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First evidence for eccentric prealternate molt in the indigo bunting: Possible implications for adaptive molt strategies

Authors:
Jared D. Wolfe at Michigan Technological University
Jared D. Wolfe
Peter Pyle at The Institute For Bird Populations
Peter Pyle
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Figure 1.
... Considering that prealternate molts may serve as an adaptation associated with the rigors of migratory behaviors (Howell 2010, Pyle and Kayhart 2010, Wolfe and Pyle 2011, Simpson et al. 2015, Terrill et al. 2020, it is not surprising they appear rare among sedentary Neotropical species. Where prealternate molts do occur among forestdwelling and resident Neotropical landbirds, they appear most common in tanagers (Thraupidae), and to date have been documented in Cyanerpes, Thraupis, Habia, Hemithraupis, Volatinia, Sporophila, Oryzoborus, and Lanio (Dickey and van Rossem 1938, Ryder and Wolfe 2009, Johnson and Wolfe 2017 genera. ...
... obs., Johnson and Wolfe 2017;Myiarchus in Tyrannidae, Pyle 1997, Guallar et al. 2009). Many species in these genera frequent canopies, forest edges, and open grasslands and may sustain a disproportionate amount of feather damage from the sun (Terrill et al. 2020), which is conceptually similar to the hypothetical framework used to explain inserted molts in Nearctic-Neotropic migrants (Pyle 1998, Pyle and Kayhart 2010, Wolfe and Pyle 2011. ...
... However, outside these forests, some African and Australian birds such as widowbirds (Euplectes spp.) and fairywrens (Malurus spp.) are renowned for prealternate molts resulting in dramatic changes in seasonal dichromatism (Mulder andMagrath 1994, Craig 2017). Widowbirds and fairywrens both occur in high ultraviolet environments, which may have led to the evolution of an inserted molt to replace worn plumage, providing an evolutionary opportunity for repurposing by sexual selection--similar to warblers (Parulidae; Kayhart 2010, Wolfe andPyle 2011). In the Neotropics, seedeaters (Sporophila) occur in brushy and sunny environments and often exhibit inserted prealternate molts like those found in widowbirds (although not as extensive) and fairywrens. ...
Ecological and evolutionary significance of molt in lowland Neotropical landbirds
Article
Full-text available
  • Mar 2021
The slow-paced life history of many Neotropical birds (e.g., high survival and low fecundity) is hypothesized to increase lifetime fitness through investments in self-maintenance over reproduction relative to their temperate counterparts. Molt is a key investment in self-maintenance and is readily shaped by environmental conditions. As such, variation in molt strategies may be a key mechanism underlying life-history trade-offs and adaptation to new environments. Here, we review molt strategies from a diversity of lowland Neotropical landbirds and examine how variation in molt strategies, characterized by differences in molt insertions, timing, extent, and duration contribute to life-history variation and adaptation to diverse ecological conditions. In addition to our synthesis, we present a case study to examine the relationship between home range size and duration of the definitive prebasic molt of a well-studied subset of Amazonian landbirds. Our results suggest a connection between prolonged molt duration and larger home range size of small-to-medium-sized Amazonian landbirds. Our aims were to identify key gaps in our knowledge of Neotropical bird molt, to stimulate further comparative studies into the evolution of molt strategies, and to highlight how variation in molt strategies may be a key mechanism underlying life-history variation across latitudes.
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... Feather colour can also be mechanically altered. Many bird species alter their plumage through biannual moults between a more cryptic non-breeding and a more colourful breeding plumage, although regular moults may have arisen simply to replace worn feathers and were only later co-opted for seasonal phenotype alteration (Pyle & Kayhart, 2010;Wolfe, 2011). Some species of birds [e.g. ...
... Different bird species show a variety of moult patterns (Stresemann & Stresemann, 1966;Pyle, 1997). Hypotheses have been posited linking feather functions to the evolution of moult patterns (Howell, 2010;Pyle & Kayhart, 2010;Wolfe, 2011) and some studies have linked patterns of moult to ecological (Kiat et al., 2020a,b;Kiat & Izhaki, 2020;Terrill, 2018;Terrill, Seeholzer & Wolfe, 2020;Wolfe et al., 2021) and evolutionary processes (Bridge et al., 2007;Delhey et al., 2020;Guallar & Figuerola, 2016;Guallar, Rueda-Hern andez & Pyle, 2020;Holmgren & Hedenström, 1995;Svensson & Biological Reviews (2022) Feather function and the evolution of birds Hedenström, 1999;Kiat, Ihzaki & Sapir, 2019). However, our understanding of the evolution of moult patterns in birds remains nascent compared to other life-history characteristics. ...
Feather function and the evolution of birds
Article
Full-text available
  • Nov 2022
The ability of feathers to perform many functions either simultaneously or at different times throughout the year or life of a bird is integral to the evolutionary history of birds. Many studies focus on single functions of feathers, but any given feather performs many functions over its lifetime. These functions necessarily interact with each other throughout the evolution and development of birds, so our knowledge of avian evolution is incomplete without understanding the multifunctionality of feathers, and how different functions may act synergistically or antagonistically during natural selection. Here, we review how feather functions interact with avian evolution, with a focus on recent technological and discovery‐based advances. By synthesising research into feather functions over hierarchical scales (pattern, arrangement, macrostructure, microstructure, nanostructure, molecules), we aim to provide a broad context for how the adaptability and multifunctionality of feathers have allowed birds to diversify into an astounding array of environments and life‐history strategies. We suggest that future research into avian evolution involving feather function should consider multiple aspects of a feather, including multiple functions, seasonal wear and renewal, and ecological or mechanical interactions. With this more holistic view, processes such as the evolution of avian coloration and flight can be understood in a broader and more nuanced context.
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... In many species, a sequence-based definition results in the prealternate moult being defined as simply including those feathers moulted for a second time within a moult cycle; i.e. replacing either formative or basic with alternate feathers, but this does not form the basis of definition. In some species the first prealternate moult can be more extensive than the preformative moult, for example in willow warbler Phylloscopus trochilus, indigo bunting, American yellow warbler Setophaga petechia and bobolink Dolichonyx oryzivorus (Pyle 1997, Wolfe and Pyle 2011, Jenni and Winkler 2020, resulting in juvenile wing feathers being replaced by first alternate feathers. In these species definitive prealternate moults are also extensive, first prealternate moults often proceed in the same sequence as the preformative moults, and a sequence-based definition for each moult is maintained despite some variability in the sequence of some (but not all) prealternate moults, as mentioned above. ...
Defining moults in migratory birds: a sequence‐based approach
Article
Full-text available
Two broad nomenclatures have emerged to describe moult strategies in birds, the ‘life‐cycle' system which describes moults relative to present‐day breeding and other life‐history events, and the Humphrey–Parkes (H–P) system which reflects the evolution of moults along ancestral lineages. Using either system, challenges have arisen defining strategies in migratory species with more than one moult per year. When all or part of two moults occur in non‐breeding areas, extra moults may fail to be recognized or they may have been discriminated temporally, whether feathers are replaced in fall, winter or spring. But in some cases feather replacement can span the non‐breeding period, and this has resulted in an inability to identify inserted moults and to compare moult strategies between species. Furthermore, recent analyses on factors influencing the extent of the postjuvenile or preformative moults have either confined this moult to the summer grounds or presumed that it can be suspended and resumed on winter grounds, which has lead to quite divergent results and interpretations. Evolutionarily, the timing, extent and location of moults show phenotypic lability whereas the sequence in which feathers are replaced is comparatively conserved. As, such, I propose defining moults on the basis of feather‐replacement sequences as opposed to timing or location of replacement, including strategies in which discrete moults can be suspended for migration and overlap temporally. I provide examples illustrating the functionality of a sequence‐based definition in three migratory North American passerines that can undergo feather replacement twice in non breeding areas, and I demonstrate how this system can effectively apply to moults in many other passerine and non‐passerine species. I recommend that authors studying the evolutionary drivers of moult strategies in migratory birds adopt a sequence‐based approach and to carefully consider replacement strategies both prior to and following autumn migration.
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... Although the study of molt and plumages is relatively advanced in North America (Pyle 1997a(Pyle , 1997b, the timing and extent of molts that occur on nonbreeding grounds of Neotropical migrants are not as well known. Several recent studies of common migratory species have revealed more extensive molt than previously known Kayhart 2010, Wolfe andPyle 2011). In addition, previously unknown molts have been detected and described (Dittmann andCardiff 2009, Sieburth and. ...
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... Different bird species show a variety of molt patterns (Stresemann andStresemann 1966, Pyle 1997). Some hypotheses have been put forward that link the way birds use their feathers to the evolution of these molt patterns (Howell 2010, Pyle and Kayhart 2010, Wolfe 2011) and some studies have linked evolutionary process to patterns of molt (Bridge et al. 2007, Delhey et al. 2020, Guallar and Figuerola 2016, Holmgren and Hedentröm 1995, Svensson and Hedenström 1999, as well as ecological processes influencing molt (Kiat et al. 2020a, Kiat and Izhaki 2020, Terrill 2018, Wolfe et al. 2021). However, our understanding of the evolution of molt patterns in birds remains nascent compared to other life history characteristics of birds. ...
On the Multifunctionality of Feathers and the Evolution of BIrds
Preprint
  • May 2021
The ability feathers have to perform many functions simultaneously and at different times is integral to the evolutionary history of all birds. Many studies focus on single functions of feathers; but any given feather performs many functions over its lifetime. Here, we review the known functions of feathers and discuss the interactions of these functions with avian evolution. Recent years have seen an increase in research on the evolution and development of feather functions because of an increase in high quality fossils with preserved feathers, new tools for understanding genetic mechanisms of feather development, new tools for measuring and analyzing feather color, availability of phylogenies and phylogenetic comparative methods, and an increase in interest in feather molt. Here, we aim to review how feather functions interact with avian evolution, with a focus on recent technological and discovery-based advances. By synthesizing research into feather functions over hierarchical scales, we aim to provide a broad context for how the adaptability and multifunctionality of feathers have allowed birds to diversify into the astounding array of environments and life-history strategies. Overall, we suggest research into avian evolution that involves feather function in any way should consider all aspects of a feathers’ functionality, including multiple functions, molt patterns, ecological/mechanical interactions, and feather wear over time. With this more holistic view, processes such as the evolution of avian coloration and flight can be understood in a broader and more nuanced context.
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... The reason behind this prioritization is obscure, although it may have arisen as a solution to reduce flight losses during remex molt, a strategy that could have been selected to reduce predation risk of inexperienced birds in species that need to replace the feathers forming the wingtip during the post-juvenile molt. This view is further supported by the fact that eccentric phenotypes are extremely infrequent in adults (Wolfe & Pyle 2011). Many eccentric phenotypes are heavier than expected but abridged II phenotypes are systematically heavier. ...
STRUCTURE, REGULATION, AND EVOLUTION OF PASSERINE MOLT
Thesis
  • Dec 2020
Molt is the process of plumage renewal by which birds maintain and adjust its functionality throughout their lifecycle. Multiple elements have been tackled in bird molt research (timing, duration, sequence, intensity, extent, feather growth rate, and plumage quality), but major gaps still exist on molt regulation, and especially on molt evolution. This thesis focuses on one molt element extensively recorded since mid-20th century but seldom studied as an individual trait: the set of feathers replaced after a given molt episode by one individual (here referred to as final molt phenotype). This is surprising because feathers differ in their function (e.g. signaling, thermoregulation, contribution to different flight functions, durability), costs of production, and morphology (e.g. exposure, mass, shape), all of which can be targeted by natural selection. Therefore, the final molt phenotype should be under strong selective pressures, suggesting that its regulation has been shaped during evolution to optimize plumage performance throughout the bird’s lifecycle. This thesis explores the potential of analyzing final molt phenotypes as is (instead of being analyzed partially or indirectly) to uncover underlying mechanisms of molt regulation and to provide insights on the evolution of molt in passerine birds. Following are the main findings presented in this thesis. Final molt phenotypes differed between the post-juvenile and the pre-breeding molts along the passerine phylogeny. A nested organization of final molt phenotypes suggested a rank of feather molt importance as underlying rule of molt. However, deviations from perfect nestedness were largely associated with the pre-breeding molt. Shared ancestry explained a large portion of final molt phenotype variation, likely due to constraints associated to plumage morphology, which is highly conserved in passerines. Phylogenetic analyses confirmed the phylogenetic independence of the pre-breeding molt and the strong phylogenetic signal of the post-juvenile molt. Further, they showed the overlooked relevance of environmental factors on the evolution of passerine molt, although their effect varied among taxonomic groups and molt episodes, thus highlighting the flexibility and adaptiveness of molt. Findings exposed in this thesis confirm the relevance of the final molt phenotype as a promising element to advance in our understanding of bird molt.
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... Photograph: Ryan S. Terrill that prealternate molts appear to be more common in long-distance migrants than in nonmigratory species and does not always produce plumage color change (Figure 2). Pyle and Kayhart (2010) and Wolfe (2011) observed that a prealternate molt that produces feathers with the same coloration as prebasic molt is a widespread phenomenon in birds and proposed that prealternate molt may not evolve for breeding plumage necessarily. Instead, they proposed that prealternate molt evolves to replace worn feathers and then can be co-opted by pressures for seasonal dichromatism. ...
Evolution of breeding plumages in birds: A multiple‐step pathway to seasonal dichromatism in New World warblers (Aves: Parulidae)
Article
Full-text available
  • Aug 2020
Many species of birds show distinctive seasonal breeding and nonbreeding plumages. A number of hypotheses have been proposed for the evolution of this seasonal dichromatism, specifically related to the idea that birds may experience variable levels of sexual selection relative to natural selection throughout the year. However, these hypotheses have not addressed the selective forces that have shaped molt, the underlying mechanism of plumage change. Here, we examined relationships between life‐history variation, the evolution of a seasonal molt, and seasonal plumage dichromatism in the New World warblers (Aves: Parulidae), a family with a remarkable diversity of plumage, molt, and life‐history strategies. We used phylogenetic comparative methods and path analysis to understand how and why distinctive breeding and nonbreeding plumages evolve in this family. We found that color change alone poorly explains the evolution of patterns of biannual molt evolution in warblers. Instead, molt evolution is better explained by a combination of other life‐history factors, especially migration distance and foraging stratum. We found that the evolution of biannual molt and seasonal dichromatism is decoupled, with a biannual molt appearing earlier on the tree, more dispersed across taxa and body regions, and correlating with separate life‐history factors than seasonal dichromatism. This result helps explain the apparent paradox of birds that molt biannually but show breeding plumages that are identical to the nonbreeding plumage. We find support for a two‐step process for the evolution of distinctive breeding and nonbreeding plumages: That prealternate molt evolves primarily under selection for feather renewal, with seasonal color change sometimes following later. These results reveal how life‐history strategies and a birds' environment act upon multiple and separate feather functions to drive the evolution of feather replacement patterns and bird coloration.
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... This score measured all body parts of male Indigo Buntings that can potentially exhibit blue plumage colouration including the crown, nape, breast, flanks, belly, back, rump, wing coverts, primary feathers, and tail feathers. Though simple, this visual assessment of the percent of body plumage that is blue has been used in previous studies, both for Indigo Buntings in winter plumage (Wolfe and Pyle, 2011), and closely-related Blue Grosbeaks in nuptial plumage (Keyser and Hill, 2000). T.E.W. was present for the capture and assessment of percent blue for all birds in this study. ...
Condition Dependence of Structural Plumage Coverage in Indigo Buntings Passerina Cyanea
Article
Full-text available
  • Feb 2018
Nuptial plumage colouration is seemingly favoured by females of avian species with regards to sexual selection. This particular secondary sexual characteristic has been previously shown to be a condition-dependent signal of individual quality among passerines with pigment-based colouration (i.e. yellows and reds). In contrast, relationships between structural plumage colouration (i.e. blues) and aspects of both physical quality and physiological function have been understudied. Using free-living Indigo Buntings (Passerina cyanea) as a study species, we compared the percentage of blue feather coverage to body condition, innate immune responses, antioxidant capacity, stress physiology, reproductive physiology, and parasitism. We found the overall percentage of blue feathers on individual birds to be positively correlated with testosterone levels and body condition, while negatively correlated with heterophil to lymphocyte ratio. Birds with more blue coverage were also less likely to harbour blood parasites. Our results indicate male Indigo Buntings with greater moult investment have better overall body condition, lower stress, increased testosterone levels, and decreased parasitic susceptibility.
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Replacement of Primaries during Prealternate Molt in North American Larus Gulls
Article
Full-text available
  • Dec 2018
We document replacement of primaries during the prealternate molt in two and possibly three species of North American gulls of the genus Larus, including the first report of such replacement in an adult Yellow-footed Gull (L. livens), the first report in the Lesser Black-backed Gull (L. fuscus) in the Americas, and possibly the first report for the American Herring Gull (L. argentatus smithsonianus). The incidence and extent of replacement of primaries is greater during the second prealternate than during subsequent prealternate molts, which is likely related to second-cycle molts in Larus being earlier than the subsequent molts. The second prealternate molt of the Lesser Black-backed Gull includes up to all flight feathers (but not all wing coverts). The sequence of replacement of primaries during the prealternate molt matches that of the prebasic molt, starting at the innermost primary and proceeding distally; however, the sequence of replacement of secondaries can differ from that during the prebasic molt, perhaps because of a difference in the underlying mechanisms controlling these molts. Prealternate molt of inner primaries can begin before prebasic molt of outer primaries is completed, a pattern resembling Staffelmauser, but all evidence suggests that the ensuing prebasic molt of the primaries begins at pi, as in terns, rather than at the point where the inner molt wave is suspended, as during Staffelmauser in other large volant birds. We propose that the occurrence and extent of prealternate molt of the remiges in Larus is correlated with the latitude at which an individual winters and/or the timing of the prebasic molt the year before, as much as or more so than with phylogeny. The possible replacement of primaries during the second prealternate molt in North American but not European subspecies of the Herring Gull could relate to some individuals of the American subspecies wintering farther south.
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A phylogenetic analysis of the evolution of moult strategies in Western Palearctic Warblers (Aves: Sylviidae)
Article
Full-text available
  • Jun 1999
Adult birds replace their flight feathers (moult) at least once per year, either in summer after termination of breeding or (in the case of some long-distance migratory species) in the winter quarters. We reconstructed the evolutionary pathways leading to summer and winter moult using recently published molecular phylogenetic information on the relationships of the Western Palearctic warblers (Aves: Sylviidae). Our phylogenetic analysis indicates that summer moult is the ancestral pattern and that winter moult has evolved 7–10 times in this clade. As taxa increased their migratory distance and colonized northern breeding areas, summer moult disappeared and winter moult evolved. Our data also allows us to trace the historical origins of unusual moult patterns such as the split-moult and biannual moult strategies: the most parsimonous explanations for their origins is that they evolved from ancestral states of summer moult. We briefly discuss our results in the light of recent criticisms against phylogenetic comparative methods and the utility of historical versus functional definitions of adapation.
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Temporal, Spatial, and Annual Variation in the Occurrence of Molt-Migrant Passerines in the Mexican Monsoon Region
Article
  • Nov 2009
Adults of several species of western North American passerines are known to migrate to the Mexican monsoon region to undergo molt from July to October before continuing migration to their wintering grounds in the neotropics, but little is known about the biology and habitat requirements of these birds on their molting grounds. Therefore we established 13 banding stations during the monsoon seasons of 2007 and 2008 in southeastern Arizona, central Sonora, and central Sinaloa. We studied the spatial and temporal occurrence of 10 previously known and 9 new species of molt migrants on the molting grounds. In many of these species most or all individuals appeared to undertake molt migration but in others it appeared to be limited to a small proportion of the population, underscoring that molt migration must be defined at the level of the individual rather than of the population. Our results suggest that during the drier 2007 monsoon season molt migrants sought out riparian habitats, whereas in the wetter 2008 season, when the flush of vegetation was greater, they were more widely distributed in drier habitats. Site fidelity to molting grounds was virtually zero, significantly less than site fidelity to banding stations on breeding and winter grounds. Our results suggest that molt migration to the Mexican monsoon region is a stochastic or plastic process, substantially influenced by individual choices related to variation in weather and the preceding breeding season. Our study also emphasizes the need to conserve a mosaic of habitats in the monsoon region appropriate for molting birds.
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Geographic variation in color, measurements, and molt of the Lesser Goldfinch in North America does not support subspecific designation
Article
  • Jan 2009
I examined 963 study skins of Lesser Goldfinches (Carduelis psaltria) from the United States to central Mexico, for color, measurements, molt, and plumage wear. These specimens had been previously assigned to as many as three subspecies. Females did not vary geographically in color. Green-backed, green-eared males predominated in the Pacific coastal United States and northern Mexico. Black-backed, black-eared males predominated in the interior, east of 106° West longitude. This west to east color difference varied clinally, and may be a simple genetic polymorphism, so subspecific distinctions cannot be justified by coloration alone. Measurements of bill, tail, and wing, but not tarsus, varied slightly but significantly from smallest along the Pacific coast to largest in south-central Mexico. Since measurements varied clinally, and overlapped extensively, subspecific separation based on size is not practical. Pacific coastal birds subjected to winter rainfall maxima had a complete postbreeding molt, with a sparse prebreeding body molt only in females, and a postjuvenal molt that replaced significantly more flight feathers in males. Interior birds subjected to summer precipitation maxima had a nearly complete or complete prebreeding molt and a usually less complete postbreeding molt. The postjuvenal and postbreeding molts of interior birds were very similar and did not differ between the sexes. Although these sexual and geographic variations of molt are striking, they may reflect phenotypic plasticity in response to environmental contingencies, rather than genetic differences. These variations in one intergrading population support doubts that the Humphrey-Parkes terminology for molts and plumages can reflect phylogenetic homologies among species.
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The molt of the Little Stint Calidris minuta in the Kenyan Rift Valley
Article
Moult data were collected during 1967–80 from some 6900 Little Stints in the southern Kenyan rift valley. Adults typically moulted from summer to winter body and head plumage during September and early October, soon after arrival. The complete pre-winter wing and tail moult began in most adults between mid-September and early October. Some birds finished by December, but others continued until February and March. Individual duration was usually between 100 and 150 days. Adults which completed this moult early often remoulted outer primaries between January and early April. Young birds acquired first-winter body plumage during October and early November. Some 90% had a complete pre-winter wing and tail moult. This usually began between December and early February, and finished during March or early April, taking about 70–100 days. In about 10% of young birds, flight feather moult was restricted to the outer primaries and inner secondaries. Birds adopting this strategy typically began moult late, during January or February. Short periods of suspension were common during pre-winter wing moult, particularly in adults. The difference in moult speed between adult arid first-winter birds was attributable in the primary, secondary and tail tracts to differences in numbers of growing feathers. Practically all birds completed a pre-summer moult involving the entire body and head plumage, most of the tertials, some or all of the tail feathers and many wing coverts. Most birds began this moult between early February and late March, and finished between mid-April and early May. It was typically later and more rapid in first-year birds than adults. In late birds, the onset of pre-summer moult was linked to the final stages of pre-winter moult. The wing moult of the Little Stint in different wintering areas is discussed. First-winter moult strategy is compared with that in other small Calidris species.
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Assessing Landbird Monitoring Programs and Demographic Causes of Population Trends
Article
Population trend data from the North American Breeding Bird Survey (BBS) have been used to identify conservation priorities and justify major conservation initiatives. Yet the BBS has been criticized for potential habitat bias and reliance on abundance indices to estimate trends. We compared 1992–2003 BBS trend estimates to trend estimates derived from bird-banding data collected as part of the Monitoring Avian Productivity and Survivorship (MAPS) program for 36 wood warbler species. Similarity in trends between the 2 monitoring programs at the survey-wide and program-wide scales suggested that each program can provide accurate trend information. The MAPS program, however, was designed primarily to complement (rather than duplicate) count-based efforts, such as the BBS, by providing estimates or indices of demographic rates. Demographic data from MAPS can be used to lend insight into proximate (demographic) causes of population trends and inform management. We illustrate this with analyses of 1992–2003 MAPS data for yellow warbler (Dendroica petechia). We used reverse-time capture-recapture models to evaluate importance of new recruits (including immigrating adults and young from the previous year) relative to surviving adults in explaining variation in trend among BBS physiographic strata. We included the number of young per adult captured (an index of productivity) as a covariate in models to assess effects of productivity on trends. Survival was the key demographic driver of recent population trends. Comparison of MAPS productivity indices and adult apparent survival rate estimates to BBS trend estimates largely confirmed this inference. We suggest that increased MAPS coverage, better coordination between MAPS and the BBS, and continued development of analytical methods that link the 2 programs will enhance the value of these monitoring efforts to land managers and conservation planners working at a variety of spatial scales.
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Influences of the El Niño/Southern Oscillation and the North Atlantic Oscillation on Avian Productivity in Forests of the Pacific Northwest of North America
Article
  • Jul 2002
To model the effects of global climate phenomena on avian population dynamics, we must identify and quantify the spatial and temporal relationships between climate, weather and bird populations. Previous studies show that in Europe, the North Atlantic Oscillation (NAO) influences winter and spring weather that in turn affects resident and migratory landbird species. Similarly, in North America, the El Niño/Southern Oscillation (ENSO) of the Pacific Ocean reportedly drives weather patterns that affect prey availability and population dynamics of landbird species which winter in the Caribbean. Here we show that ENSO- and NAO-induced seasonal weather conditions differentially affect neotropical- and temperate-wintering landbird species that breed in Pacific North-west forests of North America. For neotropical species wintering in western Mexico, El Niño conditions correlate with cooler, wetter conditions prior to spring migration, and with high reproductive success the following summer. For temperate wintering species, springtime NAO indices correlate strongly with levels of forest defoliation by the larvae of two moth species and also with annual reproductive success, especially among species known to prey upon those larvae. Generalized linear models incorporating NAO indices and ENSO precipitation indices explain 50–90% of the annual variation in productivity reported for 10 landbird species. These results represent an important step towards spatially explicit modelling of avian population dynamics at regional scales.
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