This video from Britain says about itself:
Blue Tit nest box – through the looking glass
13 July 2014
Nest box cameras are brilliant, but nothing beats watching the real thing LIVE. So I came up with the idea of making a backless nest box and sticking it to a window… and it worked! Here is some footage I recorded of the adults feeding almost fledged young.
NB. i made sure to cover up the window (with a bit of card), during the incubation stage, so as not to disturb the bird. once the chcks were well hatched i removed the card in stages, and the birds got used to it.
From the Cornell Lab of Ornithology in the USA, from their NestWatch eNewsletter, July 2015:
Should You Try a Window-View Nest Box?
Stick-on window-view nest boxes are the latest trend in birdhouses, but is this a trend that will really stick around? You may be wondering if a window-view nest box is a smart choice for the birds or for you. No long-term studies have been done on these products, but this spring NestWatch staff placed four different models on our own windows to find out if birds would use them. Below are the results of our limited field trial.
Three out of the four window nest boxes have stayed in place since the spring, plenty of time for a full nesting cycle or even two. Unfortunately, one box fell down about six weeks in, which would have been long enough for a bird to build a nest and lay eggs. It should be noted that the box which fell was the only one that did not have overhead cover.
As for nests, no birds have nested in any of our boxes to date. All are as clean as the day they were installed; not a single feather exists as evidence that they were even inspected. Staff field testers also have “traditional” nest boxes mounted around our properties which were used by House Wren, Carolina Wren, Black-capped Chickadee, Eastern Bluebird, Tree Swallow, and Downy Woodpecker (roosting only). Perhaps if these birds had no other options, they would have used the window boxes, but with other choices available, they did not.
Does our field trial mean that these boxes aren’t appropriate? Not necessarily. Some birds, like people, are just bolder than others and may take to the boxes right away. Cissy Berner reports that Carolina Wrens have used the nest box … every year since 2013. Under certain circumstances, they may provide a needed cavity where no other options exist. For example, if you are noticing birds trying to nest in unsafe nooks, these boxes could provide alternative sites. But if you have the space, you can’t go wrong with a pole-mounted traditional box equipped with a predator guard. Alternatively, a hanging-style model works well in small spaces.
If you try it, choose a model that has the features of a good birdhouse, and follow the manufacturer’s instructions for mounting. Improper mounting can result in the box falling and possibly injuring birds, eggs, or even people. If you have experience with these boxes, good or bad, please tell us. Your diverse insights can only help us give better guidance in the future and maybe even drive better product design.