Kinglets

Three Golden-crowned Kinglets on a winter spruce tree

This tiny species can survive winters in the far north, but this requires a lot of food. The equivalent amount for us would be at least twenty-seven large pizzas every day. Do you eat like a bird?

■ The circulatory system of birds is not dramatically different from ours. They have a four-chambered heart that pumps blood through arteries and veins, which carry fuel to the entire body and return waste products to be exhaled or excreted. There are differences in scale. A bird’s heart is relatively large, about 2 percent of their body weight, compared to ours, which is about one-quarter that size, under one half of a percent of our body. And their heart beats much faster than ours. A bird as small as a Golden-crowned Kinglet has a resting heart rate of over six hundred beats per minute (ten per second), about ten times faster than the average human, and during activity the heart rate doubles to over twelve hundred beats per minute.

■ Small birds lose about 10 percent of their body weight each night while they sleep. Half of that is by defecation and half is by burning fat and evaporating water. Imagine a hundred-pound human losing ten pounds overnight, and gaining it back the next day! This overnight weight loss in birds doesn’t change very much with changing temperatures, and can be even higher on warm nights because of increased evaporation. On cold nights, birds become torpid (see this page), reduce their body temperature, and stay snuggled into their feathers, using them like a big sleeping bag. In extreme cold, a healthy bird will remain torpid longer, and actually reduce their daytime activity, starting later in the morning and ending earlier in the afternoon. They rely on their ability to conserve energy and wait for warmer weather. A bird can lose 30 percent of its body weight before suffering serious effects. In those conditions bird feeders can be a critical resource, allowing birds to refuel quickly and easily.

■ What do salmon have to do with kinglets? Everything is connected, and the migration of salmon upstream is like a conveyor belt carrying nutrients uphill into the forest. Many salmon are taken by predators and scavengers and scattered in the nearby forest, where their bodies fertilize the soil. Studies show that spruce trees can grow three times faster along a stream with salmon compared to a stream without salmon. More plant growth means more insects, and that means more insect-eating birds like Golden-crowned Kinglets. Salmon provide a dramatic example of this sort of nutrient transport, but it happens all around us all the time.