We examined whether male plumage coloration signals parental quality in the American Redstart (Setophaga ruticilla), a highly ornamented, migratory warbler. We measured the relationship between both adult male arrival date and phenotype (morphology, melanin- and carotenoid-based plumage), and parental care levels of both parents. Males with brighter flank feathers made more visits to the nest and spent more time at the nest, consistent with the ‘good-parent hypothesis’. Female parental care (number of visits) was negatively correlated with intensity of red of her mate's tail feathers and positively associated with her mate's parental effort. These data indicate offspring of brighter males receive more care from both parents. Our results suggest carotenoid-based plumage traits of male American Redstarts may have an important role in intersexual signaling, and add to our understanding of the evolution of multiple ornaments.
Field Data and Feather Collection
We conducted field work at the Queen’s University Biological Station in southeastern Ontario, Canada (44° 34' N, 76° 19' W), during two consecutive breeding seasons (May–Jul 2006– 2007). The 60-ha study site is a mixed deciduous forest, largely dominated by sugar maple (Acer sacchurum) and eastern hop-hornbeam (Ostrya virginiana). We surveyed transects from 0600 to 1200 hrs EST each day from 1 May to 1 July across the study site to record the arrival date for each individual. We designated arrival date as the number of days after the arrival of the first male each season (i.e., first date of male arrival = 0; male that arrived 5 days later = 5) to standardize arrival date across seasons. We captured adult male redstarts on their respective territories using mist nests and song playback, usually within 7 days of arrival, and females during the nesting phase using mist nets near their nest location. All birds were banded with a Canadian Wildlife Service aluminum band (permit # 10766C) and a unique combination of three color bands (excluding red and orange in males); we recorded unflattened wing chord length (61.0 mm) as a measure of relative body size. We plucked a single tail feather (third rectrix; R3) and 12–15 orange flank feathers from each male (Quesada and Senar 2006) (CWS collection permit # CA 0154). We classified adult male bib size using a 1–5 scale (1 = small amount of black plumage, 5 = large amount of black plumage with intermediates given half points) following Lemon et al. (1992).
Parental Care Observations
We monitored American Redstart pairs each season (~40 pairs/ season) daily until their nest was found, and observed nests every 1–2 days following completion of nest-building until hatching and recorded the number of young. We confirmed the number of nestlings again on day 5 after hatching and continued to monitor nests until fledging. Fifty nests were observed: 25 in 2006 and 25 in 2007. We erected ground-based video cameras (Canon ZR500) on tripods >5 m from the base of the nest tree on days 5 and 7 after hatching to record parental effort. Cameras were focused on the nest and its immediate (<20 cm) surroundings, and recording occurred between 0600 and 0900 hrs EST. Each recording lasted 120 min and the first 5 min were discarded to allow parents time to recover from human disturbance. The remaining 115 min were used to calculate provisioning rates of males and females, and the time each parent spent at the nest. We recorded and analyzed a total of 148 hrs of video from 38 nests (n reduced due to high predation rates). A trained observer recorded the measures of parental care through binoculars at a distance >10 m from the nest using a stopwatch if there were more nests to be watched than cameras available (2006—day 5: n = 8, day 7: n = 5; 2007—day 5: n = 2, day 7: n = 2). There was no difference between video camera and trained observer nest watches in either the number of visits to the nest, or total time at the nest (2-sample t-test assuming unequal variance, all P values > 0.09). Nests depredated between days 5 and 7 were excluded from analysis (2006: n = 7; 2007: n = 5).