As the end of the year winds down, once again it is time to review, tabulate, quantify and summarize the local bird box trail and check out the results.
This year, 20 birdhouse were placed around the Green Bank Observatory grounds and monitored every three-to-six days to see what was happening inside. These boxes cater to the cavity nesters – primarily Bluebirds, Tree Swallows and House wrens – and observations are recorded for each visit. Records kept include nest status, number of eggs, number of young birds and status or condition of each. From this information we can generalize some conclusions, make some judgements about bird health and compare to older data taken over the last 10 years.
The numbers involved can be either a stat keeper’s dream or closer to a nightmare, but we will try to keep them short and sweet. In the big picture, we can say there were 43 nesting attempts. Most boxes had two and sometimes three efforts. As one would finish, fledge or fail, another bird would move in and take a shot at raising a family. Of these, 24 were successful or produced (fledged) at least one young bird for a success rate of 55.8 percent. By comparison open nests in nature are only successful about 25 percent of the time.
A total of 198 eggs were laid over the course of the summer. From these, there were 151 hatchlings but only 82 reached a fledging stage and left the birdhouse.
Every summer there appears a different predominant affliction or predator to limit nesting, and 2016 was no different. In fact, most nesting was impacted by the presence of blowflies this year in numbers that this observer had never seen before.
The blow fly enters the nest from the bottom and lays its eggs in the nesting material. The eggs hatch within hours and migrate up to attach to the baby birds in the nest. These tiny larvae, better known as maggots, then feed on blood and grow to the detriment of the baby birds. If left unchecked, the young birds will die at about 10 to 12 days of age. In mid-May, three boxes of Blues were discovered to be dead on the same day, a terrible set-back for these observations.
Thereafter, we attempted to periodically check into the nests occupied by young hatchling to keep them clean and the larvae at bay. Removing and replacing nests is dirty, difficult work and stressful for the young birds and many were lost in spite of the effort. Still, many were saved to fledge.
2012 was a terrible nesting year for Bluebirds as an early, warm spring inspired the Blues to nest too early. Later, freezing cold and snow in April caused many nests to be abandoned and lost.
2015 appeared to be better than usual with 50 young birds fledged. A seven-year average is about 35 birds a year fledged, so 2016 was not all that bad with 37. But it could have been a lot better.
Tree swallow fledging has also dropped off more than 50 percent over each of the last two years. The reason for that is still to be discovered.
At any rate, there still seems to be a lot of demand for housing for the cavity nesters. Well placed, well built, clean nest boxes with a 1.5 inch opening are bound to get lots of usage and can certainly add bird life to your backyard and landscape.