April 4 notes: hatching one week away?
Bald eagles are one of our earliest nesting birds in Maine. Only great-horned owls nest earlier. We have a relatively short "time in the sun" here in the north and eagles need to get an early start nesting so they have enough time to incubate their eggs (35 days), raise their young to be able to fly (10 to 13 weeks), then allow the young to perfect their flight skills (another 6 to 12 weeks) before leaving their parents in the closing days of summer. Our eagles layed their first egg on March 6, but we've documented some pairs incubating as early as mid-February. Sometimes we've observed eagles incubating their eggs with all but their heads covered in a late-winter snow.
Long periods of adverse weather can have a detrimental effect on the nesting success for eagles. Last year was a good example when we endured one of the coldest and rainiest springs on record. In 2005 we documented 385 breeding areas occupied by paired eagles. Of those, 48% (183 nests) hatched eggs, well below the 58% average success rate we've experienced in the last 15 years. The poor weather not only affected the hatching of eggs, but also reduced chick survival. The longest period of heavy rain occurred in May when chicks were still in the downy stage and have difficulty keeping warm without the constant attention of their parents. In 2005, 253 eagle chicks fledged from 183 nests. Eagle biologists use the ratio of chicks fledged to successful nests, or "brood size," as one of our important measures of the productivity of the population. Last year brood size was only 1.38 chicks fledged/successful nest, nearly 7% below the average for the last 15 years.
This year our spring weather has been unusually mild and dry - perfect conditions for nesting eagles. Charlie Todd and other state biologists have begun their initial aerial monitoring of all known nest sites in the state and occupancy of eagle nests looks good. Barring no major weather events, we may see a downy chick in the nest nest week. If past odds are a guide, we have about a 60% chance that this pair of eagles will hatch one of their eggs. Keep your fingers crossed! --Mark McCollough, U. S. Fish and Wildlife Service