You know spring is really here when you hear a song sparrow singing its exuberant song in one of Westborough’s old fields, or near the edge of a stream or swamp. Look around, and you’ll probably spot the bird itself perched at the top of a bush – a perfect place for spreading its sound. You might also hear other song sparrows somewhat farther away.

The song seems to us a celebration of spring, but a male song sparrow (Melospiza melodia) sings to proclaim his territory and to attract females. This small bird is patterned in browns, but you can usually tell a song sparrow from other sparrows by the dark spot or “shield” in the center of its streaked breast. Males tend to sing regularly from a few favorite bushes in different parts of their territory throughout the day. Their distinctive song lasts 2-4 seconds and usually starts with a few repeated notes, followed by a jumbled warble, and ends with a trill or buzz.

Many – but probably not all – song sparrows in our area migrate, so competition for territories begins in the spring as males return about two weeks before the females. A male’s territory is usually about a half to 1-1/2 acres, and it’s used for feeding, mating, and nesting – so, from the bird’s point of view, it better be good.

Males compete for territories and settle their differences over territory boundaries by singing back and forth. Song sparrows typically have five to 15 different songs – an average of nine – and can recognize up to 50 songs of other song sparrows. A male will typically repeat one song many times before switching to another. If one male repeats another’s song back to him, it’s an aggressive move. If one males switches the type of song he’s singing at the same time that another male switches, but without matching the other’s song, that’s also an aggressive move, but less so. You might hear this vocal competition going on among song sparrows, or among other local birds such as cardinals or tufted titmice.

As females arrive, they may judge and select males by the male’s territory and by his song. Apparently the quality of a male’s singing and the amount of time he spends singing (the more the better) are tied to his health – which may reflect how well he eats within his territory – so females may use these characteristics to evaluate potential mates. When a female chooses a male, she lands in his territory and remains. He may attempt to chase her out at first but eventually they’ll become a pair. They’ll move around the territory together, but the female tends to stay much more hidden than the male so she’s hard to spot.

Song sparrows in our area typically raise two broods of 3-5 chicks in a breeding season, and occasionally three broods. Early in the season, they tend to build their nests on the ground, where the cup-like nests made of grass may be hidden by dry leaves and grasses. Later, when the leaves are out, the birds may nest up to 4 feet off the ground in trees or shrubs. Both male and female gather nesting material, but the female usually builds the nest and then sits on the eggs for 13-15 days.

The time in the nest is short, with chicks leaving the nest after only 10-11 days. As with many birds, the parents continue to feed their young for a couple of weeks after they’ve left the nest. The male continues to sing and defend the territory until the second brood has become independent (around one month of age), although he may be quieter at times.

How do song sparrows get their repertoire of songs? With most songbirds, both genetics and learning contribute to varying degrees, depending on the species. In song sparrows, learning plays a large and important role. Like many other songbirds, a young song sparrow goes through four stages of learning song.

First, in the nest a few days after hatching, the nestling listens to the song sparrows around him and is particularly sensitive to their songs. Then, in the second stage, the young bird is silent for a period of time, perhaps busy learning other things. The third stage is a practice stage, much like a human child’s babbling, starting after a young bird that has left the nest tries out a variety of sounds. This stage can sometimes be heard in late summer or early fall. The fourth stage is another practice stage, when the bird’s attempts at song finally turn into adult song sparrow songs. This takes place when the birds are around 4 months old.

Song sparrow males tend to return to the same area they originally came from, so a young bird may spend time learning parts of different songs and particular sounds of other song sparrows in the area. These songs and sounds will eventually help him fit into the neighborhood. Some young males hang around, not challenging any established males, until a territory owner dies or disappears. Or a young male may become a rival for some or all of another male’s territory.

Why do song sparrows – and other birds, for that matter – sing in the springtime? Singing is related to the lengthening of daylight, which is a cue for hormone production. In response to lengthening days, the birds’ sex organs grow and produce greater amounts of sex hormones, which prepare the birds’ bodies for breeding. The hormones also stimulate the birds’ song centers – which are special groups of brain cells – to grow larger and even form new cells. In this way, male hormones such as testosterone lead to increased singing in males. In late summer and fall, as days grow shorter, hormone levels drop and birdsong diminishes. Changes in the amount of daylight in spring and fall also serve as cues for migration in species that migrate, but temperatures also influence the timing of migration.

Song sparrows eat seeds and fruit and will come to feeders, where they prefer millet. In the breeding season when adults and chicks need lots of protein, they eat insects including grubs and caterpillars.

Life for song sparrows tends to be short and intense. Every year about 30 percent of adult song sparrows die. They feed on the ground, where they are vulnerable to predators such as hawks, owls, and cats. Their nests on or near the ground often fall victim to predators, including skunks, snakes, raccoons, and crows, so a pair may need to re-nest a few times in order to successfully raise a brood. Both winter weather and migration are stressful and hazardous.

But even in the face of the dangers of life, the song sparrows’ singing seems to celebrate spring. Let’s enjoy it as we welcome the season.