Are Swift Towers a good idea?

The short answer to this question is that we don't know yet. Although many towers have been erected, most of them so far have no Swifts with a few with a pair or 2. 

The Cambridge Swift Tower, with 100 boxes was erected in 2011 at considerable cost. Despite much playing of attraction calls every year, the first occupants did not enter the boxes until 2014, when we believe just one pair settled. In 2017 there were 3 pairs, which have increased to 4 in 2018.

Our experience of a tower with 11 nest boxes erected in 2013 at Trumpington Community Orchard, Cambridge resulted in just 1 pair in the first year, which has returned every year increasing to 2 pairs in 2018.

We know of very few, if any, other occupied towers in the UK. Similar low occupancy rates are also experienced in Holland. By 2019, 476 nest chambers in Dutch towers held just 13 pairs of Swifts.
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Swift Towers are relatively expensive, and can be very expensive. They are usually nowhere near mains power, so there is the added complication and cost of installing and maintaining a solar power/battery driven system for attraction calls.

Having said all this, a successful Swift Tower can provide a great PR opportunity for Swifts. Even the Cambridge Tower, with its 4 pairs now, will provide a spectacle most summer days of between 3 and a dozen Swifts hurtling around Logan's Meadow.

Up to 20 Swifts can be seen screaming around Trumpington Community Orchard, even though there are only 2 pairs in residence.

There are successful Swift Towers in Poland, where there are far more Swifts and probably far more destruction of Swift nest sites, so lots of desperate Swifts looking for somewhere to settle.

We do not know the reason for such slow progress in the UK. It could be that Swifts 'know' what they are looking for - perhaps something similar to where they have seen other Swifts breeding and they just don't recognise a structure up on a pole as a nesting opportunity. It could just be a matter of time.

It could be that most Swift Towers are in isolated locations, not in the urban setting with which they are familiar.

It is thought that it is better to have Swift nest boxes spaced out somewhat, say at least a metre between them. There is not the opportunity to do this in a small structure. The same issue might arise with colony boxes on buildings. Indeed 100% occupancy in a colony box is rare, the best we have managed is 6 in a 9-box cabinet and 7 in another 9-box cabinet. We have also had 4 in a 4-box cabinet.

The last thing we would wish to do is to discourage anyone keen on putting up a Swift Tower, but it is important to set expectations at the right level. It should be regarded as a 3 to 5 year project, with a willingness to maintain attraction calls every summer. Unlike many nest boxing projects, you don't just put up a tower and forget about it.

If there are other opportunities on buildings in the same location, then, maybe, they should be considered first. Another council project in Cambridge was the erection of 71 Swift boxes on Edgecombe flats in 2010, costing a small fraction of the cost of the Cambridge Swift Tower. By 2016 there were 12 pairs of Swifts and 25 pairs of House Sparrows.

Churches are a particularly good opportunity, the tower is already there. Swift boxes in belfries in church towers can be very successful (see here). There are 30,000 Anglican churches in the country!
Updates since the above was written:
(Update 2019: Brian Cahalane reports 8 occupied boxes with 7 breeding pairs in his 12-chamber Stoneyford tower in Crumlin).
(Update 2020: All 12 chambers were occupied in Brian's tower)
(Update 2020: An inspection of Kingsworthy swift tower in Hampshire revealed 7 out of 20 chambers occupied)
(Update 2020: the Cambridge Swift Tower holds 3 pairs this year, down from 4 in 2019) 
(Update 2020: the Trumpington Community Orchard swift tower has 3 pairs of swifts this year, and House Sparrows have moved in for the winter) 
(Update 2020: Edgecomb flats, mentioned above, had at least 34 pairs of Swifts and many House sparrows this year) 
(Update 2021: the Cambridge Swift Tower holds 6 pairs)
(Update 2022:  Trumpington Community Orchard swift tower has 5 pairs, some House Sparrows and even bats)

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