posted March 30th, 2011; last edited April 4th, 2011 –– David Sibley

Carolina Wren mystery spots

Reader Richard Messer sent me the photos below, asking if I knew what the behavior was that displayed the white “rump spots” of the Carolina Wren. My answer is “no”. I’ve noticed spots like this a few times in the field, but never had a chance to really wonder about them. The BNA account for Carolina Wren doesn’t mention anything about this (and has very little on displays in general), and checking several other references, as well as looking for info on related species of wrens also came up empty.

Carolina Wren in normal posture, about to sing, with rump feathers hidden by the wings. Photo by Richard Messer, used by permission.

The feathers that are involved are the rump feathers, which usually lay flat against the body, under the wings, forming a smooth contour from back to tail. In this case the bird has fluffed them out to cover the wings, and in that way shows a bunch of white spots.

And the same Carolina Wren a few seconds later, after fluffing out the rump feathers so that they now cover the wings and reveal white spots. Photo by Richard Messer, used by permission.

It seems clear that this is a display – the fact that the bird is singing, and that the odd feather arrangement reveals distinctive markings – all suggests that it means something important to other Carolina Wrens.

So much basic information about common birds like this is still unknown. The function of this display, how often it is used, under what circumstances, by one or both sexes, etc. are all open questions that could be answered by an alert backyard birder. If you already know the answers, or have some ideas, please leave a comment.

Update 4 Apr 2011 – new photo

Two Carolina Wrens sleeping with feathers fluffed, which exposes the white spots on the rump. Photo copyright Judy Mojarrad, used by permission.

The photo above by Judy Mojarrad shows two Carolina Wrens sleeping under her roof. With heads turned around and bills tucked into their back feathers, and with the flank and rump feathers completely expanded, these birds look like balls of fluff. They’re fluffed up to conserve heat, and all songbirds adopt a similar pose when they sleep.

In this pose the white spots on the rump feathers might provide some camouflage, but if that was the primary purpose of the spots I would expect a lot more songbirds to show similar markings. [repeating from my comment below:] Carolina Wrens are unusual for 1) fluffing those feathers while singing and 2) having contrasting white spots there. One of the keys to figuring out whether this means anything will be watching a lot of singing Carolina Wrens to see if they show the white spots in certain situations more than others. And I also wonder: Are there any other North American songbirds that show similar white spots? OR any that fluff their rump feathers to cover their wings while singing?


Thanks to Richard for sending this to me and for allowing use of his photos. You can see the original photos at his website here

And thanks to Judy Mojarrad for sending her photo and allowing me to use it here.

31 comments to Carolina Wren mystery spots

  • Dan Lane

    These spots seem similar to the semi-concealed white patches that are frequently seen on various antbirds (family Thamnophilidae) in the Neotropics. Most often present in the back feathers between the scapulars (hence called ‘interscapular patches’), these white bases to feathers are exposed often when a bird is excited, such as when defending its territory against a conspecific.

    My own theory is that these species are usually found in the dark understory of forests, where the dim light allows few visual cues when trying to spot conspecifics. White, however ‘glows’ even under poor light, and thus is a great indicator of the position of the territorial owner to the intruder (or mate, or whomever). I suspect, given the similar ecology of Carolina Wrens (resident, present in understory often with dim lighting during the growing season, singing from obscured perches, etc.), that these white spots serve a similar purpose.

    I might add that the ‘glowing’ effect of white under low light conditions is also used similarly by nightbirds (e.g., the wing and tail flashes of nightjars–usually unique to a species within any given region–or white on throats of owls and nightjars that is only exposed while the bird is singing, etc.).

  • David Weber

    I have only seen the spots while the bird is singing. Carolina Wrens frequently perch on my deck, and the spots are always visible when they sing. So I have to agree with you that it is a form of display, perhaps to attract a mate. With the spring coming, I have to keep an eye on the Carolina Wrens’ behavior.

  • Thanks for the hypothesis and the info about antbirds, Dan, that makes a lot of sense. And thanks for your observations on singing, David, I hope you’ll keep us posted on anything more that you learn this spring.

  • Judy

    I had a pair use my front porch to get of the wind and rain. They were asleep with the white spots showing. Were they simply at rest not holding them tightly to their body, or trying to blend in with the white porch,or as Dan mentions, was it to mark the porch as their territory as they slept?

    • Hi Judy, Thanks for that observation. I think your first hypothesis (simply at rest with feathers fluffed out) is correct. All songbirds have long and fluffy feathers on that part of their body, and their primary function is to overlap the wings and provide extra insulation when the bird is resting or very cold. You’ll see a similar feather arrangement on sleeping chickadees, House Sparrows, etc etc. On most species the feathers are just drab grayish or brownish. Carolina Wrens are unusual for 1) fluffing those feathers while singing and 2) having contrasting white spots there. One of the keys to figuring out whether this means anything to the birds will be watching a lot of singing Carolina Wrens to see if they show the white spots in certain situations more than others. And now I wonder: Are there any other North American songbirds that fluff their rump feathers to cover their wings while singing?

  • Judy

    David, I would like to email you the picture I took of them on the porch if you are interested, but I don’t know how to attach it here. If you email me I can attach it if you like, and you are more than welcome to use it.

  • Angela Lanier

    I have had the pleasure of sitting in my livingroom and watching a pair of Carolina Wrens build the nest, lay the eggs (all 5 lived), feed them, and sing, sing, sing. The little ones arrived June 1, so I know they will be gone about the time I move. I have been here 4 yrs. and it wasn’t until I am about to move that I had the opportunity to see these sweet little birds in action. These are definitely parenting birds. They are no bothered by my looking at them, making sure my plant is covering them, watering my plant a little, and actually taking a small flashlight to check on them at night. To think that I tried to discourage the male from starting the nest in my golden pothos….after 3 times of cleaning the plant, I finally gave in to him. I am so happy that I did! By the way, I am in South Caroina.

  • Angela Lanier

    Can someone answer this question? All 4 Carolina Wrens flew the nest. The 5th one couldn’t. One of the parents returned for it but saw me and left. Then the baby kept trying to fly. He finally ended up taking a leap off my balcony. He was hopping into the woods where his family was calling him. I don’t know whatever happened to him. Right after the sun went down one of the parents showed up on my balcony and looked like he was looking for the nest. Did he return because the last baby never found them?

    • Hi Angela, First, congratulations on your wren family. The fifth baby wren might have been either slower to develop than the others (maybe the egg was laid later?) or had some issues with its wings or feathers that gave it trouble flying. Either way, it’s best chance of survival would be to follow the rest of the family away from the nest. The parents’ instinct to care for the young is very strong, so as long as that bird was able to call the parents would find it and feed it, wherever it ended up. The biggest danger to it would be predators such as house cats, but hopefully it was able to avoid those and just needed another day or so to grow its wing feathers and begin flying.

      • Lyn Westafer

        David, I am having my first experience with a Carolina Wren! Precious little creatures! I didn’t know what had decided to make my porch it’s sleeping quarters, but just this morning discovered that it’s a Carolina Wren. Every night he flies in and isn’t bothered by our conversation.

  • Christa

    I saw a bird grooming itself on the fence in the backyard and took some photos. I thought it was a Carolina Wren, but the white spots made me think it was maybe some other type of bird. Thank you for confirming it was indeed a Carolina Wren. The spots only appear when the bird is fluffed up. Since this seems to occur while grooming and sleeping, do you think it is more of a defensive adaptation to deter predators while they are vulnerable? Side note: They love peanut butter.

    • Christa, Thanks, I’m glad this was helpful. The function of these spots is still unknown. The original photos that I posted about show a bird that seems to be displaying, but other observations (like yours) are just birds incidentally showing these feathers while preening or sleeping. Maybe the spots at those times offer some cryptic coloration? Maybe there is no obvious reason for the spots? Keep watching and the answer might become clear someday.

  • Thanks for this post, David. I was looking at a photo of a Florida bird and wondering if those spots were particular to the subspecies or simply normally hidden; I live outside their range, so had to google it.

    You asked if there were any other species that fluff their rump feathers while singing; the first one to jump to mind is Yellow-breasted Chat. It’s another species whose range I’m outside of, but I’ve seen enough photos (such as this one: to know they do this at least some of the time. They don’t seem to show white spots on the rump, though.

    Rose-breasted Grosbeak? ( They’ve got a mottled rump, not the well-defined spots of the CARW.

    I was going to suggest Brown-headed Cowbird, too, except on reviewing photos it seems that while they fluff their body feathers, the rump feathers are largely excluded.

  • Bryan Calk

    I read this intriguing article/study a while back and just recently was browsing some old photos of mine.
    I came across this one of a Bewick’s Wren in southwest Texas displaying similar rump spots.
    So perhaps it is not unique to Carolinas?

  • Diane DesAutels

    I, too, saw a Carolina Wren with these puzzling spots. It was preening on a branch, and if I hadn’t seen its head, I wouldn’t have been able to ID it. Curious, I looked online for answers.
    According to the blog “Notes from the Wildside” , by Adrian Binns, “This bird is preening with his … mantle feathers fluffed out. The grey spots are actually the feather tips in molt. Once the bird has molted, the back will be an even color.”
    Pete Brown’s blog and a couple others have spotted-C.W. photos ID’d as young [at/in the nest], so apparently what A.B. meant was “once the young bird has molted into its adult plumage” — but he neglected to use an modifier such as “juvenile” or “immature” when he ID’d it by species.
    If that’s all it is, I’m surprised I’d never seen these spots before, even if the wings do conceal them when the bird isn’t fluffed up.

  • David

    I’ve had the same bird sleep on my porch for the last 3 years. It will go missing for a few weeks and then its back for a few nights rest and gone again.

  • Sylvia Young

    I too have found these adorable birds on my porch. Could not find anything that looked like them until now, and only because they have been fluffed up and sleeping! Thank you

  • Ron Pittaway

    Intriguing discussion. The detailed plumage descriptions in The Bird Life of Texas (Oberholser 1974) describe white rump spots in Carolina, Bewick’s, House, Winter (presumably Pacific too) and Cactus Wrens, but no mention of white rump spots in Rock, Canyon, Sedge and Marsh Wrens.

  • I just found a Carolina Wren yesterday showing off these spots. It popped up onto a perch just as some buntings flew by and sported a pose showing the white spots. I posted the photo here if you want to see it:

    Perhaps in this case it’s a display?

  • Andre Nel

    Hi Mr Sibley,

    Good day, I think that I have at least one very good theory for these spots and have photos to back this theory up. I have observed these birds over the years and there is always a pair somewhere in the yard or roosting above my doors under the awning. I have photos of where they actually tuck their tail away and fluff up their feathers completely into a round ball and this makes them look just like a pine cone. I can only imagine that they use this to camouflage themselves where they might sleep, you can imagine this before there were any buildings around. They sleep this way all night and never defecate where they sleep either. I think this is all a strategy to avoid being detected at night.

    On a side not I have a picture of the “ball” of feathers and have had a competition on my Facebook page for four years now, offering a $30 prize if anyone can guess what it is. As of yet no one has been able to guess what this “thing” is.

    Thanks for reading.

    • Hi Andre, Thanks for sharing your hypothesis. Camouflage does sound like a good explanation for these spots, at least to explain the appearance of birds that are fluffed up and sleeping. It doesn’t fit quite as well to explain the spots when a bird is singing. I suppose the bird could also need camouflage then, since it is sitting up in the open broadcasting its song, and presumably most vulnerable to attack from behind – maybe the spots make it harder for a predator to see? Or maybe the species that have evolved these spots have also started to use them secondarily as a visual display?

  • Gina B

    I have a new friend in a Carolina wren sleeps in the ceiling of what’s the balcony above my patio. Shows the white spots. seems oblivious to the patio light and didn’t care the patio door was open when it must have flown up to sleep. Second night, same exact spot. Was not here last year. I feel complimented by its presence. My patio has plants with a big tree nearby, but it does face a parking lot.

  • Judy C

    I was online looking for answers about those very white spots you are describing. This morning I saw a Carolina wren sitting atop a tree stump (about four feet high) where I have a small bird feeder. It was singing and was all fluffed up with the white spots showing. There was also a light rain. I’m a bit new to bird watching. Ran for my camera, but the wren didn’t have enough patience to wait for me!

  • eva o

    We just arrived home late from dinner out with family to find a ball of fluff on our brick ledge near our front door. I knew by the coloring it to be a wren. I was surprised to see one there with our porch light above. It was tucked into the corner as close as it could get to where our siding comes together. At first I was alarmed, but after reading these comments, I am convinced he is sleeping peacefully and will be alright. He didn’t budge as we were filtering into the house. :)

  • nicole

    I have one that hangs out in feont of my kitchen door under the overhabg every time it rains. He always sleeps there. I am going to buy him a bird house. I have been snapping pictures of him the past few weeks when he is there. I don’t know how to upload them to here. I named him Kevin :)

  • Lisa

    We have had 2 birds I am guessing now they are Carolina Wrens!! They come back to either the front porch or back patio,we love them we at dusk we are looking for them calling them our babies!! Question can u buy a bird house for them???

  • fleta

    i have one carolina wren that comes every night for bed and then leaves early morning.

  • Scott

    My wife and I thought we had bats nesting on our entrance way, but when I typed in Florida birds that slept in pairs, this site pulled up with a similar photo to our own. Beautiful creatures they are.

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