Do birdhouses need drainage
If there's no drainage featured on your birdhouse, then its a design flaw that needs to be corrected by you, or else your nesting birds will suffer.
Birdhouses do need drainage holes in order for any moisture to run out at the bottom of the box. Rain water can enter a birdhouse via its entrance hole or seep in unsealed gaps on joints of the birdhouse. Don't do anything to cover these holes but if you need to, you can drill extra drainage holes on the base.
What must be one of the most essential features of a birdhouse, is a set of several drilled holes located on the base.
Rain water or a buildup of moisture inside the birdhouse will want to drop, to which it will end up exiting the drainage holes just as it should.
For rain to enter a birdhouse is more a cause of sideways, or what is known as horizontal rain; with the largest opening belonging to the birdhouse entrance hole creating an access point for wet weather.
What is remarkable about birdhouse drainage holes is that the act as vital ventilation holes - thus drainage holes can allow moisture to escape while allowing air to pass through the interior of the box.
All this adds to a more comfortable birdhouse for breeding birds in spring and summer, or roasting birds in autumn through wintertime.
For birdhouses to go without these simple predrilled holes, moisture can build up inside creating squalid conditions, with pools of water which can lead to young birds drowning, or parents abandoning there nest.
Birdhouses do need drainage
In order for any type of birdhouse to comfortably house living birds, those birds must be able to live in a wooden box design to hold eggs and their young safely.
Birdhouses therefore do need drainage because the possibility of water entering the birdhouse is a serious one with a guarantee it will, so damp must be allowed to escape.
Rain water is the biggest issue, with sideways wind throwing in rain water in through the entrance hole, but any birdhouse design can't be 100% guaranteed waterproof. Rain water ending up in the box then is a very real concern.
Here is where drainage holes are drilled into the base of any type of bird house, whatever bird species its intended for.
Good news is, several drilled out holes on the base of a birdhouse cannot harm or be a nuisance at all to breeding birds, or their young.
Simply put, drainage holes are there to allow any potential build up of water to drop out through the base.
Birdhouses do need drainage which also acts as vital ventilation holes.
Drainage, air vent combination
Drainage in a birdhouse is a vital component of any birdhouse, thus is a requirement of a birdhouse and sign of a quality build.
In addition, drainage holes well very practical, they also act as ways for fresh air to pass through the wooden birdhouse.
Birdhouses can indeed get a little hot in spring and summer, but similarly can see a build up of condensation in the winter months; thus many holes are needed to keep the box well ventilated for breeding birds in spring or roasting birds in winter.
Up to four holes are normally drilled on the base of the birdhouse, and well this is vital for water to run off, its not enough for proper ventilation.
On the plus side the birdhouse entrance hole acts as a way for air to pass through the box via the base or entrance hole - creating comfortable ventilation.
Drainage holes with a vent combination can also be helped with use of often unintended gaps in the construction of the birdhouse; normally on the roof section or in the corners where the birdhouse wall are joined with nails or screws.
Never attempt to seal a birdhouse because these gaps can be critical to a birds health.
Moisture build up possible
Moisture building up inside a birdhouse is a possibility through condensation, with a pair of breeding birds, plus eggs or their young raising the temperature, which is especially true in summertime.
Its therefore possible moisture can be created out of thin air, with the likelihood of the birdhouse interior getting damp on the interior walls or bottom panel of wood.
I believe it to be very unlikely a birdhouse getting too damp for birds too live in, but this dampness must not only be allowed to drain out via the holes on the base, but ventilation can assist in drying up any dampness.
Well treated birdhouses in preserve can create a sort of waterproof sheen, which results in water becoming visible through running drips, whilst unable to soak into wood that's been treated.
I won't discourage you from not painting, treating or staining the birdhouse interior if necessary, but do consider a non-toxic treatment only to prevent the dampness not drying probably, thus creating a toxic consumption which the young would ingest.
Do your best to keep the birdhouse in optimal condition, with the need to drill out your drainage holes if more is needed to at least help with better ventilation.
With that in mind, never drill holes on the sides or top of the birdhouse or water would easily enter the box.
Avoid blocking holes
Unfortunately, if you forget about natural nesting material added to the birdhouse when birds setup their home, the possibility of these drainage holes getting covered is real.
Nesting material begins with a soft cushion that can be the difference between holes being covered up or not. But as this material, and the proceeding nesting material adding on top is often soft, water or moisture should still be able to drop to the base.
On your parts its vital to never add material to a birdhouse if you cannot avoid covering up the number of holes drilled out on the base.
Wood chippings is a possible source of blockages of course, so understand this can get quite dense and compact, so its possible holes can be blocked.
Raised grills to stop nesting material touching the base is vital in Bluebird birdhouses, so why not add your own to a birdhouse intended for other bird species.
Result of that is the nesting material, be it your own material or brought into the box by the female or male bird - cannot block drainage holes.
Of course the bonus being is this helps to keep the air flowing if ventilation holes are not covered up.
To conclude
Its vital any birdhouse you intend to put up in your yard features a number of predrilled holes located on the base of the birdhouse only.
If you bought the birdhouse be sure holes are included, but don't despair if they are not featured as you can drill out your own, or have a DIY savvy person do it for you.
Draining holes must be located on the base as its where rain can only drop down to.
Bonus of 4 to 6 drilled holes measuring up to half-inch each is that it becomes a way for the birdhouse to receive plenty of ventilation.
Its therefore vital these holes are not blocked as they act as both drainage and air ventilation.
Rain water can pass into a birdhouse via the open entrance hole, including through gaps not sealed up probably. Don't ever attempt to seal birdhouse joints on the side probably, as it all helps to keep the birdhouse cool in summer.
Moisture does happen through condensation even in winter, so the predrilled drainage hole, air vent hole combination and the entrance hole with any gaps help maintain a comfortable box for birds to occupy for several weeks.
Never add your own wood chippings to a birdhouse that would see the drainage holes get blocked up, as natural nesting material brought in by birds won't help the situation.
Birdhouses do need drainage to allow rain water and dampness to escape.
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