- Do you have questions about birds, bugs, bees, butterflies or other wildlife? Send your questions to Wild Things and we will try to find the answers.
Birds do three things that expend a great deal of energy: They reproduce, they molt and they migrate. Naturally enough, birds have evolved so these three events do not occur at the same time. Most birds reproduce in the spring and summer, molt in late summer and migrate in the fall.
Song sparrows (Melospiza melodia), for example, recognize that it is time to breed as the days become longer in the spring. They also take into account temperature and food availability.
When the time is right, the male song sparrow sings to attract a mate and to proclaim his territory. Female song sparrows are attracted to the males with the most accurately learned songs.
Beginning as early as late April, song sparrow females lay eggs, which hatch in two weeks. Both parents raise the first brood of three to five chicks. Upon hatching, a chick weighs less than a penny. In only 10 short days it leaves the nest weighing 10 times what it did at birth. That’s a lot of weight gain in a short period! As soon as the fledglings leave the nest, the female begins laying eggs for a new brood. The father herds the fledglings to nearby bushes, where he tends to them. In two to three weeks, a second brood of chicks hatches. The father turns his attention to these new chicks, and the first brood is now entirely on its own. (In only 24 to 30 days, the chicks have gone from newborns to independent youngsters!)
As you might have guessed, many song sparrow chicks do not survive their first year. Song sparrow parents are lucky if even one fledgling per year survives to return as a breeding adult. Only about 10 percent of song sparrows survive for three years.
It becomes more difficult to spot birds (including song sparrows) in the late summer and early fall. The nesting season has ended. Fledgling birds have grown up and can take care of themselves. Territorial boundaries become less important. And birds molt before they make their annual migration south. Because they do not fly as well while molting, birds at this time of year keep a low profile. They are quieter and their behaviors more secretive.
At molting time of year, there is still enough food around to provide birds the energy they need to grow new feathers. Song sparrows molt in August and September. They replace about 2,000 feathers during this period. For many birds, the winter plumage is duller and plainer than their summer breeding plumage. They do not look much different in summer and winter, though.
After molting, birds are ready to migrate south with fresh new feathers. (Most birds have a second, partial molt when winter ends. Some feathers are replaced, making the birds, especially the males, appear more colorful and more fit for mating. The flight feathers are not replaced, so birds fly north in spring on worn flight feathers.)
In September and October, after molting, song sparrows begin to sing and defend their territories once again. This is the time of year migratory birds may begin to travel south.
Birds that eat insects have a strict timeframe: Insect populations decrease later in the season, and are almost completely gone by the first frost. But not all birds eat insects. Some, like song sparrows, are omnivores that eat seeds and fruits as well as insects. These birds have more options about when to migrate.
Song sparrow migration is all over the map. Song sparrows that live in the far north – Alaska and Canada – migrate the farthest. These birds fly to Mexico and the Southern United States to overwinter. Other song sparrows, such as the ones in Massachusetts, may migrate, but they do not go as far south as their northern cousins. This is called leapfrog migration. The birds farthest north leapfrog over their southern relatives and overwinter the farthest south.
Song sparrows migrate at night when winds are most likely to help them on their way. They are in no rush and can wait until favorable winds develop. Some song sparrows begin migrating in August; others wait until November hoping for the fairest skies and the best tailwinds; most migrate in September or October when wind velocity at migration altitudes is generally favorable. Studies have shown that small birds expend about as much energy when soaring or gliding as they do when resting on a branch. So clearly, waiting for a good tailwind is a good survival strategy.
To make migration patterns even more confusing, some song sparrows do not migrate at all. They may stay in our area all winter. Song sparrows have overwintered in Massachusetts at least as long as people have been recording their behaviors. According to the 1906 writings of ornithologist William Brewster,
Song Sparrows winter regularly in the Fresh Pond Swamps, where they appear to find congenial shelter and abundant food during the coldest weather and the deepest snows. In the earlier years of my experience it was unusual to note more than two or three there at any one time, but now we often see a dozen or more in the course of a single morning … I have known single birds to pass the months of January and February in gardens near my home in Cambridge, as well as in certain briery thickets which formerly bordered the Charles River Marshes between the Cambridge Cemetery and the Watertown Arsenal.
Keep your eyes peeled. There may be an uptick in song sparrow numbers now as migrants from the north pass through on their way south. Look for them in low shrubs, flitting from bush to bush. Listen also for their wonderful repertoire of songs for which they get their name.
Have you taken photos of our urban wild things? Send your images to Cambridge Day, and we may use them as part of a future feature. Include the photographer’s name and the general location where the photo was taken.
Jeanine Farley is an educational writer who has lived in the Boston area for more than 30 years. She enjoys taking photos of our urban wild things.
A stronger
Please consider making a financial contribution to maintain, expand and improve Cambridge Day.
We are now a 501(c)(3) nonprofit and all donations are tax deductible.
Please consider a recurring contribution.