Reproductive correlates of plumage coloration of female Mountain Bluebirds

Abstract

Many studies have shown that the plumage coloration of male birds can act as an honest signal of quality, indicating benefits that a female could gain from pairing with a specific male. In some species, females also display ornamental plumage, but less is known about the function and potential adaptive significance of female coloration because most research has focused on male coloration. Male Mountain Bluebirds (Sialia currucoides) display full body, ultraviolet (UV)‐blue plumage, whereas female plumage is more subdued, with blue color focused on the rump, wing, and tail. During the 2011 and 2012 breeding seasons (May–July) near Kamloops, BC, Canada, we examined coloration of the rump and tail of female Mountain Bluebirds to determine if their plumage could act as an indicator of direct reproductive benefits (e.g., enhanced parental care or reproductive success) to potential mates. We found no relationship between female plumage coloration and either provisioning rate or fledging success. However, female coloration varied with age, with after‐second‐year (ASY) females having brighter, more UV‐blue tail feathers than second‐year (SY) females. In addition, ASY females with brighter, more UV‐blue tails had larger clutches. We also observed positive assortative mating by tarsus length. Because previous work with other species suggests that female body size may be a good predictor of breeding success, males could potentially benefit from pairing with larger females. However, reproductive success did not vary with female size in our study. Although our evidence that structural plumage coloration of female Mountain Bluebirds is a signal of direct reproductive benefits for males (e.g., higher reproductive success) is limited, our results (i.e., ASY females with brighter tails than SY females, and ASY females with brighter tails having larger clutches) do suggest the potential for sexual selection to act on female coloration.

Delivery rates and prey use of Mountain Bluebirds in grassland and clear-cut habitats

“…Few attributes of parents themselves, neither age nor color affected delivery rates although at the older nestling stage, there was a negative relationship between body condition and delivery rate. This corresponds to results in Balenger et al (2007) and Morrison et al (2014) where color was not associated with provisioning rate for female Mountain Bluebirds. Perhaps parents were trading off effort for the current brood with their own body condition, but what might trigger different investment strategies needs further investigation with food supplementation experiments and long-term data on lifetime reproduction to elucidate.…”

Predictors of nestling survival during harsh weather events in an aerial insectivore, the Tree Swallow (Tachycinetabicolor)

“…Lastly, the 'good parent hypothesis' could also explain female ornamentation, with male birds selecting females with more elaborate plumage ornamentation if it is a signal of the quality of parental care a female can provide (Owens and Thompson 1994;Johnstone et al 1996;Massaro et al 2004;reviewed in Tobias et al 2012). Indeed, female plumage has been positively correlated with female feeding rate, clutch size, number of fledglings produced, and nestling mass and immune response (Linville et al 1998;Silva et al 2008;Remeš and Matysioková 2013;Morrison et al 2014). The relationship between plumage ornamentation and reproductive success may depend on current environmental conditions, as different phenotypes may arise as adaptions for different environmental contexts.…”

A high-accuracy, time-saving method for extracting nest watch data from video recordings

“…This method has the potential to significantly reduce the amount of time required to obtain provisioning data. To put these time savings into perspective, Morrison et al (2014) examined 178 h of Mountain Bluebird videos (the same population examined here), which would have taken approximately 154.86 ± 36.73 h for the new observer or 75.95 ± 8.99 h for the experienced observer, based on rates recorded in this study. Use of EthoVision could have reduced analysis time down to approximately 48.06 ± 14.24 h, a time savings of 37-69 %.…”

“…Each video was designed to consist of a 2-h observation of a nest box capturing male and female Mountain Bluebirds entering and exiting the nest; however, some videos were cut short due to technical issues (n = 40 videos, 73 h total). Videos were taken once during the early nesting period (offspring 3-5 days old) and once during the late nesting period (offspring 13-15 days old), following Morrison et al (2014). Offspring provisioning was measured by manually watching each video and recording each time the male or female provided food for their young.…”