Updated: Sep 18, 2018
The Economist reports on the new paper in the journal Biological Conservation by Dr. Piotr Skorka of the Polish Academy of Sciences: https://www.economist.com/science-and-technology/2018/09/15/churches-help-to-preserve-bird-biodiversity.
Summary: Dr. Skorka and his team conducted a painstaking field analysis of hundreds of buildings on the southern Polish countryside, documenting the numbers and species of birds as well as the physical dimensions and characteristics of the buildings that these birds called home. "They then used a statistical analysis that included six measures of bird diversity to gauge the effects of different building configurations on the number of species, and the abundance of each."
Their results indicated that church buildings host the largest and most diverse populations of birds amongst common rural buildings. Churches "are complex structures, with lots of nooks, crannies, rafters, holes and towers to sleep and nest in. Churchyards also often host a diverse collection of greenery and ancient trees."
Moreoever, they found that "[t]he older a church, the greater its levels of ornithological diversity," and that "[t]he taller a building, the more species there were." "Separate bell towers also boosted numbers." "The team frequently observed birds in and around these lofty structures, well out of the reach of predators such as cats."