On August 27, 2020, I parked my car along Panhandle Road on the Delaware Wildlife Area and walked to nestbox 34, the only box left standing in the five-acre field that is home to 55 or more nestboxes during the spring and summer nesting seasons. Box-34 had fledged five House Wrens, the only wren family to have nested in the nestbox grid that is made up of ten rows of two to eight nestboxes each. Boxes are spaced 25 yards apart at right angles to form a nestbox grid for nesting Tree Swallows, an arrangement based on scientific studies published by ornithologists. (Three boxes are spaced at 22 yards to avoid brush, the minimum spacing of 20 meters determined by researchers to be acceptable by neighboring Tree Swallows.)
The grid’s nestbox posts are signposts furnished by the Ohio Division of Wildlife and I remove the boxes and their PVC drainpipe baffles from their posts before numerous hunting seasons begin in September. The steel signposts remain in the field all year while baffles and boxes are stored on my back porch and will be returned to the grid by late February or early March 2021, in an attempt to win a few bluebird nests. As always, many thanks go to wildlife technician Rick Dorn for mowing paths to all grid boxes to make my job much easier.
Tree Swallows return in March and go about claiming boxes, and first eggs usually show up in late April. This year, the first swallow egg wasn’t laid until May 3, and fifty-percent of Panhandle’s 65 nest attempts were started with first eggs by May 18, which is eight days later than the median date set by my analysis of 275 nests in 2003. Insect populations are down, along with weather that grounded flying insects. In 2020, the resultant food shortages delayed egg production and the swallows’ nesting season. Gee, is this a symptom of climate change?
Of the 65 nest attempts by swallows, 55 (84.6%) nests successfully fledged 226 young which is 23 (9.2%) fewer than 249 fledged last year. Successful nest attempts followed in six of the ten nestboxes where first attempts failed. There was no evidence pointing to any other species for causes of nest failures. (Of course, hawks leave no evidence when they snatch avian prey.) So, without evidence, I blame the failures on conspecific (same species) competition since adult swallows had to hunt further from their nests to compensate for the food shortage, leaving their nests unguarded and vulnerable to competitors. Yes, all is conjecture without real counts of insect populations in the available habitats.
Another disturbing fact is that 56 nestlings died from 27 boxes which are nearly half of the structures. Only one family lost all six of its nestlings and they had wounds on the napes of their necks which are a sign that they were killed by a fellow Tree Swallow. The other 26 nests were successful nests that fledged young, but they lost anywhere from one to five in each nest and averaged a loss of nearly two per nest.
When cavity nesting birds endure a food shortage, it is common for one or several of the nestlings to dominate the entrance hole as parents deliver food. One or several continue to grow normally as other siblings go without needed food rations until they drop behind, and either take longer to grow to fledging, or they die. During food shortages, if it is possible for siblings to share food equally, the chances are that all will die, another fact of life.
I frequently repeat the fact, based on scientific studies, that for the 45-day period when Tree Swallows use a nestbox to raise a family, they consume more than 300,000 insects, most of which are shorter than a centimeter, or one-half the width of a nickel. So, the 55 successful swallow nests in the grid would have consumed as many as 16.5 million insects in 2020, or did they?
Only two other species had successful nests in or near the grid. The already mentioned wren nest in Box-34 was the only wren nest in the grid, and it had eggs or young from July 21 to August 22, when there were only three active swallow nests remaining in the grid.
Eastern Bluebirds made two attempts to nest, and only one attempt was successful, and technically, it was not in the grid. Two boxes are east of the parking lot on the side of the road and are paired to accommodate swallows and bluebirds. Bluebirds had eggs or young from May 1 through June 5 in Box-27, while swallows raised their family from May 21 to June 28 in Box-26. Bluebirds fledged five and swallows raised three.
When I monitored the grid on April 30, a bluebird pair was working on a nest in Box-47. After I arrived home, I loaded my car with a pole, a pipe extension, two hose clamps, a baffle and a box numbered, or lettered, with a large X on its front. I returned to the grid to mount the box five yards south of Box-47, and it became box 47.X in my data book. The plan was that the bluebirds would continue to nest in Box-47 and swallows would accept Box-47.X. The plan failed after the bluebirds laid one egg. I found the egg barely visible under a swallow’s feather-lined nest cup on May 8. The swallows raised five in the usurped bluebird nest and their young fledged around June 28.
Box-47.X also raised swallows after their first nest failed. The box’s first attempt produced a first egg on May 23, making it synchronous with the swallows in the neighboring nest in Box-47. However, peace did not prevail as I found Box-47.X’s nest empty on June 12.
A new first egg appeared in Box-47.X on June 20, and the second attempt ended up raising three from four eggs. On June 20, the neighbors in Box-47 were busily caring for five 12-day-old nestlings and research has shown that such families are more tolerant of close nesters of their own species when they are busy taking care of their own nestlings.
The Panhandle Road Grid is one of six trails that I maintain and monitor on public lands throughout Delaware County, Ohio. The same trails raised 684 Tree Swallows in 2020, 843 swallows in 2019, and 970 swallows in 2018. Yes, things are becoming more challenging for our feathered bug snatchers. There’s some interesting math to be done while comparing those annual values.
During climate change, divide, calculate, worry, and conserve on.