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New to nest boxes - hole size question?

Good morning all,

So for the first time, now my feeders are up and thriving, I’m going to put nest boxes up & am planning to make them this weekend using plans from rspb website, however I have a question regarding hole size...

So I read most advise a 25mm hole size for say blue tits, but then a slightly larger size of 28mm for house sparrows; both of which species we have flying around.. my question is does such a small difference in hole size really matter? Essentially i have looked and only have a 28mm hole cutter, if I was to just put two boxes up with 28mm is there a chance the blue tits may still use one or do they really know the difference between the two sizes?

Hope this isn’t a silly question aha but wanted to be sure  Slight smile

Many thanks.

  • As Rob says,  the 28mm hole will allow other birds the size of Great Tits, sparrows to also use the box;   having said this we had 13 nesting boxes up in our last woodland garden and I preferred to have most of the boxes 28mm (next size up when you buy them);    I noticed that some blue tit chicks really struggled to get out of the 25mm  hole when fledging,    If there is a way for you to make it 26mm by filing the 25mm a bit bigger then that would help limit the nest box so blue tits or coal tits get more chance of a nest box.      Because we had Great Spotted Woodpeckers in the area we had to add a metal nest hole plate and wrapped the sides and underneath of the box with quarter inch wire mesh (one piece, stapled in place) to prevent predation and it worked very very well with no losses on boxes with wire mesh protection to them.  

    Here's a photo of the nest box ....................


    Regards, Hazel 

  • Thank you very much both for your advice and support, very helpful and appreciated :)

    I think as it’s my first time & still not 100% sure on what will happen in my garden over a spring season, I’ll just put a few different sizes and see what happens :)
  • Sorry to hijack the post, but it's a related question.

    I built a nest box to replace an old rotten one. Both are essentially hollowed out 18" sections of birch trunk with a 25mm entrance hole.

    I had plenty interested the very next day from blue tits but they never actually went inside. The way it's constructed means the "walls" are approx. 18-20mm thick.

    I wonder if this is too thick and the blue tits either can't or don't want to explore further in.

    Any ideas?
  • Hi Fierymac, welcome to the forum and never think you are hijacking any thread as all participation is always welcome too. I'm not an expert so these opinions are purely my own personal thoughts so wait for other replies too. I think most importantly for nest boxes is the position of them (facing between North and East); I don't think the thickness of the box would be an issue as long as the box is based on standard size measurements, the various tit birds can be quite fussy in choosing a box so will investigate several boxes before deciding on one, you will see them tap around the sides and roof, they will also check the inside, sometimes you can hear the female flapping around inside as they further investigate; as they bring in nesting materials the female will get the nesting bits into shape by spreading her wings out, circling round the box to get the cup shape to the nest, (hence the flapping trial when they investigate the box - or that's my thought on why they do it when they inspect boxes ) ! Also depends how long the box has been in situ, a new box may take the birds a while to get used to seeing, much like when introducing new bird feeders but if in the right place for them they may encourage use. From what the experts say 25mm will be fine for blue tits and coal tits and give them more chance at using the box as larger birds like great tits and sparrows won't fine the hole big enough; all in all, if the box is in the right place, don't worry about the thickness of the walls as it shouldn't pose a problem. Tits will be very choosy about boxes so it's pretty much down to luck at the end of the day and if one blue tit or coal tit doesn't use it then maybe another one will, good luck as there is still time for boxes to be selected. Just ensure the box is well secured so it doesn't tilt or fall from a nail/hook and preferably do not place them on fences or too close to any potential dangers from predators. Height for a attaching a tit box should be about 3 metres.     


    Regards, Hazel 

  • Hi-

    Great Tits nested in my waterpump box- it was deep- similarly I've seen them in the bottom of 3 foot high posts accessed from the top.


    ps - I don't hijack threads- I hijack hides!

    For advice about Birding, Identification,field guides,  binoculars, scopes, tripods,  etc - put 'Birding Tips'   into the search box

  • seymouraves said:
    ps - I don't hijack threads- I hijack hides!

    LOL  S,      as long as you don't hijack the other birders sandwiches and flask I'm sure you will be forgiven !    


    Regards, Hazel 

  • Thanks for the quick responses.

    That does put my mind at rest a little. The old box was used successfully for about the last five years before something over the winter enlarged the hole considerably. I'm guessing woodpecker although I've never seen one in my garden. The new box is in exactly the same spot as a direct replacement and I've fitted an internal camera for the first time too. Very excited to see what results I get.

    Was just a little concerned that the blue tits weren't impressed for some reason as they scouted it out over a few hours the very next day after it was put up, but then haven't been back. This made me wonder if they wanted to use it, but were unable to for some reason.
  • Hello Firerymac, hopefully the birds will take to the box and now that you have a camera fitted, it will be exciting to follow their progress. Good luck and keep us posted.

    Beauty is in the eye of the beholder.

  • Because sparrows are renowned for invading a bluetits nests it’s important about the size of hole, even if bluetits nested in the 28mm entrance bird box sparrows would most likely kill the chicks once hatched so basically 25mm for bluetits or it’s a free for all
  • Hi can you help I have a bird box and I have noticed a blue tit trying to widen the hole would it deter the bird if I helped by making the hole slightly larger as I feel the bird might not use the box as it could take sometime for him to chipping away at the wood. Thanks