SPECIES ACCOUNT. American redstart/ Paruline flamboyante (Setophaga ruticilla)
Ryan R. Germain* and Ann E. McKellar*
Department of Biology, Queen’s University, Kingston, ON Canada K7L 3N6
email: email@example.com; firstname.lastname@example.org
* These authors contributed equally to this work
Taxonomy: Class: Aves Order: Passeriformes Family: Parulidae Genus: Setophaga
Species: Setophaga ruticilla (Linneaus 1758)
The vibrantly coloured American redstart is a small wood warbler commonly found throughout the Opinicon region. Its Latin name, Setophaga ruticilla, is translated as “Red-tailed moth eater”, and like its common name may be considered a misnomer given the predominantly orange colouration of adult males (‘start’ is derived from the Old English word for ‘tail’). The only member of the genus Setophaga, the American redstart is unrelated to Old-World redstarts or the Myioborus redstarts (often referred to as ‘whitestarts’) of Central and South America (Parks 1961), although the shared name is due to behavioural and morphological similarities (e.g. ‘tail-fanning’ behaviour; see Foraging). Instead, American redstarts are closely related to members of the genus Dendroica, which includes many familiar species of the Opinicon region such as cerulean warblers (Dendroica cerulea), black-throated blue warblers (D. caerulescens), and yellow warblers (D. petechia) (Lovette and Bermingham 2002). American redstarts have been featured prominently in research into the behavioural ecology of migratory songbirds. Previous work on the social use of song repertoire (Lemon et al. 1987, 1992, 1994; Weary et al. 1992, 1994; Staicer et al. 2006), implications of high-quality over-wintering habitat (Marra et al. 1998; Marra and Holmes 2001; Norris et al. 2004; Studds et al. 2008; Reudink et al. 2009a), analytical techniques in the study of migration (Langin et al. 2007), and the signalling functions of ornamental plumage colouration (Reudink et al. 2009b, 2009c, Germain et al. 2010) have all contributed to our understanding of the natural history and year-round ecology of migratory songbirds. The Queen’s University Biological Station (QUBS) has played a particularly influential role in our current understanding of American redstart ecology, where a long-term study population has been the focus of many published studies mentioned throughout this account.
Description: The American redstart is a small (6-9 g) sexually dichromatic songbird. Adult males are primarily black, with
vibrant orange plumage patches on their wings, flanks (sides of breast under the wings), and tail (Figure 1A), making them clearly distinguishable from other similarly-sized warblers. Individual adult male plumage ornamentation can vary considerably; the size of the black bib may extend far down the breast of adult males or be restricted to just beyond the throat (Lemon et al. 1992), and there is a high degree of variation in the colouration of the orange plumage regions of adult males (Reudink et al. 2009b; see Breeding Ecology).
Females and yearling (second year, first breeding season) males (Figure 1B) are primarily olive-gray, with yellow colouration on their wings, flanks, and tail, rather than the orange plumage patches of adult males. Males undergo delayed plumage maturation and do not moult into their definitive black/orange adult plumage until the end of their first breeding season. In addition, when yearling males adventitiously lose feathers while in their sub-adult (gray and yellow) plumage, those feathers are replaced by adult-like black and/or orange plumage throughout the year (Rohwer et al. 1983).
The song repertoire of male American redstarts consists of two distinct song categories that are used in different social contexts. The “repeat” song is commonly associated with mate attraction; males continuously sing one repeat song early in the breeding season before and during female arrival and (for polygynous males, i.e., those with multiple female mates) while seeking secondary mates (Ficken and Ficken 1965, Lemon et al. 1985, Sherry and Holmes 1997, Staicer et al. 2006). Repeat songs include two to eleven repeated, high frequency notes and often end in notes with distinctive accents (upward or downward sweeps; reviewed by Sherry and Holmes 1997). Conversely, “serial” song is more commonly sung by males during territorial interactions, and may play a role in male-male competition (Ficken 1962, Lemon et al. 1985). Serial song consists of one to seven (unaccented) song types sung in immediate succession. Individual male serial repertoires frequently change from year to year to match those of neighbouring males, which may allow some birds to exploit the vocal features of older, higher-quality males (Ficken and Ficken 1965, Lemon et al. 1985, 1987, 1994).
Distribution: American redstarts occupy one of the most wide summer ranges of the wood warblers. They breed from Alaska east to Newfoundland, and south throughout much of the eastern United States (Figure 2). Redstarts are abundant in the Opinicon region and in surrounding areas; the roadside North American Breeding Bird Surveys (1968-2006) rank them as the fourth most common wood warbler of the Kingston region (Weir 2008).
American redstarts are long-distance migrants whose wintering range includes parts of Mexico, the West Indies, Central America, and northern South America. Based on evidence from stable isotope analysis and a small number of recaptures of banded individuals, redstarts originating from northwestern breeding areas are thought to overwinter primarily in southeastern Mexico, whereas those originating from northeastern breeding areas (incl. Ontario) are thought to overwinter primarily in the Caribbean (Norris et al. 2006). Gene flow across the current geographic range may therefore be somewhat limited, although redstarts show little genetic differentiation and lack any formal subspecific categorization (Colbeck et al. 2008).
In Ontario, spring arrival occurs mostly in May and early June, and fall departure typically peaks in August and September. Adult male American redstarts begin arriving at (QUBS) in the Opinicon region within the first week of May and are followed by females and yearling males several days to weeks later, depending on location and seasonality (RRG and AEM, unpubl. data). Breeding then begins in late May and can continue into July if early nests are unsuccessful (see Breeding Ecology).
Habitat: During the breeding season, males establish and defend territories in second-growth forests typically located near sources of water (Sherry and Holmes 1997). In the Opinicon region, breeding pairs are most often found in areas with high densities of sapling sugar maple (Acer saccharum) and eastern hophornbeam (Ostrya virginiana), in which females construct their nests (RRG and AEM, pers. obs.). Nest sites are also commonly found in and around human-occupied areas such as campgrounds, farmhouses, and the QUBS Point property (RRG and AEM, pers. obs.).
Adult male territories are typically clustered, and those of yearling males tend to be clustered in different areas, or are found peripherally to those of adults (Ficken and Ficken 1967, Morris and Lemon 1988, Lozano et al. 1996). Despite the spatial separation of adult and yearling territories, as well as potential differences in shrub density (Procter-Gray and Holmes 1981), there does not appear to be any clear difference in breeding habitat quality between age classes (Morris and Lemon 1988, but see Sherry and Holmes 1988).
Long-term studies of American redstarts in Jamaica during the non-breeding season demonstrate age- and sex-based habitat separation; adult males tend to occupy high-quality mangrove habitat, while females and yearling males are relegated to low-quality dry scrub habitat (Marra et al. 1993, Marra 2000). Winter habitat quality can have important carry-over effects into the breeding season. Male redstarts overwintering in high-quality territories begin spring migration earlier and arrive on the breeding grounds earlier than those from low-quality habitat (Marra et al. 1998, Norris et al. 2004, Reudink et al. 2009a). In addition, recent evidence from a study conducted at QUBS indicates that males arriving earlier on the breeding grounds sire a greater number of offspring and have a higher probability of maintaining multiple mating partners than late-arriving males (Reudink et al. 2009a).
Foraging: Redstarts are particularly adept aerial foragers and are often seen flitting among trees in pursuit of prey. They may also use their distinctive colour patterns in tail-fanning ‘flash’ displays to flush prey from cover, although this behaviour may be more common in the dense understory of the wintering grounds, where food is relatively scarce (Lovette and Holmes 1995, Sherry and Holmes 1997, RRG pers. obs.). Their predominantly insectivorous diet can be quite varied, but consists mostly of flies and mosquitoes (Diptera), moths and caterpillars (Lepidoptera), wasps (Hymenoptera), beetles (Coleoptera), and spiders (Araneae) (reviewed by Sherry and Holmes 1997). In the Opinicon region, redstarts will feed preferentially on moth caterpillars (the most energy-rich food available to them) when these larvae are their most abundant in late May and early June (Lovette and Holmes 1995, Langin et al. 2006).
Breeding Ecology: As they arrive on the breeding grounds, male American redstarts begin establishing territorial boundaries through song contests and physical battles (Ficken 1962). Females arrive several days to weeks after adult males (see Distribution), and pair formation occurs shortly thereafter. Unpaired males continue to sing in repeat mode (> 90% of songs) for two to five weeks while attempting to attract a female, and often move to different territorial sites during this period (Staicer et al. 2006). Both adult and yearling males that are unable to attract a mate cease singing earlier in the season and eventually depart the breeding grounds earlier than paired males (Lemon et al. 1987), again suggesting that repeat song may function in mate attraction, although this has never been explicitly tested in redstarts. Some males may defend multiple territories, and thus be mated to more than one female (Secunda and Sherry 1991). At QUBS, approximately 25% of adult males are polygynous (Reudink et al. 2009b). In addition, both male and female redstarts routinely copulate with individuals outside of their social pair (extra-pair copulations, EPCs), with recent estimates suggesting that ~43% of nests in the QUBS population contain at least one chick sired by an extra-pair male, and EPCs account for approximately 23% of all offspring (Reudink et al. 2009a).
Recent work suggests that the orange (carotenoid pigment-based) plumage colouration of adult male redstarts may play an important role in female mate choice and winter territory acquisition (Reudink et al. 2009b, Reudink et al. 2009c, Germain et al. 2010). Because such ornamentation is diet-dependent, only those males that are able to obtain and deposit enough carotenoid pigments into their feathers should be able to express a colourful plumage display (Hill 1999, 2002). Males with brighter tail colouration are more likely to secure multiple mating partners, and flank feather colouration predicts rates of within-nest paternity (Reudink et al. 2009b). In addition, male tail colouration is associated with habitat quality during the non-breeding season, suggesting that tail colouration may function in both inter and intrasexual signalling (Reudink et al. 2009c). Similarly, adult males with brighter flank feathers provide more parental care towards their offspring (Germain et al. 2010). Interestingly, ornamental plumage colouration may be subject to age-related changes across seasons (Reudink et al. 2009b). While older adult males with less carotenoid pigment saturation may appear less ornamented to the human eye, evidence for increased rates of extra-pair (outside social pair) paternity and increased rates of female parental care towards offspring of such individuals suggests that females may also use the perceived age of males to asses male quality (Reudink et al. 2009b, Germain et al. 2010).
Females begin nest-building within a few days of their arrival and may take several days to complete a nest, especially during the early part of the season. However, many nests are abandoned or depredated and females often re-build nests more quickly later in the season (~50% at QUBS; RRG and AEM, unpubl. data). Females frequently re-use material from the first nest to build subsequent nests (RRG and AEM, pers. obs.). Nests are constructed using a variety of materials, including bark strips, grasses, leaves, lichens, feathers, and mammal hairs, which are generally woven together with spider silk (Sherry and Holmes 1997). Nests are usually built at the junction of three or more branches on the main trunk of a tree or shrub (Ficken 1964).
American redstarts are single-brooded, and females typically lay three to five eggs, with clutch size decreasing throughout the season and with decreasing latitude across their range (Sherry and Holmes 1997). Mean clutch size at QUBS for 2005-2009 was 3.84 eggs (RRG and AEM, unpubl. data). Females incubate eggs for approximately eleven days, and both parents feed the chicks. At QUBS, offspring are typically ready to fledge from the nest nine days post-hatch (RRG and AEM, pers. obs.).
While brown-headed cowbirds (Molothrus ater) do parasitize American redstart nests in certain areas (Sherry and Holmes 1997), this phenomenon has never been documented at QUBS (RRG and AEM, unpubl. data). For instance, in a ten year study of 466 redstart nests in central Alberta, 12% were parasitized (Hannon et al. 2009). In this location, cowbird parasitism was found to increase predation risk to redstart nests, possibly via increased nest detectability due to louder begging by cowbird or redstart nestlings or due to increased parental feeding visits to parasitized nests. Nest failure rates at QUBS are approximately 50% annually (AEM, unpubl.data). Local nest predators are abundant and highly variable. While the majority of nests are depredated by American crows (Corvus brachyrhynchos), eastern chipmunks (Tamias striatus), American red squirrels (Tamiasciurus hudsonicus), and eastern grey squirrels (Sciurus carolinensis), predations by larger animals such as black rat snakes (Elaphe obsolete) and sharp-shinned hawks (Accipiter striatus) can be common (RRG and AEM, pers. obs).
Conservation Status: Population trends in American redstarts are complex and vary from region to region (Figure 3).
However, across their entire North American range, redstarts have experienced a slight, though non-significant decline (Sauer et al. 2008). This decline is not well understood but is thought to result from a combination of factors including forest maturation and habitat degradation both in breeding and in non-breeding areas (Hunt 1996; Sherry and Holmes 1996). Modest increases in some populations may be due to forest regeneration after logging (Cyr and Darveau 1996). A study population at QUBS has remained stable over the past ten years (AEM, unpubl. data). Despite overall population declines, American redstarts are not of conservation concern since they are still widespread and locally abundant.
Research Needs: Very little is known regarding what limits migratory bird populations. Populations of many species are declining (Robbins et al. 1989, Askins et al. 1990), and this could be due to events on the breeding grounds, on the wintering grounds, or during migration (Sherry and Holmes 1995, Newton 2006). Furthermore, events from one phase of the annual cycle could carry over to affect events during another phase (e.g., Marra et al. 1998, Sillett et al. 2000). American redstarts are a good study system for the investigation of this topic because long-term marked populations have been studied on both the breeding and wintering grounds (e.g., Marra and Holmes 2001, Hannon et al. 2009, Reudink et al. 2009a, RRG and AEM, unpubl. data), and recent studies using stable isotope analysis have highlighted the importance of carry-over effects in this species (Marra et al. 1998, Norris et al. 2004, Reudink et al. 2009a). Detailed studies on survival from one phase of the annual cycle to the next would be useful for highlighting the relative importance of events from different parts of the year. Further isotopic studies, particularly those incorporating data from both breeding and wintering populations, are needed to better establish population connectivity in order to answer questions related to trends in growth among populations.
American redstarts are also an ideal study system for investigations on delayed signalling maturation. Like many species with delayed plumage maturation, adult and yearling males are clearly distinguishable, and yearling reproductive success is typically much lower than that of adults (Ficken and Ficken 1967, Rohwer et al. 1980, Omland and Sherry 1994). However, yearling males over-wintering in high-quality mangrove habitat in Jamaica exhibit significantly more adult-like black breast plumage than those in low-quality scrub, and young males arriving earlier on the breeding grounds at QUBS likewise display more adult-like black plumage than those arriving later (Germain et al. In press). Together, these results indicate that as in adults, yearling male plumage ornamentation may play a role in signalling competitive ability for high-quality winter territories. Recent evidence suggests that male redstarts occupying territories in high-quality habitat during their first winter (as yearlings) disperse south of their natal latitude during their first breeding season (Studds et al. 2008). On the other hand, yearling males from poor-quality habitat disperse north of their natal latitude, and for both groups there is a high degree of breeding latitude fidelity after the first breeding season (Studds et al. 2008). For adult males, occupying a poor-quality winter territory leads to later arrival date on the breeding grounds (Marra et al. 1998) and ultimately reduced reproductive success (winter habitat quality inferred by stable-carbon isotope analysis, Reudink et al. 2009a). If a similar trend occurs in young males, yearling individuals breeding in the Opinicon region may arrive later in the breeding season (relative to adult males) than those from more southern breeding sites, further reducing the chances of pairing and reproductive success. There are significant challenges to conducting stable-carbon isotope analysis on yearling males who are in lower densities and may use more variable migratory stopover timing. Nevertheless, studying variation in yearling male arrival date, plumage, and reproductive success across a range of breeding latitudes may prove informative. In particular, support for the role that adult-like plumage may play in winter territoriality would be strengthened if yearling males arriving at more southern breeding sites have plumage ornamentation that more closely matches those of adults than yearling males in the north.
Literature & Further Reading
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Reviewers: Dr. MacDougall-Shackleton (Univ. Western Ont.) and Paul Handford (Univ. Western Ont.)