2019 Nesting Season Review

This season brought a number of challenges for the birds, including feather mites, unusual weather, and predators. A sudden cold spell in May seemed to be one main reason for nest failure. Still, 832 birds fledged from the nest boxes this year. As usual, most of these were tree swallows (386), followed by western bluebirds (254), then house wrens coming in third (152). White-breasted nuthatches had more success this year than usual, with 15 fledglings making it out of their nests. The ash-throated flycatchers also had more fledglings than usual (25), breaking the downward trend they had been experiencing in recent years.

Our Winters Park site, where we brought back nestboxes after a hiatus of several years, proved to have at least four previously-banded tree swallows using the nestboxes this year. For some reason, the north side of the creek was much more popular there than the south side, and the only occupants were tree swallows and ash-throated flycatchers.

The Davis Nestbox Network, a completely new site, had just a few active nests as expected for its first year, but they were quite successful and had several second clutches.

We’ll be planning a few changes to the sites over fall and winter. Moving some boxes may help against predators, and we’ll be adding a few more boxes to our smaller sites.




Finished banding

We’re finished with banding for the year! The last bluebird nestlings were banded in Winters last week. (The Arboretum chick unfortunately didn’t make it to banding day.)


One of the last bluebird nestlings banded this year

Now all that’s left in the field are a few fledge checks. I’ve been looking at the last active boxes to see if all the chicks have made it out of the nest. The second camera box, with a nest of four ash-throated flycatchers, was one of the successful nests. It was in a location with more sunshine than the last nest with a camera, so we have a lot of photos in color this time. Below is a series of some of these photos, showing the growth of these nestlings.


Flycatcher nestlings on hatch day, with one egg left to hatch


Nestlings a few days old, featuring a parent


Nestlings at about 1 week old. They were banded four days later.


Nestlings one day before they left the nest

Next week I’ll be done with all nestbox checks until next March, and I’ll be posting some of the final numbers and totals from the 2019 breeding season on Putah Creek!



There are only two more boxes of birds left to band this year — both bluebirds — and about a dozen recently-banded broods that will be leaving the nest soon. Yesterday Alison and I banded bluebirds in the Davis Nestbox Network, a second brood after a successful group of chicks fledged from the same nest. All that’s left to band is a nest with four birds in Winters, and then a single nestling in the Arboretum. The chicks will soon be exploring the rest of their environment and hopefully avoiding the dangers around them.


Trees around Northstar Pond in Davis, where bluebirds have been busy feeding their young.

The remaining inactive nestboxes have been cleaned out to prepare them for next year. Below is an old tree swallow nest with extra lining, including turkey feathers and what I believe are egret feathers, among others.


Tree swallow nest being removed from the nestbox after the end of the breeding season.

I’ve seen a few more fledglings flying around our sites lately. Hopefully we’ll see them building nests next year too.


Putah Creek at Interdam in Winters.



Recently at our Interdam site, I was lucky enough to spot a little group of fledged chicks sitting in a tree (though I could only photograph them through binoculars). It was close to what I believe was their native nestbox, and they were being fed by a parent. It was very cute to see them sit in a row together. It’s also great to have some confirmation that they made it out of the nest safely.


Four tree swallow fledglings on a branch. Can you spot them?

Now it’s time to clean out most of the nestboxes. The last viable nestbox eggs of the year have hatched – bluebirds at the Arboretum. This box and seven other boxes will be banded by early August, and that will be it for the breeding season. Then we’ll be looking at our data and preparing for next year. I’ll be updating here soon with some final numbers from this breeding season.


Bluebird eggs and newly-hatched chicks in their nest

It was a colorful day in Winters last week when I checked and cleaned the nestboxes there. There are often hot air balloons above the town, but that day they were close overhead and landed near the creek. I also spotted a peacock on a residential street. I’ve heard there are peacocks at Lake Solano too. One of the perks of fieldwork is that I see something different nearly every day.


Hot air balloon next to Putah Creek in Winters


Peacock on the street in Winters



Late-summer nesting

Many of the nestbox birds are still busy taking care of nestlings and even laying a few new eggs. It looks like I’ve banded my last house wren for this year, but there are still bluebird nests that have new eggs being incubated.


Western bluebird nestling after banding

Left: bands for bluebirds. Right: nestbox with two cloth bags full of birds during banding.

The incubation period is also our best chance to catch adult birds, so I’ve been able to recapture more birds and put new bands on previously-unbanded parents. Recapturing banded adults lets us see that they’re still alive, and it shows us how far their nest is from the last place we saw them.


Newly banded female bluebird. She’s incubating eggs at Russell Ranch.

I recently moved the nest camera box to Russell Ranch, where there is another nest of ash-throated flycatchers. They’ve been doing very well, and they’ve just been banded. The camera will stay on them until they fledge.


Ash-throated flycatcher (ATFL) nestlings in the nest camera box. The parents laid the eggs in an old bluebird nest, with very little of the usual fur lining of ATFL nests.

We’ve seen a few rattlesnakes at our sites this season. I stepped pretty close to one once without seeing it, but thankfully it just slithered away to avoid me. I found this reminder to watch my step, a discarded snake skin, at our Old Davis Road site recently.


The weather along the creek has been hot but mostly pleasant lately. I’m hoping we don’t have any more heat waves until after the young birds are all out of the nest.


A nestbox hanging in an oak tree at Picnic Grounds


Summer updates

July is usually our last month of nesting activity overall, with just a few active boxes left to monitor in August. This season is still quite busy, though. About a quarter of our nestboxes are still active with eggs or nestlings. All of our most common species are still raising chicks, and all of our sites still have at least a few active boxes. The nestlings are doing well in general, although I worry what the coming triple-digit weather will mean for them.


House wren chicks and egg in a very deep twig nest


Tree swallow nestling during banding in Winters


One of the bluebird nests at the Arboretum had a very small egg! The three other eggs were fertilized and have now hatched, but the small one likely did not have a yolk to begin with. Runt eggs like this are rare.



Winters Putah Creek Park, one of our nestbox sites, has been having a pretty successful year. We hadn’t been able to monitor nestboxes at this site for a few years due to restoration work on the land, but now we’re back and the birds seemed to have no problem finding the boxes again — at least on the north side. The south side of the creek has less activity so far, but there were two successful nests. Each time I visit this site lately, there are many people working hard to water the new native plants and keep up the restoration work. Soon enough, the new bushes, trees, and other vegetation will grow larger along the creek and improve the habitat for wildlife.


Further up the creek, at our Interdam site near Lake Berryessa, I discovered a mallard nest hidden in the grass. The female flew out each week when I passed the spot, so I took a closer look and sure enough, there was a large nest with eggs. (I covered it again with grass and left soon after.)


Lastly, here is a photo of a bee from this morning. There are bees at many of our nestbox sites taking advantage of the abundant flowers at these beautiful places. The buzzing is a nice background sound to our work.



Unusual nests

We always seem to see some nests with unexpected or dramatic developments during the field season. One species will take over another species’ nest, or birds will get creative with nest design, among other things.

The nest shown here on the left was a tree swallow nest that was taken over by an ash-throated flycatcher, but the old tenant’s eggs (the white eggs) ended up alongside the new ones (brown flecked eggs) instead of being buried under the new nest material. The photo on the right shows a similar situation with a bluebird egg alongside an ash-throated flycatcher egg. These nests both ended up abandoned by all of the competing species. It must be a lot of work to defend a nest.


Though it’s hard to see in the picture above, there are nine ash-throated flycatcher eggs in this nest! They usually don’t lay more than seven eggs per clutch. Unfortunately, these eggs disappeared, probably due to a predator.


Sometimes multiple species get their turn to use one nestbox. This nest was a successful tree swallow nest with chicks that fledged, and the parents seemed to be done with it for the season. A few weeks later, there were strips of bark and pieces of fur, indicating an ash-throated flycatcher may be taking it over. The nest camera box had the opposite switch of species, at the same site.


I’m not sure which species started this nest. It has fur, hair, leaves, sticks, and other plant material – possibly a Bewick’s wren, which are rare for our nestboxes. It seemed to have more fur the next time it was checked, and flycatchers were seen nearby, so maybe it’s been taken over.



While I’m out checking the songbird nestboxes, I sometimes see other species’ fledglings. A small great-horned owl family was watching me work the other day, and I managed to get a photo through my binoculars.

In general, the nestboxes at our sites are becoming less active at this point in the season. However, there is a wave of second clutches hatching and fledging now, so I’ve been banding a lot again. The new nestlings are doing very well lately!


A new tree swallow hatchling, still just wiggling out of its shell