6 Mountain Bluebirds fledged
10 Western Bluebirds fledged
5 Tree Swallows fledged
15 Western Bluebirds died
5 Young Tree Swallows disappeared. Predators?
With 15 boxes monitored, the results are disappointing. This was especially so, given the number of Bluebirds that were ready to fledge -- and then all to be found dead in their nests. At least the cattle were out of the park, so none of the boxes were knocked off their posts.
At first we thought the unusual wet weather was to blame, because it could have created a blowfly situation, as one group of dead Western Bluebirds had maggots on them. However, after reading an article in the North American Bluebird Society summer 2020 journal, I wonder if the lack of insects was the cause of the deaths. Most of the deaths happened just before fledging, so perhaps the adults were unable to keep up with the hungry mouths. We saw adults around while the bluebirds were alive. It is possible that the adults died or abandoned the nests for lack of food.
The article I refer to is "Insect Populations Continue to Plummet -- What Does This Mean for Bluebirds?" by Bernie Daniel, PhD. After sharing the recent drastic decline in insect populations worldwide, a few possible causes are suspected:
intensification of agriculture (in our case the decimation of grassland just to the west of the bluebird trail);
the development of newer generations of pesticides, which are a little too effective on insects (phenylpyrazoles and neonicotinoids in particular);
biological factors such as pathogens introduced by species from other continents;
unfavourable conditions brought on by climate change.
Next year we plan to switch up the locations of some of the boxes. We will also clean out the boxes in the fall.
Maybe, we'll have to start providing meal worms for the bluebirds!!! How will we do that?