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The Great Lakes and nearby agricultural midwestern United States together represent a geographical challenge to migratory land birds during flight and stopover. We explored large-scale migratory responses of land birds encountering the Great Lakes as revealed by weather surveillance radars (WSR-88D) and two smaller specialized radars. Those responses reveal comprehensive landscape- or regional-scale migratory patterns that would otherwise have been difficult to infer. Analysis of radar echoes showed birds crossed the Great Lakes in large numbers, although we also found evidence of birds avoiding lake crossing in some locations. Around dawn, birds over water in numerous locations frequently exhibited an increase in migratory height (dawn ascent) and often an accompanying reorientation toward nearest land if they were within ∼28 km of shore. Those behavioral responses to the Great Lakes influence the resulting distribution of birds stopping over in the intervening terrestrial landscapes.
A heretofore unknown population of the endangered Red Siskin (Carduelis cucullata) was discovered in southwestern Guyana, ∼950 km from populations along the Venezuela coastal cordilleras. Most Venezuelan populations have been greatly reduced by the pet trade during the past 150 years, thus the newly discovered Guyana population represents an opportunity to insure the survival of this highly endangered species in the wild. Breeding of Guyanese siskins coincides with both breeding periods (May to early July and November—December) that have been documented in Venezuela. Breeding behavior, vocalizations, feeding habits, and immature plumages are described.
We addressed the evolution of long-distance migration in and the historical biogeography of Catharus thrushes within a phylogenetic framework. Catharus thrushes are a Nearctic–Neotropical genus consisting of five migrant and seven resident species. We reconstructed a molecular phylogeny using a combined analysis of cytochrome-b and ND2 genes. Phylogenetic reconstructions indicate the nonmonophyly of migratory Catharus species. The Neotropics are the most likely ancestral geographic area for the entire lineage, and migratory species are sister to resident taxa whose ranges are restricted to Central America, Mexico, or both. Resident behavior may be ancestral within the lineage, with migratory behavior evolving three times, although confidence in those reconstructions is equivocal in many cases. However, uncertainty in ancestral character states presents an interesting scenario including potential drop-offs of resident species from migratory ancestors.
Geographic patterns of variation in morphological characters in the Curve-billed Thrasher (Toxostoma curvirostre) have been recognized by the description of seven subspecies. Twelve standard measurements, as well as three colorimetric characters and two color pattern characters, were analyzed to test whether subspecies limits predict patterns of variation. Measurement error was addressed by measuring each character three times and calculating the mean. A total of 821 male study skins were used, representing 29 locations. A variety of analysis revealed two major groups, an eastern and western group, divided by the Sierra Madre Occidental. Those two groups had previously been recognized as the curvirostre and palmeri groups, respectively. Those groups were also recovered by analysis of mtDNA. The two groups fulfill the requirements for species. The Tiburón Island (T. c. insularis) sample was distinct for several characters; however, small sample size precludes formal taxonomic recommendation. Within the two major groups, most characters showed incongruent clinal patterns of variation that did not match subspecies limits.
Seasonal changes in food choice by migratory birds often reflect changes in relative food abundance and increased energetic demand. Hermit Thrushes (Catharus guttatus) in southeastern Louisiana are highly frugivorous during winter but forage exclusively on arthropods just prior to spring migration. We hypothesized that this switch to an exclusively arthropod diet would lead to an increase in fat reserves compared to a frugivorous diet, and that fat birds would initiate migration sooner and display more migratory activity than lean birds. We tested these hypotheses on captive Hermit Thrushes maintained on either an arthropod only diet or a mixed fruit and arthropod diet and measured changes in fat score, body mass, and nocturnal migratory activity (Zugunruhe) from February to April 2000. We found that the arthropod-only treatment led to greater body mass and greater amounts of subcutaneous fat than the mixed fruit and arthropod treatment by the third week of the experiment. Despite those differences, body mass was not correlated with intensity of Zugunruhe. We also did not find a significant difference in intensity or onset of Zugunruhe between treatments. We concluded that because Hermit Thrushes are short-distance migrants, large fat reserves are not crucial for their migration. Consequently, fruit and arthropods appear to be equivalent with respect to migratory behavior.
In a previous study we found that survivorship of several species of permanent-resident, temperate-zone birds was positively related to forest fragment size and presence of supplemental food, and negatively related to extent of snow cover (Doherty and Grubb 2002). Here, we test the hypothesis that such trends are related to differential nutritional condition during winter. Employing rate of growth of induced feathers, we found that woodlot size and presence of supplemental food interacted to increase the nutritional condition of Carolina Chickadees (Poecile carolinensis) and that Tufted Titmouse (Baeolophus bicolor) nutritional condition was reduced in years with high snow cover. Assuming that nutritional condition is positively related to survivorship, these results have possible implications for the viability of permanent-resident birds in small woodlots, with the effects on subordinate species in foraging flocks in very small woodlots possibly being the most severe.
Western Sandpipers (Calidris mauri) have been previously shown to undergo seasonal changes in the fatty acid composition of their fat stores, even though they do not show the marked seasonal variation in diet common to many migratory passerines. We investigated the effect of dietary fatty acid composition on the fatty acid composition of adipose tissue in captive Western Sandpipers by feeding birds experimental diets with different fatty acid composition. In addition, we determined the effect of total percentage of fat content of the diet (5 vs. 10%) on fatty acid composition of depot fat. Birds maintained normal body mass (24–27 g) throughout all experimental treatments. Most adipose fatty acids were sensitive to dietary manipulation to some extent. Changes in fatty acid composition of the diet had the largest effect on adipose tissue composition for the essential polyunsaturated fatty acid linoleate (18:2), whereas it had the least effect for the monounsaturated fatty acid oleate (18:1). The saturated fatty acid palmitate (16:0) demonstrated an intermediate capacity to alter fatty acid composition of adipose tissue. Total amount of fat in the diet did not influence the effect of diet on fatty acid deposition. Results of dietary manipulations in this study suggest that diet does explain some of the variation in fatty acid composition observed during migration in Western Sandpipers, but that certain fatty acids can be modulated independently of diet (probably through de novo synthesis, postabsorption modification, or both).
Distribution of genealogical lineages within a species is likely the result of a complicated series of ecological and historical events. Nested-clade analysis is specifically designed as an objective phylogeographic approach for inferring evolutionary processes on a spatial and temporal scale for small subclades within a larger set of intraspecific relationships. Here, we use nested-clade analysis as well as other phylogeographic methods to investigate the evolutionary history of California Thrasher (Toxostoma redivivum) populations. Inferences resulting from nested clade analysis suggest a history that includes past fragmentation, range expansion, and isolation-by-distance. Along with root information, those inferences enable the construction of a biogeographic scenario for this species involving general southern ancestry, an early north–south division, northward range expansion, and a southward back-expansion into an already populated southern region. Isolation-by-distance is also identified, particularly in southern California, indicating that gene flow between localities does occur but is restricted. Many conclusions drawn from this study are concordant with geologic data as well as phylogeographic scenarios drawn for other codistributed California taxa.
Trends in Thick-billed Murre (Uria lomvia) populations at Prince Leopold Island and Coats Island, Nunavut—colonies at opposite ends of the species range in the eastern Arctic—were compared over the period 1985–2000. Population trends were monitored by daily counts of fixed study plots on six or more days each year. At Coats Island, annual mean counts were well correlated with numbers of breeding pairs located on separate breeding study areas, suggesting that the monitoring counts provided a useful index of the breeding population. Overall, counts at both colonies increased over the period of observations (by 2.1% annually at Coats Island and 1.5% at Prince Leopold Island), but a period of significant decline occurred during 1989–1991 and numbers remained stable after 1998. Fluctuations at the two colonies were well-synchronized. Changes in numbers from year-to-year were positively correlated with the mean mass of breeders during the first half of incubation. Hence, birds appeared to be in poorer condition in years when the population decreased. The similarity in fluctuations at colonies as far apart as Coats and Prince Leopold islands suggests that population changes may be determined by events on the common wintering grounds. The correlation between changes in counts and body mass at Coats Island suggests that the common factor may be one that affects the availability of food during the nonbreeding period.
Fragmentation of grassland habitat may increase predation rates on grassland passerine nests and contribute to population decline of several species. Studies that simultaneously document the nest predator community and associate predator species with edges created by fragmentation have not been conducted for grassland habitats. The purpose of our study was to evaluate the effects of using miniature video camera systems to document predation events, identify grassland passerine nest predators in grazed pastures, and determine whether predation patterns of nest predators known to prefer wooded edges differed from those of other nest predators. In 1998–2000, we deployed cameras at 89 nests of Savannah Sparrows (Passerculus sandwichensis), Grasshopper Sparrows (Ammodramus savannarum), Song Sparrows (Melospiza melodia), meadowlarks (Sturnellaspp.), and Bobolinks (Dolichonyx oryzivorus) in southwestern Wisconsin pastures 16–169 ha in size. Abandonment rates were higher for nests with cameras than for nests without cameras (P = 0.04). Trampling rates did not differ between nests with and without cameras. There was limited evidence of differences in predation rates between nests with and without cameras. Predation rate was high in the early incubation stage. Grassland passerine nests were depredated by at least 11 different species in that system, and the predator community differed from those documented in similar studies in other regions. Raccoon (Procyon lotor), thirteen-lined ground squirrel (Spermophilus tridecemlineatus), and snakes (Thamnophisspp. and Elaphespp.) were most common. Over one-third of documented predation events were caused by species that prefer wooded edges. Those species usually depredated nests located closer to wooded edges than to any other type of edge, but there was no evidence that those species restricted their movements to depredate nests within a certain distance from wooded areas in the landscape compared to grassland specialist species (P = 0.28). Predators known to prefer wooded edges traveled up to 190 m into pastures and up to 150 m from wooded areas. Effects of edge predators in pastures are likely to extend beyond the 50 m suggested by other grassland passerine studies.
In birds, large egg size often enhances subsequent offspring survival, but most previous studies have been unable to separate effects of egg size from other maternal influences. Therefore, we first evaluated variance components of egg size both within and among individual female Ruddy Ducks (Oxyura jamaicensis), and then tested for egg-size-dependent survival of ducklings in the wild by switching complete broods among females. Forty broods consisting of 244 individually color-marked, day-old ducklings of known egg size were given to foster mothers, and survival was monitored to one month. Analysis of mark–resighting data showed that offspring survival was best modeled to include effects of egg size and hatching date; survival probability increased with egg size, but declined with advancing hatching date. Duckling body mass, body size, and body condition measured at hatching were positively correlated with egg size. Unlike most other duck species, and for reasons that are speculative, egg sizes varied within clutches nearly as much as they did among clutches. Selective mortality of small egg phenotypes during the first weeks after hatching likely is the result of smaller duckling size and reduced energy reserves, characteristics that must be particularly unfavorable in adverse environments.
Birds have few reliable indicators of aging. Pentosidine is a product of nonenzymatic glycation that accumulates in tissues of an animal over its lifespan. The intent of this study was to determine if accumulation of skin pentosidine in birds of known ages changed as a function of time. Skin samples were obtained from the breast of 45 birds of various species obtained from the national aviary. In addition, foot webbing samples were obtained from 17 California Gulls (Larus callifornicus) of known ages. Collagen was measured by a hydroxypro-line spectrophotometric method and pentosidine was quantified using reverse phase high-performance liquid-chromatography. Pentosidine concentration in the skin and foot webbing increased linearly with age (P < 0.001). Hydroxyproline concentrations from the foot webbing were comparable to that measured in the skin; however, pentosidine concentrations were approximately one-fourth of that in skin. Knowledge regarding longevity of birds could provide information for species survival programs and insight into variations in longevity of an entire population.
Carotenoid-based colors serve important sexual-signaling functions in many animals, but the proximate factor(s) underlying their expression has sparked controversy. In particular, the relative contributions of dietary and physiological mechanisms have been questioned of late. However, no studies have concurrently quantified levels of food intake or pigment processing in any species to examine the comparative effects of pigment acquisition and use on integumetary coloration. Here, we studied within- and between-sex patterns of food intake and plasma pigment circulation in the Zebra Finch (Taeniopygia guttata) to assess how sexually dichromatic, carotenoid-based bill pigmentation serves as an indicator of pigment access in the diet and carotenoid transport through the bloodstream. First, in a food-choice study, we found that males and females did not consume different types or amounts of food, despite dramatic sex differences in bill coloration. Similarly, variability in carotenoid-based bill pigmentation within each sex was uncoupled from levels of food consumption. Next, we used high-performance liquid-chromatography (HPLC) to quantify the types and amounts of carotenoids circulating through blood. Male and female Zebra Finches circulated the same four major carotenoid pigments in blood plasma (lutein, zeaxanthin, anhydrolutein, and β-cryptoxanthin), but males circulated a significantly higher concentration of plasma carotenoids than did females. Within both sexes, individuals that circulated more carotenoid pigments displayed more brightly colored bills. In sum, these results suggest that physiological factors such as pigment transport may play a more important role in shaping variability in carotenoid-based bill coloration in this species than does diet. Future studies should be aimed at identifying the proximate determinants of plasma carotenoid circulation in these birds as well as how circulated pigments are used to produce maximum color displays.
We studied the effect of the secondary metabolite emodin on food intake, food assimilation mass coefficient (AMC), feeding bout rate, and defecation rate in a frugivorous bird, the Yellow-vented Bulbul (Pycnonotus xanthopygos). Emodin is found in the ripe fruits of Mediterranean buckthorn (Rhamnus alaternus), which is commonly eaten by P. xanthopygos. Emodin (0.005 and 0.01% wet mass) increased dry matter AMC by 8–10% after isolating the effect of food intake. At a concentration of 0.001%, emodin increased the AMC of nitrogen, fat, and organic remains (mainly carbohydrates and proteins). Apart from emodin, fruits of R. alaternus contain a variety of secondary metabolites that may interact with each other and influence bird digestion. Artificial food laced with crude Rhamnus fruit extract increased food intake and dry matter AMC. Emodin (0.01% wet mass) increased the average time between defecations, but did not affect the time interval between feeding bouts nor the average amount consumed per feeding bout. We speculate that emodin increases food retention time. Longer retention time may explain the observed increase in AMC. Our results suggest that sometimes secondary metabolites in ripe fruit may not be detrimental to frugivores and the presence of emodin in the pulp of ripe buckthorn fruits might be selectively adaptive to the plant.
Greater Rheas (Rhea americana) are precocial birds that show uniparental male care. We evaluated the extent of nest attention by males and estimated its effect on viability and survival of eggs. We assessed whether male absences during incubation were constrained to avoid embryos reaching lethal temperatures or to minimize risk of egg predation. We estimated (1) effect of nest attention on viability of eggs by comparing egg temperature in nests with and without male attention; and (2) effect of male care on egg predation, by comparing survival of eggs in nests with and without male care. Rhea males attended the eggs for 42 days, but effective incubation started 5–7 days after laying of the first egg. The proportion of time that males spent at the nest increased from 64% during egg laying (days 1–10) up to 97.5% during mid and late incubation (days 20–40). Male absences occurred at the warmest hours of the day and their lengths were positively correlated with the temperature of the environment. Male nest attention reduced the rate of egg losses and kept eggs above lower lethal temperatures for embryos during the night. We also estimated relative cost of parental care after hatching by comparing the time allocated to feeding and vigilance by males with chicks, males in nonreproductive groups, and nonreproductive solitary males. Males took care of the chicks for 4–6 months. They allocated less time to feeding and more time to vigilance than males in groups of adults or solitary males. Investment in vigilance decreased as chicks aged. Our results indicate that Greater Rhea males would require high levels of energetic reserves to start a breeding attempt. That high demand could explain why less than only 20% of the males attempt to nest during a breeding season.
We observed Mexican Jays (Aphelocoma ultramarina) and Northern Flickers (Colaptes auratus) from June 2000 to March 2001, recording interspecific associations and inter-actions. Flickers were seen with jays only once in summer, but they were observed together 62 times in winter, in mixed flocks of up to 20 jays and 12 flickers, while jays were alone only 4 times, and flickers were alone 31 times. Jays always initiated flock movement, and flickers followed. Flickers were more likely to forage when they accompanied jays than when they were alone. While jays searched under and around oaks for acorns and grasshoppers, flick-ers probed for subterranean ants. We found no evidence that flickers attempted to rob the jays' acorn caches, and we observed no agonistic encounters between the two species. Avian predators approached mixed flocks on six occasions, and in each case flickers responded to jay alarm calls by flying with the jays into oak foliage. All predation attempts were unsuccessful. We conclude that Northern Flickers most likely were associated with Mexican Jays in winter because of increased security from predation, and not because of shared resources.
We characterized several equivocal aspects of the breeding biology of the brood parasitic Brown-headed Cowbird (Molothrus ater) at a study site in northeastern Illinois. A total of 175 offspring and a partial sample of parents were sampled and genotyped at six microsatellite loci. A combination of sibling-group and parentage assignment enabled us to characterize mating behavior and area used for reproduction by breeding adults, even for those not sampled. We assigned a mean of 4.7 (range 1–13) and 4.4 (range 1–16) offspring to 33 female and 32 male parents, respectively. Adults typically reproduced with a “primary partner” but up to three partners were common. Offspring females and males were spread over 9 and 12 ha, respectively. Half of the polygynous males produced offspring with an additional mate that parasitized nests near to or within areas overlapping those of their primary partner. That suggests that mate choice takes place at females' egg-laying areas as opposed to more remote social areas. Multiple females frequently parasitized a single host nest and areas used for reproduction overlapped extensively for individuals of either sex. High frequencies of parasitism and superparasitism indicate a high cowbird density relative to that of hosts. Frequent promiscuity by cowbirds at our site contrasts with other studies reporting monogamy and may be due to higher densities of breeding cowbirds at our site.
Defense of group-held resources is a common and widely accepted function of territorial interactions between neighboring groups. In addition, territorial interactions could provide opportunities to assess members of neighboring groups and reproductive opportunities there, or to solidify status in the home group. We studied group-level characteristics and individual participation in territorial encounters in the cooperatively breeding Brown Jay (Cyanocorax morio). Intergroup encounters at stable territory boundaries include both aggressive and affiliative behavior, which suggests that a territorial encounter could function as both a resource defense mechanism and as an arena for social interactions. Territory characteristics that increase the probability of contact between groups (long boundaries, large combined group size, and home range overlap) explain much of the variation in frequency of territorial encounters. Male-biased dispersal was more common to neighboring groups with long boundaries, supporting the idea that frequent interactions between neighbors facilitate dispersal. Females usually inherit breeding positions on their natal territories, and participation in intergroup encounters by females does not vary with age or breeding status. In addition to defending group resources, females on their natal territories could be defending their positions in the breeding queue. Immigrant females are not likely to breed successfully, or to disperse again, and they participated less than expected. Participation by both natal and immigrant males varied by age; young males, at the ages when dispersal and intergroup forays are most likely, participated more than expected, whereas older males (≥4 years) participated less. That is consistent with the hypothesis that participation in intergroup encounters facilitates dispersal and improves integration into social groups. Because extragroup matings occur in this population, both breeding females and males could be assessing neighboring individuals for mating opportunities. Resource defense and social facilitation are not mutually exclusive hypotheses, and our observations suggest that both are important components of territorial encounters in Brown Jays.
We examined nestling paternity, fate of nests, and prior experimental manipulations in Hooded Warblers (Wilsonia citrina) to test the hypothesis that those factors influenced the warblers' fidelity to their previous breeding site (general breeding area), territory (specific nesting and feeding area within general breeding area), and mate the following year. Field re-search was conducted at Hemlock Hill Biological Research Area in northwestern Pennsylvania from 1991 to 1998. Hooded Warblers returned to Hemlock Hill at an average annual rate of 47% over seven years. Significantly more males than females returned in 1992 and 1995, but overall difference between male and female return rates was not significant. Frequency of males returning to their former territory (58%) was greater than frequency of females returning to their former territory (29%). When mates from the previous year returned, remated pairs (n = 13) occupied their former territory more often than they occupied a new territory. Average number of young fledged per nest tended (P = 0.06) to be greater for females that returned to Hemlock Hill than for females that did not return. There was also a tendency (P = 0.09) for females that returned to the breeding site to have more nests with extrapair young than those that did not return. Territory fidelity and mate fidelity for both males and females were not related to prior nest fate or paternity of young. During those years, we conducted two relatively long-lasting experimental manipulations: vegetation removal from nest sites and radiotagging. Those experimental manipulations did not significantly affect future selection of breeding site, territory, or mate. Thus, whereas male Hooded Warblers demonstrated greater territory fidelity than females, only females were possibly affected by factors that we examined from the previous year, specifically extrapair fertilization and prior reproductive success or failure.
The Puerto Rican Plain Pigeon (Columba inornata wetmorei) was listed as endangered in 1970. Transect-survey and nest-monitoring data were collected to estimate reproductive parameters and to assess effects of weather, food, predation, and habitat. We monitored 377 of 423 nests found in east-central Puerto Rico during February-September 1986-2000. The largest sampling effort was conducted in May-June 1998, and 131 nests were found along 8,460 m, resulting in a nest density (D̂) of 5.26 per hectare or 356 nesting pairs (N̂) in the surveyed area (a = 67.7 ha). Nest spatial distribution was highly clumped (b̂ = 3.2) and transect surveys were highly variable (CV = 40%). Thus, 34,000 m needed to be surveyed for a desired coefficient of variation (CV[D̂]) of 20%. Nest density varied widely during May-June 1986–2000. With a CV about the trend line of 121%, from 18 to 28 years of data would be needed to detect an increase or a decrease (r) of 5–10% in log-transformed nest density estimates through linear regression analysis (alpha = 0.15 and power = 0.80). Whereas food abundance had positive and significant relationships with nest density and number of fledglings produced, predator density had negative and significant relationships with nesting success and the number of fledglings produced. Predation accounted for 79% of nest losses (n = 183). Mayfield's estimates of nesting success averaged 40% and an average of 0.5 fledglings were produced per nesting pair. Because Plain Pigeons are able to produce fledglings from three or more broods per year and have extended nesting seasons (with a nest density peak usually occurring in May-June), we hypothesized that hatch-year and after-hatch-year survival rates of 50–65% and a yearly productivity of 1.4–2.0 fledglings per nesting pair were enough to offset mortality. Our optimism is tempered by the fact that Plain Pigeons have not been reported nesting outside east-central Puerto Rico, where rapid destruction and fragmentation of second-growth forests, catastrophic weather, food availability, nest predation, illegal hunting and poaching of nestlings may interact and cause an irreversible population decline. Managers should focus on conserving and restoring second-growth forest fragments to provide food and cover throughout the year. Additional recommendations are given based on the results of our study, which was part of a larger study of factors affecting the reproduction of columbids on Puerto Rico and its territories.
We investigated individual and resource-dependent variation in ability of female Zebra Finches (Taeniopygia guttata) to lay supranormal clutches in response to egg removal, and effect of continuous laying on (1) egg composition and (2) plasma yolk precursor levels. Egg removal significantly increased the number of eggs that individual females laid, but that response was diet-dependent: on a high-quality (egg-supplemented) diet, females laid 12.4 ± 1.0 more eggs compared with their pretreatment clutch size; whereas on the low-quality (seed-only) diet, females laid only 4.9 ± 1.2 more eggs. Removal clutch size (i.e. total number of eggs laid in response to egg removal) was positively correlated with pretreatment mean egg mass and clutch size on the low-quality diet, but not on the high-quality diet. That suggests that there is interindividual variation in egg-laying ability (“large-egg” females had a greater capacity to respond to egg removal than “small-egg” females), but that higher resource levels can overcome individual differences. Egg mass did not vary with laying sequence in supra-normal clutches (up to 22 eggs); however, there was a significant decrease (6%) in yolk protein content of additional eggs that was apparent by the tenth egg laid (i.e. only 4–5 more than the normal clutch size). Plasma levels of the two yolk precursors, vitellogenin and very-low-density lipoprotein (VLDL), were independent of diet and did not differ in individual birds at the 1 egg stage versus the 14 egg stage. However, there was a systematic change in relationship between yolk lipid content and plasma VLDL levels, from nonsignificant for third-laid eggs to significant and positive for sixteenth-laid eggs. We propose a possible mechanism linking female condition and egg-laying ability: good quality females, capable of laying extended clutches, are able to maintain production of generic VLDL for their own metabolic needs, as well as producing yolk-targeted VLDL, whereas poor quality females are not.
Most species of birds have a uropygial gland, also known as a preen gland, which produces oil that birds spread through their plumage when preening. The plumage of waterfowl deprived of uropygial oil becomes brittle and is subject to breakage. For other groups of birds, however, the importance of preen oil remains unclear. Previous workers have argued that preen oil may serve little or no function in Columbiforms (pigeons and doves). We tested that assertion by removing uropygial glands from Rock Doves (Columba livia) and assessing their plumage condition after several months. The results of that experiment showed significant degradation of plumage in the absence of oil. Our results are the first rigorous demonstration that preen oil is important for plumage condition in nonwaterfowl.
We tested one possible function of preen oil—that it has insecticidal properties and that reduction in plumage condition on birds without glands is due to an increase in ectoparasites. We tested that hypothesis for feather-feeding lice (Phthiraptera:Ischnocera) using both in vitro and in vivo experiments. Lice raised in an incubator died more rapidly on feathers with preen oil than on feathers without oil, which suggests that preen oil may help combat lice. However, removal of the preen gland from captive birds had no significant effect on louse loads over the course of a four-month experiment. Although the results of our in vivo experiments suggest that preen oil may not be an important defense against lice, further experiments are needed. We also consider the possibility that preen oil may protect birds against other plumage-degrading organisms, such as bacteria and fungi.
One function of territorial defense may be to facilitate mate guarding by resident males. To assess the importance of mate guarding in territoriality, we examined the spatial pattern of intrusions by male Willow Ptarmigan (Lagopus lagopus) on the territories of other males and we compared use of territorial space by paired and bachelor males. Because intruding males tended to remain near territorial boundaries of other males more than expected by chance, we expected paired males to avoid areas near boundaries, where the chances of the female encountering another male would be higher. We found that before females had settled onto territories, all resident males used boundary areas of their territories extensively. After females settled, however, paired males remained almost exclusively in the cores of their territories, whereas bachelor males continued to use primarily the edges of their territories. Those patterns of space use suggest that the benefits of having more exclusive access to a mate may be one of the selective forces driving territorial behavior in this species.
We studied snag use for foraging by Black-backed Woodpeckers (Picoides arcticus) one year after a fire in an eastern black spruce (Picea mariana) boreal forest in Quebec, Canada. We searched for signs of foraging (bark flaking and excavation holes) by Black-backed Woodpeckers on 6,536 snags sampled in 56 plots located in portions of the burned forest that had not been salvage logged. A logistic regression model was developed based on the presence or absence of foraging signs. Results showed that Black-backed Woodpeckers used larger snags that were less deteriorated by fire (qualified as high-quality snags). Direct field observations of individuals foraging on 119 snags also indicated that used snags corresponded to those of high predicted quality. Finally, we assessed the relationship between food availability and snag characteristics by measuring the density of wood-boring beetle larvae holes on 30 snags of different size and deterioration classes. High-quality snags contained higher prey densities (wood-boring beetle holes) than smaller and more deteriorated snags. We recommend that forest blocks characterized by large and less deteriorated trees be preserved from salvage logging in recently burned boreal forests in northeastern North America.
Vitellogenin is a lipophosphoprotein found in plasma of egg-producing birds prior to laying that may be used to identify fecund females whose reproductive status is otherwise unknown. We captured Marbled Murrelets (Brachyramphus marmoratus) at sea in Desolation Sound, British Columbia, and used vitellogenin to (1) identify variation in egg production between 1999 and 2000, (2) predict timing of subsequent breeding stages on the basis of egg production, and (3) describe proportion of captured females producing eggs. We also used vitellogenin to investigate a capture bias previously detected in mist-netted birds in the study area and found a corresponding bias in number of egg producers caught. Dates that egg producers were present (27 April to 6 July 1999, 20 April to 6 July 2000) indicate that breeding is highly asynchronous in that species but was similar in both years. Predicted chick-fledging based on vitellogenin analyses was within one day of first sightings of fledglings at sea in both years, confirming that the vitellogenin technique provides accurate information on breeding chronology. Percentage of egg producers (54% in 1999, 56% in 2000) were similar in both years. Vitellogenin analyses provided a chronology very similar to that previously estimated using multiple techniques in the same study area (1996–1998), confirming that vitellogenin analyses alone may be used to describe chronology when sampling encompasses the entire laying period. We recommend that technique for use in other studies of secretive species where egg production cannot normally be monitored by direct observation.
On the basis of plumage coloration and mitochondrial DNA variation, four main groups are recognized within the Fox Sparrow (Passerella iliaca): the red group (iliaca, RE), sooty group (unalaschcensis, SO), thick-billed (megarhyncha, TB), and slate-colored (schistacea, SC). To establish phylogenetic relationships among those four groups, we analyzed 2119 base pairs of sequence from four mitochondrial regions: ND2, ND3, cytochrome b, and control region. The control region is less variable than the coding genes surveyed. Both maximum parsimony and maximum likelihood resolved the same ingroup relationships (RE(SC(TB,SO))). However, placement of the root could not be established, even with four outgroups. Lack of resolution of the root is due to the nearest living relative of the Fox Sparrow being over 11% divergent. Despite lacking a clear root, the data suggest that the two taxa connected by a hybrid zone (TB, SC) are not sister species, which has implications for species limits because under the biological species concept they should be lumped. We recommend that all four main groups be recognized as species.
We report the first case of mycoplasmosis in the western range of the House Finch (Carpodacus mexicanus). This disease originated in the eastern United States and has been previously documented only in eastern introduced House Finch populations where it reached epizootic proportions causing extensive and widespread mortality. Documentation of this dis-ease in western Montana suggests that previously disjunct eastern and western populations of House Finches are now mixing in the northern part of their range. More importantly, as native House Finches are highly susceptible to this novel pathogen, western populations may now be at risk of high mortality, similar to that experienced by non-native eastern populations. Close monitoring of this disease in the western part of the House Finch range will provide important insight into the dynamics of the emerging disease and evolution of resistance to the pathogen.
The age at which female gulls first reproduce is poorly documented. We examined plumage and reproductive organs of Laughing Gulls (Larus atricilla) collected from May–August 2000–2001 at John F. Kennedy International Airport, New York, to determine age-specific reproductive effort. Each gull was classified as one year old (hatched in previous year), two years old, or ≥3 years old on the basis of color patterns of the hood and tail feathers and fifth primary flight feather. For females, each ovary was examined to determine if post-ovulatory follicles were present. In 2000 and 2001, the first gulls with postovulatory follicles were recorded on 15 and 18 May, respectively. Overall, 54% of the 211 two-year-old female Laughing Gulls collected during June–August showed evidence of egg laying compared to 88% of the 320 gulls ≥3 years old. None of the 50 one-year-old females examined showed evidence of egg laying. Although a lower proportion of two-year-old females laid eggs compared to older gulls, we found no difference (P ≥ 0.06) in mean number of postovulatory follicles or in frequency distribution of numbers of postovulatory follicles for the two age classes for those birds that did lay eggs. Within each sex, mean body mass increased (P < 0.05) with age. Mean left testis length of males increased (P < 0.05) with age. Our findings clearly established that two-year-old female Laughing Gulls can contribute significantly to the annual reproductive effort and that some adult (≥3 years old) females did not lay eggs.
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