Nothing brings a warm summer day to my mind like the sound of cedar waxwings.

Although these birds can be seen in Maine throughout the year, cedar waxwing population numbers may vary throughout the winter, as they travel around in search of winter-fruit bearing trees. In summer, though, they settle down to the serious business of bearing and raising young.

Whenever I’ve heard these birds, conditions seem to conspire to create a picture of the whole environment, creating a mind-movie I play when I am in need of relaxation: Their sibilant, high-pitched “seeeee” or “bzeeee” calls drift through warm summer air sweet with the scent of pine pitch; a light breeze makes trees whisper; and fluffy white clouds sail through a beautiful blue sky.

Because cedar waxwings are almost exclusively fruit-eating (they do add insects to their diet in spring and summer, but rely on fruit more so than do other birds), they are highly nomadic. This is the case during winter, especially, but in summer their reliance on fruit often precludes breeding site fidelity; these birds more likely will settle wherever there is a superabundance of fruit crops.

As you may have guessed, plantings of fruiting trees have greatly benefited waxwings. They’ll harvest the fruit of holly, mulberry, elderberry, crabapple, junipers, dogwood and viburnum, among others; and of course, the fruit of cedars, this association having given rise to their name. They will even eat the flowers of fruiting trees along with the fruit, as well as drink tree sap.

Another aspect of their biology – their late breeding season – reflects their reliance on fruit. Cedar waxwings time the arrival of their young to coincide with the season’s emergence of fruit, with first broods appearing from early June, depending on the location. Although the parents feed their young insects for the first two days of life, they quickly switch to feeding mostly fruit after this short period. As do hummingbirds, waxwings do well on sugary, lower-protein diets.

Waxwings also may start a second brood in July, when most other birds are busy feeding growing fledglings or even getting ready to migrate south. Their young are easy to spot – their plumage is grayer, they lack the full black facial masks, and their chests are streaked. They also constantly call attention to themselves by making an inordinate amount of noise.

Waxwings are one of the few noninvasive bird species experiencing an increase, rather than decline, in population. However, threats to their well-being still exist. Because they rely so heavily on fruit, they are vulnerable to pesticides, and many birds have died after eating the fruit of trees recently sprayed with the poison.

Plantings of ornamental trees near roads or on highway meridians have led to flocks being decimated by collisions with vehicles. Window strikes also take their toll; even if you do not have fruiting trees planted around your house, you may want to put up netting or screening to decrease or prevent window-related deaths, in waxwings as well as other birds.

Another cause of mortality, curiously, is the consumption of fermented fruit; this seems to cause death in two ways. Either the birds become so intoxicated they sustain fatal injury after falling to the ground or the presence of alcohol or other toxins causes death directly. Why the birds cannot or do not detect the presence of these harmful toxins, and avoid fruit that has fermented, is not known.

Chris Corio, a volunteer at Fields Pond Audubon Center in Holden, can be reached at fieldspond@juno.com