In my last column, I discussed the delights of looking at birds’ beaks; focusing on a small part of a bird can be the key to unlocking your understanding of birds’ relationships and ecological roles. You can do something similar with behavior properties. Notice how different birds live in different ways and how these behaviors reflect both larger evolutionary groupings and specific adaptations to a particular species’ place in the world. I recommend starting with perhaps the most fundamental question of social behavior: to stream or not to stream?
But why do some birds gather in flocks? The two main reasons are to avoid predators and to find food.
Having more eyes in a group means that a hawk or other threat is quickly raised. Meanwhile, species with aggregated food sources such as seeds or berries often benefit from foraging together. That’s why finches, or berry-eating waxwings, travel in groups – when food is found, there’s usually enough to go around. For hawks or many insectivorous birds of prey, which are more common, crawling doesn’t make much sense as an evolutionary strategy.
For many of our familiar songbirds, you’ll only see a seasonal flocking pattern, with birds splitting into pairs during the nesting season. Although some birds maintain territories throughout the year to gain access to food sources or other resources, one of the most important reasons for territoriality (ie, protecting a particular area and preventing other birds of the same species from entering it) is for males. birds to protect their companions from contact with rivals.
Why don’t many songbirds flock in the spring, even when food is plentiful? Jealousy.
So now, when nesting is well past its prime, is flocking season. This is easily seen in two of the most obvious groups of fall migrants: shorebirds and ducks. Both of these families come from the north every year and spend the winter in large herds. In the spring you will see each group in turn preparing for the end of the herd season. Some shorebirds will put on their breeding plumage before heading north to find nesting sites and mates, while ducks will begin mating in distinct pairs at their wintering grounds.
But you can see this shift toward streaming in your neighborhood, too. Berry-eating warblers and waxwings travel mostly in single-species flocks in search of fruit trees. Seed-eating house finches, goldfinches, crown sparrows, and California quail do the same with a specific portion of plants or rich seed sources in a well-stocked backyard feeder.
In the forest, numerous songbirds will congregate in mixed-species flocks as they focus on similar prey. A walk through the oak trees can seem peaceful until you are suddenly surrounded by chickadees, vireos, kinglets, nuthatches and creepers.
There are other songbirds that are less inclined to flock even in winter. Less extensive subbirds, which feed on a mixture of scattered seeds and insects, have a lifestyle that is less acceptable to the flock than leaf gatherers. Migratory fox sparrows and hermit thrushes may fall into this category, as well as the resident Bewick’s wrens, which are generally solitary in winter.
The latter are birds that neither migrate from north to south nor roam widely in search of winter food. For a few of these, it may not make sense to stay in the same area as their breeding partner, taking advantage of some of the benefits of teamwork while avoiding the hassle of finding another suitable mate when spring rolls around again. For some birds, winter pairs can be quite empty. Red-tailed hawks and great horned owls, mockingbirds and spotted towhees will all live in general proximity to their mates during the winter, often without obvious cooperative activity.
But for a few species, mating is a constant of life throughout the year. Go out into the woods and look for the oak titmice. You can almost always find two of those little gray-fleshed birds together. Or venture out into your backyard or neighborhood to see my favorite pair of birds, the California towhees. These two quiet brown sparrows protect each other every month of the year. And every month of the year, you can hear their crackling medley duets, the clearest conversation of a never-separated couple.
Jack Gedney’s On the Wing airs every Monday. He is co-owner of Wild Birds Unlimited in Novato and author of The Private Lives of Public Birds. He can be contacted at email@example.com.