Winter Nesting

March 2, 2018

Though March is upon us and it is still winter by the calendar, and perhaps human standards, there are a number of birds here in NH that have already, or are about to, start nesting!  What are these species, and what may be some of the advantages of starting so early?

NH’s earliest nesting bird is the Great Horned Owl.  Often sitting on eggs as early as February, they have already had a head start.  Other common owls in NH, the Barred and Saw-whet owls for example, lay eggs a bit later into March but still early in comparison to most birds.  Most species of owls don’t build nests, but rather use old woodpecker holes or cavities in trees, the tops of trees that have snapped off or the old stick nests of crows, ravens or hawks.  

Great Horned owls lay between 2-4 eggs during a season when many birds have migrated out of state, or are spending their winter trying to find enough food to stay warm!  The female does the incubating of eggs while the male hunts and delivers food to her at the nest. As you can imagine during winter months the eggs cannot be left exposed to cold temperatures even for a short time.

After around 30-35 days of incubation the young owlets hatch with a layer of down, barely able to hold their heads up.  The female continues to brood and feed them whatever the male delivers. She tears the prey into small bite sized pieces and delivers them with a delicacy that is hard to visualize from such a large beak! The young will remain in the nest until they begin to grow flight feathers at about 6-7 weeks. By this point the young can regulate their own body temperature, the female has left the nest and both adults deliver to the hungry brood.   As the young branch out from the nest and learn to fly, the adults continue to deliver food to them within the nesting area. It will be late summer or even into the fall before the young are fully on their own and dispersing to find their own territory.

Bald eagles also start the nesting season early.  In NH pairs of eagles return to their nesting sites as early as January to spend time adding to their nest and beginning courtship displays.  They will lay 1 or 2 eggs as early as mid- February, with both adults taking responsibility for incubation, though it is the female that spends most time on the nest.  As with the Great Horned, the eggs must be constantly incubated to prevent cooling. A bird’s body temperature is 100-104F, so even during the coldest winter nights the eggs are kept warm against the bare belly or “brood patch” of the incubating female.  

Eggs hatch generally 45 days later; eaglets covered in white down must be kept warm until they can maintain their own body temperature and have a good covering of contour feathers that act as a raincoat. Both the male and female share in feeding and brooding the young.  Provided there is enough food, the young eaglets reach nearly adult size at 6 weeks, but won’t take their first test flights for a few more weeks. As they begin to practice flight skills around the nest , the adults will continue to feed them whether they are in the nest or perched nearby.  As with most birds, the adults will continue to feed them even if they end up on the ground. Through the summer, the young are dependent on the adults for food as they learn to hunt and practice the skills they will need to survive.

Ravens are another northern bird that gets a head start on spring nesting season.  They too will nest in February or March in some parts of their range, laying 4-6 eggs.  Both adults share incubation duties, though like the other two the female does the bulk of this work, with the male doing the majority of hunting.  Incubation is 30-35 days and the young remain in the nest until late spring. They too begin branching out as they test their flight skills, while the adults provide the food and education the young need to feed themselves.  Ravens often stay together in family groups through the first fall and into winter.

So, what are the advantages and disadvantages of getting such an early start to the nesting season, and why these birds?  Why don’t our resident Chickadees or Blue jays also start early? (there certainly is enough food around our winter bird feeders!)

What these three birds have in common is that they produce eggs with a long incubation time, and young with a long adult dependency in comparison to many song birds.  They are also large birds. Laying eggs and incubation is energetically expensive, and during cold winter temperatures a larger body mass certainly helps reduce heat loss.  In comparison, small songbirds use huge amounts of energy in the winter to stay warm and prevent heat loss. They feed constantly just to make it through one cold winter night.  

With a long incubation period, and a long span of time dependent on the adults, late hatching young simply wouldn’t have enough time for the young to learn all they need to know before the winter months arrive and hunting becomes more challenging.  The long parental dependence in good weather is a boost as they learn important hunting skills. Songbirds tend to have shorter nesting cycles; incubation in chickadees is 10-13 days. Young chickadees hatch with their eyes closed and leave the nest within 14-16 days!  With this short time span, many songbirds can produce multiple broods in a season.

A disadvantage for the eagles, ravens, and owls of course, is that a hard winter with deep snows and cold temperatures can affect whether a pair can successfully hatch eggs and get their young to a fledging age.  The success of a nesting pair of owls can often depend not only on prey populations, but also the snow conditions effecting hunting success and whether they have the food energy they need to maintain themselves and their growing young.

As the snows and rains lead into March, be mindful of the birds that are settled down on their eggs.  It must be a challenge, but they have evolved a strategy that works. They have many more weeks of fluctuating temperature and weather conditions before their eggs hatch and the new challenges of feeding a hungry brood begin!  

You can help our winter nesting birds by staying away from known nest sites at this critical time.  Incubation is a sensitive time and adult birds may abandon their nest too long in the cold weather if they are disturbed.  A spotting scope or binoculars can allow watching from a safe distance. Even better, you can watch a variety of nests from the comforts of your warm house by checking for various “eagle cams” on the internet.