Animals have developed diverse reproductive strategies to ensure their young are born when food, shelter, weather conditions and other external factors favor their offspring’s survival. In Virginia’s temperate climate, most species are geared to reproducing in the spring.
Insects and other species that depend on ambient temperatures just to function at all, let alone breed, particularly depend on warming weather. Many of their predators give birth to their young at the same time, to take advantage of prey abundance to feed their young.
However, nature is complex and species have adapted and evolved to take advantage of this complexity, stretching and shifting their breeding seasons so they can out-compete species with similar needs and avoid predators.
As Donald Stokes writes in his book, “Stokes Guide to Nature in Winter”: “Most people believe that all things associated with breeding behavior happen in spring, but this is far from the case. The breeding of most mammals and the courtship of many birds occurs in the middle of winter.”
There are several reasons for this early start. For species geared toward raising their young in the spring, the length of gestation has to be factored in. The larger the animal, usually, the longer the gestation.
For students of nature, we often miss the abundance of nature that the warmer seasons offer and try to content ourselves with catching up on our reading about natural history. However, we don’t have to wait until spring to enjoy nature outside. Donald Stokes encourages us to study the more subtle aspects of nature winter offers – to go deep rather than broad in our observation skills. His book, “Stokes Guide to Nature in Winter: Northeast and North Central America,” gives keys to identifying plants and animal signs this time of year as well as delving into natural history pertaining to the season.
To learn more about the lives of native Virginia mammals, including when they are active during the year and their reproductive strategies, read “Mammals of the Carolinas, Virginia, and Maryland” by William David Webster, James F. Parnell and Walter C. Biggs, Jr.
If you don’t know the mating clack of the wood frog, hear it and other herp sounds at the Virginia Herpetological Society’s website, virginiaherpetologicalsociety.com. While wood frogs may have already bred in some locations, spring peepers are not far behind.
Other species have a good food supply year-round, which enables them to give birth in winter and gain a competitive advantage for their young. These include predators of overwintering birds, rabbits, and some species of rodents and other mammals.
One such predator, the great horned owl, is the earliest owl to nest, in January or early February. Incubation for these owls lasts a month, on average, so their eggs usually hatch out before spring arrives. Red-shouldered hawks and bald eagles follow close behind, starting courtship in late January and laying their eggs in March or April.
Woodcocks start their unusual courtship behavior as soon as the ground thaws enough that they can find their favorite food, earthworms. It’s possible to hear the male’s beeps as early as January, but this species more typically starts its bizarre courtship display late February.
Mammals share one reproductive edge with birds – the ability to maintain an internal temperature that enables them to be active in winter, including mating and reproducing. The Virginia opossum, our only marsupial, may start mating in January. Gestation is remarkably short – 12 to 13 days, because most development takes place in the mother’s pouch after birth. This allows opossums to give birth in the heart of winter. Following close behind is the North American raccoon, whose mating can be triggered by increasing daylight as early as late January.
Black bears breed in the summer, but the females give birth in winter – early January to mid-February. While in the relatively mild climate of Virginia, male black bears may go in and out of denning, during the winter pregnant females stay in the den in a state of torpor, a modified form of hibernation, to give birth and start raising their cubs. This half-awake state enables them save energy but be able to better defend themselves and their cubs should a predator intrude.
Several rodents, which typically outstrip most other mammals in their reproductive ability, get busy starting their families in winter. Virginia’s largest rodent, the beaver, starts mating in January. Gray and fox squirrels produce two litters, mating in midwinter and in June, as does the tiny southern flying squirrel. Red squirrels start their courtship a bit later. Spending the winter in a state of torpor in their underground nests, groundhogs start breeding as soon as they reemerge, as early as late February. Some mouse species breed year-round.
While reproductive strategies are fascinating and diverse, one really stands out – that of mustelids. Most species in this mammal family – which includes weasels, otters, and skunks – can delay implantation of fertilized eggs until almost a year after mating, which is generally just after the young are born in the spring or summer. The striped skunk and least weasel are exceptions, with the former breeding in February or March and giving birth two months or so later, and the latter mating and giving birth year-round.
Mating in January, gray foxes have the edge over their canid cousins, red foxes and coyotes, as well as bobcats, which don’t get the urge to merge until late in winter. One of the favorite prey of these species, the prolific eastern cottontail, also starts breeding in late winter, producing up to four litters per year.
Most reptiles and amphibians, who like insects have no internal mechanism for keeping warm, must wait for the rising temperatures of spring to reproduce. However, one species, the wood frog, has evolved to breed during warm spells in the middle of winter, before many of its competitors and predators are out and about. High levels of glucose in the liver and leg muscles, which functions as antifreeze, gives this amphibian its reproductive edge.
While it’s snowing as I write this, I know romance is in the air for many of my wild neighbors.