Theres a good reason most North American birds nest in late spring or early summer: The weather and water are warmer, prey abounds, and insects and fruits are plentiful enough for rearing hungry chicks. But not all species adhere to this schedule. Some get a head start on parenthood by laying eggs before the arrival of springsometimes as early as fall.
These early nesters might be motivated by a variety of reasons. In some cases, they may be able to take advantage of food sources and environmental factors during colder months. And in other cases, as with some raptors, chicks often need more time to develop their hunting skills. Egg-laying times also tend to vary by location for most widespread North American bird species. Lower latitudes often have warmer winters, allowing southern populations to lay earlier than their northern counterparts.
Below are five bird species that have bucked the trend by rearing chicks in winter and late fall.
Fitness and Laying Intervals
When wild birds lay their eggs depends on a variety of factors. The fitness of the birds is correlated with the clutch size and the date of laying. Early-season breeding females depend on a plentiful supply of food in their territory and mate with more powerful sexual cues. When food is scarce, laying intervals lengthen. Early-season breeders have a higher rate of successful reproduction than later-season breeders. Stressors like molting and winterization prove difficult for birds that decide to lay a second clutch of eggs later in the season. Predation and diminishing food supplies are two additional threats that late fledglings must deal with.
Day duration, or photoperiod, has a significant impact on the reproductive window as well. Day length influences hormone levels in prospective partners and the types of food sources that are most common in the surroundings.
Great Horned Owls
The Great Horned Owls’ mating calls fill the woods near Denver Holt’s home in Mission Valley, Montana, every January. Holt has been researching owls for more than 30 years and is the founder and principal investigator of the Owl Research Institute. He hears the prey birds getting ready to nest, and the duets of hoots come like clockwork. According to Holt, “the Great Horned Owls really get started laying their eggs from mid-February to early March.”
Great Horned Owls nest earlier than any other North American owl species, and they arent exactly picky about where they raise their family. These big owls have been observed nesting in tree cavities, cliffs, abandoned buildings, old eagle nests, and even on the ground.
Great Horned Owls, one of the biggest owl species in North America, breed early to allow their young more time to grow; the young remain near the nest until they are about seven weeks old. This timing guarantees that the owlets fledge early in the spring, when a plentiful supply of juvenile rodents and other prey affords them the chance to refine their hunting techniques. When they reach adulthood, they will need to be able to kill a wide range of prey, including large waterfowl like herons and geese as well as earthworms and insects.
Following their fledging, young owls spend the summer with their parents honing their hunting techniques. Some even persist in pleading with their parents for food well into November. Its a long, long breeding season, Holt says.
It’s not easy to start a family when there is still snow on the ground. Great Horned Owl mothers remain with their offspring until the young can control their body temperature on their own. Her feathers act as warm insulation, and the chicks are kept warm by a bare area of skin called a “brood patch,” which is covered in blood vessels. Mom and the nestlings are only fed by the male during this time. He will primarily feed on rodents and small mammals, but will also occasionally eat any other easily obtained prey. Because of their adaptable diet and readiness to nest almost anywhere, Great Horned Owls are among the most common and hardy birds in North America, found from the icy Arctic all the way down to South America. “They inhabit every imaginable habitat within that range,” according to Holt. Great Horned Owls are a pretty adaptable species. .
The Effect of Latitude
Latitude plays a role in breeding season as well. Compared to birds in southern latitudes, wild birds residing in high latitudes, like numerous sandpipers, have to condense their breeding season into a significantly smaller timeframe. The short season causes even their young to develop much more quickly.
Temperature directly affects egg laying in many wild birds. Changes brought about by warmer temperatures include plants blossoming earlier and the availability of other foods earlier. Some birds are laying eggs outside of their typical seasons due to abnormally high temperatures. Research indicates that temperature has a much greater impact on laying dates than either food availability or duration of the day.
In temperate regions, many birds lay their eggs in the traditional spring fashion. Signature increases in birdsong can begin as early as mid-January. Longer days and higher temperatures that come with springtime guarantee an abundance of food sources, especially in the form of insects. The laying of blue tits’ eggs corresponds with the appearance of caterpillars. Migratory birds return and establish territories immediately. Even non-migratory birds may establish new territories in spring. Wild birds start building nests in trees, on the ground, or even in buildings that were built by humans. Once mated, females can produce one egg per day. The famous American robin, which is frequently seen as a sign of spring, can build four or five nests in a single season.
Some wild bird species begin laying eggs in winter. The crossbill uses the abundance of winter pine seeds to its advantage by laying eggs as early as January. Some bald eagles start their breeding season in January and continue until August. Breeding pairs can start breeding as early as late winter because they overwinter in temperate climates.
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