FAQ's on Monitoring for Predators, Pests, Parasites and other Problems 

Do I really need to monitor the nestbox? Can't the Bluebirds take care of themselves?
How often should I monitor?
What should I look for?
There's something that looks like a maggot in my nestbox. What is it? Will it hurt the Bluebirds?
There are wasps building nests in my nestboxes. How can I get rid of them?
There are ants in the nestbox. Will they hurt the birds? How can I prevent them from getting into the box?
What should I do about earwigs?
I think the Bluebirds have mites. Do I need to get rid of them?
When I looked in the nestbox, all the eggs (or babies) were gone/broken (or pecked)! What happened? (House sparrows)
When I looked in the nestbox, all the babies were dead! What happened?
Most of the eggs have hatched, but one or more have not. What should I do?
I'm certain my nestlings are only 14 days old, they've fledged already, but they can't fly. What should I do?
Do Bluebirds get West Nile Virus?
Is there any danger of contracting Hanta Virus from a nestbox?

Do I really need to monitor the nestbox? Can't the Bluebirds take care of themselves?
Regular nestbox monitoring will alert you to a host of problems that you can take steps to correct, possibly saving a nestful of eggs or nestlings from an unnecessary, premature death. It will also allow you to look for signs of another possible predator -- a two-legged one. In recent years, vandalism of Bluebird nestboxes has become a problem in some areas, causing some monitors to place locks on their nestboxes, and take other preventive steps in high-risk areas.

How often should I monitor?
Opinion sometimes varies on frequency of monitoring. Those who monitor extensive Bluebird trails are usually can't monitor as frequently as those who have nestboxes on their own property. Most Bluebirds in backyard nestboxes will readily become accustomed to daily checks, however, and many people feel it is best to monitor frequently in order to catch signs of any problems early on. Some Bluebirds seem to tolerate daily monitoring. Bluebirders with extensive trails usually monitor weekly.

What should I look for?
You can learn to recognize whether the nest in your nestbox is that of a Bluebird or of another species. (See FAQ's on Competing Species for a chart depicting the nests of several common cavity-nesters) Also, by recording when egg-laying commences, and when the last egg is laid, you will be able to calculate the approximate time when hatching should take place (13-14 days after last egg is laid). Checking on the eggs during hatching will alert you to problems any of the chicks may be having with hatching. You will also then be able to determine approximately when fledging may occur (17-18 days after hatching); also you will be able to calculate when you should stop monitoring the nestbox to prevent premature fledging (Day 12 after hatching). You will also be looking for signs of trouble, some of which are listed in the questions below.

There's something that looks like a maggot in my nestbox. What is it? Will it hurt the Bluebirds?
The larvae of the Blowfly is a bloodsucking parasite that weakens or kills nestling Bluebirds.

Nests that have been infested with Blowfly should be replaced. It is a good idea to keep a spare nest on hand for such emergencies. If you don't have a saved nest, then dried lawn clippings can be placed in the nestbox in a shape roughly approximating the original nest's shape. Have handy a small box or dish to place the nestlings in, remove the old nest, and insert the new one, and replace the nestlings. If you see any larvae attached to the nestlings, they should be removed gently, so as not to hurt the nestlings, using your fingers or tweezers. Work quickly but carefully.

There are ants in the nestbox. Will they hurt the birds? How can I prevent them from getting into the box?
Certain types of ants can sometimes infest a nest and cause problems, most notably Fire Ants. These have been known to sting and kill Bluebird nestlings. Some people have used a ring of axle grease smeared all the way around the mounting post in order to discourage ants from climbing the post. This can be effective, but in hot weather the grease will run and cease to be effective. Another solution which some people have found very effective is Tanglefoot, available at hardware stores (such as Aubuchon) or online at Forestry Suppliers, Inc. The method involves applying a ring of garden tape around the mounting post, then smearing the Tanglefoot to the tape, being careful not to get it on your clothing, as it is sticky and messy. For a detailed discussion of ants in Bluebird nestboxes see Ant Discussion on Bluebird-L.

What should I do about earwigs?
While rather disgusting-looking, earwigs are not known to be harmful to Bluebirds, either the adults or the young. They are vegetarians. However, if their presence makes you hesitant to monitor the nestbox, this could be a problem. Do not, however, use any pesticides in the nestbox in order to get rid of the earwigs. An extensive discussion on the topic of earwigs can be found here: Earwig Discussion on Bluebird-L

I think the Bluebirds have mites. Do I need to get rid of them?
Mites are not usually a problem for Bluebirds. You may see some mites in the nestbox, but unless there are an extraordinary number of them, you do not need to do anything about them until the nestlings fledge. Cleaning the nestbox after fledging should get rid of the mites.

When I looked in the nestbox, all the eggs (or babies) were gone (or broken)! What happened?
If the eggs, chicks or female are gone, the nest being partly pulled out of the hole, or you observe some remains or feathers on the ground near the box, or scratch marks near the entrance hole, you should suspect predation by a cat, raccoon, possum, or squirrel. The best defense against this kind of predation is the proper nestbox mounting on a slick metal pole with a predator baffle. A bird-feeder baffle meant to deter squirrels is not sufficient to deter a raccoon. Nestboxes should not be mounted on fence posts or trees, because these cannot be baffled against predators. Please see the FAQ's on Bluebird Housing for more detailed information on nestbox placement, mounting and baffling. Another possibility is predation by another bird, such as a Grackle, Bluejay or Starling. In cases where predation persists after the installation of a baffle on the mounting post, consider installing an additional predator guard around the nestbox opening, such as the Noel Predator Guard. If the eggs appear to have been pierced or broken, or the babies pecked, two possibilities would be House Sparrows or House Wrens.  Please see the Competitors FAQ's for further information on dealing with these species. The House Sparrow is a non-native species classified as a pest, and must be dealt with aggressively. House Wrens are native songbirds, and protected under law; however there are steps that can be taken to discourage them from competing with Bluebirds for nesting sites.

If all the eggs or chicks are gone, but the nest itself has not been disturbed, and you observe no signs of scratch or claw marks on the nestbox, you might suspect predation by a snake. Snakes are one of the primary reason why a nestbox should never be mounted in a tree, or on the side of any structure, no matter how high. Snakes can climb anything!

The Stovepipe Predator Baffle is the best known protection against snakes. If you live in an area known to be inhabited by snakes, you may also need the Harry Krueger Snake Trap to offer the best level of protection possible for your Bluebirds.

When I looked in the nestbox, all the babies were dead! What happened?

Is the nest wet? Has the weather been unseasonably cold?  Most likely the nestlings died of hypothermia. Nestboxes should be more closely monitored in cold, wet weather to prevent this tragedy.  Duct tape can be used to cover the ventilation holes, making the nest less susceptible to the cold. If the nest has already gotten wet, it can be replaced with a dry nest (or dry grass clippings, if no spare nest is available). If any nestlings are dead in the nest, remove them, and put live nestlings back in.

Is the nest dry? The nestlings bloated, but unmarked? No signs of pecking, no scratch marks on the box? Is there no evidence of Blowfly infestation? Suspect poisoning by pesticides/herbicides. Nestboxes should not be mounted in areas where pesticides will be used. If you haven't used any pesticides or herbicides, is it possible that a neighbor has? If so, then move the box to an area where no pesticides will be used.

Most of the eggs have hatched, but one or more have not. What should I do?
That depends on how long it has been since the other eggs hatched. It is not absolutely necessary to remove unhatched eggs from the nest. Sometimes the parents will push an undeveloped egg out of the nest anyway. However, there is a possibility that if the egg breaks open, the smell could attract a predator. Also, in very hot weather an undeveloped egg may explode and foul the nest. A good rule of thumb is to wait until the third morning after the last egg hatches (For example, if all the other eggs hatched on Monday, you would wait until Thursday morning); then you can safely remove the unhatched eggs from the nest and "candle" them to see if you can detect anything other than just liquid inside.

If one or more of the eggs hatches 48 hours or more after the rest, you should be prepared for the fact that those nestlings may not be able to fly when the others fledge. See the next question for information on what to do in this case.

I'm certain my nestlings are only 14 days old, they've fledged already, but they can't fly. What should I do?
Your nestlings may have been frightened into fledging early by an attempt from a predator. Observe the fledglings closely. If they are actually unable to fly after several hours, then you may have to capture them, and place them back in the nestbox with a 1" hole reducer added. This makes the opening to the nestbox too small for the nestlings to get out, but will allow the adults to feed them. The hole reducer should be removed when it would have been time for the babies to fledge.

If only one of the nestlings appears unable to fly, but the rest have made it to nearby trees, you may have miscalculated the time for fledging, or there may be one nestling that hatched later than the others. Again, observe the fledgling carefully. Sometimes it will take longer for the smallest fledgling, or one that was a little late hatching, to be able to fly. If it will be dark soon, and the fledgling still has not been able to fly, you may need to place it back in the nestbox overnight, with a 1" hole reducer added. The reducer may be removed the following day, when you will be there to observe whether or not the fledgling is then able to fly. 

Do Bluebirds get West Nile Virus?
Some states have reported finding Bluebirds testing positive for West Nile virus. The most important measure in preventing the spread of West Nile in both humans and birds is mosquito control. This can be accomplished by removing all sources of standing water, cleaning and refilling birdbaths daily.

Is there any danger of contracting Hanta Virus from a nestbox?
The only way of contracting Hanta virus from a nestbox is if the box were being inhabited by a rodent. When opening nestboxes for inspection in the spring, do so carefully, and if you find that a rodent has taken possession of it over the winter, be very careful that in cleaning the nestbox you do not breathe in any of the nesting material. Information on Hanta Virus can be found here: CDC