Effects of age and weather during moult on mountain bluebird Sialia currucoides structural colouration

Abstract

Birds exhibit a vast array of colours and ornaments and while much work has focused on understanding the function and evolution of carotenoid‐based colours (red, orange, yellow), structural colouration (blue, green, purple, iridescent) can also play a key role in sexual signaling. Several studies have examined how factors such age may influence structural colour, however few studies have looked at how structural colour may be influenced by environmental conditions such as variation in weather conditions experienced during moult. In this study, we examined variation in structural colour expression in relation to age as well as rainfall and temperature during post‐breeding moult for a population of mountain bluebirds Sialia currucoides in western Canada over nine breeding seasons. Overall, we found structural colouration was explained by sex, age and weather patterns during moult. At a population level, tail and rump feathers from males were more colourful (higher brightness and chroma, hue values shifted more towards UV) than females, and adults were more colourful than juvenals. Male and female rump feathers generally became less colourful with age. Noise‐receptor colour models revealed colour differences were discernible among sexes, suggesting bluebird colouration is an important sexual signal. Tail and rump plumage variation was associated with weather during moulting periods, though the effects were sex‐ and age‐dependent. Female plumage was generally more colourful following wetter and warmer early summers, while males were more colourful following warmer late summers, and plumage of older birds was more resilient to colour variation due to weather patterns. We suggest that more rainfall may increase insect abundance and thus improve food intake and overall condition of mountain bluebirds. This is one of the first studies to examine how both age and weather conditions concurrently influence the expression of structural colours in birds.

Disentangling the mechanisms of signal evolution in Tyrannidae flycatchers, part II: plumage elaboration evolved with migration behavior, but is also affected by diet, climate, and drift

“…Additionally, we examined whether species living in closer proximity displayed greater color divergence as a test of the species recognition hypothesis. We predicted (1) plumage of both sexes would be largely driven by migration behavior, diet, climate, and habitat because these aspects have been found to influence coloration in other groups (e.g., Reudink et al 2015, Simpson et al 2015, Ward et al 2021, and (2) we would find less support for the species recognition hypothesis because many Tyrant flycatchers exhibit similar plumage within genera but display pronounced vocal differences (investigated in Part I of this study). We further aimed to broaden the understanding of avian ecology and evolution in historically underrepresented regions because many of the species in our study occur exclusively in Central and South America (Nuñez et al 2021).…”

Short-term weather patterns influence avian body condition during the breeding season

“…We found that for most species analyzed (14 out of 18), age was an important driver of scaled mass index. Age-dependent responses to weather variables have been demonstrated previously via numerous pathways including differential migratory phenology (Jarjour et al, 2017), phenological (Bonamour et al, 2020) and phenotypic plasticity (Ward et al, 2021), and existing studies on body condition (Gardner et al, 2016(Gardner et al, , 2018McLean et al, 2018). A wide body of existing literature also suggests that body condition fluctuates as birds age (Angelier et al, 2011;Rockwell et al, 2012;Welcker et al, 2015), due in part to the fact that adult birds may outcompete juvenile birds for more limited resources in times of extreme weather (Rockwell et al, 2012).…”

A tail of plumage colouration: disentangling geographic, seasonal and dietary effects on plumage colour in a migratory songbird

“…Melanin‐based plumage in fox sparrows Passerella iliaca also changes colour over time (Weckstein et al 2002), possibly due to UV exposure or accumulation of dirt and oils on the feathers (Montgomerie 2006). Additionally, colour in many species changes with age – sometimes dramatically through delayed plumage maturation (Hawkins et al 2012) and sometimes more subtly as individuals age (Marini et al 2015, Ward et al 2021); therefore, it is important for studies to assess the environmental, biological, ontological and temporal influences on feather colour to help unravel the mechanisms regulating this phenotypic trait.…”