When I lived in Santa Cruz, California, I often heard tiny rubber-ducky squeaks emanating from a dying Monterey pine outside my window. Sunny mornings might bring in 4 or 5 smart little brown-capped birds flying
in long swoops from a nest tree hidden in a nearby park. I was watching
the communal lifestyle of the Pygmy Nuthatch, one of the smallest of North America’s cooperatively breeding birds.
Up to 40 percent of all Pygmy Nuthatch nests involve at least one and up to three helpers. These are always males—sons or brothers of (usually) the male in the reproductive pair. Helpers hang around for a year, sometimes two, helping feed the incubating female and then the nestlings. Their help improves the chance that young will fledge from the nuthatch nest, and it also allows the adult birds to enter winter in better physical condition.
Cooperation doesn’t end in autumn. Pygmy Nuthatches practice controlled hypothermia to get through cold nights. Entire flocks of them huddle together in roost holes to conserve heat—researchers have seen as many as 150 emerge from a single tree!