In cities around the world, anti-bird spikes are used to protect statues and balconies from unwanted birds - but now, it appears the birds are getting their own back.

Dutch researchers have found that some birds use the spikes as weapons around their nests - using them to keep pests away in the same way that humans do.
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He says the spikes were pointing outwards, creating a perfect armour around the nest.

A trip to the hospital roof confirmed it - about 50m (164 ft) of anti-bird spike strips had been ripped off the building - all that remained was the trail of glue.

https://www.bbc.co.uk/news/science-environment-66163943

Bird nests made from anti-bird spikes

The use of man-made, even sharp materials for nest building in birds is well known.
The first report of a crow’s nest made of barbed wire dates back to 1933, and recent
(news) reports document the use of e.g. nails, screws, and drug users’ syringes in
avian architecture. Here we report the first well-documented study on nests of carrion
crow Corvus corone and Eurasian magpie Pica pica that almost entirely consist of
material that is meant to deter birds: anti-bird spikes. Carrion crows in Rotterdam (The
Netherlands) and Eurasian magpies in Enschede (The Netherlands), Antwerp (Bel-
gium), and Glasgow (Scotland) tear entire strips with sharp metal pins off buildings
and use them as nesting material. Two anti-bird spike nests, now in the collections of
Natural History Museum Rotterdam (crow) and Naturalis Biodiversity Center (mag-
pie), were analyzed for composition and structure. Magpies may use the anti-bird
spikes not just as ordinary nest material, but specific placement in the dome, over-
arching the nest, hints at functional use. The anti-bird spikes may be used by birds in
the same way as they were intended to be used by humans: to ward off (other) birds.
Crows, for example, are known to prey on magpie eggs and offspring and the spe-
cific choice of this sharp material could benefit nest defense, for which magpies may
normally rely on thorny branches. Other magpie domes observed were constructed
with barbed wire and knitting needles. In the Anthropocene, now that living biomass
is outweighed by anthropogenic mass, alternative nesting materials are increasingly
being adopted by urban birds. With birds even using bird deterring materials like
anti-bird spikes as nesting material, anything may become part of a bird’s nest.

https://www.hetnatuurhistorisch.nl/fileadmin/user_upload/documents-nmr/Publicaties/Deinsea/Deinsea_21/Deinsea_21_17_25_2023_Hiemstra_et_al.pdf