2017 Season Brief Overview

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).


Tree Swallow

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.


Putah Creek – picnic grounds

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.


Male Western Bluebird

-Evelien de Greef


House Wren re-sight

Birder Rick Williams observed a color banded House Wren along Willow Slough just southeast of Woodland. Based on the color band combination, we can see that this House Wren was from a box at Russell Ranch, banded (as a nestling) in mid-May this year from a brood of 6 chicks. This young wren traveled at least 12 miles from the Putah Creek to Woodland! Here are a couple photos from Rick:

banded howr

Banded House Wren (blue over silver on R leg, black over green on L leg) seen on 8/27/17. Photo: Rick Williams


Banded House Wren seen again on 9/3/17. Photo: Rick Williams

Because of the color bands, we were able to pinpoint which nestbox and brood the bird was from. This is valuable information for us because then we can observe dispersal patterns. If you see any color banded birds around, please let me know! 🙂

-Evelien de Greef

Update on the last bluebird nest

Yesterday morning I banded the last bunch of babies, four healthy bluebird nestlings doing very well. Here’s the mom with a cricket:


Western Bluebird female

Two boys and two girls, a nice mix. Here’s a picture of two of them:


Western Bluebird nestlings

There was a juvenile bluebird nearby and kept looking at me while I was handling the babies. It’s possible that this guy was from the bluebird pair’s first clutch and is helping raise the second clutch, but he has no leg bands so I cannot say for sure. He wasn’t acting protective and didn’t have food, so also possible that he was just curious and hanging out.


Western Bluebird juvenile

That’s it for the season! We’ll have to wait till next year for the next round of baby birds.

-Eveilen de Greef

Final hatch!

Our final nest has hatched! My previous post stands corrected, as the last bluebirds to be banded will be this handful at Mace Blvd (assuming they don’t get eaten first).


4 Western Bluebird nestlings ~6 days old

Yes, it is mid-August and we have young chicks on our nestbox highway. This cheeky bluebird decided to lay her eggs at the end of July, a couple days after I had said the end of the season is near.


Western Bluebird momma

This one nest is extending our season by almost a month. I’ll band these chicks in about a week and a half, and then give them another week and a half for fledging. This means we may have about 3 more weeks before we can officially say the nestbox season is over. For comparison, in the 2016 season the last day of field work to check fledging statuses for the last boxes was on August 9th. This year it’s looking like ~September 4th.

Migrants are already starting to come by for fall migration. It’s very bold for the bluebird parents to raise a brood this late, but perhaps our super wet winter has increased the abundance of insects. Spring is well over so let’s hope there’s enough food for the chicks.

-Evelien de Greef

Banding the last Bluebirds

Today I banded what are most likely the last boxes of chicks on our nestbox highway. One at the Arboretum, and the other at Russell Ranch. The reason I say “most likely” is because we still have one nest of incubating eggs, but I’m a bit doubtful it will hatch due the timing. The nest currently with eggs started about a week and a half ago, which is very very late for breeding season. If it turns out to be a successful clutch, I predict it would hatch by the end of next week.


Western Bluebird nestling

This bluebird chick (above) is the only chick for this brood. The hatch rate was not high for this 2nd clutch (started with 5 eggs). But I believe he will still have brothers and sisters because I saw some young bluebirds hopping around nearby that had bands indicating they are from the 1st clutch from the same box. Although I don’t have confirmation that the parents are the same, I believe it is very likely that the same pair raised both clutches at that particular box.

Here’s one of the fledged bluebirds:


Western Bluebird fledgling with visible band

I wish I had better photos, but they all hopped away as I got closer. You can see color bands and the service band on these guys below. You might have to zoom in, but the one in the sun is probably the easiest one to see.


Group of 3 banded Western Bluebird fledglings at the UCD Arboretum

I thought it was pretty neat to see the youngsters from the 1st clutch on the same day when banding the baby from the 2nd clutch. In just a couple weeks the solo nestling will be able to join his family group. If you want to see the young bluebirds running around, you can visit the Oak Grove section of the UCD Arboretum.

Here’s a handful of 3 bluebird nestlings, from the last brood at Russell Ranch.


Western Bluebird nestlings


Western Bluebird nestlings

This week and last week we’ve already started to clean out inactive nestboxes. We clean the boxes out to provide roosting habitat for wintering birds, and also to prepare a clean slate for next year’s activity. Right now we have 5 boxes left that are in the middle of their fledging period, and 1 final clutch of eggs in incubation at Mace Blvd. We shall see if the final nest will hatch or not. Otherwise, the last nestlings of the nestbox season has been banded today.

-Evelien de Greef

Most recent hatch & other updates

Yesterday we had one hatch, a Western Bluebird nest, at Russell Ranch. This is one of the last remaining boxes with activity along the creek. This box will be banded in a couple weeks. We have a couple bluebird nests left that may still hatch at Picnic Grounds and at the Arboretum. There are a few more boxes we are banding soon including the last Tree Swallow nestling to be banded tomorrow, and the last House Wrens within a week. The end of the season is near.


Western Bluebird nest with recently hatched chicks – 7/19/17

I was hopeful this morning when checking the Interdam site that some of the last Tree Swallow nests would’ve hatched by now, but they remain unhatched and notably cold today with parents no where in sight. Here’s one of the unhatched nest that had a whopping 8 eggs (that seems a lot for a Tree Swallow):


Tree Swallow nest with 8 eggs. Photo: Haruka Endo

I’m not surprised that a large clutch of 8 swallow eggs didn’t hatch, I feel like it would be very hard for a female swallow to successfully incubate that many eggs. But a few other nests with more normal-sized clutches also didn’t hatch. A lot of these birds were on their eggs for a month or longer (keep in mind incubation normally takes about 2 weeks), but for what ever reason their eggs didn’t make it through, and the parents left once they realized that. This is not uncommon for the 2nd half of the breeding season.

This morning at Interdam we also saw some recently fledged Tree Swallows being fed by their parents, and a group of Western Bluebirds (both young and adults) foraging in the grass. The bluebirds did not carry leg bands, perhaps they came from a natural cavity. I love seeing young bluebirds with their speckled chests – they are quite cute. Unfortunately I left my memory card at home today so I do not have any photos to share of the juvenile bluebirds. An additional treat today was hearing a Lazuli Bunting singing on the other side of the creek.

Although nestbox season is not completely over yet, I am already starting to miss these guys. What better way to start the mornings than with baby birds?


Tree Swallow nestling

-Evelien de Greef

Bat, possible cowbird egg, and more!


Yesterday morning Hanika Cook found a bat roosting in one of the nestboxes in an orchard by Winters. I believe this is the first time we’ve ever observed a bat in one of our bird nestboxes! I went to go look later in the afternoon to see for myself and try to get a picture, and there he was, a little myotis perched in the upper corner of the nestbox. The nestbox had an old fledged bluebird nest. Unfortunately I was not quick enough to get a photo before he flew out, but here’s a little sketch on the right. I’ll try to make a better sketch later.

At our site at Old Davis Rd, we have a nest that has a possible Brown-headed Cowbird egg in a Western Bluebird nest. About a month ago the cowbird egg was laid and then the bluebirds laid their clutch shortly after (the order of events seems a bit unusual to me), but anyway, after a few weeks of incubation, none of the eggs hatched. I do not believe the hatching failure is related to having a cowbird egg in there, it just happened to be dud eggs. It is not uncommon for a clutch to fail when it’s this late in the season. We have a few nests that were incubated for a month and unfortunately didn’t hatch. The bluebird eggs in the photo below look very pale and almost white but that is because they are cold and dead.


Old nest with Western Bluebird eggs and a possible Brown-headed Cowbird egg

We banded a wave of batches of birds the past couple weeks. There are still a handful of boxes left to band, and lots of boxes to check soon for fledging success. This is what we like to see for a fledged nest, lots of poop and no dead chicks:


Fledged Tree Swallow nest

There is still potential for a few new hatches, which we will see by the end of this week. Otherwise, this Tree Swallow may be part of one of the last batches of swallows. Check out his developing feathers, he’ll be able to leave his nest in just about 7-10 days!


Tree Swallow nestling

Here are a couple pictures of our summer volunteers who have shown up consistently to help check boxes and band birds in the summer heat. 🙂

I will end this post with a photo of a Lawrence’s Goldfinch, which was a nice surprise for Haruka and I to see at one of our sites this morning near Winters.


Lawrence’s Goldfinch (male)

-Eveilen de Greef