Nest type and other species traits
We extracted species-level nest information from the website Birds of
the World (BW) (Billerman et al. 2020) and Beruldsen (1980). We
searched for information on all species of songbirds (suborder Passeri),
following the taxonomy from Jetz et al. phylogenies (4685 species), with
manual resolution of taxonomic names between BW and Jetz et al. For each
species we collected information on nest type, which was classified into
two broad categories: domed (defined as having a side entrance or a
roof, or as being globular) or open (defined as a cup or a platform, or
cases where there is only a mat of leaves, or vegetable material).
Additionally, we recorded whether the species was a cavity nester or
not, whether the species built both domed and open nests, or whether the
nest was described as a pouch. This information was collected because in
some species (e.g. Icteridae) nests are so elongated that they
effectively look more liked domed than open nests. With these variables
we generated fine scale classifications (six categories: open, domed,
open nest inside cavity, domed nest in cavity, both types and pouch),
and this classification was used in initial analyses. Based on results,
we further merged data into broader categories, to increase sample size
in each category. The main nest categories used were: domed, open or
cavity nesters, or just domed vs. open nests (further explained in
statistical analyses). Our final dataset included 3175 species with nest
information (68% of all Passeri).
Given that response variables like range size can be associated with
body size and species latitude, we also collected information on body
size for each of the species from Wilman et al. (2014) and
information on the mean latitude from their distribution range from
Sheard et al. (2020), to control for the effects of these
variables. As a measure of colonisation of novel habitats we also
collated information of species’ presence in urban environments (data
from IUCN, collated in Ducatez et al. (2020). This was recorded
as 1 (presence) or 0 (no presence).
To test whether there are differences in the costs of nest building
across nest types, we used the time spent building nests as proxy of the
energetic cost. We searched for information on the average number of
days that takes a species to construct a nest, if a range was given, we
used the middle of the range as representative for the species. We also
collected information on who builds the nest (females, males or both),
given this could affect the time of nest construction.