Checking the Nest Boxes

Now that there are eggs in most of our nestboxes, I've been checking them weekly to see how they're doing.

Here's a photo of one of our two Eastern Bluebird (Sialia sialis) nests. It looks like two of the eggs have hatched and you can see the small hatchlings. You can also see the unhatched egg. I think they're less than a week old because when I checked it the week before there were three eggs in the nest. Their gestation period is about 12 to 14 days. The hatchlings are almost naked with just a few tufts of hair-like feathers along their back and head.

In this photo, taken one week later, they are noticeably larger and are more covered with down. They are starting to look more like birds and the head and beak of one is clearly visible. It takes them around 3 to 5 weeks to fledge, so they've got a way to go.

One of our nest boxes had what I thought were wren eggs because they were white with brown spots and I'm familiar with them. When I checked the box last week, however, there was a bird sitting on the nest which I think is a Black-crested Titmouse (Baeolophus atricristatus). I'm not an expert so this is not a positive identification, but that species was identified during our bird species survey last fall. I'll have to ask my expert consultants to be sure.

I'm assuming the bird was the mother and she was hunkered down and trying to make herself small and invisible. You can see she's even flattened her crest. I'm sure she was frightened so I took the photo quickly and closed the door. I've seen birds fly out and away from nest boxes when I approached, so I was surprised to find one on the nest. I'm impressed at her bravery and motherly instincts!

Walking The Nest Box Trail

We walked our nest box trail today, as part of our wildlife management activities. We have eight boxes up now, with plans for more. We put them up in October last year and have been checking them semi-regularly since.

We're now in the nesting season and this is our first formal check. We keep a log of what we find and take photos as part of the record. In a random check a couple of weeks ago, I noticed that some of the boxes had nests in them, so we wanted to check every one.

Five of the boxes contained nests. I wonder why the birds decided not to use three of them, or at least not yet. Two of the unused ones are along our driveway, so I thought maybe there is too much human activity nearby for them to be attractive. One, though, is not near our daily activities.

This is nest box #1 which is near our house. The nest is made of ashe juniper needles, a few twigs and leaves, and some fur. The fur might be from our dogs.

Nest box #6 is near our neighbor's horse pasture and it has quite a bit of horse hair in it. It also has bits of cellophane and grass stems. The nest is lopsided and tilted. It looks like the opening is off to the side, in the lower right of this photo.

Nest box #7 is also near our neighbor's horse pasture, but it looks different than #6. The nest is round and level with the opening on top.

Nest box #8 which is near one of our wildlife water dishes had three eggs in it! The eggs are very small and a uniform light blue. I estimate they're about 1/2 inch long. The nest is made almost entirely of grass and is very neat, round, and well-made. We think they're bluebird eggs but I'm going to ask an expert for confirmation.

Nest Boxes - Moving In

I checked three of our blue bird nest boxes last week and they all showed signs of nest-building!

I happened to go by two of them as I was trucking water out to the wildlife water dishes and decided to check them. After seeing those two with nests in them, I checked on one by the house and it too contained a nest. I think the odds are that all of them have nests in them, but because of the rains we haven't had a chance to check them all.

The first one was right next to one of the wildlife water dishes on the eastern edge of our property. The nest is made of grass stems and fills about half of the box. You can see the cedar shavings, that were in the box at the start, at the bottom.

I couldn't see any eggs in the nest, but the view into the nest was difficult because it was filling so much of the box. I will take a mirror next time to be able to see inside. Eastern bluebirds make their nests from grasses, so this might be one.

The next box is further south on the same eastern fence line. This one is definitely made of different materials than the first one. It appears to contain grass, twigs, feathers, and fur. It also appears to be at an earlier stage of construction, but that's only a guess because it's smaller. It looks looser and more disorganized than the first one. My guess is this one is another bird species, but I don't know which.

It stopped raining today and the sun is shining. Maybe we'll make the nest box rounds and get a full inventory of the activity. Along with all the other signs of spring, the birds are building homes!

Checking Nestboxes

We went for a hike today and checked the bluebird nestboxes while we were out. It's not nesting season, which is in the spring, but it's good to get in the habit of checking them. We try to make the rounds about every two weeks. Even though the bluebirds aren't nesting, other bird species or animals may decide to use the boxes and it's worth checking them.

I've posted about the bluebird nestboxes before. They're built so that you can easily open a door and look inside. At some point, hopefully, we'll find a nest inside and be able to count any eggs.

All eight boxes were empty, but some appeared to have been visited. One had bird droppings in it. Several showed signs of occupancy because the wood shavings at the bottom were concave and piled up around the edges. You can see the concavity in this photo.

Our nestbox trail goes by our neighbor's corrals and one of their horses came over to see what we were doing. Unfortunately, we didn't have any carrots or apples for him, but he was quite friendly. We'll  have to remember to bring a treat next time.

Another Update on the Second Wren Brood

I estimated that the second Carolina Wren brood would fledge on July 22nd.

I checked the nest on July 19th and the 4 wren chicks were still in the nest. When I checked again on the morning of the 20th, they were gone. The only thing remaining was the sole unhatched egg and it was slightly outside the nest, on the shelf upon which the whole nest rested. I took the egg and held it up to the light. It appears to be uniformly translucent, so I don't think it was ever fertilized.

Here's a photo of the egg with a scale, so you can get an idea of how large the eggs are. They're really quite small - about 5/8" inch on the long axis. The adult birds are about 5 to 6 inches long, but that includes tail feathers. They stand about 4 inches high.

After discussion with Mary, we're not sure what happened. At first I thought that the chicks fledged early or my estimate was off.

However, when the first brood fledged, we continued to see the young wrens around the garage as they became comfortable with their new flying ability. This time, we haven't seen them. The nest doesn't look disturbed, but we wonder if a predator got them.

It's sad to think that they might not have made it, but that too is a course that nature can take. I hope they fledged and that there are now four more Carolina Wrens in our back yard, but we'll never know for sure.

Update on the Second Wren Brood

Here's a photo of the 5 eggs in the Carolina Wren's second brood. This was taken on July 4th, so it's about 12 days after the first egg was laid, but only 8 days after the last egg was laid.

The second brood started hatching on July 9th. I checked the nest at 5:30 pm and 2 eggs had hatched. I checked the nest again a bit later, at 7:00 pm and 1 more egg had hatched. July 9th is 13 days after the last egg was laid. Their incubation period is 12 to 14 days, so they were right on schedule, counting from the day the last egg was laid.

One possibility I thought of to explain how the eggs can hatch within a day of each other even though they were laid a day apart is that the mother wren doesn't start the full incubation until they are all present. I think the embryo development is controlled by temperature and I noticed that the mother wren wasn't always in the nest until the last egg was laid. This would explain how the early eggs and the later eggs hatch within a day: they don't really start developing until she keeps them fully warm. This photo was taken on July 9th. There are 3 hatchlings although one is hard to see behind the rear egg.

One more egg had hatched when I checked the next day, on July 10th, at 7:30 am. Now there was only 1 egg remaining to hatch.

By the next day, July 11th at 4:00pm, the last egg had not hatched and I started to suspect that something was wrong. Either the egg had not been fertilized or something happened in its development.

On July 17th, the egg is still in the nest which surprised me because I thought the parents would remove it when it didn't hatch. The 4 baby wrens are developing nicely and I estimate they'll fledge around July 22nd which is 12 to 14 days after they hatched.

Another thing I observed whenever I peeked in the nest is that the baby wrens look exhausted. The first brood always looked active when I approached and frequently opened their mouths trying to get fed. The second brood just lies there. I noticed it's quite warm in the garage. The high temperatures are now approaching 100 degrees and there is no breeze in the garage.

What seemed like a good choice of nest location on the mother wren's part in the spring now appears to be not be so good.

Second Wren Brood

After the wrens fledged at the end of May, I left the empty nest on the shelf in the garage, thinking they might use it again.

I had been checking the nest intermittently and on June 23rd, there were two eggs in it. When I told Mary about it, she said she had seen a Carolina Wren fly out of the garage the day before and had looked in the nest and hadn't seen any eggs.

I then checked the nest every day after: June 24th, 25th, and the 26th, and every day there was another egg in the nest. The mother wren stopped laying at 5 eggs, so this brood is 1 smaller than the last one.

I've read more about Carolina Wren nesting habits. There are several resources on the web. This is a good one. There is another good one here. The wrens mate for life and typically have two broods a year. The male usually makes several nests and the female picks which one to use. The multiple nests may be to confuse predators as to where the eggs are.

We attended a talk by Dr. Peter English, who is from the School of Biological Sciences at the University of Texas in Austin, about birds at our last Hays County Master Naturalist Chapter meeting. He mentioned that bird eggs average about 20% of the mother's body mass in size and how incredible it is that she lays one a day for several days. I think when I saw the two eggs on June 23rd that she started laying the second brood on June 22nd and we just didn't notice them until there were two eggs in the nest.

This means they should hatch about 12 to 14 days after, around July 4th to 6th. One thing I'm not sure about is how they can hatch synchronously, within a day of each other, if they were laid a day apart. A day difference in a total of 12 to 14 days of development seems fairly significant. I'll keep an eye on the nest and see when they hatch.

Baby Wrens Update 2

Here are 3 more photos of the Carolina Wren chicks at days 8, 10, and 12. It's interesting to see them developing.

On day 8, their eyes are beginning to open and their feathers are mostly black. 

On day 10, their eyes are fully open and their feathers are turning brown.

On day 12, they're starting to look like adult wrens. You can see the white stripe above the eye. They're noticeably larger, too. The nest is looking pretty crowded. They are almost ready to fly.

The baby wrens finally fledged on Sunday, May 30th. By my reckoning, this was day 14 after they hatched, which agrees with what I read about their development time line.

My last photos of them were on Friday, May 28th or day 12. I did take a photo of the empty nest, just for completeness. I checked on them Saturday morning and they were still in the nest and also when I checked in the evening.

I checked on them Sunday morning and they were still there. When I checked in the afternoon, however, they were all gone.

I've seen them flying around inside and around the garage. It seems they're still learning their way because they look a bit clumsy, especially when landing. I also noticed that I'm seeing them less and less, so I think as they gain ability and confidence, they're roaming farther.

I'm glad I got to follow their development. It's something I never before had a chance to do and I learned quite a bit. Their average lifespan in the wild is about 6 years, and I'm sure I'll see them around.

Baby Wrens Update 1

Here's a quick update on the baby wrens.

I think the wren eggs hatched on May 16th and my earlier photo shows them at 1 day old. The following 2 photos show them at 4 and 6 days old.

They're developing rapidly, as you would expect if they're going to fledge by day 14. At day 4, they still have bare skin showing, but by day 6 they're completely covered by feathers. Their eyes are still shut.

I'm trying really hard to not disturb them constantly. The parents are not in the nest all of the time. In fact, I did not see them when I took these two photos. Before, when I took photos of the eggs and then when I would check to see if they'd hatched, the mother bird was always in the nest.

The parents must be out gathering food and I've seen a Carolina Wren in oak trees near the garage.

Baby Wrens

Mary called me at lunch last week. She noticed a bird had made a nest in our garage on a shelf among some spray paint cans. When I got home I went out to get some photos. As I approached the mother bird took off and although I didn't get a good look, I could tell she was a small brown bird with a pointy beak.

I was able to get a few photos, but didn't want to take too long or disturb the mother. The nest was about five feet off the floor and made from leaves and twigs. It looks like the inside is lined with hair, possibly dog fur.

The eggs were white with brown spots and were about 1/2 inch long. There were 6 eggs in the nest.

Mary and I are not bird experts, but we have access to several in our Master Naturalist Chapter. I posted the photos to our Chapter's forum and quickly got an identification.The bird was most likely a Carolina Wren. We looked the bird up in our Peterson bird guide and it looked like the correct identification. We thought it might also be a Bewick's Wren which is very similar, but the Carolina is a bit redder.

I wondered how long they had been there and when they would hatch, but had no clue. These photos were taken on Tuesday, May 11th, so I would just have to keep watching and see when the chicks hatched.

On May 17th, Mary told me that there were now baby wrens in the nest! I took this photo that day, and I think the chicks are less than a day old. As you can see, they only have a few feather tufts on the head and are bare otherwise. They have huge eyes. They're really quite ugly, but in a "cute" way. All six eggs have hatched. I looked up the incubation period for Carolina Wrens and it's about 12 to 14 days, so the eggs were laid in early May, probably around May 3rd. The eggs hatch synchronously, within 24 hours of each other.

The parents coax the young ones out of the nest after 12 to 14 days, so I'll keep an eye on their progress and keep you updated.