When house wrens (Troglodytes aedon) first began visiting my yard some years ago, I was not aware that they are extremely protective parents. I didn’t see them as often as birds of other species since they don’t come to my feeders and were not using nest boxes.
The past couple years, however, they have become more comfortable in my yard and began building their nests in boxes after all. This became problematic for me and especially the other species who use the boxes — Eastern bluebirds, Carolina chickadees and brown-headed nuthatches. The reason?
House wrens do their utmost to drive other birds out of their territory so that there is no competition for food needed by their nestlings and fledglings. This protectiveness makes them go so far as to peck other birds’ eggs, which they have done with chickadees and bluebirds in my yard.
Very unfortunately (and upsetting to me), they even killed two nestling nuthatches one year. The other two nuthatch babies managed to fledge. This behavior led a birder, Althea Sherman, to launch a crusade against house wrens in scientific journals in the early 1900s. Now, there are instructions online on how the wrens can be discouraged, for example, on a website devoted to bluebirds.
This year, Eastern bluebirds (Sialia sialis) were tending four eggs in one box and a house wren tried to invade. The parents were very protective and successfully drove the wren away (photo below). Another pair of bluebirds had nested early and managed to guide their young to fledging. They then abandoned my backyard for nesting and the house wrens had no rivals for nest boxes in that area for the rest of breeding season.
House wrens are one of the bird species banded in my yard each year for the Smithsonian Institution’s Neighborhood Nestwatch program. This year the bird bander noticed their nest with babies in a backyard nest box, so she upped the chances of catching one by counting on their extremely protective nature.
A net was put up not far from the box and the bird bander played the call of another house wren. This resulted in both mama and papa wren getting inadvertently caught up in the net while trying to drive away the intruder. They were both banded and then immediately let go so they could resume feeding their babies.
The four woodpiles in my backyard were like a larder for them because they host a plethora of insects.
And the house wrens are obviously not that choosy about which insects they eat. Mama and Papa brought a large variety to their ever-hungry nestlings.
The parents were also very good at keeping the nest clean.
The three nestlings appeared to be producing numerous fecal sacs so that mom and dad were constantly checking the nest for them and flying them away.
At one point, it was interesting that when the male wren brought a large insect to the nest, he handed it over to the female, who was waiting a bit after having just given the babies food.
Eventually, the large meal was delivered to the nestlings.
As the days went by, the nestlings became louder and more insistent on being fed and the parents scarcely paused in their efforts to keep the meals coming and the nest clean. It must have been a relief for the parents when the babies finally left the nest box because they could now take a breather now and then.
Right after fledging, the parents were still busy. The fledglings had not yet flown far so I could see the first post-fledging feeding session for one young wren.
I had learned that house wrens sometimes incorporate spider egg sacs into the nests they build because the hatched spiders eat nest parasites and thereby help protect the developing nestlings! The parents also fed mother spiders and egg sacs to their young. Just after fledging I caught a circle-of-life moment when a parental wren fed a mother spider with her attached egg sac to a fledgling – the death of the poor insect furthered the life of the new bird.
I could see and hear the parent house wrens continuing to feed the fledglings that afternoon. But after a while they appear to have moved to another yard, where they likely weren’t dealing with humans closely watching.
The Eastern bluebirds have a new nest in my front yard now with four eggs, so my nest watching can continue for a while. And the juvenile birds of other species coming to the feeders are entertaining, too.