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.

May Birding Notes on Patch

Female ruby-throated hummingbird

My monthly Northfield Patch blog post, May Birding Notes, is now live. This month's edition discusses hummingbirds, orioles, bluebirds, sparrows, swallows, tanagers, warblers, hawks and vultures. May 6 was our first day this year to see both hummingbirds and orioles, and on May 12 I saw my first-ever orchard oriole in a large oak in the Carleton Arboretum.

Here's a preview:

Most of the spring bird migration has occurred, with a big last push expected this coming week. Our summer avian residents are now here. Here are some recent birding observations in and around Northfield:

Hummingbirds: We put out our hummingbird feeder at the beginning of the month, and I first noticed a hummingbird on May 6. Lately we have been seeing females numerous times a day, but sometimes also a male. The ruby-throated hummingbird is the only hummingbird to be expected in this part of the country. If you see one with a pale throat, it is the female. The irridescent red throat of the male can sometimes look purple or black, depending on the light.

Read the rest here.

The King of Orange - Baltimore Oriole at Feeder

I've had plenty of opportunity to observe our feeders the last few days while at home recuperating from minor surgery. I've been hoping to capture a male oriole at the oriole feeder in good light, and finally had the chance this evening. He and his mate have been regular visitors the last couple of weeks, but they don't stay long and are quick to depart if they sense motion nearby, so it's not easy to get a photo set up. This time he hung around for just long enough. By the time I pressed the shutter again, he was gone.

Baltimore oriole (male) at feeder

He gives a long percussive chittering call when he arrives at the feeder, which helps me look up at the right time to see him; I've noticed that blue jays also often announce their arrival. I suppose it is a territorial/possessive statement ("MY feeder. MY grape jelly."), but I appreciate that he announces his presence since I never tire of seeing this beautiful bird, which is just with us for a few months each year.

The songs and calls of the Baltimore oriole are quite varied. You can hear several versions at the All About Birds site. I don't hear the percussive call I've described in any of these samples; it may be the "sharp, repetitive chuck" that is described as an alarm call in the text. None of these samples offers the  song that's on my Audubon bird clock, either -- the one that sounds like "Figaro Figaro Figaro."

We offer both grape jelly and orange halves at this feeder but, although orioles are said to like oranges, the oranges are ignored while the jelly is gobbled down.

More About Turkey Vultures

Earlier this spring we saw five turkey vultures atop an abandoned barn while checking our bluebird boxes near Northfield (see March 24 blog post). A few weeks later we saw two turkey vultures on the edge of the hayloft of the same barn and wondered if they might be nesting there (see April 27 blog post). Last weekend in the same area we saw nine turkey vultures soaring overhead, quite close to each other, and soon afterwards we passed the barn again and found seven turkey vultures resting on the roof.

I did some more reading about turkey vultures, and learned that they roost in large community groups but tend to forage independently during the day. So my early guess that a group seen together in early spring suggested the previous year's family unit is not necessarily right at all.  But it's interesting to learn that they are communal birds.

The bird on the far right, above, is spreading its wings while resting. This is a common stance for the turkey vulture and is known as the "horaltic pose." The Turkey Vulture Society says:

The stance may serve multiple functions, including warming the body and drying the wings. Research on this pose suggests that turkey vultures spread their wings in the mornings, once the sun's intensity reaches a certain level, to raise their body temperature (which they lower at night by a few degrees as an energy saving mechanism). [see Turkey Vulture Facts page]

This photo was taken at about 4:20 p.m., for what that's worth.

 If you see turkey vultures circling in an area, it does not necessarily mean there is a dead animal nearby. The same site says, "Circling vultures may be gaining altitude for long flights, searching for food, or playing."

I like the idea of such large birds playing.

Bluebird Trail, Week 7 - Mom on Nest, First Fledging & Tree Swallow Eggs

Mama bluebird on her nest

While we were checking Trail 2 today,  a female stayed on her eggs when we opened one of the boxes. We have had a bird fly from a box as we've opened it before, but this was the first time one has stayed. It was quite a magical moment. We weren't able to ascertain how many eggs she's sitting on -- last week there were two eggs in this nest, so if she has the typical clutch of five, she's probably been incubating them for about four days and they'll hatch in another 8 to 10 days.

Trail 2 Box 4 nestlings at about 10-11 days

The nestlings are already quite advanced in the other Trail 2 box that has bluebirds in it (see photo above). We didn't know just when they hatched, but we estimate them to be at 10 or 11 days today, as shown in the photo above. This is the first photo we have that shows a nestling with an eye open. You can see they are becoming quite well covered with feathers.

Our very first nestlings, those in Box 9, have fledged. They were due to do so this past week, and on Saturday we found the box empty and the nest flattened out to accommodate the nestlings as they grew. You can see from the dark edges of the nest in the photo below that the nest was quite wet underneath. There was a lot of rain last week, and that box's opening faces south, exposing it to the prevailing direction of many of our rainstorms. Fortunately, as far as we can tell, the nestlings' health was not compromised. We cleaned out the box after taking this photo so that it is available for another nest. From what we've read, building the nest is an integral part of the reproductive urge, so it doesn't help to leave an old nest in place -- and starting fresh is more sanitary.

Flattened nest left after bluebird nestlings fledged

Nestlings are also very close to fledging in Box 16, if they have not already done so, and the Box 14 nestlings are due to fledge in the next few days.

Tree swallow nest with eggs in Box 15

We were very excited to find six eggs in our Box 15 tree swallow nest yesterday. We love seeing these feathery nests. We several times noticed tree swallows at Box 1 on our property today, as well -- one of the pair of boxes that have remained mainly empty but suffered the early chickadee loss to a house sparrow. And there is a bit of new moss in the other box, so we're hoping a chickadee is trying again. Still, we can sometimes hear a house sparrow nearby, so that threat remains.

Last week I did an abbreviated recap of our trail results. It's helpful to me to keep more detailed notes here, however, so those appear in the list below. Our Trail 1 totals so far: 25 nestlings! 5 fledged, 10 more are close to fledging, 5 more will probably fledge toward the end of this week, five more young nestlings, and only one nest still with bluebird eggs in it -- the worrying slow clutch of three pinkish eggs. This week they felt cold. The parents are always close by, but perhaps they just don't have the hang of this incubation business. We also have a nest of six tree swallow eggs. On Trail 2 we have four or five nestlings that should fledge in the week ahead, plus an unknown number of bluebird eggs being incubated in another nest, and one tree swallow egg so far in a third nest.


Trail 1:

1. Tree swallows observed on the box; box remains empty.
2. (Paired with #1) New moss this week, so we put the chickadee sleeve back on this box to reduce the entry hole size.
3. House wren had started to put sticks into nestbox -- removed. 
4. (Paired with #3) This is now clearly a tree swallow nest with large feathers; no eggs yet.
5. Five nestlings, 11-12 days old.
6. (Paired with #5) Tree swallow nest. No eggs.
7. House wren nest with one egg.
8. (Paired with #7) Now empty; previously contained a few strands of grass for several weeks. Wrens can clear nests.
9. Our first clutch to fledge. Nestbox was empty; we cleaned it out.
10. (Paired with #9) Complete nest, no eggs  - no change.
11. Discontinued  
12. Discontinued
13. Five nestlings approx 5 days old.
14. Nestlings close to fledging; parents still vigilant on wire when a tree swallow approach the box, so we suspect fledging has not occurred yet.
15. Tree swallow nest with six eggs.
16. Nestlings may have fledged or will do so shortly - we did not open the box. We did not open this box last week either, as parents were very protective.
17. This box contained a substantial bed of moss for two weeks, but was suddenly empty last week -- a sign of possible house wren activity.
18. (Paired with #17) Three pale pink bluebird eggs, cool. These eggs are past the age when they should have hatched with consistent incubation. Parents are always nearby and vigilant (swooping down at us protectively), but we fear incubation has not been successful.
19. Tree swallow nest - no eggs.
20. (Paired with #19) Partial nest.

Trail 2:

1. Nest with several tiny dark downy feathers.
2. Bluebird stayed on nest so we could not count eggs. Last week there were two cold eggs, so assuming a total clutch of five, probably four days into incubation.
3. Tree swallow nest, one egg.
4. Five nestlings approx. day 10-11.

Splish Splash, Goldfinches Taking a Bath

Here is a little slideshow I made from a series of shots of a pair of American goldfinches having a really good splash in a puddle.

Bluebird Trail, Week 6 - 20 Nestlings!

This week sped by, and we did not visit any of the nestboxes after Monday. As a result, the photo I posted last Tuesday of the Box 9 nestlings on day 8 will be our last photo of them, unless we are lucky enough to get any photos after they fledge. Today (Sunday) they are at day 14 since hatching, and standard bluebird monitoring advice is not to open the box from about day 13 on unless there is a compelling need, because it is too close to their fledging date (most often 17-18 days, though it can take several days longer).

By day 13 or so they are fully feathered, and the fear is that they may be startled into fledging prematurely, which could endanger them. This risk is thought to be less with the top-opening Gilbertson boxes we are using than with front-opening or side-opening boxes, but we don't want to take any chances. But we will try to stop by later this week, and in the weeks ahead as we continue to monitor these boxes, to see if we can see any sign of them out and about with their parents. The male, in particular, will continue to tend to them for several weeks to come; mama, in the meantime, may start building her next nest almost immediately.

Box 5 nestlings at Day 4 

Our fourth clutch of eggs, at Box 5, hatched probably Tuesday or Wednesday last week, and so were about at day four when we stopped by on Saturday (above). You can see some feathers lining this bluebird nest.

Tree swallow nest - note prominent, curling feathers. No eggs yet.

We were able to get a photo of the tree swallow nest in Box 15 (above) on Saturday. Bluebirds and tree swallows both make their nests of dried grass, but tree swallows make much more liberal use of feathers in the nest, and the feathers tend to curl up to surround the eggs (though there are no eggs yet in either the box above or the one below), rather than merely lining the nest. We have seen small feathers in several of our bluebird nests, such as the one with the nestlings above, but in comparison tree swallow nests are very feathery indeed.

Tree swallow nest on Trail 2 - no eggs yet

Above is another tree swallow nest. It is from the other set of boxes we are temporarily (?) looking after. We'll call those boxes Trail 2. Currently there are four nestboxes on Trail 2 -- two are paired, and the one above is one of those. There are two new bluebird eggs in the other box of this pair, and we have five new bluebird nestlings in one of the other boxes as of Sunday. We're waiting to see what develops in the fourth box, which contains a grass nest that looks as if it could be either a bluebird or a tree swallow nest at this point.

I am somewhat concerned about tree swallows using these Gilbertson nestboxes we are monitoring, ever since reading the opinion of the author of treeswallowprojects.com that these boxes, which have just a four-inch diameter, are dangerously small for tree swallow use, since tree swallows have larger clutches than bluebirds. People who put up nestboxes specifically for tree swallows are urged on that website never to use a box with a floor area smaller than 5 x 5 inches. I suppose cavity-nesters take what they can find to some extent, both in the course of their long natural history as well as in this age of humans providing nestboxes. One would think that a bird would "know" if a nesting cavity is too cramped for success, and would avoid it, but the treeswallowprojects site says that is, sadly, not the case. I will be interested to find out from Minnesota bluebirders who like the Gilbertson boxes what their experience has been with raising healthy tree swallows in them.

Below is one of the Trail 2 tree swallows, who sat very quietly nearby while we checked the box nearby and returned to this post when we walked past again after checking the other boxes. Tree swallows (and bluebirds too -- see below) are quite capable of diving at you from the air if they think you're too close to their nest, so we were quite surprised that this one did not display any aggressive protective behavior, though it was certainly watchful.

Tree swallow on fence wire

I took this next photo last weekend. I like the near-dusk softness of the landscape surrounding this handsome male bluebird.

Male bluebird at dusk

Box totals from our regular trail: 20 nestlings! There are five nestlings each in Box 9 (about 14 days old), Box 16 (about 12 days old), Box 14 (about 10 days old), and Box 5 (about 5 days old). As far as we know, they are all healthy. We did not look inside Box 16 this weekend, because the parents did dive at us when we approached the box, so we probably will not see those nestlings again for the same reason discussed at the start of this post -- they will very soon be too close to fledging.

There are still three pink eggs in Box 18, which is the same number as there were a week ago. They felt cool to the touch yesterday. The parents are always nearby and very vigilant, but we're not sure the incubation is proceeding as it should, so that is worrying. Stay tuned...

Not-So-Solitary Sandpipers in Flooded Field

Saturday evening, while doing our bluebird nestbox rounds south of Northfield, we noticed that the afternoon's heavy rains had left standing water in many farm fields. Flooded fields are prime habitat for migrating shorebirds, so we were on the lookout. At one particularly wet spot I saw something small and pale, so we pulled over to take a closer look.

We saw one, and then another, and eventually as many as seven or eight medium-sized shorebirds -- not all together, but here and there in ones and occasionally twos. A red-winged blackbird flew at one and flushed it, and we noted that the two birds were of very similar body size, which gave us a useful reference point. When we got close enough to see it, a noticeable white eye-ring confirmed the identification: these were solitary sandpipers. I just checked the comparative body length of the two species, and our impression of similar size was correct: solitary sandpipers are about 8.5 inches and red-winged blackbirds are about 8.7 inches.

We have most often seen these one at a time, as their name suggests, but the Cornell Lab's All About Birds site says, "While not truly solitary, it does not migrate in large flocks the way other shorebirds do," and National Geographic Complete Birds of North America notes that they are "usually seen singly or in small groups." Wet, grassy areas are a common setting for solitary sandpipers. On May 1 last year, in fact, we saw one in a flooded low area of lawn near our house, right in Northfield.

Like most of the shorebirds we see in Minnesota, these are just passing through on their way from their winter homes, ranging from southern Mexico into much of South America, to their breeding grounds in Canada and Alaska.

I was fascinated to learn just now, as I read about these pretty shorebirds, that they actually nest in trees, in the abandoned nests of songbirds, particularly particularly those of the American robin, rusty blackbird, eastern kingbird, gray jay, and cedar waxwing. The Cornell Lab site says, "Of the world's 85 sandpiper species, only the solitary sandpiper and the green sandpiper of Eurasia routinely lay eggs in tree nests instead of on the ground." This nesting habit was not discovered until 1903, 90 years after the species was first described by ornithologist Alexander Wilson.

So here are the things about solitary sandpipers that will stick in my mind:

• White eye-ring
• Same size as a red-winged blackbird (the legs and bills are very different, obviously)
• Flooded fields are likely habitat (this is true for a number of shorebird species, of course)
• They nest in trees!

Bluebird Nestlings at 8 Days

Here is the first group of nestlings again, eight days old as of Monday. Look how much more room they take up in the nest than they did a week ago. I was surprised how relatively unresponsive they were this time compared to earlier visits, displaying only one brief gape in the whole bunch. We thought perhaps their bellies were full and they were sleeping (and we did look closely to make sure they were actually moving) -- but then I read that right about this age, nestlings start to react differently. (Sialis.org) Instead of gaping when the box is opened, they hunker down with their eyes closed.

Eyes -- that's right, at this age their eyes may well have opened. We did not see any evidence that the eyes on this bunch had opened yet, but they may just have been keeping them closed. Their feathers are starting to come through; you can see them on the wings quite clearly.

Here's a nice page on Sialis.org that follows a brood day-by-day from hatching to fledging.