revolves around social hierarchy and the protection of their mate. Those cute black-and-white fluff balls do, in fact, form hierarchies in their flocks. Male-female pair-bonds begin to form in the fall, after the breeding season, when winter foraging flocks of up to a dozen chickadees aggregate. Chickadees tend to pair with each other based on social rank, so the alpha male will pair with the alpha female, the beta male will pair with the beta female, and so on.
Once a female chickadee pairs with an alpha male, she immediately receives a number of benefits such as experiencing less bullying from other males in the flock. Aggression often takes place around food sources. Less bullying leads to better feeding opportunities for females paired with dominant males. The decrease in aggression is due, in part, to the active protection a female receives from her mate, as a dominant male chases off subordinate members of the flock in order to allow the female to feed freely.
Females receive an immediate positive benefit from this protection, better access to food. Males, on the other hand, might work their tail feathers off in the process. Protecting their mate leads to a dramatic increase in energy usage and increases the potential for injury during aggressive interactions. Benefits for the male, however, may come over time. If the male’s protection improves his mate’s condition, she may lay more eggs, lay larger eggs, or lay earlier in the nesting season. Chicks that are born at the start of the breeding season are, in general, more likely to survive and join their first winter flocks earlier, making them more dominant in the new hierarchy.
The next time you see a flock of chickadees flitting around your feeders, try to recognize these winter pair-bonds. When three chickadees are at the feeder and one of the birds chases another bird away, you will know that it is all in the name of love, even if there is not mistletoe hanging above your feeders.
Reference: Lemmon, D., M. L. Withiam, and C. P. L. Barkan. 1997. Mate protection and winter pair-bonds in Black-capped Chickadees. The Condor 99: 424-433.
Gates Dupont is a first-year undergraduate studying biology at Cornell University. He is interested in bird migration and its implications on avian conservation.