This past season the Putah Creek nestbox highway has fledged almost 850 chicks! Once again, the Tree Swallows are the most abundant in number of fledglings, followed by House Wrens, Western Bluebirds, Ash-throated Flycatchers, and White-breasted Nuthatches. Other species we had in our boxes this year are House Sparrow and Brown-headed Cowbird (1-2 attempts each, unsuccessful).
Our west-most site at the Interdam reach takes the lead on productivity relative to box numbers. We had more than 400 Tree Swallow fledglings total across 8 sites, and Interdam produced more than 1/5 of them!
Although the number of clutches was about the same (just a little lower this year) compared to 2016, the boxes produced about 80 more fledglings this season. Perhaps the winter flooding wiped out some predators (mainly rats), causing an increase in both number of eggs as well as an increase in hatching and fledging success rates. The flooding could have also helped by bringing in more insects for food for the nestlings.
Another notable difference this year was a lower number of Ash-throated Flycatchers using the nestboxes (about half as many as last year). The ATFL nestbox numbers aren’t usually high anyway, but dropping from 20 nesting attempts last year to 10 attempts this year is a bit surprising.
More details regarding the 2017 season coming soon.
On a side note, the UC Davis Arboretum (separate from the putah creek nestbox highway) was filled by Western Bluebirds this year. It looks like the bluebirds are making themselves quite comfortable at the oak grove section of the Arboretum. Over the past few years, they’ve been filling up more and more of the previously unoccupied boxes.
-Evelien de Greef