Global incidence of female birdsong is predicted by territoriality and biparental care in songbirds

This is a dataset of 1309 songbird (passeri) species for phylogenetic comparative analysis of female song incidence, elaboration, and length, and associated code and phylogenetic trees to recreate the analyses in the associated publication.
Ordinal scales are based on published species accounts, primarily Birds of the World (see publication for full list and description of all song variables).
Song variables are provided in both nominal and numerical ordinal formats.
We scored three aspects of female song: (1) song incidence, (2) song quality or elaboration, and (3) song length.
For each of these song variables, headers are listed in parentheses, with nomial headings listed first and numerical ordial headings listed second.
Song incidence (DimorphSongOccurrence; DimorphSongOcc_ord; "occ") – How often or to what extent do females sing compared to males? 0 = female song absent, 1 = female song rare (most individuals do not sing; female song has only been observed in a few individuals or certain populations some years), 2 = female song occurs occasionally (it is observed periodically in some individuals but occurs noticeably less than male song or only during truncated parts of the year), 3 = female song occurs regularly (it can be reliably observed in many or most individuals but is somewhat less obvious than male song), 4 = female song occurs to the same extent as male song, 5 = females sing more than males.
Elaboration (DimorphSongElab; DimorphSongElb_ord; "elb") – To what extent are female songs described as ‘elaborate’ compared to male songs? This often included qualitative descriptions of song complexity, amplitude, or strength (e.g., female songs were often described as softer or weaker than male song). 0 = female song absent, 1 = female song is substantially less elaborate than male song, 2 = female song is somewhat less elaborate than male song, 3 = female song is similarly elaborate to male song, 4 = female song is more elaborate than male song. Because length was scored independently of elaboration, we did not include information on song length in this elaboration score.
Length (DimorphSongLength; DimorphSongLen_ord; "len") – How does the duration of female songs compare to male song? 0 = female song absent, 1 = female song is substantially shorter than male song, 2 = female song is somewhat shorter than male song, 3 = female song is similar in length to male song, or 4 = female song is longer than male song.
Female song present vs absent (FemSongFinal_PrsAbs; prs_abs) - For some analyses, we also collapsed song incidence into a binary variable representing female song absent (absent=0) vs present (present=1)

The predictor variables used to test hypotheses associated with female song were compiled from several sources including:
(1) daily nest predation rates from Unzeta et al. 2020: Unzeta, M., Martin, T. E., & Sol, D. (2020). Daily nest predation rates decrease with body size in passerine birds. The American Naturalist, 196, 743-754.
(2) life- and natural history traits from Dale et al. 2015: Dale, J., Dey, C. J., Delhey, K., Kempenaers, B., & Valcu, M. (2015). The effects of life history and sexual selection on male and female plumage colouration. Nature, 527, 367-370.
(3) territoriality and duet data from Tobias et al. 2016: Tobias, J. A., Sheard, C., Seddon, N., Meade, A., Cotton, A. J., & Nakagawa, S. (2016). Territoriality, social bonds, and the evolution of communal signaling in birds. Frontiers in Ecology and Evolution, 4, 74.
A brief description of each predictor variable is below. For more details, see the supplementary methods associated with the publication.
Daily nest predation rates (DPR) – Calculations from both personal field data (as exposure days calculated by the Mayfield method; Mayfield 1961) and nest success reported from the literature. Cavity nesters were omitted from Unzeta et al. 2020, but added to the current study when available from field studies (T. Martin unpublished data) and the literature (Martin 1995, Martin and Clobert 1996, Remes et al. 2012).
Breeding latitude (degrees_from_equator) – Each species’ geographical location was computed as the latitude (degrees from equator) of the breeding range centroid.
Body size (log mass; log_CRC_species_mass) – Body mass data was collated from Dunning 2008. These data were log-transformed prior to statistical analysis.
Sexual size dimorphism (SSD_wing) – Sexual size dimorphism was calculated as the log (male wing length) − log(female wing length) to provide a proportional index of relative sizes of the sexes. See Dale et al. 2007 for a detailed explanation of this metric.
Biparental care (paternal_care) – Biparental care was scored as 0 = absent or 1 = present primarily based on data provided in Cockburn 2006.
Cooperative breeding (cooperation) – Cooperative breeding was scored as 0 = absent, 0.5 = suspected, or 1 = present also primarily based on data from Cockburn 2006. For species in our data set not present in Cockburn 2006, additional parental care scores were obtained from del Hoyo et al. 2003-2011.
Social mating system (mating_system) – Social polygyny was scored on a four-point scale following Owens and Hartley 1998, with 0 = strict social monogamy, 1 = monogamy with infrequent instances of polygyny (<5% of males; e.g., lazuli bunting, Passerina amoena), 2 = mostly social monogamy with regular facultative social polygyny (5 to 20% of males; e.g., American redstart, Setophaga ruticilla), and 3 = obligate resource defence polygyny (>20% of males; e.g., red-winged blackbird, Agelaius phoeniceus) or lek polygyny (e.g., lance-tailed manakin, Chiroxiphia lanceolata).
Migratory behaviour (Migratory) – Migration was scored on a scale from 0 to 2, with 0 = resident (breeding and non-breeding ranges identical), 1 = partial migration (some overlap between breeding and non-breeding ranges), 2 = complete migration (no overlap between breeding and non-breeding ranges). Assignments were made based on the range maps within del Hoyo et al. 2003-2011.
Territoriality (Territory) – Species were classified as 0 = non-territorial, 1 = seasonally or weakly territorial, or 2 = year-round territorial. We defined year-round territoriality as territory defence lasting throughout the year rather than residency within a restricted area, including migrants that are territorial on both the breeding and non-breeding grounds. Species that are vocal and aggressive (responsive to playbacks) for part of the year but remain in the same area silently for the rest of the year were classified as seasonal rather than year-round territorial. Seasonal or weak territoriality primarily included species with broadly overlapping home ranges or that joined mixed species flocks. Non-territorial species never defend territories and included species that defend a very small area around a nest site.
Duetting (Duet) – Duets were scored as 0 = absent or 1 = present for each species and were defined as acoustic signals involving two individuals. In line with previous work, duets had to be composed of long-range acoustic signals that are coordinated or stereotyped in some way, whether they be loosely synchronous, regularly alternating, or precisely interwoven. While duets of songbirds are often comprised of songs, duets could include other long-range vocalizations with song-like functions. Duet presence/absence was scored based on a variety of sources, including published literature, field observations, regional experts, and sound archives.
Female Song Present, Absent, or duetting species (prs_abs_duet) - a 3 category ordinal scale of
In addition to the above predictor variables, we measured seasonality and wing length (see Dale et al. 2015 for a description of these variables). These two variables were highly correlated (r > 0.85) with latitude and Log mass, respectively, and we therefore left them out of final analyses.
Additional variables are included from the original datasets of Unzeta et al. 2020, Dale et al. 2015, Tobias et al. 2016.