Grieves Leanne A, Gilles Marc, Cuthill Innes C, Székely Tamás, MacDougall-Shackleton Elizabeth A, Caspers Barbara A
Department of Psychology, Neuroscience and Behaviour, McMaster University, Hamilton, Ontario, L8S 4M4, Canada.
Department of Behavioural Ecology, Bielefeld University, Konsequenz 45, Bielefeld, 33615, Germany.
Biol Rev Camb Philos Soc. 2022 Jun;97(3):1193-1209. doi: 10.1111/brv.12837. Epub 2022 Feb 6.
Smell is a sensory modality that is rarely considered in birds, but evidence is mounting that olfaction is an important aspect of avian behaviour and ecology. The uropygial gland produces an odoriferous secretion (preen oil) that can differ seasonally and between the sexes. These differences are hypothesized to function in olfactory camouflage, i.e. minimizing detection by nest predators (olfactory crypsis hypothesis), and/or intraspecific olfactory communication, particularly during breeding (sex semiochemical hypothesis). However, evidence for seasonal and sex differences in preen oil is mixed, with some studies finding differences and others not, and direct evidence for the putative function(s) of seasonal variation and sex differences in preen oil remains limited. We conducted a systematic review of the evidence for such changes in preen oil chemical composition, finding seasonal differences in 95% of species (57/60 species in 35 studies) and sex differences in 47% of species (28/59 species in 46 studies). We then conducted phylogenetic comparative analyses using data from 59 bird species to evaluate evidence for both the olfactory crypsis and sex semiochemical hypotheses. Seasonal differences were more likely in the incubating than non-incubating sex in ground-nesting species, but were equally likely regardless of incubation strategy in non-ground-nesting species. This result supports the olfactory crypsis hypothesis, if ground nesters are more vulnerable to olfactorily searching predators than non-ground nesters. Sex differences were more likely in species with uniparental than biparental incubation and during breeding than non-breeding, consistent with both the olfactory crypsis and sex semiochemical hypotheses. At present, the data do not allow us to disentangle these two hypotheses, but we provide recommendations that will enable researchers to do so.
嗅觉是一种在鸟类中很少被考虑的感官方式，但越来越多的证据表明嗅觉是鸟类行为和生态的一个重要方面。尾脂腺会分泌一种有气味的分泌物（尾脂），其在不同季节和性别之间可能会有所不同。这些差异被认为具有嗅觉伪装功能，即尽量减少被巢穴捕食者发现（嗅觉隐匿假说），和/或种内嗅觉交流功能，特别是在繁殖期间（性信息素假说）。然而，关于尾脂季节性和性别差异的证据并不一致，一些研究发现了差异，而另一些则没有，并且关于尾脂季节性变化和性别差异的假定功能的直接证据仍然有限。我们对尾脂化学成分这种变化的证据进行了系统综述，发现95%的物种（35项研究中的57/60种）存在季节性差异，47%的物种（46项研究中的28/59种）存在性别差异。然后，我们使用59种鸟类的数据进行系统发育比较分析，以评估嗅觉隐匿假说和性信息素假说的证据。在地面筑巢的物种中，孵化期的性别比非孵化期的性别更可能出现季节性差异，但在非地面筑巢的物种中，无论孵化策略如何，出现季节性差异的可能性相同。如果地面筑巢者比非地面筑巢者更容易受到嗅觉搜索捕食者的攻击，那么这一结果支持嗅觉隐匿假说。单亲孵化的物种比双亲孵化的物种更可能出现性别差异，繁殖期比非繁殖期更可能出现性别差异，这与嗅觉隐匿假说和性信息素假说均一致。目前，这些数据还无法让我们区分这两种假说，但我们提供了一些建议，使研究人员能够做到这一点。
