Hermit Thrush Research Articles

Poecile atricapillus (Black-capped Chickadee) Feeding Catharus guttatus (Hermit Thrush) Nestlings

We describe what we believe to be the first recorded instance of an adult Poecile atricapillus (Black-capped Chickadee) feeding the young of a different species. On 25 June 2017, we observed a Black-capped Chickadee feeding 3 Catharus guttatus (Hermit Thrush) nestlings. We recorded a video of this behavior the following day, in which the adult Black-capped Chickadee delivered food to the Hermit Thrush nestlings 12 times in 105 min of continuous recording. The Black-capped Chickadee also removed fecal sacs from the nest. At the end of this video, 1 of the nestlings fledged. We did not observe an adult Hermit Thrush feeding the nestlings during the entire recording. The considerable differences in body size, nesting strategy, and nestling growth rate between these 2 species comprise a unique instance of interspecific parental feeding that resulted in successful fledging.

Early singers attend to conspecific but not heterospecific behavioural cues at dawn

During the dawn chorus songbirds initiate singing activities just prior to sunrise. Environmental factors affect the timing of the dawn chorus, but relatively little is known about how behavioural cues influence chorus timing. We assessed whether early playback of conspecific and heterospecific song influenced chorus start times in two early‐singing temperate species, hermit thrush Catharus guttatus and veery C. fuscescens. We used arrays of GPS time‐synchronized recorders to record the dawn chorus at 30 locations. In each location, thirty minutes prior to natural chorus initiation, we broadcast: 1) an early singing species (hermit thrush or veery), 2) a late singing species (black‐throated green warbler Setophaga virens or Nashville warbler Oreothlypis ruficapilla), 3) a noise control, and 4) also recorded without playback (silent control). Playback treatments were separated by two‐three days at each location. Both hermit thrush and veery sang significantly earlier in response to conspecific playback compared to noise or silent controls. Both species also sang earlier in response to conspecific playback compared to the day before or the day after playback. Neither species sang earlier in response to heterospecific playback (regardless of whether the broadcast species was a naturally early or late song initiator) compared to noise or silent controls. Our results support the theory that the dawn chorus is a communication network where individuals attend primarily to conspecific cues; heterospecific song appears to have minimal impacts on the chorus start times of the two early‐singing species we investigated.

Hierarchical temporal structure in music, speech and animal vocalizations: jazz is like a conversation, humpbacks sing like hermit thrushes

Humans talk, sing and play music. Some species of birds and whales sing long and complex songs. All these behaviours and sounds exhibit hierarchical structure-syllables and notes are positioned within words and musical phrases, words and motives in sentences and musical phrases, and so on. We developed a new method to measure and compare hierarchical temporal structures in speech, song and music. The method identifies temporal events as peaks in the sound amplitude envelope, and quantifies event clustering across a range of timescales using Allan factor (AF) variance. AF variances were analysed and compared for over 200 different recordings from more than 16 different categories of signals, including recordings of speech in different contexts and languages, musical compositions and performances from different genres. Non-human vocalizations from two bird species and two types of marine mammals were also analysed for comparison. The resulting patterns of AF variance across timescales were distinct to each of four natural categories of complex sound: speech, popular music, classical music and complex animal vocalizations. Comparisons within and across categories indicated that nested clustering in longer timescales was more prominent when prosodic variation was greater, and when sounds came from interactions among individuals, including interactions between speakers, musicians, and even killer whales. Nested clustering also was more prominent for music compared with speech, and reflected beat structure for popular music and self-similarity across timescales for classical music. In summary, hierarchical temporal structures reflect the behavioural and social processes underlying complex vocalizations and musical performances.

Geographic variation in song structure in the Hermit Thrush (Catharus guttatus)

ABSTRACT Although the Hermit Thrush (Catharus guttatus) exhibits distinctive morphological and genetic differences across its breeding range (Alvarado et al. 2014), comparatively little is known about geographic variation in song structure and whether song variation corresponds with those morphological and genetic differences. To address this, we collected recordings from throughout the species' breeding range and assessed frequency and temporal characteristics of song structure. Eastern and western birds differed dramatically with respect to song structure, most notably with respect to introductory note frequencies: eastern birds exhibited a larger range of introductory note frequencies than western birds. They also differed with respect to temporal characteristics: western birds sang longer introductory notes, but shorter post-introductory portions, than eastern birds. Numerous differences in structure were also detected within each lineage. For example, within the western lineage, introductory note fre...

Commentary: Cats prefer species-appropriate music.

Commentary: Cats prefer species-appropriate music.

Migration patterns of San Francisco Bay Area Hermit Thrushes differ across a fine spatial scale

AbstractEffective conservation of short-distance migrants requires an understanding of intraspecific variation in migratory patterns across small spatial scales. Until the advent of ultra-light geolocation devices, our knowledge of the migratory connectivity of songbirds was limited. For the Hermit Thrush (Catharus guttatus), subspecies delineations and connectivity patterns have been unclear in the portion of their breeding range in western North America from southeastern Alaska to northwestern Washington, where individuals wintering in the San Francisco Bay Area of California purportedly breed. To determine breeding locations and migratory timing of the Bay Area’s wintering Hermit Thrushes, we deployed geolocators at sites to the north and south of the San Francisco Bay. We compared results from these two regions to one another and to connectivity patterns suggested by subspecies definitions. We collected morphometrics to identify regional differences. Hermit Thrushes that wintered in the North Bay had a wider and more southerly breeding distribution from the British Columbia coast to northwestern Washington, whereas South Bay thrushes migrated to southeastern Alaska and the British Columbia coast. In general, North Bay thrushes departed wintering grounds and arrived on breeding grounds earlier than South Bay thrushes, but we cannot eliminate sex as a factor in these differences. Regional morphology differed only in bill length. Intraspecific isolation in glacial refugia during the Late Pleistocene may explain these fine-scale geographic variations in migration patterns and morphology.

Overtone-based pitch selection in hermit thrush song: unexpected convergence with scale construction in human music.

Many human musical scales, including the diatonic major scale prevalent in Western music, are built partially or entirely from intervals (ratios between adjacent frequencies) corresponding to small-integer proportions drawn from the harmonic series. Scientists have long debated the extent to which principles of scale generation in human music are biologically or culturally determined. Data from animal "song" may provide new insights into this discussion. Here, by examining pitch relationships using both a simple linear regression model and a Bayesian generative model, we show that most songs of the hermit thrush (Catharus guttatus) favor simple frequency ratios derived from the harmonic (or overtone) series. Furthermore, we show that this frequency selection results not from physical constraints governing peripheral production mechanisms but from active selection at a central level. These data provide the most rigorous empirical evidence to date of a bird song that makes use of the same mathematical principles that underlie Western and many non-Western musical scales, demonstrating surprising convergence between human and animal "song cultures." Although there is no evidence that the songs of most bird species follow the overtone series, our findings add to a small but growing body of research showing that a preference for small-integer frequency ratios is not unique to humans. These findings thus have important implications for current debates about the origins of human musical systems and may call for a reevaluation of existing theories of musical consonance based on specific human vocal characteristics.

The effects of Forest Stand Improvement Practices on occupancy and abundance of breeding songbirds

Silviculture can play an important role in managing avian habitat. In 2010 the Vermont Natural Resource Conservation Service, in conjunction with Audubon Vermont, implemented a Forest Stand Improvement initiative designed to improve timber quality while increasing habitat diversity for forest breeding songbirds. To evaluate the effectiveness of this program in improving avian habitat, we conducted point count surveys of breeding birds in harvested and control sites in 2012 and 2013, 1–3years post-harvest. Harvesting resulted in mean decreases of 18% in basal area, 10% in canopy cover, and 10% in canopy tree density while piles of woody debris per ha increased by 402%. Occupancy and abundance estimates for 24 and 18 bird species respectively were derived using Program MARK. Compared to controls, occupancy rates of four songbird species were greater on harvested sites – rose-breasted grosbeak (Pheucticus ludovicianus), yellow-bellied sapsucker (Sphyrapicus varius), chestnut-sided warbler (Setophaga pensylvanica), and mourning warbler (Geothlypis philadelphia)—while occupancy of one species—black-and-white warbler (S. fusca)—was significantly lower. Two species were significantly more abundant at harvested sites—rose-breasted grosbeak and yellow-bellied sapsucker—while two species were less abundant—hermit thrush (Catharus guttatus) and black-and-white warbler. Piles of woody debris left after harvests were negatively associated with site occupancy for 3 out of 10 understory species. Overall, our results suggest that this program retains all interior forest species and has a slight positive impact on gap and early successional species abundance and occupancy in the first 1–3years post-harvest. This study provides the first quantitative examination of the impact that Vermont NRCS’s Forest Stand Improvement program has had on forest breeding birds.

What to do when stopping over: behavioral decisions of a migrating songbird during stopover are dictated by initial change in their body condition and mediated by key environmental conditions

The behavioral decisions of migratory songbirds during migration stopovers can markedly influence the pace, efficiency, and success of migration. An individual’s fuel stores are considered in theory to directly dictate subsequent stopover behavior (e.g., extent of foraging or vigilance, when to depart), although such decisions at stopover must also consider atmospheric factors (e.g., wind, precipitation) that influence the energetic costs of migration. We conducted the first study to date that directly manipulated the fuel stores of newly arrived songbirds at a stopover site, evaluated their effect on movement behavior and departure decisions, and assessed how atmospheric factors mediated these behavioral decisions. Hermit thrushes (Catharus guttatus) captured during fall migration at a southern New England, USA, offshore island stopover site and subsequently released with increased fuel stores moved less and made more tortuous movements, were more likely to depart on a given night and regularly resumed migration earlier and in a seasonally appropriate direction relative to individuals released with little change in fuel stores. The importance of fuel stores in modifying behavioral decisions increased throughout the migration period, presumably in response to declining food abundance. Precipitation suppressed migrant movements during stopover and precluded departure. Migrants departed in light winds with little respect to wind direction. The pervasive influence of fuel stores on migrant stopover behavior underscores the central role of fuel acquisition in the dynamics, speed, and success of migration, as well as the importance of quality stopover sites to migratory birds.

Integrative tracking methods elucidate the evolutionary dynamics of a migratory divide.

Migratory divides, the boundary between adjacent bird populations that migrate in different directions, are of considerable interest to evolutionary biologists because of their alleged role in speciation of migratory birds. However, the small size of many passerines has traditionally limited the tools available to track populations and as a result, restricted our ability to study how reproductive isolation might occur across a divide. Here, we integrate multiple approaches by using genetic, geolocator, and morphological data to investigate a migratory divide in hermit thrushes (Catharus guttatus). First, high genetic divergence between migratory groups indicates the divide is a region of secondary contact between historically isolated populations. Second, despite low sample sizes, geolocators reveal dramatic differences in overwintering locations and migratory distance of individuals from either side of the divide. Third, a diagnostic genetic marker that proved useful for tracking a key population suggests a likely intermediate nonbreeding location of birds from the hybrid zone. This finding, combined with lower return rates from this region, is consistent with comparatively lower fitness of hybrids, which is possibly due to this intermediate migration pattern. We discuss our results in the context of reproductive isolating mechanisms associated with migration patterns that have long been hypothesized to promote divergence across migratory divides.

Listening to Eliot’s Thrush

The essay takes a fresh look at Eliot’s “water-dripping song” in The Waste Land . It seems impossible for the ornithologically minded Eliot not to have known that the hermit thrush’s song does not sound like dripping water. In fact, nowhere in ornithological writing — and certainly not in his source, Chapman’s Handbook of North American Birds — is it described in these terms. Emphasizing the humorous potential of Eliot’s display of “bogus scholarship,” the essay argues that Eliot’s ludic bird masks not only the darker presence of its poetic predecessor in Whitman’s “When Lilacs Last in the Dooryard Bloom’d” but also the poet’s own longing for the fluid pleasures of his lost North American childhood.

Earthworm invasions and the decline of clubmosses (Lycopodium spp.) that enhance nest survival rates of a ground-nesting songbird

Invasive earthworms have numerous adverse effects on soils, plants, and vertebrates in forests of North America. Relatively little research has linked earthworm invasions to population vital rates of vertebrates while also assessing habitat characteristics that drive these responses. Furthermore, most investigations of earthworm impacts on plants have focused on graminaceous, woody, and herbaceous species. At sites representing different stages of earthworm invasion, we studied a group of fern-like plants, the clubmosses (Lycopodium spp.), that may be adversely affected by invasions of Lumbricus spp. earthworms, are harvested by humans, and are commonly used by ground-nesting songbirds as a nesting substrate. We found a strong inverse association between Lumbricus biomass and the presence of two clubmoss groups, those with a tree-like growth form (i.e., “tree clubmosses”) and those with a finger-like growth form (i.e., “common clubmosses”). Despite finding no relationship between clubmoss presence and visual concealment of nests, we provide evidence that two ground-nesting songbirds, the Ovenbird (Seiurus aurocapilla) and Hermit Thrush (Catharus guttatus), preferentially place their nests near tree clubmosses and that the presence of tree clubmosses increases Ovenbird nest survival probability by 32% on average. Although ecological mechanisms for the relationships between Lumbricus invasions and clubmosses and between tree clubmosses and Ovenbird nest survival are unclear, our findings provide additional motivation to manage forest ecosystems against earthworm invasions. In addition, we highlight the need to manage the human harvest of clubmosses to promote sustainability of clubmoss populations that are simultaneously threatened by earthworms and harvest and to minimize adverse impacts on songbirds.

Surveillance for Ixodes pacificus and the tick-borne pathogens Anaplasma phagocytophilum and Borrelia burgdorferi in birds from California's Inner Coast Range

We investigated the involvement of birds in the ecology of the western black-legged tick, Ixodes pacificus, and its associated zoonotic bacteria, Borrelia burgdorferi and Anaplasma phagocytophilum, at two interior coast-range study sites in northern California. Anaplasma phagocytophilum, the agent of granulocytic anaplasmosis (GA), and B. burgdorferi s.s., the agent of Lyme disease (LD), are tick-borne pathogens that are well established in California. We screened blood and ticks from 349 individual birds in 48 species collected in 2011 and 2012 using pathogen-specific PCR. A total of 617 immature I. pacificus was collected with almost three times as many larvae than nymphs. There were 7.5 times more I. pacificus at the Napa County site compared to the Yolo County site. Two of 74 (3%) nymphal pools from an Oregon junco (Junco hyemalis) and a hermit thrush (Catharus guttatus) and 4 individual larvae (all from Oregon juncos) were PCR-positive for B. burgdorferi. Blood samples from a golden-crowned sparrow (Zonotrichia atricapilla) and a European starling (Sturnus vulgaris) were positive for A. phagocytophilum DNA at very low levels. Birds that forage on ground or bark and nest on the ground, as well as some migratory species, are at an increased risk for acquiring I. pacificus. Our findings show that birds contribute to the ecologies of LD and GA in California by serving as a blood-meal source, feeding and transporting immature I. pacificus, and sometimes as a source of Borrelia infection.

How migratory thrushes conquered northern North America: a comparative phylogeography approach

Five species of migratory thrushes (Turdidae) occupy a transcontinental distribution across northern North America. They have largely overlapping breeding ranges, relatively similar ecological niches, and mutualistic relationships with northern woodland communities as insectivores and seed-dispersing frugivores. As an assemblage of ecologically similar species, and given other vertebrate studies, we predicted a shared pattern of genetic divergence among these species between their eastern and western populations, and also that the timing of the coalescent events might be similar and coincident with historical glacial events. To determine how these five lineages effectively established transcontinental distributions, we used mitochondrial cytochrome b sequences to assess genetic structure and lineage coalescence from populations on each side of the continent. Two general patterns occur. Hermit and Swainson’s thrushes (Catharus guttatus and C. ustulatus) have relatively deep divergences between eastern and western phylogroups, probably reflecting shared historic vicariance. The Veery (C. fuscescens), Gray-cheeked Thrush (C. minimus), and American Robin (Turdus migratorius) have relatively shallow divergences between eastern and western populations. However, coalescent and approximate Bayesian computational analyses indicated that among all species as many as five transcontinental divergence events occurred. Divergence within both Hermit and Swainson’s thrushes resembled the divergence between Gray-cheeked Thrushes and Veeries and probably occurred during a similar time period. Despite these species’ ecological similarities, the assemblage exhibits heterogeneity at the species level in how they came to occupy transcontinental northern North America but two general continental patterns at an among-species organizational level, likely related to lineage age.

Predicting impacts of future human population growth and development on occupancy rates of forest-dependent birds

Forest loss and fragmentation are among the largest threats to forest-dwelling wildlife species today, and projected increases in human population growth are expected to increase these threats in the next century. We combined spatially-explicit growth models with wildlife distribution models to predict the effects of human development on 5 forest-dependent bird species in Vermont, New Hampshire, and Massachusetts, USA. We used single-species occupancy models to derive the probability of occupancy for each species across the study area in the years 2000 and 2050. Over half a million new housing units were predicted to be added to the landscape. The maximum change in housing density was nearly 30 houses per hectare; however, 30% of the towns in the study area were projected to add less than 1 housing unit per hectare. In the face of predicted human growth, the overall occupancy of each species decreased by as much as 38% (ranging from 19% to 38% declines in the worst-case scenario) in the year 2050. These declines were greater outside of protected areas than within protected lands. Ninety-seven percent of towns experienced some decline in species occupancy within their borders, highlighting the value of spatially-explicit models. The mean decrease in occupancy probability within towns ranged from 3% for hairy woodpecker to 8% for ovenbird and hermit thrush. Reductions in occupancy probability occurred on the perimeters of cities and towns where exurban development is predicted to increase in the study area. This spatial approach to wildlife planning provides data to evaluate trade-offs between development scenarios and forest-dependent wildlife species.

Habitat Partitioning and Niche Overlap of Two Forest Thrushes in the Southern Appalachian Spruce–Fir Forests

Abstract. Guilds of species that share ecological similarities or recent ancestors are often the basis of studies concerning habitat partitioning. An interesting result of many of these studies is that means of partitioning in one area of sympatry may be different from those in disjunct areas of overlap. Here, we quantified the differences in habitat preference of two forest thrushes in the southern Appalachian Mountains. The Hermit Thrush (Catharus guttatus) has recently expanded its breeding range south along the spine of the Appalachians into the spruce—fir forests of Virginia, North Carolina, and Tennessee. There, it shares breeding habitat with the congeneric Veery (C. fuscescens), previously the only forest thrush breeding in this area. We used several multivariate analyses of habitat variables within both species' territories to understand how these species partition the available habitat and to test if these means of partitioning are similar to those found by other studies. We calculated the niche...

Elevational differences in estimated fattening rates suggest that high-elevation sites are high-quality habitats for fall migrants

ABSTRACT. Many migrant songbird species use high-elevation habitats for stopovers in fall throughout North America, but whether these are good migration habitats as indicated by high fueling rates or other measures has not been previously quantified. At high-quality stopover sites, birds can refuel while maintaining their optimal or preferred migration schedules. We used plasma metabolite analysis to estimate fueling rates of four songbird species during the fall migration period over 3 years at two high-elevation (1,200 m above sea level) and two low-elevation (<25 m above sea level) sites in southwestern British Columbia. For three species with more frugivorous diets during fall—the Fox Sparrow (Passerella iliaca), Golden-crowned Sparrow (Zonotrichia atricapilla), and Hermit Thrush (Catharus guttatus)—estimated fattening rates (defined as residual plasma triglyceride levels) were 37–65% higher at high-elevation sites than at low-elevation sites. By contrast, the largely insectivorous and smaller-bodied ...

Repertoire composition and singing behaviour in two eastern populations of the Hermit Thrush (Catharus guttatus)

Although it is highly recognisable, relatively little is known about the repertoire composition and singing behaviour of the Hermit Thrush (Catharus guttatus). To address this, we recorded spontaneously singing males in two eastern populations (Halifax, NS (n = 11) and Hancock County, ME (n = 7)) and analysed the recordings with respect to repertoire size, basic song type characteristics and song syntax. Males had song type repertoires of 7–12 song types, and no song type sharing between individuals was observed within or between populations. While frequency-related structural characteristics of the song types were the same between the populations, song type duration (especially that of the introductory note) differed significantly. The song types within each repertoire could be categorised into high and low song types based on introductory note frequency, and these song type categories also differed with respect to the amount and distribution of spectral energy. In both populations, males sang with immediate variety, never repeating the same song type consecutively, and preferentially used some song-type to song-type transitions more than others. In addition, we found correlational evidence of changes in singing behaviour (e.g., the relative use of low versus high song types) over the course of the breeding season. We discuss these findings in the context of other songbird research as well as their implications for future work examining how Hermit Thrush males utilise their songs in defending territories and attracting mates.

Nesting Density of Hermit Thrushes in a Remnant Invasive Earthworm-free Portion of a Wisconsin Hardwood Forest

I observed an exceptionally high density of Hermit Thrush (Catharus guttatus) nests (3.1 nests/ha) over two breeding seasons in an isolated 1.3-ha portion of an earthworm-free study site in the Chequamegon-Nicolet National Forest, Wisconsin. This density was much greater than the 0.1 to 0.6 nests/ha observed over the rest of the study area and exceeds by an order of magnitude most previously reported estimates for this species. The mean distance among Hermit Thrush nests in earthworm-free sites (215 m; 95% CI = 180–250 m) was lower than in invaded sites (250 m; 95% CI = 236–264 m); this difference was not statistically significant. Nest density did not differ significantly between categories. An abundance of suitable nest sites in a favored nesting substrate (clubmoss; Lycopodium spp.) could have contributed to the exceptionally high density of Hermit Thrush nests observed. High Hermit Thrush nest densities may occur in association with forest floor conditions that are characteristic of earthworm-free areas.

Long‐term changes in spatial distribution of birds responding to a group‐selection timber harvest

AbstractWe investigated the spatial response of 20 bird species to a group‐selection timber harvest within a 40‐ha forest stand over a 20‐year period (5 yr preharvest and 15 yr postharvest). To characterize the spatial response of each species, we examined trends in 3 metrics: proportion of harvest‐created canopy‐gap area that occurred within the area used by a species in each year, average distance to the nearest gap of all observations of a species in a year, and distribution of distances between observations and gaps for each species in each year. Eight species (eastern wood‐pewee [Contopus virens], winter wren [Troglodytes troglodytes], hermit thrush [Catharus guttatus], Nashville warbler [Vermivora ruficapilla], black‐and‐white warbler [Mniotilta varia], pine warbler [Dendroica pinus], common yellowthroat [Geothlypis trichas], and white‐throated sparrow [Zonotrichia albicollis]) responded positively to the timber harvest (i.e., the proportion of gaps in their area of use increased, the distance from gaps decreased, and their use of gaps and edges [0–25 m from gaps] increased). In contrast, veeries (Catharus fuscescens), black‐throated green warblers (Dendroica virens), and ovenbirds (Seiurus aurocapillus) avoided gaps and edges. Changes in spatial distributions were generally short‐lived; by 15 years postharvest the use of the harvested areas by nearly all species had approached preharvest levels. The spatial response of birds to group‐selection timber harvesting indicates that there are unlikely to be serious long‐term effects of the harvest on forest bird populations. However, there may be more subtle, short‐term effects, such as crowding of mature‐forest bird species into surrounding forest, which merit further study. © 2012 The Wildlife Society.