Winter World_ The Ingenuity of Animal Survival - Bernd Heinrich [126]
In Jack London’s story “To Build a Fire,” the old-timer on Sulphur Creek had told the cheechako that “no man must travel alone in the Klondike after fifty below,” or as Alaskans quip when it is very cold “it’s a two-[or three?] dog night.” Similarly because of the danger posed by cold, golden-crowned kinglets in the Maine winter woods travel in groups of two to three or more and like goldcrests, they huddle at night. Huddling saves energy. How much heat loss an Alaskan reduces by huddling with a husky has not, to my knowledge, been accurately measured, but one goldcrest huddling with another reduces its heat loss by about 23 percent, while in trios heat loss is lowered by 37 percent, similarly to bushtits (Psaltriparus minimus), which also save the same amount of energy overnight by huddling in pairs or trios. Whatever it is that kinglets are known to do, it still doesn’t quite add up because the large energy savings achieved by huddling are insufficient to offset differences between energy reserves and energy demands. Even with huddling, hypothermia (reductions in body temperature) in kinglets is likely inevitable.
Deep torpor at night would confer large energy savings. But body temperature is unlikely to be allowed to go much lower than about 10°C, because the birds can’t risk losing the ability to shiver to keep from freezing solid if temperatures at night dip to -30° to -40°C. Survival, even with a body temperature of 5° to 10°C, would likely be impossible without the one thing I suspect matters most and that we know the least about: shelter. Migrating goldcrests stopping on a bare rocky island off Scotland, where there was no snow and little vegetation to hide in, were discovered overnighting in the open, often in groups, but many of them died overnight (Brockie 1984).
Pagels and Blem have reported seeing a golden-crowned kinglet entering a squirrel’s nest. If golden-crowned kinglets regularly overnight in squirrels’ nests, then that should indeed go a long way toward solving their problem. In magnitude, it would be the equivalent of them inventing fire, because it would conserve body heat by enormously reducing convective heat loss. However, squirrels are notorious predators of (young) birds who can’t fly, and red squirrels even prey on young snowshoe hares. A tiny kinglet would be a tasty snack for a squirrel. How would a kinglet know if a squirrel nest is uninhabited and worth the risk of entering?
In the winter of 2000–2001, I hunted for and examined dozens of both red and flying squirrel nests in the Maine woods. I became skeptical that these very snug nests (see Chapter 5) could be or were used by kinglets that were active in the same coniferous woods. First, although each nest had two entrances, these entrances were difficult to find. To introduce my hand into a squirrel’s nest I had to force it through thick dense nest material; it felt like forcing one’s hand through an elastic glove opening that normally stays shut. Could a bird squeeze through? I found no bird feces inside any nest. In all the snow caves where ruffed grouse had overnighted, I found dozens of fecal pellets, and I presume that kinglets entering squirrel nests with a full stomach at night would also have had to void their bowels in the night. I therefore asked Blem for more details. He e-mailed me: “My single observation of kinglets and squirrel nests was very brief, but I definitely thought the bird disappeared in the nest. I could not say that it went into a main entrance. It seemed that it just went into the loose leaves on the outside of the structure.”
Since reading about Pagels and Blem’s interesting and provocative observation I have been stimulated to stay alert and try to find out where kinglets spend their winter nights, because all indications are