Do all birdhouses need a perch
Perches that are mounted to the front of a birdhouse have always been a hot topic in birdhouse design, but I can say for certain success comes with no perch attached.
Birdhouses for your small to medium size common backyard birds don't need a perch, as much as a perch isn't needed outside their tree cavity, to which is where birds normally nest in the wild. Some birds of prey like the Barn or Barred Owl can benefit with a platform, only its safer to remove the perch for others.
Never is a perch of any kind needed to be mounted to the front of a birdhouse, made to be put up on a wooden post or a tree where a birdhouse is commonly mounted on.
Where you can get away with a perch - or what will appear more like a platform - is one mounted to a wooden birdhouse intended for Owls. Even then, Owls can continue to use a birdhouse without a perch as they'd use the entrance hole for perching.
However, let's not forget Owls are birds of prey who can benefit with a platform, which will be used as a perch for when Owls or Kestrels seek out prey on the ground.
When it comes to Chickadees, House Finches or even Woodpeckers, these more common backyard birds will never, ever need a perch.
So that means if your birdhouse doesn't have a perch in place already, you won't have to be concerned about mounting one on to see any kind of success. In no way can a birdhouse see success with a perch... no more than a birdhouse without a perch.
Perches only go towards assisting predatory birds like Woodpeckers to enter inside the box to steel eggs or kill the young. And that includes squirrels or raccoon's who can also do a real harm to the birdhouse occupants.
If indeed a perch is mounted to your bird house but it can't be removed for some reason or another; which can be a brightly painted perch that doesn't match the bird house - then you would be better off painting the perch to at least keep it discreet as possible.
NO perch is needed at all
When it relates to your common backyard birdhouse birds, then the answer is no; never will any kind of perch be needed for a birdhouse intended for backyard birds.
Perches can be present of which, it can stay if it doesn't only exist to accommodate other, larger nuisance birds or predatory wildlife. Remember that as a perch can only go towards making life hard for the occupants.
Of course the longer the perch is the more problematic it will become as larger and more dangerous natural predators to birds can use it - in hope of grabbing eggs or killing the parents.
What you must remember is ALL common backyard birds are fully capable of clinging or perching at an awkward angle on the side of a wooden birdhouse with absolutely no issues at all.
This technique is ingrained in their natural behavior thus are evolved to cling onto the side of a vertical surface - with a rugged surface rather than super smooth surface- which cab help wild birds cling of course.
With practical yet recommended birdhouses made in wood, all birds who enter and exit the box will have no difficulty in doing so.
Birdhouses do not need a perch for all backyard birds, but that isn't the case when talking about common birds of prey.
Safer to chop off perch
To be honest with you, even if your birdhouse comes with a perch attached to the front, the safe thing to do will be to remove the perch - as birdhouses for small birds shouldn't have a perch, because as I've mentioned, it only assists predators.
Likely style of perch affixed to a birdhouse intended for those belonging to common backyard birds will be a long wooden dowel, which doesn't belong at all.
With that in mind, to be sure we're on the same page, here are bird species who shouldn't have a perch on their house; and that includes Bluebirds shouldn't have a perch at all nor should those made for Wren's, Sparrows, Chickadees, Starlings, House Finches, Woodpeckers and many others.
Think about it for a moment, when birds nest in a cavity within a tree trunk somewhere in the wild, you wouldn't expect a perfectly developed perch sitting outside their entrance hole, would you.
No you certainly wouldn't, so make life easy on your birdhouse birds because a box without a perch, is only going to be more practical, as well as safe.
Take it from nature with any kind of birdhouse put up in your yard never needing a perch, with a perch never needed in a natural tree bird nest.
If a perch exists on your wooden birdhouse I can only recommend you chop, saw or break it off, in order for the house to become a safer living area for wild birds.
Perch can be present for others
All birdhouses don't need a perch but those that do probably relate to birds of prey, of which wouldn't refer to most of use.
Large birds like Owls or Kestrels can have a perch mounted on the outside of their bigger birdhouse entry hole, as large birds like this can do with some assistance for entering and exiting the box.
In fact, birds of prey will perch outside their birdhouse at night, with Owls especially using their incredible binocular vision to pick out rodents on the ground.
Owls or Kestrels will use what is likely to be a platform rather than a rounded rod or dowel to perch - as it can hold their additional weight - plus any pray brought back to the birdhouse
Certainly the American Kestrel can go without a perch, whereas most Owls will need some kind of perch
While the Barn and Barred Owl would appreciate any kind of perch, their cousins in the Northern Saw-Whet and Eastern Screech Owl - can use a birdhouse put up on a tree, without a potential nuisance perch being in their way.
Summary
Its not true as not all birdhouses need a perch, only it can relate to a few species with most of them being Owls.
When it comes to your common birdhouse bird, then I can assure you they don't need a perch whatsoever.
Smaller backyard birds like Titmouse to Woodpeckers have always nested in old tree cavities without a perch in place when in the wild - so where a perch becomes relevant in your backyard, is never.
Birds will never need a perch mounted to the front of the birdhouse because birds can cling or perch at any angle, without a perch in place.
Perches will get used but in reality it will only become a stepping stone by cats, larger nuisance birds or wildlife to access the birdhouse interior.
What birdhouses can do with a perch will belong specifically to the Barred and Barn Owl, with others happy to go without.
If a perch does exist on your current birdhouse then I can only advise you to chop it off with a saw, as soon as you possibly can.