It is important that we monitors always INSPECT nests when nestboxes are cleaned out between broods and after “alleged” fledgings.   I get questions how I know fledgings actually took place at nestboxes at locations where I cannot watch closely the goings on.   Here are some tips and examples of nests after inspection:

First, I make sure I monitor at least once a week.  I prefer about every 4 days. I can keep a better handle on happenings if I monitor more than once a week.

After I think there has been a successful fledging, I can actually tell by looking at the remaining nest if indeed a fledging took place as opposed to a snake predating the older nestlings.   The parents always “change diapers” or clean up the nests of the fecal sacs.   During the fledging period, usually within a 24 hour period (sometimes a little longer if the parents think it’s not safe or a nestling is weaker than the others), the parents don’t bring food to the nestlings as often or clean up their waste matter to entice them to make the first flight.   The adults will also swoop down to the nestbox and call to them to come out.  It’s fun to watch if you can do so!   Most of the time during fledging, the waste matter (fecal sacs) remains in the nest as the young birds fledge.   If a snake gets them, their usually is no waste matter in the nest.  The parents are diligent the nest stays clean.   When I see a flattened nest with waste matter, that’s a good sign the youngster made it!

Note:  I always look for waste matter left on the front-side of the box under the entry hole.  That’s a good sign they made it out OK, leaving a bit of matter behind as they fly out. This is cleaned off between broods by me so the box is as clean of the birds’ waste matter as much as  possible.

When cleaning out a nestbox, I turn nests over looking for blowfly larvae and other possible parasites in the nest material which are not visible in the box itself (such as the beginnings of ants or mites).   It’s really important to always remove used nests but PARTICULARLY those that shows parasites, such as the example of this first brood nest for this season (first time I ever had blowfly larvae in first nests).   The female likes to build a new nest for the second and possibly third broods.  Clean nesting material is good.  Otherwise, she may bring in new nesting materials and build on top of old nests that could have parasites in them.  This also brings the nest higher to the entry hole, which is not a good idea for the safety of the nestlings.  The youngsters did make it out OK according to what I could determine in the nest you see in Photo 2 below, but there was the beginnings of the hatched blowfly eggs in the first brood.  The larvae in the nest cause harm to the nestlings if they multiply and then the nest is heavily infested with them.  The more larvae present in young nestlings’ nest material, the more chance they become anemic from losing blood to the larvae, which feed on them at night.

In the photos below, you’ll find two photos of nests:

First photo shows a clean pine needle nest.  I inspected it in detail from top to bottom — no evidence of any larvae, no larvae nest “dust” (the blowfly breaks up the nesting material to a fine dust usually found on the bottom of the nest along where the nestbox floor is located where they rest during the day), and as you can see, there is waste matter not picked up by the parents.  When I inspect nests during breeding, I always take a small spatula and lift the nest up a little to look for the dust, a sign of possible blowfly larvae.

The second photo below shows the bottom of a nest (what appeared to be a clean nest on top when I first looked) when I flipped it over, this is what I found…this detail of blowfly larvae in first brood nestings material went into my trail notes.   This is the earliest I’ve ever seen the larvae appear in nesting material along my trail.   I am thinkig the early warmer weather this Spring may be why–only theory on my part–nature’s way.   Blowflies in birds nest has been going on for centuries.  However, by installing manmade nestboxes, my goal is for the bluebirds to fledge, so I make sure as best I can that they make it successfully to bird life outside of the box.   Monitorig is fun but it’s work, too–I don’t want to monitor boxes to find sick or dead birds.  It’s best not to have a nestbox up if you don’t take care of the birds using them.

Bottom line to monitors:  Always inspect nests to know for sure what happens in the nest during breeding season.   What remains of the nest tells a story.   Never drop old nests near the nestbox, as this attracts predators to the area.   Always take it away in a plastic bag and dispose of it later. Any pristine clean nests I have I keep for emergences that could be possible later.

Anyone know what emergencies I would need a clean, used bluebird nest for?  There are two possible reasons.  I will update this post with the answers.  Leave a comment here, if you wish, if you know what the reasons are.

One more thought:  we can’t assume once the nestling fledge, they actually survive to adulthood.  Survival rate will vary on the young birds that fledge.   We can’t assume every empty nest means all young birds live a long life.   If possible, if you have a nestbox by your home, you can look for the fledglings in the area in your tree branches, put out a platform feeder with mealworms to entice the adults to feed the mealworms to the fledglings, and you can watch them for another month or so as they learn to find food for themselves.  If the youngsters don’t make it, nature rules.   It’s probably good the bluebirds try more than once per season to breed.   The chickadee generally has only one brood per year–interesting to me why some species breed 2-3 broods and others once.   The House Sparrow breeds average 5 times per season!   The start earlier and breed later each season.   The one sparrow species not native to North America breeds often!

I surmised the young birds fledged successfully in this nest. The waste matter remains behind which is normal during the fledging period. After turning this nest over and inspecting it, there was no evidence of parasites. The nest was clean on the bottom side. With gloves, I pick off the dried matter and keep the nest handy for possible emergencies later. The nest I keep is clean through and through. These are white pine needles.

The young birds made it out with evidence of matter on top side. However, when I turned it over to inspect it, this is what I found on the bottom of the nest. I tossed this out in a tied plastic bag in a waste can away from the nestbox.


  1. Hi, Elaine. I’m sorry to hear of that sad loss of babies. Truly it’s heartbreaking to see, especially when you anticipate the joy of fledging. I don’t think it was a snake, as a snake doesn’t leave remnants of their “meal” on the ground. Usually snake predation shows only the absence of the baby birds and a nest looking fairly flattened but undisturbed. It could have possibly been a raccoon, a feral cat, or an avian predator. What did the nesting material look like? Was it in disarray with some of the nesting material coming out of the entry hole, with some of it on the ground next to the nestlings’ feathers? I’ve heard PVC may not be the best ground guard to use. I suppose greasing it might help. I still think the stovepipe works the best to deter most ground predators. Hopefully, since that tragedy, you’ve had more successes in fledgings with minimal predation. Thanks for sharing your story.


  2. I’m very grateful for he detailed information and photos you include. A couple of summers ago I had a tragic loss of young bluebirds nearly ready to fledge. As I approached the nest box I was horrified to see many tiny blue feathers scattered on the lawn.
    Perhaps a snake or a raccoon was able to climb around the pvc pipe which proved to be not a reliable deterrent. The destruction of those little beauties saddened me deeply.


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