Age, condition and dominance‐related sexual ornament size before and during the breeding season in the black grouse Lyrurus tetrix

Abstract

Male ornaments function as honest cues of male quality in many species and are subject to intra‐ and intersexual selection. These ornaments are generally studied during peak expression, however their size outside the breeding season may determine ultimate ornament size and costliness, and as such reproductive success. We investigated whether male black grouse Lyrurus tetrix eye comb size was related to age, condition and measures of male dominance before and during the breeding season. Total combined eye comb size began to increase ~70 d before the start of the breeding season. Adult males (aged ≥ 2 yr old) had consistently larger eye combs than younger males (1 yr old) both before and during the breeding season. Heavier and more dominant adult males (attending the lek more frequently and successfully reproducing) had larger eye combs. For younger males, those that were heavier had larger eye combs. Additionally, males that spent more time on the lek showed increased eye comb size as the breeding season approached. Overall we find that ornament size is positively related to dominance and condition before and during the breeding season. Since dominance is accrued through year‐round interactions in many species, the ability to maintain larger signals over prolonged periods, including outside of the breeding season, is likely to be beneficial for adults. For younger males, it is likely that they cannot sustain or are constrained from producing larger eye combs over long periods of time. They therefore prioritise growth of their ornaments later, and according to the amount of time they spend on the lek.

Identifying and locating carotenoids in supra‐orbital combs of male black grouse (Lyurus tetrix) using Raman and transmission electron microscopy: A histological study using rehydrated tissue samples

“…25°00′ E–25°18′ E). Total comb size (cm²) was calculated in ImageJ (Rasband, 2018) for each individual using stills from digital video recordings of both combs against a 1 cm scale reference (see Harris et al, 2018). The tips of a small number of dermal spikes were removed from the eye comb tissue using a sterile, sharp blade at the time of capture before releasing the bird.…”

“…Sample collection has previously been described in Harris et al, (2018Harris et al, ( , 2020. Briefly, black grouse were caught between January and May, between 2007 and 2008, using oat-baited walk-in traps at five lek sites in central Finland (lat.…”

“…Though birds use mainly plumage‐based colouration (Cooney et al, 2019; Dale et al, 2015) bare‐skin signals are also widespread and include coloured eye rings (Pérez‐Rodríguez & Viñuela, 2008), coloured legs and feet (Torres & Velando, 2005) and wattles and eye combs (Harris et al, 2018). Despite showing variation in size, colour or structure, bare skin signals have received less attention than colourful plumage displays (Iverson & Karubian, 2017), with only a handful of studies examining the internal structures and underlying anatomy of skin‐based signals (e.g., (Negro et al, 2006; Peneaux et al, 2020; Prum & Torres, 2003) despite their importance in intra‐ and interspecies communication.…”

“…In this study, we sought to describe the structure of these spikes (Figure 1). These eye combs show large (>fivefold) size differences between the breeding and nonbreeding season within the same individual, while also exhibiting considerable variation across years and among individuals (Harris et al, 2018(Harris et al, , 2020). An eye comb's red colouration is thought to derive from carotenoid pigment deposition due to their characteristic reflectance spectra (Harris et al, 2020) and the presence of carotenoids in combs of related species, such as the Red Grouse, Lagopus lagopus (Mougeot et al, 2007).…”