Linda Moore of Georgia captured this incredible but disturbing footage on a nest cam at about 8 p.m. on 6/22/07. It shows what appears to be a House Wren removing three out of four newborn (1-2 day old) Eastern Bluebird chicks from a nestbox. Fortunately Moore was watching the video feed and immediately went outside with her husband and their dogs and a flashlight. They found all four babies on the ground, flung in every direction. They returned the babies to the nest. The House Wren? returned the subsequent night and again removed the babies. The Moores replaced them, and took steps to protect the young until they were too old to be removed (usually more than 4-5 days). The young survived, only because the Moores witnessed the attack. Thank you to Web Video Zone for hosting this video - their set up allows for much higher quality than YouTube. (If you don't see a button at the bottom, click on the photo to start.)
Above: the nestlings that survived two House Wren attacks, on Day 8 and 9 (since two hatched the second day) after hatching. The runt in the 6:00 position may have been injured in the attack, and is not as vigorous as the other nestlings, which are doing well. Below, on Day 10-11.
Days 12-13. Baby is on the top of the pile.
Note how fast the attack occurred. This video - unedited, happening in real time - is only 51 seconds long, and three of the babies are removed in less than 20 seconds. Bluebird parents must leave the nest periodically to get food for the hatchlings, and House Wrens are very quick. These unsuspecting hatchlings, whose eyes will not open until 8-11 days after hatching, hear the noise, think it is a parent, and gape, begging for food. The third baby that was removed in the video was only 3-4 hours old. In the second attack, Moore reported that the House Wren grabbed onto the edge of a baby's gaping mouth, pulled it through the hole, lost its grip and then grabbed it again and threw it out of the box. Another nestling was grabbed under its wing. Some folks did not think that House Wrens were common in this part of GA, and the BBS Map shows low populations. However, the Moores did find a House Wren nest in a neighbor's box, about 400 feet away from this box.
Unlike House Sparrows, House Wrens are native birds, and are protected under the Migratory Bird Treaty Act. However, there are some options to prevent them from using a nestbox or to deter them from attacking other active nests. See House Wren Deterrence. Carolina Wrens (with a bold white eyeline) are not known to attack other birds' nests.
I believe that nest cams (tiny cameras, often infrared, placed inside a nestbox) will bring our understanding of cavity nesters and their predators to a whole new level. Also, if the Moores had not witnessed the attack, they would have come out to an empty nestbox the next day. Though the babies were tossed onto the ground, another predator might have come by afterwards to take them, so there would not have been much evidence unless sticks (from a House Wren nest) showed up in the box afterwards.
Note that the intro photo is not Linda's nestbox - it's one of mine, where I caught a House Wren on my birdcam dismantling an active Tree Swallow nest.
"Phoenix" (the smallest) finally fledged on 7/12/07. The babies left on days 21-22 (counting hatch day as day 1). 17-18 days is more common.
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