This column continues the discussion of Bicknell’s thrush, one of the most elusive breeding birds in Maine. By the time you read this column, most male Bicknell’s thrushes will be done singing for the breeding season.

Bicknell’s thrushes have an unusual mating system. Most of our songbirds are monogamous during the breeding season. A male pairs with a single female and the male defends the breeding territory against intrusions by other males.

Not so for Bicknell’s thrushes. Their mating system is an open, communal system. Males do not maintain exclusive territories. Several males may sing from one area in the same day.

Males and females both mate with multiple partners. Any given nest holds a genetic hodgepodge of offspring. The nest will have eggs laid by a single female but because of her multiple partners, some nestlings will be siblings and others will be half-siblings. Males may have offspring in several nests, corresponding to the multiple females they mate with. Thus, a nestling in one nest may have half-siblings in other nests. Now that is a complicated family structure.

A male will bring food to more than one nest, so the nestlings in any given nest may be fed by multiple males as well as by the mother.

Ornithologists refer to this mating system as polygamy. Nearly 95 percent of bird species show monogamy and most of the remainder display polygyny, in which one male may have multiple female partners but each female has only the one male partner. Red-winged blackbirds are a local polygynous species. Polygamy is quite rare, so it’s really neat to have a polygamous species in the Maine avifauna.

The entire population of Bicknell’s thrushes is estimated to be around 125,000 individuals, making Bicknell’s thrush a species of concern for environmental managers. These birds nest at fairly high density – an average of about 50 pairs per 100 acres – so habitat alteration of even a small area can have serious repercussions.

Conservationists worry about winter habitat degradation as well. The entire population winters mostly just a few islands in the Greater Antilles. Around 90 percent of Bicknell’s thrushes winter on Hispaniola.

Bicknell’s thrush was named after Eugene Bicknell, an amateur ornithologist who discovered the species in the Catskill Mountains in the late 1800s.

NEW BIRDING APP

A number of bird-related apps are available for smart phones and tablets. Some that I find particularly useful are BirdTunes, Merlin, National Aubudon’s Birds, iBird Pro and Sibley Birds.

The new Warbler Guide App takes birding apps to a new level. This resource is a companion to the marvelous field guide of the same name by Tom Stephenson and Scott Whittle that was published last year.

Like the apps above, the Warbler app provides vocalizations, photographs, line drawings and distribution maps for the birds covered. The Warbler app has full information on all of the 56 species of warblers that occur in the United States.

A skilled birder can identify a bird from five views: above, below, side (left or right), head-on and tail-on. Sometimes a head-on view is all you get, or perhaps you get an obscured underside view through dense foliage. To clinch the identification, you really need to know all sides of the bird.

One beauty of the Warbler app is that you can see a warbler from any angle you want. Three-dimensional models of each species are provided. Using your finger, you can change the orientation to match the view you saw in the field.

The Warbler app has a great filter to allow you to quickly zoom in on an identification using morphological features as well as song features.

See this video to learn more: bit.ly/1KRbI61. The Warbler Guide App is a game changer.

Herb Wilson teaches ornithology and other biology courses at Colby College. He welcomes reader comments and questions at

whwilson@colby.edu