faunascope

House Wren nest box, July - August 2007

Today we begin the story of a family of house wrens that occupied a bluebird nest box in the summer of 2007.

If we inspire you to learn more about wrens, or you want to see pictures of them outside the nest, see Sialis, Wikipedia, or the Internet Bird Collection.

Day 3 after first hatching

House wrens compete for nesting space with sparrows, swallows, and bluebirds.  All of these birds nest in cavities.  However, wren nests are easy to identify, because wrens often build a large barrier of twigs in front of a grass nest.

 

The wrens work very hard to fit the twigs through the small entrance hole.  Often the ground beneath the entrance to the nest is littered with twigs that the wrens have dropped in their many attempts.

 

Wrens, like bluebirds, lay one egg per day.  Typically, there are 3-6 eggs. This nest had four.  We begin this nest’s story on Day 3, two days after the first egg hatched.

 

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At this point three chicks are visible.  They are huddled for warmth.  Because chicks are born without feathers, their most visible features are their bills and their feet!

House Wrens, Day 3 (continued): Yum, insects for breakfast!

You won’t usually see house wrens at your bird feeder.  They eat insects and spiders almost exclusively.

    

Here we see a parent bringing the chicks a katydid.  Even though it’s as large as the chicks, it’s quickly consumed.

   

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House Wrens, Day 4: Parents handoff food

Just one day later, the chicks are already more active.   But they have no feathers yet, and must rely completely on their parents for food.  (Here’s your vocabulary word for the day: altricial.)

 

House Wren parents both bring food to the nest.  Here we see one adult taking a handoff (perhaps a cricket?) from the other.

 

For the first few days, the parents may also contribute warmth when they aren’t fetching food.  This one is settling down to do just that.

   

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House Wrens, Day 4 (continued): Take out the poop!

By day 4, the chicks will poop almost every time they eat.  The baby wrens will stay in the nest for 12 to 18 days.  The parents bring food to the nest between 10 and 20 times per hour.  That’s a lot of poop!

This video shows you how the parents keep the nest clean.  The secret is that when the chicks defecate, it comes out neatly bundled inside a thin membrane called the fecal sac.  The parents can easily scoop this up and dispose of it outside the nest.

Some scientists have noted that many species of birds drop the sacs far from the nest, in order to avoid leaving clues that might attract predators to the nest.

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House Wrens, Day 5: Mom provides food and warmth

By Day 5, the three chicks are visibly more active. The mother is still providing warmth, and may spend ten or fifteen minutes at a stretch warming the chicks with her brood patch.

At one point in this clip, we can see that one egg has not yet hatched. At this point, it won’t. It may have gotten too cold, or the shell may have been too weak.

In this clip, the mother also spends time rooting around in the nest. I’m not sure whether she is grooming the chicks, looking for fecal sacs, or searching for parasites like mites. If anybody has ideas on this, please leave us a comment below!

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House Wrens, Day 8: Eyes open

The differences from day 5 to day 8 are dramatic. The chicks are now much larger (compare the size of their mouths in this video with the previous one). Their eyes are open now, and you can see the feathers forming on their heads and necks.

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House Wrens, Day 9: Feathers coming in nicely

Development continues, and we can now see the feathers coming in on their wings.

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House Wrens, Day 10 (7 a.m.): Markings visible on some feathers

Once again we see an adult feeding and then removing a fecal sac. When the chick lifts his butt, we can see that wing and body markings are starting to appear.

Each chick also spends lots of time grooming itself. This may be because growing feathers is itchy, or because the nests contain many blood-sucking mites.

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House Wrens, Day 11 (7 a.m.): It’s getting crowded in here!

The chicks spend lots of time moving around within the nest, and crawling over each other. This one works hard shoving his sibling to get to one side, then changes his mind and comes back to the other!

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House Wrens, Day 11 (continued): Hey, there’s another world out there!

One chick finally climbs out of the nest to look out the entrance hole. The copycat instinct seems pretty strong, since another quickly follows suit (and manages to intercept the food delivery!). Sometimes there’s no reward for being first, I guess.

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House Wrens, Day 13: Flown the coop

House wrens fledge (leave the nest and make their first flight) between 12 and 18 days after hatching. Generally, the more chicks, the longer it takes before they fledge. This is because when food must be divided among more chicks it takes each longer to reach the proper weight.

After about the tenth day, the chicks will leave the nest early if they feel threatened. And that’s what happened in this case. While working around the nest, I bumped the pole supporting the nest box. In no time at all, the three chicks took flight. Each glided in a different direction and happily they all made it to nearby trees. Also fortunately our resident crows, which sometimes prey on fledglings, were elsewhere. So the chances that these chicks will survive are quite good.

Here is one last shot of the empty nest. You can see the unhatched egg. According to a study at Cornell in 2000, 17% of all house wren nests contain at least one unhatched egg.