We used this binary measure of allopreening because rates of allopreening are available for a few species only.We implemented extensive Web of Science and Google Scholar searches using the terms “allo*preen*”, “mutual preen*”, “allo*groom*”, and “mutual groom*”, in combination with the species’ binomial nomenclature and common name(s).We searched published sources for information on the following aspects of avian pair bonds: parental cooperation over offspring care (using scores from Remeš et al.
The notion that allopreening reinforces pair bonds has gained widespread acceptance (e.g., Harrison and Harrison 1997; Dagg 2011; Mandal 2015), but to date this hypothesis has been examined in only a handful of species.Rather than basing our analyses on a single phylogenetic tree and assuming this tree was known without error, we instead used a distribution of 100 phylogenetic trees extracted from constraint, Jetz et al. We used the Markov chain Monte Carlo (MCMC) (Hadfield and Nakagawa 2010) approach implemented in the “mul Tree” package (Guillerme and Healy 2014) in R (v.3.2.2, R Core Team 2013), which runs the models on all 100 trees and summarises the resulting 100 parameter estimates.2012) and ultimately increases participant fitness (Dunbar 1991; Silk et al. 2010; Mc Farland and Majolo 2013) by reducing stress and removing ectoparasites (Boccia et al. Allopreening can aid ectoparasite removal (Brooke 1985; Villa et al. However, if hygiene is the primary function of allopreening, why does this behavior occur in certain species only?One possibility is that gregarious species, in which frequent physical contact among individuals facilitates parasite transmission, are more prone to ectoparasites (Boyd 1951).Many avian species, however, do not allopreen and the relationship between allopreening and pair bonding across species remains unexplored.