The evolution of pattern camouflage strategies in waterfowl and game birds

Abstract

Visual patterns are common in animals. A broad survey of the literature has revealed that different patterns have distinct functions. Irregular patterns (e.g., stipples) typically function in static camouflage, whereas regular patterns (e.g., stripes) have a dual function in both motion camouflage and communication. Moreover, irregular and regular patterns located on different body regions (“bimodal” patterning) can provide an effective compromise between camouflage and communication and/or enhanced concealment via both static and motion camouflage. Here, we compared the frequency of these three pattern types and traced their evolutionary history using Bayesian comparative modeling in aquatic waterfowl (Anseriformes: 118 spp.), which typically escape predators by flight, and terrestrial game birds (Galliformes: 170 spp.), which mainly use a “sit and hide” strategy to avoid predation. Given these life histories, we predicted that selection would favor regular patterning in Anseriformes and irregular or bimodal patterning in Galliformes and that pattern function complexity should increase over the course of evolution. Regular patterns were predominant in Anseriformes whereas regular and bimodal patterns were most frequent in Galliformes, suggesting that patterns with multiple functions are broadly favored by selection over patterns with a single function in static camouflage. We found that the first patterns to evolve were either regular or bimodal in Anseriformes and either irregular or regular in Galliformes. In both orders, irregular patterns could evolve into regular patterns but not the reverse. Our hypothesis of increasing complexity in pattern camouflage function was supported in Galliformes but not in Anseriformes. These results reveal a trajectory of pattern evolution linked to increasing function complexity in Galliformes although not in Anseriformes, suggesting that both ecology and function complexity can have a profound influence on pattern evolution.

A global analysis of bird plumage patterns reveals no association between habitat and camouflage

“…First, it could be due to the coarse scale at which we investigated the association between habitat and plumage patterns. Many of the empirical studies that demonstrate a camouflage function of patterns in non-colour changing animals show an association in one or a limited number of species (e.g., Lovell et al, 2013; Kang et al, 2014; Marshall, Philpot & Stevens, 2015b.; Wilson-Aggarwal et al, 2016) or were found via predator–prey computer simulations (e.g., Stevens, Yule & Ruxton, 2008; Stevens et al, 2011; Scott-Samuel et al, 2011; Troscianko et al, 2013; How & Zanker, 2014; Hughes, Troscianko & Stevens, 2014; reviewed in Marshall & Gluckman, 2015). At the level of microhabitats, some studies demonstrate that individual behaviours may facilitate camouflage, such as a behavioural choice to rest on backgrounds that enhance camouflage (Tsurui, Honma & Nishida, 2010; Lovell et al, 2013; Kang et al, 2014; Marshall, Philpot & Stevens, 2015b.; Troscianko et al, 2016; Wilson-Aggarwal et al, 2016).…”

“…Specifically, irregular patterns (mottled) tend to function in stationary camouflage while those that regularly repeat a pattern or motif (bars, spots) function in motion camouflage, which are in turn predicted to be more effective in closed and open habitats, respectively (Marshall & Gluckman, 2015). Birds are the most well described taxonomic group of animal and can be found in all types of habitats on all major landmasses (Gluckman & Cardoso, 2010; Jetz et al, 2012), making them particularly well suited for investigating sensory ecology hypotheses.…”

“…1; Gluckman, 2014; Marshall & Gluckman, 2015; Gluckman & Mundy, 2016). Most studies of camouflage focus on single or few species (Marshall & Gluckman, 2015) that may not be representative of broad scale selection pressures.…”

“…1; Gluckman, 2014; Marshall & Gluckman, 2015; Gluckman & Mundy, 2016). Most studies of camouflage focus on single or few species (Marshall & Gluckman, 2015) that may not be representative of broad scale selection pressures. Here, we investigated whether sensory ecology theory could explain convergent evolution in the camouflage plumage patterns of birds at the global spatial and taxonomic scale, i.e., with a global spatial extent, using large spatial units, and data on most land bird species.…”

Peer Review #2 of "A global analysis of bird plumage patterns reveals no association between habitat and camouflage (v0.1)"

“…Crucially, visual modelling studies have shown that such local adaptation can prevent detection by the actual visual systems of predators, such as hunting birds (e.g. Marshall et al, 2015), thus indicating that camouflage tends to be optimised to local habitats under natural selection.…”