The American robin sings a carol of two- and three-note phrases, but early in the day males throw in an extra sibilant phrase. Carlos Osorio/Associated Press

The next few weeks represent the pinnacle of bird concerts. Male songbirds are singing vigorously and often to attract a mate and to fend off other males seeking to usurp their territory.

Learning to identify the various songs and calls of birds is a joy and a worthy goal. At this time of year, most expert birders identify 90% of the birds they encounter by sound. The variety of bird sounds means that one’s education in auditory identification is never done.

There are tons of resources to allow you to improve your identification of bird sounds. I wrote favorably of the app Merlin, produced by the Cornell Laboratory of Ornithology. This app will identify sounds (and photos) of birds. The app is free for download for iPhones and Android phones.

Another free app is the Audubon Bird Guide, produced by the National Audubon Society. Multiple recordings of vocalizations and photographs of different plumages provide a valuable learning tool. The AllAboutBirds.org website offers many recordings of bird vocalizations with useful text.

Close listening to bird songs often rewards the listener with a deeper appreciation of these songs. I’ll describe some variations of Maine bird song that I find fascinating.

You need to be an early riser to appreciate the first three examples. The eastern phoebe’s song is a familiar, insistent fee-bee song. But early in the morning, males throw in an extra syllable, fee-buh-bee. Why? We have no idea, but I love listening for that variation.

We also don’t understand the early morning variations of two other common nesting birds. The American robin sings a carol of two- and three-note phrases: cherrily, cheer up, cherrily, cherrily, cheer up, cheer up. Early in the day, males throw in an extra sibilant phrase, effectively described as hissely. Listen for that phrase when the robin outside your house starts singing at 4 a.m.

The chipping sparrow song is a dry trill, given from a perch in a tree. Back in the days before telephones had ring tones, I met a woman who called chipping sparrows the telephone birds because she always felt like she needed to answer her phone when a sparrow was singing its regularly spaced trills.

Shortly after dawn, chipping sparrows alter their singing behavior. Males from adjacent territories will fly down to a common area and sing from the ground. Rather than a long trill, the songs are short, staccato-like bursts. Whatever it takes to impress a female.

The hermit thrush is one of our most accomplished singers. The song consists of a sustained whistle followed by a number of flute-like phrases. The song is haunting and hopelessly beautiful. Listen for the change in pitch of the whistle between songs. The pitch alternates between a low pitch and a high pitch in consecutive songs. Again, we have no clue as to why this variation occurs.

A birder hears the distinctive song of an American redstart: a series of thin notes, ending in a strongly accented note. She looks in the trees to try to see the songster, expecting a black bird with orange in the wings, sides and tail. But no. The singing bird is gray with yellow on the sides, wings and tail. Do female American redstarts sing?

No, this singing bird is a second-year male whose plumage mimics female plumage. The birder is seeing a phenomenon called delayed-plumage maturation. We know that older males tend to be more successful in attracting mates and first-timers often fail to gain a territory.

So, a second-year bird uses stealth to try to mate with a female. Its female-like plumage does not raise the ire of a territorial male and its song alerts a female who is up for an extra-pair affair that he is available.

Delayed plumage maturation also occurs in Baltimore orioles and red-winged blackbirds as well.

We have some species in which females sing as well as males. Northern cardinals, song sparrows, Baltimore orioles and house finches are examples.

Herb Wilson taught ornithology and other biology courses at Colby College. He welcomes reader comments and questions at whwilson@colby.edu