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.

Garter Snake

Here's a very nice garter snake that was lying on our road as I approached our gate a couple of weeks ago.

He was about 4 feet long and I was only able to get the one photo before he slithered into the tall grass.

It was cloudy and had been drizzling all day. This is the second snake I've seen on our road in a few months and I started wondering about why I always, or at least frequently, see them on the road.

I think part of the reason is they like to warm themselves on the road. But I think a more important factor is selection bias. I see them on the road because that's where they are easy to see!

I was reminded of this yesterday while mowing the grass. As I came rumbling by, I caught a glimpse of a fairly large, light-colored snake. I didn't see it well enough to identify it, but I wouldn't have seen it except that it moved away and I had just passed by and cut the grass. It makes sense that, living in the country, there are many snakes around, but most remain unseen. As we're walking by, they either move silently away, or we're too unobservant to notice them.

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.

More Feral Pigs!

Mary saw 5 feral pigs outside our east gate yesterday morning. They were all smaller than the one we saw in early June, and in the same area.

When she let our dogs out, they ran over to the fence near the gate, barking the whole time, and the pigs ran away. They're clearly not afraid of the house, but the dogs do keep them away.

It's somewhat disturbing that there were more of them, but I'm sure that their numbers on our property varies quite a bit. As I mentioned before, they can be very harmful to the environment and habitat, and we have seen signs of their rooting up the soil. I later walked over to where Mary saw them and there were no signs of rooting.

We'll just have to keep track of them and continue our efforts to control them. In addition to hunting, we also have a trap out, but so far, it hasn't caught one.