Thursday 3 August 2017

A successful Polish Swift tower design

Although many Swift towers have been erected, few have more than a pair or 2 of Swifts. We were therefore impressed by this design, the "Jerzykowniki” tower, which has been erected in 13 locations in Poland, 5 of which have acquired new occupants in the first year or two.

This story was sent to us by Katarzyna (Kasia) Szczypa

The tower “Jerzykowniki”
Lidzbark Warmiński (Warmia-Masuria region)
Following the erection of a stork platform, which, not unexpectedly, had failed to attract any storks to central Warsaw, the Stork Nature Society decided instead to design a tower suitable for Swifts, House Sparrows, Starlings and Tits.

All of the photos in this post are taken by Adam Tarłowski (ornithologist and designer of the tower from, and Mariusz Grzeniewski (ornithologist from who have been protecting Swifts for 10 years.

A total of 13 “Jerzykowniki” Swifts towers have been installed since 2014 in Poland. Seven towers in Warsaw and six in other locations were set up in areas such as parks and among blocks of flats. Mariusz and Adam together with the Stork Nature Society control 11 of them.

The tower “Jerzykowniki”
in Warsaw (Bielany district)
Successful breeding pairs were found in 5 towers. One of them, 2 years after installation, had 4 breeding pairs in 2016 and 6 pairs in 2017. This was achieved without playing attraction calls!

The remaining 4 towers had one breeding pair each in 2016. The tower is not only effective, it is also an attractive design.

Each tower has 24 nest chambers arranged in a hexagonal structure with 6 chambers on 4 levels. Various hole shapes and sizes are included ranging from sizes suitable for tits to sparrows and starlings. A simple narrow door on each of the 6 sections allows for inspection and maintenance.

The drawing below, by Adam Tarłowski, gives indications of overall dimensions.

Footnote: Jerzykowo is a Polish town.

An adult Swift and 2 Swift chicks on top of a House Sparrows nest

Wednesday 2 August 2017

Thoughts on concave design

It is not unusual for eggs to move out of Swifts' nests. Sometimes an adult will deliberately pick up an egg and dump it outside the box. However, other times it seems to be accidental as some Swifts have been observed on webcams moving eggs out, either by shuffling or with the head while adjusting nesting material.

We have already shown conclusively that Swifts prefer nest boxes with a concave (here). Although Swifts appear to be most comfortable as they snuggle down in a deep concave, are concaves made by a spherical scoop, with a sloping periphery the best shape?

These thoughts were prompted when swifts in one of my daughter's nest boxes with a concave scoop 85mm diameter and 22mm deep, 2 eggs were moved out in 2016 and then 5 eggs in 2017.

We all know that Swifts are individuals and maybe some Swifts are more clumsy than others, but when this particular concave was replaced by one with a vertical periphery and a shallow depression in the bottom, they went on to incubate the 5th and 6th eggs, hatching one of them (which, at the time of writing is doing well). The replacement concave extended for the whole width of the box.

A discussion on SLN yielded the following experiences:

David Makin had a similar experience to the above with Swifts displacing 4 eggs in 2016 and another 4 in 2017 from a concave 22mm deep, before finally laying a replacement clutch of 2 eggs which they went on to hatch.

Brian Cahalane makes his concaves out of a 30mm thick piece of wood in which he cuts a 100mm diameter hole. The bottom is therefore flat, but Brian paints the bottom with glue and then throws a handful of feathers in. Anything with a flat bottom is not going to cause the eggs to move to the centre, but the feathers may well provide the necessary shape for this. Brian never gets eggs displaced from these concaves, but he has had a small number of eggs displaced from shallower concaves over the years.

Mark Glanville has this experience:
"My scoops are not really cups but made from off-cuts to fit exactly into the box with no gaps between them and the sides. Most of my boxes are 8" wide so I tend to use a piece of wood 8" by 8". They are all homemade with 100mm diameters and I use wood filler to make the edges of the concave smooth. I aim to have at least 2" clearance between the concave and the sides/back of the box. I am sure that having it all on the same level has helped reduce the number of eggs/young being flicked out on changeover duties. The concave depth varies between 12mm and 22mm. No reason for this other than I use the same wood left over from building the box. One thing I do add on the 12mm scoops is a bead of mastic (2-3mm high) around the rim of the concave to give it a bit of a lip. All my scoops are lined with feathers with extra being added around the rim. 

Louise Bentley comments that the Swifts do look most comfortable in her concave, but still they pushed one egg out on their first breeding attempt, which hatched after being replaced by Louise.

Tanya & Edmund Hoare agree with Mark and suggest that more horizontal space around the concave could help, and suggest that a concave in the floor of the box could be a solution.

To add to the above, I have measured a number of natural nests. They are about 85mm diameter, and depth up to ~20mm, and usually the periphery is a wall of feathers. It is not unusual to find a natural nest wedged into a corner or side of the box. There is little in the way of any horizontal surface outside the periphery. Some nests can be quite high.

So what does one conclude about this?

Concave scoop tool
The diameter of a Swift's egg is ~16mm, so any "cliff" over about 8mm should keep the eggs in. 

Therefore I would conclude that a concave with a vertical periphery at least 10mm high (say) and some sort of depression in the bottom is ideal. The depression can either be achieved by machining the right shape (suitable for a product) or by gluing feathers in the bottom (suitable for the DIY enthusiast).
Concave made of Kingspan wall insulation

Whether sticking feathers to a concave is worth doing is not known, the experiments have not been done, but certainly feathers scattered in the nest box are readily used by Swifts.

Some horizontal surface around the concave may be a good idea.

As a next step I have had a tool made to make vertically sided shallow scoop concaves with a diameter of 85mm.

The pictures above show the tool and a prototype concave made out of insulation (yes, it is highly inflammable) coated with PVA glue to resist Great Tits and House Sparrows. 

The attraction of this material is that it is very easy to machine.

These concaves are so light that they do need sticking down.

I have had a number of concaves made of this material in boxes over the winter, and none have been damaged so far. The next step is to see what Swifts think of them.

[UPDATE June 2018 - we found 3 concaves heavily damaged by Great Tits - so this idea is now abandoned]

Update January 2018
Using a sheet of 12mm soft fibreboard, cut into 12cm squares - one can get 200 squares out of a 2440 x 1220 sheet costing about £14. This will make 100 concaves - so 14p per concave.

We used an 85mm hole saw to cut a hole in one square, then glued it to a second square.
Then scoop out the second square with the tool described above.

As most of the material is removed by the hole saw, there is far less dust.
The result looks very good - vertical sides to keep the eggs in and a concave bottom to keep the eggs in the middle.

The finished product is coated in PVA glue to deter Great Tits

85mm hole saw, concave and scoop tool