They’re a familiar sight in parks and on lawns all across the U.S. Their clear, whistled songs sweetly wake us on fresh spring mornings and usher in soft, warm twilights. They are so common they are familiar to those who don’t know much about birds – known as a symbol of spring. For all this familiarity, there are still secrets – hidden gems – in the family life of the American robin.

Robins are usually monogamous but apparently not much is known about their courtship rituals, or how mates choose one another. So little is known about this aspect that “The Birds of North America” species account mentions multiple-year pairings “are most likely due to chance.” Because the birds most often return to the same area to breed year after year, this may be possible; but if one mate fails to return, how does the surviving bird choose another? And how do first-year breeders choose mates?

How intriguing – these birds live virtually under our noses, yet little is known about the process of pair formation.

Another little-known fact is the robin’s habit of roosting in large numbers. This not only occurs in winter – when certain other birds roost in large aggregations – but throughout the year. The composition of the roosts depends upon the season as well as where they are in their reproductive stages. Research gathered for the BNA shows that only adult males occupy roosts during the breeding season; females and young gather together in their own roosts once nesting is completed; and all join together in one roost for the winter. These flocks can become quite large; one estimate had a communal robin roost numbering more than 200,000 birds.

The BNA has several observations of robins actually sharing nests. There is mention of an article in a 1991 issue of WildBird magazine of a robin and a cardinal nesting together – in the same nest at the same time. I would have loved to have gotten hold of this article, but could not find it anywhere. Also, I found a reference to the American Midland Naturalist journal, a periodical I was able to find. In this I read several delightful accounts of nest sharing. The first described how two female robins cooperated in building a nest: one bird brought material to the other, who then placed it in the nest while the first flew off to gather more. To quote the author, J.C. Howell, “They went about their work with little friction between one another.”

There is a photo of the two birds snuggled together in the nest, incubating as many as eight eggs – priceless.

Another account describes a robin sharing a nest with a mourning dove. Both parents alternated incubation duties and feeding of nestlings; incredibly, this occurred two years in a row. However, the writer is quick to add this little disclaimer: “While no hostilities were observed it was probable that the relations were not always amiable as the remains of a robin egg were on the ground beneath the nest. Furthermore both species did not incubate at the same time.”

I had to chuckle at this one.

There are still many intriguing mysteries in the life of this common backyard bird. If you should find one nesting in your yard, pay close attention – you just might find something surprising.

NEWS bird columnist Chris Corio can be reached at bdnsports@bangordailynews.net