The concept of trade-offs pervades the world. Weighing costs against benefits or risk against reward is a useful model for behavior.
Let’s start with an investment comparison. Suppose you have a tidy sum of money you want to invest. One option is to purchase treasury bills. You are virtually guaranteed to get your initial investment back when the T-bill matures but the interest you earn will be modest. The low risk is a big plus, the low return not so much.
At the other extreme, you might invest your money in a venture capital deal. Here the risk is high (you could lose all of your money), but there is the possibility of a huge return. Here we have high risk but possibly high reward.
Of course, a mixed investment plan might be the most prudent of all. The addition of some investments with only moderate risk but the chance of moderate returns can balance out a portfolio.
These investment strategies can serve as a metaphor for nesting behavior in birds. All of our songbirds as well as a number of other birds in diverse families have altricial reproduction. The young are born naked and blind. They are unable to produce enough heat to keep themselves warm. Of course, they are defenseless against a nest predator like a hawk, snake or even red squirrel.
The process of raising young until they can fledge requires 10-13 days of incubation (usually by the female) and then feeding the rapidly growing nestlings for another 10-13 days.
The adults are sanitation engineers as well. Many nestling predators detect their prey by odor, so it is paramount to get rid of smelly wastes that might attract predators. Chicks of altricial birds produce a membrane around their poop to form what is called a fecal sac. One of the parents takes the fecal sacs away from the nest and drops them elsewhere. Keep an eye out for robins, song sparrows and other backyard birds carrying their fecal sacs.
Remarkably, a nestling goes from a helpless chick to a fledged bird in less than two weeks.
Mom and dad will usually accompany the fledged young for a while, so the parents’ work is not done when the chicks leave the nest. If a nest fails due to weather, predators or parasites, birds with altricial development have plenty of time to attempt a replacement brood.
The other extreme in breeding type is termed precocial development, and is seen in ducks, loons, grouse, quail, shorebirds and others. Mom lays eggs that are rich in yolk, the prepackaged nutrition for the development embryos. As a result, precocial chicks hatch out fully feathered with their eyes open. These chicks can walk soon after hatching and are soon feeding themselves. Incubation periods are longer than seen in altricial birds. A typical precocial clutch will need to be incubated for 21 days.
Mothers will tend to the flightless brood after hatching. In many species, the father is an absentee parent. But the time to fledging is much longer than in altricial birds. Ruffed grouse chicks are not capable of flight for five weeks or more after hatching.
The trade-off then is for parents to work extremely hard for a short period of time (altricial development) or invest less energy in tending the young on a daily basis and have young at risk from predators for a long time because they take so long to fledge.
Some species show an intermediate strategy. Hawks hatch with a coat of down and with vision (precocial traits) but require parental nourishment (an altricial trait).
Now is a great time to keep an eye out for nesting behavior in birds. If you find evidence of nesting, report your valuable sighting to the Maine Breeding Bird Atlas (www.maine.gov/ifw/fish-wildlife/maine-bird-atlas/index.html).
Herb Wilson teaches ornithology and other biology courses at Colby College. He welcomes reader comments at
whwilson@colby.edu
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