Showing papers in "The Auk in 1999"
TL;DR: It is suggested that feather degradation may contribute to the deterioration of feathers and be a selective force in the evolution and timing of molt during the summer when the bird becomes wet, for example during thunderstorms.
Abstract: We sampled bacteria from the plumage of 1,588 individuals of 83 species of birds. Feather-degrading bacteria, those able to extract energy and nutrients by breaking up 3-keratin, were isolated from 134 individuals in 32 species. Nine of 11 samples of feather- degrading (keratinolytic) bacteria were identified as Bacillus licheniformis, one as B. pumilus, and one as a Bacillus of undetermined species. A strong correlation between occurrence of keratinolytic bacilli and the number of birds sampled per species suggests that feather-de- grading bacilli are widespread among birds. The bacillus occurred on 6.7 to 10.7% of birds and showed little annual variation. The incidence of birds with feather-degrading bacilli was highest in late fall and winter and lowest in early spring and late summer. The bacilli oc- curred most frequently on the venter and less commonly on the dorsum and tail. They oc- curred most frequently on ground-foraging species and least frequently on aerial-foraging species. Regardless of avian species, time of year, or area of the bird from which the bacilli were isolated, the rate at which bacilli degraded feathers was similar. Because bacilli are active only when conditions are warm and humid, we suggest that they degrade feathers during the summer when the bird becomes wet, for example during thunderstorms. Such feather degradation may contribute to the deterioration of feathers and be a selective force in the evolution and timing of molt. Received 6 October 1997, accepted 29 July 1998.
248 citations
TL;DR: Nectar is an exclusively parental food type in Orange-tufted Sunbirds, and the methodology can be used to determine whether adult hummingbirds feed nectar to their nestlings.
Abstract: That we always clearly detected a small dose of dyed sugar solution in the color of feces of hand-fed chicks, and that we failed to detect any color changes in chick fecal sacs during our feeder presentation, suggest hat parent sunbirds feed none or only negligible amounts of feeder sugar solution to their chicks. Moreover, no detectable amounts of sugar occurred in nestling esophagi or excreta fluid samples, despite the fact that we could simulate such a measurable effect through hand-feeding chicks with nectar. Therefore, we conclude that nectar is an exclusively parental food type in Orange-tufted Sunbirds. It has been suggested that hummingbirds feed nectar to their chicks (Hainsworth 1977). To our knowledge, however, no one has documented this empirically. Therefore, we suggest that our methodology can be used to determine whether adult hummingbirds feed nectar to their nestlings. Acknowledgments.--This study was funded by a grant from the Mitrani Center for Desert Ecology and is paper number 258 of the Mitrani Center.
238 citations
TL;DR: The authors' analyses indicate that geese, swans, and sea ducks show high levels of winter philopatry, with homing rates varying between 49 and 98% to small study areas, and that both genetic and ecological mechanisms may play a role in the evolution of philipatry to the wintering ground.
Abstract: Philopatry in migratory species can apply to any location used during the annual cycle. The degree of philopatry influences the genetic structure of populations, but only at the stage of the annual cycle when pair formation and gene exchange occur. Because pair formation in birds typically occurs during the breeding season, most studies have fo- cused on breeding-site philopatry. Waterfowl (Anseriformes) are an important exception to this pattern because pair formation often occurs during the winter months. Yet, surprisingly few studies have examined winter philopatry in waterfowl. To serve as an impetus for future research, we summarize published information on winter philopatry in waterfowl and ex- amine these patterns in light of current hypotheses proposed to explain philopatric behavior. Our analyses indicate that geese, swans, and sea ducks show high levels of winter philopatry, with homing rates varying between 49 and 98% to small study areas. In contrast, return rates (0 to 20%) and homing rates (35 to 85%) to large study areas probably are comparatively lower for dabbling ducks and pochards. Unfortunately, detailed comparisons among groups are hindered by variation in the scale at which philopatric behavior is evaluated (ranging from <1 km2 to 105 kM2), and by confounding of return rates with homing rates. Future studies of winter philopatry would benefit by the adoption of a more standardized meth- odology. Many of the hypotheses proposed to explain breeding philopatry apply equally well to winter philopatry. In particular, both genetic and ecological mechanisms may play a role in the evolution of philopatry to the wintering ground. Additional field studies are needed to test these hypotheses, and we suggest future directions for a more detailed ex- amination of this neglected area of research. Received 9 September 1996, accepted 28 April 1998.
183 citations
TL;DR: This first cladistic analysis of the furnariids demonstrates the general utility of nest characters in reconstruction of avian rela- tionships, and it provides a test of monophyly for several furnariid taxa.
Abstract: We reviewed the tremendous architectural diversity of ovenbird (Furnari- idae) nests based on literature, museum collections, and new field observations. With few exceptions, furnariids exhibited low intraspecific variation for the nest characters hypothe- sized, with the majority of variation being hierarchically distributed among taxa. We hy- pothesized nest homologies for 168 species in 41 genera (ca. 70% of all species and genera) and coded them as 24 derived characters. Forty-eight most-parsimonious trees (41 steps, CI = 0.98, RC = 0.97) resulted from a parsimony analysis of the equally weighted characters using PAUP, with the Dendrocolaptidae and Formicarioidea as successive outgroups. The strict-consensus topology based on these trees contained 15 clades representing both tra- ditional taxa and novel phylogenetic groupings. Comparisons with the outgroups demon- strate that cavity nesting is plesiomorphic to the furnariids. In the two lineages where the primitive cavity nest has been lost, novel nest structures have evolved to enclose the nest contents: the clay oven of Furnarius and the domed vegetative nest of the synallaxine clade. Although our phylogenetic hypothesis should be considered as a heuristic prediction to be tested subsequently by additional character evidence, this first cladistic analysis of the fur- nariids demonstrates the general utility of nest characters in reconstruction of avian rela- tionships, and it provides a test of monophyly for several furnariid taxa. Received 29 July 1998,
179 citations
TL;DR: It is suggested that the high dispersal ability of birds (especially dabbling ducks) has important implications for recovery of branches using molecular systematics and Geographic origin for most internal branches is ambiguous using several reconstruction methods.
Abstract: We constructed a phylogeny for the dabbling ducks (tribe Anatini) based on cytochrome-b and ND2 mitochondrial gene DNA sequences. This phylogeny differed in several important respects from a morphological phylogeny developed by Livezey (1991), including the distinctiveness of the blue-winged ducks from other dabbling ducks, the inclusion of the genus Tachyeres and exclusion of Callonetta from the subtribe Anateae, and the lack of support for Mareca as a genus separate from Anas. Characters from three other data sets showed greater consistency with the molecular topology than with the morphological topology. The molecular phylogeny divides the dabbling ducks into four distinct groups: (1) four South American genera, including Amazonetta, Lophonetta, Speculanas, and Tachyeres; (2) the Baikal Teal (Anas formosa); (3) the blue-winged ducks and allies; and (4) a large clade including wigeons, pintails, mallards, and several teal lineages. An examination of the distributions of species in light of the phylogeny indicates relatively little biogeographic structure. Geographic origin for most internal branches is ambiguous using several reconstruction methods. We suggest that the high dispersal ability of birds (especially dabbling ducks) has important implications for recovery of branches using molecular systematics.
178 citations
TL;DR: Nesting vocalizations may be partly responsible for the observed difference in predation risk during the nestling period at par- asitized and nonparasitized natural nests, but other factors such as nest site or parental be- havior are likely to influence the risk of both parasitism and nest predation.
Abstract: Models concerning the evolution of avian begging behavior predict that nest- lings of brood parasites should beg more loudly or frequently than nonparasitic nestlings and that the exaggeration of begging calls in general may be limited by the risk of nest pre- dation. This study is the first to test experimentally for a link between brood parasitism, nestling vocalizations, and the risk of nest predation. Begging calls at Indigo Bunting (Pas- serina cyanea) nests parasitized by Brown-headed Cowbirds (Molothrus ater) were louder and more frequent than those at nonparasitized nests. Predation rates at Indigo Bunting nests were significantly higher at parasitized nests than at nonparasitized nests during the incu- bation period and over the entire nesting cycle, and there was a trend for such a difference during the nestling period as well. I performed an artificial nest experiment to test for an effect of nestling vocalizations on the risk of nest predation. Nests broadcasting cowbird begging calls (300 calls/h at 80 dB) experienced the highest predation rates, followed by nests broadcasting bunting begging calls (60 calls/h at 74 dB), followed by silent nests. The overall difference among predation rates for the three treatments was significant, but follow- up pairwise comparisons detected a difference in predation rates only between nests broad- casting cowbird begging calls and silent nests. Thus, nestling vocalizations may be partly responsible for the observed difference in predation risk during the nestling period at par- asitized and nonparasitized natural nests, but other factors such as nest site or parental be- havior are likely to influence the risk of both parasitism and nest predation. Received 2 Sep-
151 citations
TL;DR: Analysis of group means for seven sampling events showed that body-mass change in a group of individuals was related to mean circulating levels of each metabolite, i.e. to a characteristic metabolite profile.
Abstract: Individual quality is often assessed using a static measure of body condition, such as size-corrected body mass. Plasma metabolites have the potential to provide information on the dynamics of physiological state and thus may be better measures of individual performance capacity (and fitness). We studied relationships between rate of mass change and circulating levels of triglycerides, glycerol, and β-hydroxybutyrate in captive Western Sandpipers (Calidris mauri). The rate of mass change over one and two days prior to blood sampling was positively related to residual triglyceride (controlling for body mass at sampling) and negatively related to residual glycerol and residual β-hydroxybutyrate. The relationship between metabolite level and mass change was still apparent over a seven-day interval for glycerol, but not for the other two metabolites. In a stepwise multiple regression of mass change over two days (controlling for body mass), only β-hydroxybutyrate and glycerol were entered in the model at P < 0.15. Analysis of group means for seven sampling events showed that body-mass change in a group of individuals was related to mean circulating levels of each metabolite, i.e. to a characteristic metabolite profile. Thus, it may be feasible to employ these metabolites to assess habitat quality based on animal performance (e.g. at migratory stopover sites), or to understand the effects of climatic or anthropogenic factors on the health and survival of animals.
120 citations
TL;DR: It is suggested that experience as a helper offers a more reliable cue to nest-site quality than breeding experience because helpers are associated with nests only during the nestling phase when few nests are depredated.
Abstract: We determined whether nest-site characteristics influence reproductive suc- cess and whether experience influences nest-site selection in a population of cooperatively breeding Long-tailed Tits (Aegithalos caudatus). Nest predation was high; only 17% of breed- ing attempts resulted in fledged young. The height of nests was an important determinant of success; low nests were significantly more successful than high nests. A breeder's age, natal nest site, and breeding experience had no significant effect on nest-site selection. How- ever, failed breeders who helped at the successful nests of conspecifics built subsequent nests lower than nests built prior to their helping experience. Failed breeders who did not help showed no reduction in the height of subsequent nests. Moreover, the subsequent repro- ductive success of failed breeders who helped was significantly higher than that of failed breeders who did not help. We conclude that helpers gain information on nest-site quality through their helping experience and thus gain a direct fitness benefit from their cooperative behavior. We suggest that experience as a helper offers a more reliable cue to nest-site quality than breeding experience because helpers are associated with nests only during the nestling phase when few nests are depredated. In contrast, although successful breeders may expe-
117 citations
TL;DR: A significant relationship between mean group size and the history of occupancy of particular territories and the probability of nest cavities being built in microclimatically favorable live limbs is found, suggesting that larger groups residing on more stable territories were better able to construct nests with optimal characteristics.
Abstract: Acorn Woodpeckers (Melanerpes formicivorus) at Hastings Reservation in central California prefer to nest in dead limbs in large, dead valley oaks (Quercus lobata) and California sycamores (Platanus racemosa) that are also frequently used as acorn storage trees. Based on 232 nest cavities used over an 18-year period, we tested whether preferred or modal nest-site characters were associated with increased reproductive success (the nest-site quality hypothesis). We also examined whether more successful nests were likely to experience more favorable microclimatic conditions or to be less accessible to terrestrial predators. We found only equivocal support for the nest-site quality hypothesis: only 1 of 5 preferred characters and 2 of 10 characters exhibiting a clear modality were correlated with higher reproductive success. All three characteristics of nests known or likely to be associated with a more favorable microclimate, and two of five characteristics likely to render nests less accessible to predators, were correlated with higher reproductive success. These results suggest that nest cavities in this population are built in part to take advantage of favorable microclimatic conditions and, to a lesser extent, to reduce access to predators. However, despite benefits of particular nest characteristics, birds frequently nested in apparently suboptimal cavities. We also found a significant relationship between mean group size and the history of occupancy of particular territories and the probability of nest cavities being built in microclimatically favorable live limbs, suggesting that larger groups residing on more stable territories were better able to construct nests with optimal characteristics. This indicates that there may be demographic, as well as ecological, constraints on nest-site selection in this primary cavity nester.
113 citations
TL;DR: It is concluded that habitat quality for Ovenbirds may be lower within 150 m of unpaved roads in extensive forested landscapes, affecting territory density and possibly reproductive success.
Abstract: Numerous studies have reported lower densities of breeding Ovenbirds (Seiurus aurocapillus) adjacent to forest edges. However, none of these studies has considered habitat use and reproductive success to address mechanisms underlying the observed pattern, and most were conducted in fragmented landscapes and ignored juxtapositions of forest with narrow openings such as roads. We studied the influence of forest roads on Ovenbird density in an extensively forested region of Vermont, evaluating habitat use and reproductive success relative to mechanisms proposed to explain the density-edge relationship. Territory densities on seven study plots were 40% lower within edge areas (0 to 150 m from unpaved roads) than within interior areas (150 to 300 m from roads). We simulated the distribution of Ovenbird territories and concluded that passive displacement, where birds perceive habitat interfaces as boundaries and limit their territories entirely to forest habitat, did not account for the observed density-edge pattern. Territory size was inversely related to distance from roads, providing an alternative explanation for reduced densities near edges and suggesting that habitat quality was higher away from roads. Pairing success was lower within edge areas than within interior zones, but the difference was not statistically significant. The proportion of males that produced fledglings did not differ between edge and interior areas. We conclude that habitat quality for Ovenbirds may be lower within 150 m of unpaved roads in extensive forested landscapes, affecting territory density and possibly reproductive success.
112 citations
TL;DR: Examination of the evolutionary rate of change in bill and hindlimb morphology shows that the family Scolopacidae and the subfamily Recurvirostrinae evolved more rapidly than the species of Charadriinae.
Abstract: We studied the relationships between bill and hindlimb morphology and for- aging behavior in 17 species of shorebirds within a phylogenetic framework. The results show that the evolutionary change in bill length is related to the evolutionary change in for- aging strategies from visual hunting to tactile hunting. We also found evolutionary rela- tionships between an increase in bill length and both plunging and sweeping foraging move- ments, and a decrease in bill length and "routing" behavior. No relationships were found between hindlimb morphology and movement pattern (continuous hunting species vs. pause-travel species). Examining the evolutionary rate of change in bill and hindlimb struc- tures shows that the family Scolopacidae and the subfamily Recurvirostrinae evolved more rapidly than the species of Charadriinae. Results from our ecomorphological and evolution- ary analysis support the hypothesis by Zweers and co-workers on the evolution of feeding
TL;DR: The at-sea distribution of the threatened Spectacled Eider (Somateriafischeri) has remained largely undocumented as discussed by the authors, and the authors conducted aerial surveys to provide visual confirmation of eider flocks and to estimate numbers of birds.
Abstract: The at-sea distribution of the threatened Spectacled Eider (Somateriafischeri) has remained largely undocumented. We identified migration corridors, staging and molting areas, and wintering areas of adult Spectacled Eiders using implanted satellite transmitters in birds from each of the three extant breeding grounds (North Slope and Yukon-Kuskokwim Delta in Alaska and arctic Russia). Based on transmitter locations, we conducted aerial sur- veys to provide visual confirmation of eider flocks and to estimate numbers of birds. We identified two principal molting and staging areas off coastal Alaska (Ledyard Bay and east- ern Norton Sound) and two off coastal Russia (Mechigmenskiy Bay on the eastern Chukotka Peninsula, and the area between the Indigirka and Kolyma deltas in the Republic of Sakha). We estimated that >10,000 birds molt and stage in monospecific flocks at Mechigmenskiy and Ledyard bays, and several thousand molt and stage in eastern Norton Sound. We further identified eastern Norton Sound as the principal molting and staging area for females nest- ing on the Yukon-Kuskokwim Delta, and Ledyard Bay and Mechigmenskiy Bay as the prin- cipal molting and staging areas for females nesting on the North Slope. Males marked at all three breeding grounds molt and stage in Mechigmenskiy Bay, Ledyard Bay, and the Indi- girka-Kolyma delta region. Males from the Yukon-Kuskokwim Delta molt and stage mainly at Mechigmenskiy Bay. Equal numbers of males from the North Slope molt and stage at all three areas, and most males from arctic Russia molt and stage at the Indigirka-Kolyma delta region. Postbreeding migration corridors were offshore in the Bering, Chukchi, and Beaufort seas. In winter, eiders were in the Bering Sea south of St. Lawrence Island. Our estimates from surveys in late winter and early spring suggest that at least 333,000 birds winter in
TL;DR: The evolution of reproductive patterns in waterfowl and environmental influence on life-history traits: Growth, survival, and fecundity in Black Brant is studied.
Abstract: HOYT, D. F. 1979. Practical methods for estimating volume and fresh weight of bird eggs. Auk 96: 73-77. LACK, D. 1968. The proportion of yolk in eggs of waterfowl. Wildfowl 19:67-69. LARSSON, K., AND P. FORSLUND. 1992. Genetic and social inheritance of body and egg size in Barnacle Goose (Branta leucopsis). Evolution 46:235-244. LESSELLS, C. M., F. COOKE, AND R. F. ROCKWELL. 1989. Is there a trade off between egg weight and clutch size in wild Lesser Snow Geese (Anser caerulenscens caerulenscens)? Journal of Evolutionary Biology 2:457-472. MERENDINO, T., C. D. ANKNEY, D. G. DENNIS, AND J. 0. LEAFLOOR. 1994. Morphometric discrimination of Giant and Akimiski Island Canada Geese. Wildlife Society Bulletin 22:14-19. NEWELL, L. C. 1988. Causes and consequences of egg weight variation in the Lesser Snow Goose (Chen caerulescens caerulescens). M.S. thesis, Queen's University, Kingston, Ontario. REYNOLDS, C. M. 1972. Mute Swan weight in relation to breeding. Wildfowl 23:111-118. ROHWER, F.C. 1992. The evolution of reproductive patterns in waterfowl. Pages 486-539 in Ecology and management of breeding waterfowl (B. D. J. Batt, A. D. Afton, M. G. Anderson, C. D. Ankney, D. H. Johnson, J. A. Kadlec, and G. L. Krapu, Eds.). University of Minnesota Press, Minneapolis. SAS INSTITUTE, INC. 1985. SAS user's guide: Statistics, 5th ed. Cary, North Carolina. SCOTT, D. K., AND M. E. BIRKHEAD. 1983. Resources and reproductive performance in Mute Swans, Cygnus olor. Journal of Zoology (London) 200: 539-547. SEDINGER, J., P. L. FLINT, AND M. L. LINDBERG. 1995. Environmental influence on life-history traits: Growth, survival, and fecundity in Black Brant. Ecology 76:2404-2414. SIEGFRIED, W. R. 1976. Breeding biology and parasitism in the Ruddy Duck. Wilson Bulletin 88:566574. WELLER, M. W. 1956. A simple field candler for waterfowl eggs. Journal of Wildlife Management 20:111-113. WELLER, M. W. 1957. An automatic nest-trap for waterfowl. Journal of Wildlife Management 21:456458. WESTERKOV, K. 1950. Methods for determining the age of game bird eggs. Journal of Wildlife Management 14:56-67. ZAR, J. H. 1984. Biostatistical analysis. Prentice-Hall, Englewood Cliffs, New Jersey.
TL;DR: The results suggest that the behaviors or physiological changes induced by T are potentially costly and that such costs may in part be incurred through elevated B.
Abstract: Hormonal manipulations with implants allow examination of the costs and benefits of behaviors and physiologic states mediated by a given hormone. As a part of on- going research into the effects of the steroid hormone testosterone (T) in Dark-eyed Juncos (Junco hyemalis), we measured the corticosterone (B, a steroid hormone secreted by the ad- renal in response to stress ) response to the stress of capture and handling in males treated with T (T-males) and in control males (C-males). Although B may be essential for energy mobilization, chronic or repeated exposure to elevated levels of B can have many negative effects. Because T mediates many behaviors that may increase the likelihood that an indi- vidual will encounter stressors, we predicted that plasma B would rise more rapidly in T- males than in controls. In the first few minutes post-capture, the increase in B levels was significantly higher in T-males than in controls. B levels in samples collected 10, 30, and 60 min post-capture were consistently higher in T-males than in C-males; however, the differ- ence was not statistically significant. Because previous work has shown that T-males reduce their parental contribution, we compared females that were mated to T-males and C-males (hereafter T- and C-females). B levels of T-females increased sharply in the first few minutes post-capture, whereas in C-females they did not; however, the responses were not statisti- cally different. Males had higher initial levels and a greater B-response to stress than females when data were compared irrespective of treatment. Our results suggest that the behaviors or physiological changes induced by T are potentially costly and that such costs may in part be incurred through elevated B. Received 25 November 1997, accepted 5 May 1998. IN MOST NORTH-TEMPERATE BIRDS, circulating levels of testosterone (T) in males are elevated during the sexual phase of the breeding season
TL;DR: This work sequenced 890 base pairs of the mitochondrial cytochrome-b gene for 28 of the 29 icterid genera and subgenera and found strong evidence of five lineages of blackbirds: grackles and allies; caciques and oropendolas; orioles; meadowlarks and allies%; and a monotypic cup- nesting cacique lineage.
Abstract: New World blackbirds (Icteridae) have long served as model systems for stud- ies of avian ecology, evolution, and behavior. However, this work has been conducted in the absence of a strong phylogenetic hypothesis for the group. We sequenced 890 base pairs (bp) of the mitochondrial cytochrome-b gene for 28 of the 29 icterid genera and subgenera rec- ognized by Blake (1968). We found strong evidence of five lineages of blackbirds: grackles and allies; caciques and oropendolas; orioles; meadowlarks and allies; and a monotypic cup- nesting cacique lineage. However, we found little support for any further structure among these five lineages and no strong evidence supporting icterid monophyly. Our results set the stage for forthcoming work on relationships within lineages and for higher-level studies that address blackbird monophyly and relationships among lineages. Received 9 February 1998,
TL;DR: The song system of the Banded Wren is described, with emphasis on within-species variation in repertoire size, song-type sharing, and singing mode, and some of the correlates of this variation are identified.
Abstract: We describe the song system of the Banded Wren (Thryothorus pleurostictus), with emphasis on within-species variation in repertoire size, song-type sharing, and singing mode, and identify some of the correlates of this variation. Unlike most of its duetting con- geners, males are the primary songsters in this species. Songs are discrete, 2 to 5 s in du- ration, and consist of softer introductory buzzes and rattles followed by several repeated frequency-modulated whistles or note complexes and a loud terminal trill. Song types are highly distinctive. Repertoire size averaged 19.7 song types (range 15 to 24) and did not vary among three populations located within 8 km of each other in northwestern Costa Rica. Song-type sharing between neighboring males averaged 77% (range 48 to 90%) and was sig- nificantly higher among males inhabiting a continuous forest habitat area (78%) than among birds in two broken-forest/second-growth areas (62%). Populations separated by 8 km shared few song types (10%). Singing mode encompassed both the immediate variety and eventual variety patterns found in other passerines, as well as a continuous range of inter- mediate variety between these two extremes. We used switching rate and a modified Shan- non-Wiener index of song-type diversity to quantify variation in singing modes. High- switching, high-diversity singing was associated with the dawn chorus and with soft singing in the presence of the male's mate. High-switching, low-diversity singing (alternation be- tween two or three song types) was associated with countersinging from a distance. Low- switching, low-diversity singing (repeat mode) occurred during and after highly escalated boundary encounters. Thus, unlike most discrete-repertoire species described to date, Band- ed Wrens decreased their switching rate in increasingly agonistic contexts. Received 10 April 1998, accepted 17 November 1998.
TL;DR: The results suggest that primary cavity nesters are sensitive to subtle characteristics of trees that reflect hardness, some of which may not be apparent in the external appearance of the trees.
Abstract: Cavity-nesting birds that excavate nest holes may be limited by the availability of suitable substrates for excavation. Suitability of trees for excavation may be influenced by substrate hardness and excavation strength of the bird. Excavation strength, in turn, may vary among bird species, causing nest-tree selection to vary among excavator species. We examined use of quaking aspens (Populus tremuloides) for nest trees as a function of tree hardness in four species of woodpeckers: Williamson's Sapsucker (Sphyrapicus thyroideus), Red-naped Sapsucker (S. nuchalis), Downy Woodpecker (Picoides pubescens), and Hairy Woodpecker (P. villosus). Hardness of trees was measured at 95 nest trees, 94 neighboring trees, and 150 random trees using a new technique described here. Other investigators have speculated that the gross external appearance of trees/snags can be used to estimate hardness. Hardness decreased from live trees to partly dead trees to dead trees and with increasing height in trees, but hardness was not related to other external features such as numbers of conks or percentage of the tree covered with bark. All four bird species chose nest trees that were softer than neighboring or random trees, and nest trees were softer at nests than at other heights measured. The four species selected trees of different hardness for nesting; Red-naped Sapsucker and Hairy Woodpecker chose harder trees than Williamson's Sapsucker and Downy Woodpecker. These results suggest that primary cavity nesters are sensitive to subtle characteristics of trees that reflect hardness, some of which may not be apparent in the external appearance of the trees.
TL;DR: In this paper, the authors distinguish between active and passive dispersal gap-crossing and active-and passive home-range gap crossing by permanent-resident birds wintering in 47 woodlots in an agricultural landscape.
Abstract: Gap-crossing may be defined as any movement by animals across swaths of inhospitable habitat. Such behavior is the least understood of the factors that control metapopulation dynamics. We differentiate among active and passive dispersal gap-crossing and active and passive home-range gap-crossing. From observations of active home-range gap-crossing by permanent-resident birds wintering in 47 woodlots in an agricultural landscape, we conclude that larger birds were more likely than smaller ones to cross gaps, and to cross wide gaps, and that proximity and prevalence of woodlands in the surrounding landscape were consistently positively related to the proportion of species that crossed gaps. We discuss these results in relation to the migration equation of Baker and the marginal value theorem of Charnov. Knowledge of decision rules relating active home-range gap-crossing to resource levels within individual habitat fragments and risk of movement among fragments appears to be important for valid calculations of local population densities and metapopulation persistence.
TL;DR: Weighted parsimony and maximum-likelihood analyses supported Hypocnemis as the sister taxon to Drymophila; the genus Myrmotherula was not monophyletic, supporting previous allozyme analyses and finding that spacer regions between genes also provided phylogenetically informative characters from the level of suboscine families to within the biological species that the authors studied.
Abstract: We assessed levels of genetic differentiation based on mitochondrial DNA sequences (portions of the cytochrome-b and ND2 genes) at several taxonomic levels in thamnophilid antbirds. Our focus was to investigate genetic differentiation among populations of two species in the genus Drymophila and to identify the sister genus to Drymophila. In addition, we present evidence of high levels of population subdivision in Hypocnemis cantator (Warbling Antbird). This widespread Amazonian taxon co-occurs, on a local scale, with D. devillei (Striated Antbird). Sequence divergences among populations of D. devillei and D. caudata (Long-tailed Antbird), two bamboo-specialists, often exceeded 2% between populations. Divergences within H. cantator, a species with more generalized habitat requirements and a more continuous distribution, were even higher, including 5.7% divergence between samples separated by 350 km of apparently continuous Amazonian forest. At higher taxonomic levels, genetic distances suggest that antbird genera and biological species are old. Genetic divergence between the two species that comprise the genus Hypocnemis was 9.3%, and divergence between D. devillei and D. caudata averaged 7.2%. Weighted parsimony and maximum-likelihood analyses supported Hypocnemis as the sister taxon to Drymophila; the genus Myrmotherula was not monophyletic, supporting previous allozyme analyses. In addition to the protein-coding sequences, we found that spacer regions between genes also provided phylogenetically informative characters from the level of suboscine families to within the biological species that we studied. Received 31 March 1998, accepted 7 April 1999.
TL;DR: A phylogeny for the grackles and allies is presented and it is determined that ND2 is evolving more rapidly than cytochrome b, however, this difference in evolutionary rate does not result in significant incongruence between phylogenies derived from the two gene regions independently.
Abstract: Within the New World blackbirds, the lineage of grackles and their allies contains several species that have been extremely well studied by avian biologists. Using mitochondrial DNA (mtDNA) sequences, we present a phylogeny for the grackles and allies that serves as a basis for comparative studies in this group. We compare two gene regions and determine that ND2 is evolving more rapidly than cytochrome b. However, this difference in evolutionary rate does not result in significant incongruence between phylogenies derived from the two gene regions independently. A combined weighted analysis provides a completely resolved phylogeny for this group. In general, this phylogeny has higher support than the phylogenies derived from the two genes independently. Two major clades are identified in this combined phylogeny (1) a completely South American clade, and (2) a largely North American/Caribbean/Central American clade. This phylogeny has important implications for the study of behaviors and morphology.
TL;DR: It is concluded that the contributions of magpie- jay helpers in- creased breeder fitness, and the indirect and direct benefits gained by helping probably fa- vored its expression by nonbreeding group members.
Abstract: We investigated the mechanisms by which helpers contribute to breeder re- production in a Costa Rican population of White-throated Magpie-Jays (Calocitta formosa). Helpers provided a substantial proportion of all feedings to female breeders and their off- spring, proportionately more than most species of cooperatively breeding New World jays. Breeding males typically fed breeding females and offspring less frequently than expected, however. There was little evidence of brood division in the sense of individual provisioners (breeders or helpers) preferentially feeding particular fledglings within a brood. The rate of provisioning per recipient increased as a function of group size only during the pre-incu- bation period (provisioning of the laying female). Provisioning rates per nestling and per fledgling were not correlated with group size, and the number of offspring fledged per suc- cessful nest did not increase with group size. Helpers did reduce the provisioning burden on breeders, however, and occasionally were the primary care-providers of fledglings, which allowed breeders to renest. More successful nests were produced in groups with many help- ers than few, resulting in more fledged young per year. Mechanisms contributing to this "helper-effect" included more nesting attempts per year and a higher likelihood of renesting after a successful attempt. We conclude that the contributions of magpie- jay helpers in- creased breeder fitness, and the indirect and direct benefits gained by helping probably fa- vored its expression by nonbreeding group members. Received 30 October 1997, accepted 18 June 1998.
TL;DR: This paper measured population dynamics and cooperative breeding in an isolated population of Florida Scrub-Jays (Aphelocoma coerulescens) on an urban barrier island in southern Brevard County, Florida.
Abstract: I measured population dynamics and cooperative breeding in an isolated population of Florida Scrub-Jays (Aphelocoma coerulescens) on an urban barrier island in southern Brevard County, Florida. In 1992, the scrub-jay population consisted of 29 breeding pairs within six population clusters that comprised two subpopulations. By 1998, the pop- ulation declined to 10 pairs in four clusters because of poor reproductive success. The fre- quency of breeding by one-year-olds was related to the availability of breeding vacancies that increased as the population declined. Nearly half of the breeding vacancies were filled
TL;DR: It is hypothesize that during molt, Wood Thrushes may need access to "safe havens" where protection from predators is protected, and that a conservation strategy that focuses on identifying and protecting nesting habitat is inadequate if the events and needs during the postbreeding events are inadequate.
Abstract: We report movements and habitat use during the postbreeding period of ra- dio-tagged adult Wood Thrushes (Hylocichla mustelina) at the United States Marine Corps Base, Quantico, Virginia, from May to October 1993 to 1995. Thirty of 61 radio-tagged adults stayed on the study area up to two months after they finished reproductive activities. During this time they underwent molt. Of these 30 birds, 11 (6 females and 5 males) molted in the same sites where they nested, 4 males moved to stands of deciduous saplings adjacent to their nesting territories, and 15 (4 females and 11 males) moved to molting sites 545 to 7,291 m from their nesting territories. We found no clear patterns that sex or reproductive success were related to the probability of moving away from nesting sites to molt, nor that the lo- cation of molting adults was correlated with the presence of fruiting plants. However, struc- tural attributes of the vegetation that may enhance predation avoidance, such as the number of woody stems, the density of the understory, and the number of deciduous saplings, were significantly higher in molting sites than in nesting sites. We hypothesize that during molt, Wood Thrushes may need access to "safe havens" where protection from predators is en- hanced. Our study strongly suggests that a conservation strategy that focuses on identifying and protecting nesting habitat is inadequate if the events and needs during the postbreeding
TL;DR: Songbird species differ in how their songs vary geographically, and the vocal behavior of Black-capped Chickadees exhibits an especially intriguing pattern of variation, and isolated groups of males may express divergent songs and singing behavior.
Abstract: Songbird species differ in how their songs vary geographically, and the vocal behavior of Black-capped Chickadees (Poecile atricapillus) exhibits an especially intriguing pattern of variation. Throughout most of their range (i.e. from Nova Scotia to British Colum- bia), males sing a simple two-tone "fee-bee-ee" (with the "fee" slightly higher in frequency than the "bee-ee" and an amplitude break between the "bee" and "ee"), and each male shifts the pitch of his single song type over a range of about 800 Hz. Birds sing differently, however, on the islands of Martha's Vineyard, Chappaquiddick, and Nantucket off Massachusetts. Is- land singing differs from mainland singing in four ways: (1) most island songs are mono- tonal, with the two whistles on the same frequency; (2) island songs exhibit much greater structural diversity than mainland songs; amplitude breaks may occur in the first, second, or both main whistles; (3) island males typically have repertoires of two or more different songs; and (4) song dialects occur both between and within the islands (even on Chappa- quiddick, which is only 6 km wide). Song dialects and repertoires of different songs also occur in some Black-capped Chickadee populations in Oregon and Washington. The dis- tinctive singing of birds on Massachusetts' offshore islands, and of birds in Oregon and Washington, may have arisen because these populations are sedentary and isolated. In main- land populations, young chickadees often migrate or irrupt, and the considerable movement of these young birds could promote uniform behavior from coast to coast among mixing populations. Geographic uniformity of song among mainland males is perhaps also main- tained by young males learning an "average" song from their sound environment. In con- trast, isolated groups of males (as has been shown for young birds of typical fee-bee-ee pop- ulations in the laboratory) may express divergent songs and singing behavior. Received 16
TL;DR: Observations in Tree Swallows breeding along the Hudson River of New York in areas highly contaminated with polychlorinated biphenyls are consistent with the possibility that chemical contaminants interfered with behavior.
Abstract: Considerable attention has been directed toward documenting the effects of environmental chemicals on the endocrine systems of vertebrates, especially on development and reproduction. Given the well-documented role of hormones in controlling behavior, one would expect to see abnormal behavior in contaminated wildlife. We describe abnormal nest- building behavior in Tree Swallows (Tachycineta bicolor) breeding along the Hudson River of New York in areas highly contaminated with polychlorinated biphenyls (a group of chemi- cals known to disrupt endocrine systems). Previous studies of Tree Swallows have shown that nest quality is an important component of reproductive success. Swallows breeding in contaminated areas built smaller nests of lower quality compared with those in uncontam- inated areas. Our observations are consistent with the possibility that chemical contaminants interfered with behavior. Received 31 October 1997, accepted 11 May 1998.
TL;DR: The results showed that male participation in incubation tends to be negatively associated with extrapair fertilization rates, thereby providing support for Ketterson and Nolan's (1994) hypothesis that this particular form of pa- rental care may be especially restrictive to male extrapair mating activities.
Abstract: Avian species differ markedly in the extent to which males contribute to pre- hatching and posthatching parental care. In a recent comparative study, Moller and Birkhead (1993) concluded that diversity in male parental care was associated with differences among species in extrapair paternity. Specifically, their results showed a significant inverse rela- tionship between extrapair paternity and male contributions to feeding of nestlings. We used a revised and updated data set in an attempt to replicate their study. In contrast to their results, we found no evidence that the evolution of male posthatching care was strongly cor- related with paternity. Instead, our results showed that male participation in incubation tends to be negatively associated with extrapair fertilization rates, thereby providing ten- tative support for Ketterson and Nolan's (1994) hypothesis that this particular form of pa- rental care may be especially restrictive to male extrapair mating activities. Received 15 Sep-
TL;DR: The results indicate a harmful edge effect from forest fragmentation for Pied Flycatchers because offspring mass is related to fitness through brood survival to the next breeding season, and evidence that pairs nesting at the extreme edge were forced to use suboptimal foraging areas, whereas interior pairs had a complete circle of suitable habitat in which to forage.
Abstract: We conducted an experimental study of nest-site selection and breeding suc- cess of Pied Flycatchers (Ficedula hypoleuca) in artificial forest edges. The nest-site selection experiment revealed a clear pattern in the order of occupancy of nest boxes by males: boxes situated at the edge between the forest stand and the clearcut were consistently avoided by the earliest-arriving males, which preferentially selected boxes 50 to 100 m from the edge. We also wanted to assess the possible fitness consequences associated with the observed nest location by moving randomly selected breeding pairs to a new location with respect to dis- tance from the edge. The body mass of offspring was lower in nests moved to the edge than in nests moved into the interior of the forest stand. Body mass may be correlated with the lower feeding rate observed at edge nests compared with interior nests. We present evidence that pairs nesting at the extreme edge were forced to use suboptimal foraging areas (i.e. a semicircle of habitat), whereas interior pairs had a complete circle of suitable habitat in which to forage. Pied Flycatchers did not use clearcuts for foraging. Birds may try to com- pensate for suboptimal foraging area by increasing their food-search efficiency, or they may try to enlarge their foraging area by increasing its radius. Both strategies may increase the energy consumption of adults and the time spent searching for food, which may, in turn, decrease feeding frequency. However, we found no support for increased energy consump- tion. Nest-predation rate, food availability, and survival of parents were not associated with the distance of the nest from the edge. Our results indicate a harmful edge effect from forest fragmentation for Pied Flycatchers because offspring mass is related to fitness through brood survival to the next breeding season. Received 15 December 1997, accepted 31 October 1998.
TL;DR: Song development in the laboratory and singing behavior and population movements among free-ranging males are reexamined, reinforcing the idea that song improvisation among North American Sedge Wrens is a developmental strategy.
Abstract: Can the diverse styles of song development in songbirds be understood in an evolutionary context? Are song imitation and song improvisation strategies that evolved in identifiable ecological circumstances? Differences among Cistothorus wrens suggested that song imitation was used in stable, resident populations by Marsh Wrens (Cistothorus palus- tris), but that song improvisation evolved in the more nomadic populations of North Amer- ican Sedge Wrens (C. platensis). Toward understanding this seemingly unique strategy of improvisation by North American Sedge Wrens, we reexamined song development in the laboratory and singing behavior and population movements among free-ranging males. Nestling Sedge Wrens were collected in North Dakota and during their first year of life tu- tored with 10 Sedge Wren song types; throughout the experiment, males were in adjacent cages and could both hear and see each other. Songs of the laboratory birds were not close imitations of songs from the training tape or immediate neighbors; rather, songs were either improvised (different from but most likely derived from training songs) or invented (no sim- ilarity to other songs in their environment). In nature, males at a Nebraska site also had unique song repertoires, a pattern that is consistent with the improvisational mode of song development. Our field surveys also verified that Sedge Wren populations are highly mobile, arriving at or departing from breeding sites at seemingly odd times of the summer breeding season. These data, together with evidence of song imitation among sedentary populations of Sedge Wrens in Central and South America, reinforce the idea that song improvisation among North American Sedge Wrens is a developmental strategy. Because songs are impro- vised, each male is unique, but songs do not vary geographically; hence, it seems likely that males and females can communicate with one another no matter where they find themselves in the geographic range of the species. Received 30 January 1998, accepted 14 August 1998. WHEN THE BEHAVIORS of closely related spe- cies differ in some fundamental way, we expect that close examination of life histories will help us understand how these species' differences have evolved. Mating systems, for example, can be related to the distribution of resources (Crook 1964, Verner 1964). Foraging behaviors
TL;DR: In this article, the authors proposed procedures for integrating vocal characters with morphology and geographic distribution in making species determinations in thamnophilids and applied this methodology to populations of antwrens in the Myrmotherula surinamensis complex.
Abstract: Current species-level taxonomy of Neotropical birds is in need of reassessment but lacks objective methodology and criteria for the ranking of allopatric populations. Previously (Isler et al. 1998), through empirical analysis of pairs of syntopic species, we developed methods and standards for employing vocalizations in determining species limits in the family Thamnophilidae. Building on this study, we now propose procedures for integrating vocal characters with morphology and geographic distribution in making species determinations in thamnophilids. We applied this methodology to populations of antwrens in the Myrmotherula surinamensis complex (including three subspecies of M. surinamensis and M. cherriei). Four diagnostically differentiated populations were identified, all of which corresponded to named taxa. Each population (some of which are narrowly sympatric) was distinguished unambiguously by morphology and vocalizations. Under these objective and conservative standards, we recommend that Myrmotherula surinamensis, M. multostriata, M. pacifica, and M. cherriei be recognized as distinct species. The level of differentiation found between M. surinamensis and M. multostriata illustrates the minimum threshold recommended for species status of allopatric populations of thamnophilid antbirds and should provide a useful reference point for future considerations of species limits.