Colour change in a structural ornament is related to individual quality, parasites and mating patterns in the blue tit

Abstract

Carry-over effects refer to processes that occur in one season and influence fitness in the following. In birds, two costly activities, namely reproduction and moult, are restricted to a small time window, and sometimes overlap. Thus, colour in newly moulted feathers is likely to be affected by the costs of reproduction. Using models of bird vision we investigated male colour change in a free-living population of blue tits (Cyanistes caeruleus) in three sampling occasions: spring 1, winter and spring 2. We related crown, tail, breast and cheek feather colouration after the moult (winter) to the intensity of infections by blood parasites during reproduction (spring 1). In the following spring (spring 2), we explored mating patterns with respect to changes in feather colour (springs 1 vs. 2). Males that were less intensely infected by the malaria parasite Plasmodium while breeding showed purer white cheek feathers in winter, which may indicate higher feather quality. Increased brightness in the white cheek was associated with better body condition during reproduction. In the following season, males with brighter cheeks paired with females that had noticeably brighter cheek patches compared to the male's previous mate. These results suggest that the conditions experienced during reproduction are likely to affect moult and thus feather colouration, at least in the white patch. High quality individuals may allocate resources efficiently during reproduction increasing future reproductive success through variation in mating patterns. Carry-over effects from reproduction might extend not only to the non-breeding phase, but also to the following breeding season.

Individual Quality and Extra‐Pair Paternity in the Blue Tit: Sexy Males Bear the Costs

“…Here, we found that after season 1, males with more extra‐pair offspring increased their white cheek brightness, which has already been related to higher individual quality (Badás et al. ). The following season (season 2), males with brighter cheek feathers tended to gain paternity and sire more extra‐pair young.…”

“…Achromatic contrasts confirmed that this color change between seasons could be perceived by avian vision (JND scores, available in Badás et al. ).…”

“…; Badás et al. ), but whether tail brightness is a sexually selected ornament in the blue tit awaits further confirmation.…”

“…For all seasons, relative quantum photon catches were obtained to build models of blue tit vision (Endler and Mielke 2005;Stevens et al 2009). From this, three variables describing color were obtained for each color patch (hue, saturation, and luminance), because this is the most common approach used to model avian color vision and coloration in recent ecological studies (Stoddard and Prum 2008;Kemp et al 2015; see Badás et al 2018 for details on the formulas used).…”

“…Finally, we extracted JND scores, or Just Noticeable Differences (Siddiqi et al 2004), to describe perceptibility of color change between seasons 1 and 2 through chromatic (color) or achromatic (luminance) contrasts. JND scores between seasons 2 and 3 are available in Badás et al (2018).…”