Bluebird Trail, Week 8-9 - Tree Swallows & House Wrens

This week's update covers the last two weeks. We checked the Trail 1 boxes during a very light drizzle on May 20, which we found was good weather for catching birds on their nests. Dave saw three tree swallows on nests that day while I, still in the early days of recuperating after eye surgery on the 17th, rested in the car and just took notes. We weren't able to get to Trail 2 last week. This week I was feeling much stronger, and we visited both trails on the morning of May 27, which was a hot day with temperatures already well into the 80s.

Most of the nestbox activity right now is from the tree swallows, as most of our bluebirds have fledged their first broods and are working on their second nests and eggs.

Tree swallow in nestbox incubating eggs

This is my favorite photo of the week -- a female tree swallow who stayed on her nest when we checked this nestbox on Trail 2. The light was right to catch her beautiful coloring contrasting with the cloud of white feathers. We quietly and carefully put the box back.

Tree swallow eggs in nestbox

Here is another tree swallow nest with eggs, from one of the boxes on Trail 1. I can't get over how beautiful and comfortable-looking the tree swallow nests are, with all the feathers they use to line the nest. I try to imagine being a little naked nestling, and I would much rather be in a tree swallow nest than a bluebird nest, which is generally just dried grasses with no downy lining. However, I understand that bluebirds are more fastidious about removing the nestlings' fecal sacs from the nestbox, so from that perspective I guess I'd rather be a bluebird nestling.

Tree swallow atop sparrow spooker above nestbox

In the last couple of weeks we were excited to have a pair of tree swallows building a nest in one of the nestboxes at our house, where we've had a hard time getting any successful nests going. We set up the spotting scope in our living room so we could keep tabs on  the activity there. Above, a tree swallow perches atop a "sparrow spooker" that dangles orange construction ribbons over the top of the nestbox; this is thought to discourage house sparrows. The tree swallows found it to be a handy perch. Below, before we saw a house sparrow enter the box which led us to put up the sparrow spooker, the female is looking out of the nestbox while her mate watches from above. 

Tree swallows at nestbox

We have continued to be plagued with house sparrows at this location, but we have also been hearing house wrens quite a bit lately, and it was a house wren that eventually cleaned the tree swallow nest out and drove the pair away. From what we hear, this is typical wren territorial behavior -- they clean out other birds' nests and leave the box so pristine it's as if it was vacuumed out. House wrens will sometimes destroy other birds' eggs, as well. Because of this consistent difficulty with both house sparrows and house wrens, we decided to take down the two boxes at our house. Although they offer some good bluebird habitat, they are just too close to the house (encouraging house sparrows) and some large trees (encouraging wrens).  We loved watching the tree swallows from our living room, and for a couple of days we saw bluebirds at the other box as well, which was a real thrill, but the wrens cleaned that box out too. We feel it's not safe for the bluebirds, tree swallows and/or chickadees at this location, so we thought it was better to take these boxes down.

Tree swallow nestlings, approx. day 2

Above is the first set of tree swallow nestlings we've had. There are appear to be six nestlings that I am guessing are about two days old, based on our records of when the eggs were laid and this guide to tree swallow nestling development at the Tree Swallow Projects site. They are quite similar to bluebird nestlings at this age, but less hairy. The female was in the box when we approached but flew out, allowing us to quickly confirm that the nestlings had hatched. We left as quickly as we could so she could get back to the babies.

House wren eggs

House wrens, unlike the nonnative house sparrow, are federally protected native birds. Once they have an active nest -- not just twigs in a nestbox, but a nest cup and/or eggs -- it is illegal to disturb or remove the nest. Sialis.org, the excellent bluebird site, has a good page about managing house wrens. The All About Birds site has useful breeding information: they lay 3-9 eggs, incubate them for 9-16 days and nestlings fledge in 15-17 days. We now have two active house wren nests on Trail 1, both in nestboxes that had seen very little activity all spring until the last week or two, when the wrens (which typically don't arrive in this area until May) got busy.

The full trail report follows. We have, to the best of our knowledge, fledged 30 bluebirds and have 5 new eggs this week. One nest of 3 eggs (box 18) seems to have failed, but as far as we can tell we had full success of all bluebird eggs in the other nests, as we saw no unhatched eggs or dead nestlings. We have 6 tree swallow nestlings and 5 more nests with tree swallow eggs. We have 2 house wren nests with eggs.

Follow our full bluebird trail adventures here.

Trail 1:

1. After several days of tree swallow activity, a house wren cleaned out the nest and we had also seen a house sparrow enter the nestbox, so we have reluctantly taken this box down.
2. (Paired with #1) After recent chickadee activity that didn't develop into a nest, a bluebird pair was seen at this box so we removed the guard that made the hole smaller for chickadeees. A house wren cleaned out the bluebirds' nesting material. We have now taken this box down.
3. There were two house wren eggs here on May 20 and 7 house wren eggs on May 27. 
4. (Paired with #3) Tree swallow nest with 5 eggs. Female was on nest May 20 and flew from the nest May 27. Probably now 8-10 days into incubation; we should see nestlings next week.
5. 5 bluebirds fledged, probably close to a week ago (we observed an adult on top of the box on May 20 and knew they were close to fledging so we did not check the box that day). House wren twigs in box on May 27; we cleaned out the nestbox.
6. (Paired with #5) Tree swallow nest -- did not check on May 20; 6 eggs on May 27.
7. House wren nest with 7 eggs. This box had one egg on May 12 and 7 eggs on May 20. Assuming they lay an egg a day, these eggs are now about 10 days into incubation and may hatch at any time now.
8. (Paired with #7) Tree swallow nest with no eggs on May 20 and 2 eggs on May 27.
9. We cleaned this box out two weeks ago after fledging our first set of bluebirds. On May 20 there was a full new nest and on May 27 there were 5 bluebird eggs.
10. (Paired with #9) On May 20 we removed the unused duplicate bluebird nest that had been there all along. On May 27 the box remained empty.
11. Discontinued  
12. Discontinued
13. 5 bluebirds fledged, probably early last week. We did not check the box on the 20th, which was approx. day 13 since hatching. We cleaned out the empty nestbox on May 27.
14. 5 bluebirds fledged between May 12 and May 20, when we cleaned out the empty nestbox. On May 27 there was a full new nest.
15. 6 tree swallow nestlings, approximately day 2 on May 27. There were 6 eggs on May 12 and female remained on nest during check on May 20 so we could not count the eggs again. There might be a 7th, but photo (above) appears to show 6 nestlings.
16. 5 bluebirds fledged close to May 12. We cleaned out the box on May 20. On May 27 there was a full new nest.
17. This box earlier showed signs of a chickadee nest, but was emptied probably by house wren between May 5 and May 9 and still remains empty.
18. (Paired with #17) Three pale pink bluebird eggs, cool. These eggs are well past the age when they should have hatched with consistent incubation (2 eggs were noted April 25 and there have been three eggs thereafter). Parents were always previously nearby and vigilant but were not observed on May 27.
19. Tree swallow nest with approx 7 eggs.
20. (Paired with #19) Complete bluebird nest with female present.

Trail 2:

1. Nest with no eggs -- no change.
2. (I previously reversed the description of #2 and 3 contents.) Tree swallow nest; 1 or 2 eggs on May 13; not checked May 20; female remained on nest May 27 so we could not count eggs. Assuming a clutch size of 6 or 7, incubation is probably 9-10 days along and we should see nestlings next week.
3. (Paired with #2)  5 bluebird nestlings approx. day 5 on May 27 based on appearance and incubation history.
4. 5 bluebirds fledged between May 13 (day 10 or 11) and May 20. We planned to clean out the nestbox on May 27, but it appeared that new nest material has been built over the old nest so we did not disturb it. Tree swallow was present on top of the box and there was a large white feather in the nest, so this may have become a tree swallow nest.