How mourning doves are able to increase their numbers into the millions

The longer I watch mourning doves, the more I wonder. How do these birds that appear to be so dimwitted persist in such great numbers? There are hundreds of millions of them.

Let's see if we can figure this out.

How they measure up

Spring, summer, autumn or winter - the mourning dove (Zenaida macroura) is the most common native dove to be seen in the suburbs.

It is brownish-beige above and pinkish-brown below. With its long tapered tail, the bird measures 10½ inches long.

This dove has some subtle but handsome markings, including an iridescent blue-and-pink shimmer on its neck. Its dark, large eyes are circled with pale blue skin and black spots decorate its pointed wings. Males are a bit more colorful than females.

Even if you can't get a clear view, the mourning dove can be easily identified by the way its wings whistle in flight.

Dovish word play

While its slow, soft "ooah-ooo-oo-oo" call is often heard early in the morning, that is not the source of its name. It is a source of confusion since some people think they are hearing an owl hooting.

Given how early doves will sometimes call, this confusion is understandable. As the dove's call has a plaintive tone, other folks, back in the day, thought the bird was mourning the loss of a loved one. And so we have our mourning dove.

Speaking of missing a mate, experiments with penned doves showed that when a female mourning dove was taken from its partner, the male's rate of cooing increased tenfold.

At the bird cafeteria

If you feed birds, you will note other aspects that separate mourning doves from other seed-eaters such as chickadees or cardinals.

Birds that live in trees use their feet together to grab on to a branch or twig. On the ground they hop, with both feet, from spot to spot. Birds that spend a lot of time on the ground, such as pheasants and doves, walk rather than hop. As doves walk, they characteristically bob their heads as they search for seeds.

Mourning doves are definitely herbivorous. Besides feeder seeds, their diet consists of corn, wheat, crabgrass, prairie grass, foxtail grass, and spurges.

In addition, if you have a bird bath, watch the way doves drink compared to other birds. The other species grab a beak full of water and tilt their head up so that they can swallow with the help of gravity.

Mourning doves, along with pigeons, can actually suck up water. They don't need any help from gravity. This leads us to another dove distinction - crop milk. And no, I'm not talking about a crop like corn or soybeans.

Avian crops

An enlarged esophagus in a bird's neck is referred to as a crop. The crop acts as a temporary food storage organ. Depending on the seed's size, a crop can hold hundreds to thousands of seeds. The record number of seeds found in a mourning dove's crop was over 17,000 bluegrass seeds!

In the case of doves, the lining of this organ secretes "crop milk," which is fed via regurgitation to the young birds. Both sexes produce crop milk for the nestlings, which brings us to mourning dove nests.

Nest code violation

How can I put this? Mourning doves build shoddy, flimsy nests that somehow manage to keep a few eggs in place. They place these feeble structures in almost any available site, regardless of the precarious nature of the location. Their nests can be found on the ground as well as in a tall tree, deciduous or coniferous.

The doves will also place nests on vines, shrubs, other bird nests, building ledges, flower pots, or even on a hanging mop! As long as the surface is somewhat horizontal, the doves are good to go. Human activity, and related risks, do not deter a pair of determined mourning doves.

Once the female selects a site, the male brings small twigs, grass blades, and pine needles to his mate. Nest building takes seven to 10 hours over two to four days.

The resulting shallow saucer is so flimsy that an observer can often see the white eggs through the nest when standing underneath. As you might guess, this skimpy nest does not offer much protection for the eggs during severe weather.

Surprisingly, the nest only has to hold two to three eggs, the average clutch size. Why so few? Crop milk.

Studies suggest that a pair of reproducing doves can only produce enough crop milk to successfully raise two squabs, the term for young pigeons or doves. This dove milk is high in fat and protein and helps the nestlings grow quickly.

Other seed-eating birds will catch insects when raising young in order to provide their nestlings more protein. Mourning doves don't need to switch to an insect diet. Their crop milk contains more protein and fat than human or cow milk.

Quick-growing squabs allow mourning doves to make up for their small clutch size by raising multiple broods. In warm regions, they may have as many as six broods. I guess that's one way to keep the dove population going.

Fly, hop or die

Another way to survive is to be a strong flier, which mourning doves are. The bird's long tail and long, pointed wings allow it to fly at speeds of up to 55 mph! This dove's scientific species name, macroura, is Greek for "long tailed."

The mourning dove's flight ability does not always protect it from a hungry hawk. At Stillman, the dove's principal aerial predator is the Cooper's hawk.

If a hawk attempts to catch a nesting mourning dove, it will fly to the ground and pull the ol' broken wing act to lure the hawk away from the nest. The doves' attempts at escape are not always successful. If you walk the trails at Stillman, you'll eventually discover a pile of mourning dove feathers left behind by a satiated Cooper's hawk.

Death from hunters, disease

Besides hawks, humans hunt mourning doves. In fact, the species is classified as a game bird. Since it only weighs about 4.5 ounces, it must take a mess of mourning doves to make a meal. Perhaps this explains why, at the very least, 20 million are shot annually.

I've seen higher estimates of hunting mortality. Even at the high end, this is probably only 15% of the overall fall (hunting season) population of mourning doves.

Besides predation, wild birds, such as mourning doves, have a variety of parasites and diseases. Keep in mind that many of these natural afflictions may not kill a bird but can make it easier for a snake or hawk to catch it.

Survival summation

Considering all of the above, I guess I can understand this species' success. Mourning doves breed prodigiously, don't spend much time building a nest, build a nest almost anywhere, survive on seeds, and don't have go to the store to pick up a quart of milk!

• Mark Spreyer is the executive director of the Stillman Nature Center in Barrington. Email him at stillmangho@gmail.com.