Warbler Species Research Articles

Spruce budworm outbreaks and the incidence of vagrancy in eastern North American wood-warblers

The Tennessee (Vermivora peregrina), Cape May (Dendroica tigrina), Bay-breasted (D. castanea), and Canada (Wilsonia canadensis) warblers and the Ovenbird (Seiurus aurocapillus) appear to show positive numerical responses to outbreaks of the spruce budworm (Choristoneura fumiferana); the Magnolia (D. magnolia), Black-throated Green (D. virens), and Blackburnian (D. fusca) warblers may occur in lower numbers during outbreaks because of increased competition with these budworm specialists. Thus, we predicted that the number of fall vagrant Tennessee, Cape May, and Bay-breasted warblers and Ovenbirds occurring in California are highly positively associated with budworm population density, positively intercorrelated, and negatively associated with numbers of Magnolia, Black-throated Green, and Blackburnian warblers. A 23-year (1972-1994) data set of budworm population densities and vagrant warbler occurrences in California showed that (i) budworm population density was an excellent predictor (explaining about 50% of the variance) of numbers of occurrences of the Cape May, Bay-breasted, and Canada warblers; (ii) all warbler species tended to co-occur, with numbers of Cape May and Bay-breasted warblers especially highly intercorrelated; and (iii) Magnolia Warbler numbers were negatively associated with those of budworm specialists, but Black-throated Green and Blackburnian warblers showed no association.

Song transmission and auditory perception of distance in wood warblers (Parulinae)

The influence of breeding habitat on the evolution of song structure was examined in four wood warbler species of the sub-family Parulinae. The effects of song degradation on the ability of territorial paruline males to estimate distance by means of acoustic cues was also investigated. Song transmission characteristics of paruline breeding habitats were compared in southeastern Ontario, Canada; songs native to the habitat in which they were broadcast did not degrade less than foreign songs. The response of territorial paruline males to playback of ‘near’ (undegraded) and ‘far’ (degraded) conspecific songs broadcast from the same position within the territory at the same amplitude were then compared. Males responded to near songs as they would to a conspecific territorial intruder and with less intensity to far songs, suggesting that males may use cues from song degradation to estimate distance to vocal conspecifics. Our results from transmission and playback experiments are discussed with respect to the ranging hypothesis, which proposes that selection should favour males that structure songs to minimize their degradation, so that songs function to disrupt or intimidate rivals by providing unreliable distance cues.

Factors affecting songbird communities using new short rotation coppice habitats in spring

The aim of this study was to describe the songbird communities occupying willow and poplar short rotation coppice (SRC) crops during the breeding season, and to identify the features of existing plantations that affect their abundance. Songbird point-counts were undertaken at 66 different plots of SRC at 29 sites throughout Britain and Ireland during spring 1993. Measures of vegetation and coppice management in each plot were also taken. The songbird species using the SRC survey plots were similar to those reported from traditional coppice habitats. Willow SRC contained more resident and migrant songbird species than poplar SRC. Warbler species and buntings in particular were rarely recorded from poplar plots. Finches, tits and thrushes were recorded equally from both willow and poplar. More migrant species were recorded from year 2 willow coppice (i.e. in its third growth season since winter cutting) than in either year 1 or year 3. Most resident species selected older willow or poplar coppice growth up ...

Evolutionary changes in a song control area of the brain (HVC) are associated with evolutionary changes in song repertoire among European warblers (Sylviidae)

Determining relations between brain structure and function is a principal focus of evolutionary neurobiology. Here we investigate covariation between singing behaviour and the neuroanatomy in eight species of sylviid warblers from the closely related Acrocephalus and Locustella genera. We found a significant positive correlation between repertoire size and the volume of the higher vocal centre after controlling for variation in brain size and phylogenetic relatedness across species. This group is of particular interest, as earlier work has shown that an increase in male song complexity (as measured by syllable repertoire size) is caused by sexual selection pressure acting through female choice. Thus, in males of Acrocephalus species (which have complex songs), sexual selection appears to have led to increases in both syllable repertoire size and the relative volume of the higher vocal centre. In contrast, Locustella species have very simple songs, and repertoire size and the relative volume of the higher vocal centre remain small in males of these species. These results indicate that sexual selection may have shaped the evolution of a particular behavioural trait (song) by altering the relevant controlling area of the brain (higher vocal centre).

Coexistence in Mediterranean warblers: ecological differences or interspecific territoriality?

We studied the coexistence of four species of Sylvia warblers living in Mediterranean matorral in order to identify the respective role of ecological segregation and of interspecific territoriality in explaining the local distribution of these four species. Data on habitat use, foraging behaviour and interspecific spacial segregation were collected on Corsica and on Spargi (Sardinia) islands. Despite large overlap in patch selection and in foraging behaviour the four species did segregate ecologically and behaviourally while foraging (differences in the choice of plant species used for foraging, in the height of the plant selected, in the selection of the portion of the plant volume used and in the selection of the plant structure explored). Complementarity in foraging behaviour was observed in the morphologically and ecologically closest species: the Dartford (Sylvia undata) and the Marmora's (Sylvia sarda) warblers. We did not observe any evidence of direct interspecific interactions in song, alarm, or aggressive behaviour. Nor did we observe patterns of spatial distribution that would support the idea of coexistence by interspecific territorial exclusion. These results contrast with the results of Cody & Walter (1976) suggesting interspecific territoriality in Mediterranean Sylvia warblers. They are consistent with other published results emphasizing ecological differences as explanation for species coexistence.

New Approaches to the Analysis of Population Trends in Land Birds

Although there is strong evidence that a few Neotropical migrant land birds have severely declining populations, we know of no evidence of general overall declines. One widely cited analysis of data from the Breeding Bird Survey (BBS), the only continental—scale monitoring program for land birds in the breeding season, indicates declining populations in eastern forests in the 1980s, but other analyses conclude that most species have had stable or increasing populations in the last 25 yr. These conflicting results call for a new perspective. Here, we propose two approaches to the analysis of BBS data that emphasize the detection of temporal and geographic variation in population trends. The first approach uses nonlinear regression to detect temporal changes in population trends, and permits the construction of graphs that compare nonlinear trends among regions. The second approach provides statistical tests of multispecies patterns of geographic variation in population trends. We report analyses of BBS data for 1966 to 1992 for the 26 species of wood warblers (Parulinae) for which the most data are available and the chance of obtaining reliable estimates is best. Using pooled data for all 26 species for eastern and central North America, nonlinear regression indicated declining populations in the Appalachian Mountains and the Eastern Foothills in the 1970s, and stability elsewhere. As examples of the use of this first approach in single—species analyses, we give maps, graphs, and statistical tests to illustrate variation in population trends by physiographic strata in the Blue—winged Warbler (Vermivora pinus) and the Ovenbird (Seiurus aurocapillus). As an example of the second approach, we applied a probit—normal model to a matrix of increases and decreases in the 26 species in 37 geographic strata. The analysis identified specific highland areas as having unusually high proportions of declining populations. These results suggest that correlates of elevation should be considered as factors possibly regulating populations of warblers and other land birds. Our perspective is that focus on studies of temporal and geographic variation in population trends of all birds, including Neotropical migrants, could help conservation biologists identify where species and groups of species are in the most trouble.

Geostatistics as a Tool for Examining Hypothesized Declines in Migratory Songbirds

Data from the North American Breeding Bird Survey (BBS) indicate significant declines in the populations of several species of songbirds, including several Neotropical migrants. These declines have been attributed to habitat destruction and fragmentation on the breeding grounds, in strategic migratory stopover sites, and on the wintering grounds. Using BBS data from the 1967—1989 period and universal kriging, we produced maps of abundance change for two declining species of wood warblers to test hypothetical spatial scenarios of decline over entire breeding ranges. These species were the Cerulean Warbler (Dendroica cerulea) and the Prairie Warbler (D. discolor). We found considerable variability in the location of areas of decline when comparing successive 5—yr periods. In some comparisons, areas of decline were concentrated in the centers of abundance of these species, and in others, they were scattered throughout their range. We also found that the direction and intensity of population trends was quite sensitive to the methods used for calculating abundance. Our results indicate that, even for species where significant long—term declines have been reported, considerable variation exists in the direction of abundance change, both geographically and temporally. Although most of the long—term declines reported in particular species at local and regional scales are undeniable, gaps in our knowledge still prevent us from incorporating these trends into a global model of the annual cycle of Neotropical migrants.

A new species of Phylloscopus warbler from Sichuan Province, China

A new species of leaf warbler (Sylviidae: Phylloscopus) is described from the mountain Emei Shan, Sichuan Province, China. Morphologically it is extremely similar to, yet significantly different from, the sympatric Blyth's Leaf Warbler Phylloscopus reguloides and White‐tailed Leaf Warbler Phylloscopus davisoni. Songs and calls are both very different from P. reguloides and P. davisoni, and playback tests confirmed the specific status of the new species.

Prey abundance and male parental behaviour in Acrocephalus warblers

This study examined the prey abundance at nesting sites of five different Acrocephalus warbler species. Intraspecific variations in prey density were analysed to determine the relative significance of this ecological factor for different mating systems and components of male parental behaviour. The Great Reed Warbler Acrocephalus arundinaceus, a facultatively polygynous species, nested in areas with the highest insect abundance. Its intraspecific variation in prey density (between different territories) was the highest while the male: female offspring feeding ratio was the lowest. At the other extreme, the monogamous Moustached Warbler Acrocephalus melanopogon and Reed Warbler Acrocephalus scirpaceus nested in areas with the lowest prey abundance and lowest intraspecific variation. Males of these species had the highest involvement in feeding young. In the Moustached Warbler and Marsh Warbler Acrocephalus palustris, an intraspecific comparison revealed a negative correlation between insect abundance and the male feeding component; a tendency in this direction was found for the Reed Warbler, while no correlation was evident in the polygynous Great Reed Warbler. These data demonstrate a general pattern relating prey abundance, mating systems and male parental investment on an interspecific level. However, intraspecific correlations revealed a net of complex interdependence. One of the factors which may be important is resource predictability. We found a significant correlation between certain vegetation types and insect abundance. The vegetation composition of territories is further influenced by interspecific dominance relationships whereby the dominant Great Reed Warbler occupies territories with the vegetation type which correlates with high prey abundance while the overlapping Moustached Warbler and Reed Warbler are restricted to areas with lower insect density.

Correlates of Wing Morphology with Foraging Behaviour and Migration Distance in the Genus Phylloscopus

Wing size and shape variation in thirteen species of Old World leaf warblers, genus Phylloscopus, were examined using wing formulae and principal components analysis. Data were taken from male individuals in breeding populations in Northern India and Japan. Species with longer wings migrate further and hover less than species with shorter wings. Species with more pointed wings migrate further and are more arboreal than species with rounder wings. Findings agree with those from previous studies on the genus Phylloscopus. Both foraging behaviour and migration distance have affected wing size and shape evolution in the genus.

Stopover Site Fidelity of Four Migrant Warblers in the Iberian Peninsula

This paper analyses by means of ringing data the stopover site fidelity of four warbler species (Sylvia atricapilla, Sylvia borin, Phylloscopus collybita and Acrocephalus scirpaceus) during their migrations across the Iberian Peninsula. The mean recovery rates observed during migration periods (mean 0.28, range 0-0.54) were around 50% of the ones observed during the breeding and wintering seasons (mean 0.51, range 0.41-0.58). These differences in recovery rate were statistically significant in all species but Acrocephalus scirpaceus. This warbler, with its more restricted habitat requirements, showed higher recovery rates during the spring and autumn migration periods confirming the hypothesis that species depending on scarce, patchily distributed stopover habitats during their migrations show stronger stopover site fidelity during their journeys. Our results support the view that some migrant species actively select stopover sites during their migrations.

ERNST MAYR AND THE ORIGIN OF SPECIES.

Evolutionary biology has a punctuated history. It arose as a conceptual macromutation on November 24, 1859-disgorged, as Mencken (1931) put it, one stupendous and appalling dose-and has undergone stasis or slow anagenesis ever since. Indeed, much of the field still consists of repeated demonstrations of phenomena first described by Darwin, or of epiphenomena derived from them. The study of speciation, however, is a conspicuous exception. Despite the title of his famous book, Darwin was notably unsuccessful in solving the real problem of organic diversity: why plants and animals in a habitat fall into discrete, nonoverlapping packages. It is widely accepted that his failure came from his inability to conceptualize species as noninterbreeding groups (see Mayr 1959) and to recognize that the origin of species was identical to the origin of the barriers to interbreeding. Because Darwin considered species to be only highly evolved morphological varieties (indeed, The Origin of Species should have been called The Origin of Adaptations), he confused adaptation within lineages with the origin of new lineages. Although the two are connected, the former does not automatically produce the latter. Understanding how one species of warbler becomes adapted to its habitat does not explain why four other distinct species-and no intermediates-occupy the same patch of forest. One solution was suggested by geneticists like Bateson and Goldschmidt, who correctly conceived the species problem to be the explanation of organic gaps, but then mistakenly ascribed them to single mutations causing large morphological change. This idea foundered on the lack of a convincing scenario for fixing these mutations and on the evidence that species differed in not one but many genes. For many years after Darwin, the origin of species remained the most important unsolved problem of evolution. The mathematical evolutionists of the modem synthesis had little to say about this problem, and much of what they did say was wrong. Our modern theories of speciation derive almost entirely from a naturalist and an experimentalist, Ernst Mayr and Theodosius Dobzhansky, and their two classic books, Genetics and Origin of Species (Dobzhansky 1937) and Systematics and the Origin of Species (Mayr 1942), later rewritten and expanded as Animal Species and Evolution (Mayr 1963). On the occasion of Mayr's ninetieth birthday, I am pleased to pay him tribute by discussing and evaluating his four major contributions to the species problem. Three of these-the emphasis on discontinuous organic forms, the encapsulation of such discontinuities in the biological species concept, and the theory of allopatric speciation-are milestones of evolutionary biology that constitute the modem dogma of speciation. Mayr's fourth contribution, the idea of revolutions in isolated populations, is decidedly less important, and, it seems to me, probably incorrect. It will be impossible to discuss Mayr's work without also mentioning that of Dobzhansky, whose genetic expertise made the theory of speciation a true product of the modem synthesis.

Song repertoires do not hinder neighbor-stranger discrimination

Through playback experiments and a comparative study we tested the hypothesis that song repertoires hinder individual recognition by song in birds. Our playback tests take advantage of the peculiar singing behavior of two species of parulid warblers: the American redstart (Setophaga ruticilla) and the yellow warbler (Dendroica petechia). Males of both species sing either the same song repeatedly (“repeat mode”) or a repertoire of songs in series (“serial mode”). Subjects were played the repeat song and the serial songs from a territorial neighbor and from a stranger some territories distant. Counter to the prediction of the hypothesis, they discriminated equally well between neighbors and strangers when the several serial songs were used as when the single repeat song was played. Thus, neither the small repertoires used by redstarts in serial mode (2–8 songs) nor the larger ones used by yellows (an average of over 20 songs) appear to hinder neighbor-stranger discrimination. In our comparative test, we examined the relationship between neighbor-stranger discrimination and repertoire size among 20 species for which data were available. Using two comparative methods, we did not find the predicted significant negative relationship.

A new species of Phylloscopus warbler from central China

A new species of leaf warbler (Sylviidae: Phylloscopus) is described from the mountains of central China. Morphologically it is slightly, yet significantly, different from the partly sympatric P. (proregulus) chloronotus. However, both song and calls are very different, and playback tests elicited no response from either species to the other's song. There are also differences in habitat preference and breeding biology of the two species.

Post‐juvenile moult in relation to dispersal and migration in the ChiffchaffPhylloscopus coltybita

An examination of 191 juvenile Chiffchaffs in Cleveland, north‐east England showed all birds renewed body, head and tail covert feathers during post‐juvenile moult. Replacement of inner greater coverts, tertials and central tail feathers occurred in the majority of birds. Start of moult occurred at around 53 days of age and finished about 45 days later. Premigratory dispersal took place before or in the early stages of moult and during mid‐moult birds remained sedentary with migration occurring as birds finished moult. Body weights associated with migration are discussed speculatively. Commencement and extent of moult was more similar to that of Blackcaps than other warbler species previously studied (Norman 1981, 90). It is suggested this was influenced, in part,by the shorter migrations of Chiffchaffs and Blackcaps to their winter quarters.

Territorial spacing and interspecific competition in three species of reed warblers.

Ecological and temporal aspects of the occurrence and dispersion patterns in three reed warbler species were examined. This provided insight into their intra-and interspecific territoriality. Seasonal changes in the occurrence of territorial males in a reed bed along a gradient from the shore landward were studied. The results demonstrate that intra- and interspecific spacing depends on interspecific dominance and/or ecological constraints. In this case it was shown that there is competition for common habitats between reed warblers and great reed warblers, whereas the moustached warbler is ecologically segregated. The reasons for these dispersal patterns are discussed. They do not appear to enhance the availability of food resources. It seems more likely that territorial spacing might function to reduce nest predation.

TARGETS OF SEXUAL SELECTION: SONG AND PLUMAGE OF WOOD WARBLERS.

Extant hypotheses predict that, in the face of sexual selection, avian song and plumage may evolve in a concerted fashion, in an antagonistic fashion, or in ways unrelated to each other. To test these ideas regarding which traits sexual selection targets, and the consequences for other traits, we analyzed patterns of song complexity and plumage dimorphism in 56 species of wood warblers (Parulinae). Overall, males of more dimorphic species sang shorter songs more often, but did not have more complex songs. However, when monomorphic species were excluded from the analysis, we found that the total time spent singing and repertoire size increased with plumage dimorphism. Monomorphic species are predominantly ground-nesters and the greater risk of nest predation for these species may constrain males from becoming more visually conspicuous. Thus, sexual selection may have been restricted to targeting song in these species. Even though song may have been the only target of sexual selection in ground-nesting species, overall, song in those species is not more complex than in species that nest above the ground. We propose that traits targeted by sexual selection evolve in concert, except when constrained by some ecological factor.

L’évolution récente de l’avifaune du Nord-Est marocain : pertes et gains depuis 35 ans

The author studied the avifauna of north-eastern Morocco from 1953 to 1959 as a resident naturalist, and visited the area occasionally afterwards. A more recent visit enables him to review the drastic changes, both negative and positive, which took place in the past 35 years, due to demographic pressure and agricultural development. On the plateau steppe, the numerous birds of prey and corvids which used to nest on the scattered betoum trees Pistacia atlantica have now disappeared, the « dayas » being presently used for cultivation. On the other hand, the large raptors, social corvids, and bald ibises Geronticus eremita, formerly breeding on the cliffs of the Debdou-Tlemcen ridge, also disappeared due to direct human persecution. Conversely, the small species of larks, chats, finches, and warblers are now as numerous as before. On the contrary, the damming of the River Moulouya and the irrigation of 30,000 ha of the coastal plain, have drastically altered the course of the river and the shape of the delta, creating oxbow lakes and increasing significantly the size of the original wetlands. These artificial wetlands now attract large populations of water birds, 18 species of which were found breeding versus 4 in 1959. Among them, the Marbled teal Marmaronetta angustirostris and the Purple gallinule Porphyrio porphyrio are now firmly established. Palearctic migrants were also observed in large numbers in this area. The lower Moulouya wetlands should now be protected as soon as possible.

Foraging Segregation of Australian Warblers (Acanthizidae) in Open Forest near Sydney, New South Wales

Nine species of Australian warblers (Acanthizidae) occur together in open eucalypt forests near Sydney, New South Wales. The ecological segregation of six of these species, which foraged primarily in shrub and tree vegetation and are similar sized (5-8 g), was studied during 1984. Seasonal data were obtained for five species; Weebill Smicromis brevirostris, White-throated Warbler or Gerygone Gerygone olivacea, Striated Thornbill Acanthiza lineata, Little Thornbill A. nana and Buff-rumped Thornbill A. reguloides. The sixth species, Brown Thornbill A. pusilla, was uncommon and seasonal comparisons were not possible. As has been reported for similar species associations in the northern hemisphere, the species studied differed in prey attack behaviour, foraging heights, use of plant species and selection of foraging substrates. There were significant seasonal differences in the use of foraging resources. For example, bark was more important as a foraging substrate in autumn and winter than in spring and summer. A. reguloides foraged more on the ground outside the breeding season than when nesting. The increased abundance of flying insects during summer correlated with an increased use of hawking and snatching as prey attack behaviours by all species. Despite their differences, species broadly overlapped in their use of resources and had similar niche breadths. Overlaps in the use of resources were greatest during spring, when prey resources were probably most abundant, and least in autumn when prey decreased in abundance. The forest in which the study was conducted was dominated by two species of eucalypts. Birds selected between these species but used the same foraging behaviours in each. Despite the selection between eucalypt species, the limited array of plant species had little effect on species richness. Comparison of niche breadths for the same species at other sites where there were different numbers of co-existing species suggests that niche breadth and overlap may be primarily determined by the availability of resources (e.g. substrates, plant species) and not by competitive interactions between the species themselves.

Use of song types by the Chestnut-sided Warbler: evidence for both intra- and inter-sexual functions

Males of many wood warbler (Parulinae) species use different song types in different contexts, yet the exact functions of the two main song type categories remain unclear. We studied the use of songs by both experimental (males whose mate had been removed from the territory) and control male Chestnut-sided Warblers (Dendroica pensylvanica) during the dawn hour and midmorning throughout the breeding season. Unpaired males sang more accented-ending songs and fewer unaccented-ending songs than paired males during all observation periods. Accented-ending songs appeared to be used primarily in the absence of intrasexual stimuli, and the percentage of unaccented-ending songs that was used during the nesting cycle appeared to fluctuate directly with the intensity of defense by the male of both his female and his territory. During courtship the male sang accented-ending songs on those infrequent occasions when he did sing in the immediate presence of his female, regardless of her location and the presence or absence of other males. These critical observations seem most consistent with the conclusion that the accented-ending songs are primarily intersexual. The unaccented- and accented-ending categories of song types appear to be used mainly as intra- and inter-sexual messages, respectively.