Directional selection and repeatability in nest-site preferences of Semipalmated Plovers (Charadrius semipalmatus)

Using marked individuals, we assessed directional selection and repeatability of nest-site characteristics of Semipalmated Plovers (Charadrius semipalmatus Bonaparte, 1825) on Akimiski Island, Nunavut, Canada, 2002–2005, to test the hypothesis that long- and short-term selection patterns were in the same direction. Plovers placed nests in microsites (1 m2 scale) with more pebbles and less bare mud and vegetation than what was available in the environment, indicating long-term selection for these features. Linear (directional selection) effects were stronger than quadratic (stabilizing or disruptive) effects in 3 of 4 years and in the analysis of all data. In the combined 4-year sample, significant directional selection occurred in the opposite direction than that present when comparing used and available sites. Birds with more bare mud and vegetation and fewer pebbles at their nest sites were more successful than birds with pebbled nest sites. Repeatability of nest-site preferences was low and nonsignificant. Neither successful nor unsuccessful pairs chose significantly different nest-site characteristics in subsequent nesting attempts, but options for moving to different nest sites may be limited by interannual site fidelity. Wide individual variability and low repeatability of nest-site characteristics suggests behavioral flexibility in the population. Applying quantitative genetic techniques to patterns of habitat selection may allow researchers to predict the degree to which animals can adjust to changing environments.

Local- versus landscape-scale effects on the demography of three forest-breeding songbirds in Ontario, Canada

Reproductive success of songbirds breeding in forest fragments can be influenced by local habitat characteristics and by anthropogenic land uses in the surrounding matrix such as exurban development and agriculture. Effectively managing these songbirds requires an understanding of which spatial scales most strongly influence their demography. We conducted a multiscale study to investigate the relative influence of local vegetation characteristics and landscape composition at two spatial scales (100 and 2000 m) in a predominantly agricultural landscape on songbird demography. Density, pairing success, nest success, and productivity were assessed for Ovenbirds ( Seiurus aurocapilla (L., 1766)), Wood Thrush ( Hylocichla mustelina (J.F. Gmelin, 1789)), and American Robins ( Turdus migratorius L., 1766) in 16 deciduous forest fragments in southeastern Ontario. Demography of Ovenbirds was most strongly associated with local vegetation characteristics, while demography of Wood Thrush and American Robins was most strongly related to landscape composition within a 2000 m buffer. For all three species, cross-scale correlations influenced nest success, although other demographic parameters were less affected. We conclude that relationships between local- and landscape-scale metrics and songbird demography are complex, species-specific, and differ among reproductive parameters, necessitating a multiscale approach to management.

Factors influencing the turnover and net isotopic discrimination of hydrogen isotopes in proteinaceous tissue: experimental results using Japanese quail

Stable hydrogen isotopes (δ(2)H) are commonly used in studies of animal movement. Tissue that is metabolically inactive after growth (e.g., feathers) provides spatial or dietary information that reflects only the period of tissue growth, whereas tissues that are metabolically active (e.g., red blood cells) provide a moving window of forensic information. However, using δ(2)H for studies of animal movement relies on the assumption that tissue δ(2)H values reflect dietary δ(2)H values, plus or minus a net diet-tissue discrimination value, and that the turnover rate is known for metabolically active tissue. The metabolic rate of an animal may influence both diet-tissue discrimination values and isotopic tissue turnover rate, but this hypothesis has not been tested experimentally. To examine the metabolic hypothesis, an experimental group of 12 male and 15 female captive Japanese quail (Coturnix japonica) was housed at 8.9°C for 90 d to elevate their metabolic rates (mL CO(2) min(-1)), and a control group of 12 male and 13 female quail was housed at room temperature during the same period. For both experimental and control birds, diet-tissue discrimination values were estimated for red blood cells and feathers. To determine turnover rate, experimental and control birds were switched from a (2)H-enriched diet to a (2)H-depleted diet, with red blood cells sampled before and after diet switch. Metabolic rate did not influence red blood cell hydrogen isotope turnover rate (η(2)(p) = 0.24)) or diet-feather isotope discrimination values (η(2)(p) = 0.86). Diet-feather hydrogen isotopic discrimination had a significant sex plus treatment interaction effect; female feathers were depleted in (2)H relative to food regardless of treatment, whereas male feathers were enriched in (2)H. The effect of sex suggested that experimental studies should examine whether coeval males and females differ in blood δ(2)H levels during certain periods of the annual cycle.

Logging affects fledgling sex ratios and baseline corticosterone in a forest songbird

Silviculture (logging) creates a disturbance to forested environments. The degree to which forests are modified depends on the logging prescription and forest stand characteristics. In this study we compared the effects of two methods of group-selection (“moderate” and “heavy”) silviculture (GSS) and undisturbed reference stands on stress and offspring sex ratios of a forest interior species, the Ovenbird (Seiurus aurocapilla), in Algonquin Provincial Park, Canada. Blood samples were taken from nestlings for corticosterone and molecular sexing. We found that logging creates a disturbance that is stressful for nestling Ovenbirds, as illustrated by elevated baseline corticosterone in cut sites. Ovenbirds nesting in undisturbed reference forest produce fewer male offspring per brood (proportion male = 30%) while logging with progressively greater forest disturbance, shifted the offspring sex ratio towards males (proportion male: moderate = 50%, heavy = 70%). If Ovenbirds in undisturbed forests usually produce female-biased broods, then the production of males as a result of logging may disrupt population viability. We recommend a broad examination of nestling sex ratios in response to anthropogenic disturbance to determine the generality of our findings.

Avian nest success, mammalian nest predator abundance, and invertebrate prey availability in a fragmented landscape

Avian nest success is largely determined by predation, but factors affecting the abundance of potential nest predators are rarely studied. We used an information–theoretic approach to assess relative support for models including invertebrate biomass, mammalian nest predator abundance, and percent cover at nests as explanatory variables for nest success of Ovenbirds ( Seiurus aurocapilla (L., 1766)) and Wood Thrush ( Hylocichla mustelina (J.F. Gmelin, 1789)). We ranked models including local vegetation characteristics and landscape composition at two spatial scales (100 and 2000 m) as explanatory variables for the abundance of mammalian nest predator groups and for prey biomass. The nest success of Ovenbirds was best explained by a positive association with percent cover by forbs and seedlings, whereas a positive relationship with prey biomass best explained the nest success of Wood Thrush. Most mammal genera were associated with landscape composition within 100 m of the study sites, and most were positively associated with housing density. Prey biomass was best explained by a positive association with less intensive agriculture within 2000 m. Implementing silvicultural techniques that preserve important habitat features within fragmented forests, limiting housing density within 100 m, and increasing the amount of less intensive agriculture within 2000 m of forest fragments may improve nest success for forest songbirds.

Quality of mature aspen and maple forests for breeding Yellow-bellied Sapsuckers (Sphyrapicus varius)

Mature aspen (genus Populus L..) and maple (genus Acer L.) forests appear to be high-quality breeding habitat for Yellow-bellied Sapsuckers ( Sphyrapicus varius (L., 1766)). To explore some of the mechanisms that influence quality of the breeding habitat, we measured demographic and breeding resources in four forest stands each of 95-year-old quaking aspen ( Populus tremuloides Michx.) and 182-year-old sugar maple ( Acer saccharum Marsh.) in Algonquin Provincial Park, Ontario, from 2007 to 2009. Population density was higher, egg laying earlier, clutches larger, hatching success greater, and per capita and population fledgling production higher in maple stands compared with aspen stands. Longer nest-building and prelaying stages in aspen stands delayed egg laying by 5 days relative to maple stands. The delay in egg laying in aspen stands may have been caused by lower quality sap resources, which then resulted in lower productivity. Adults delivered smaller food loads to nests in aspen stands than in maple stands, which may have increased nestling mortality in aspen stands. Although per capita fledgling production was lower in aspen stands than in maple stands, Yellow-bellied Sapsuckers in both forests were able to replace themselves, suggesting that mature deciduous and mixed-deciduous forests, in general, are high-quality breeding habitat for this sapsucker.

Conserving migratory land birds in the new world: do we know enough?

Migratory bird needs must be met during four phases of the year: breeding season, fall migration, wintering, and spring migration; thus, management may be needed during all four phases. The bulk of research and management has focused on the breeding season, although several issues remain unsettled, including the spatial extent of habitat influences on fitness and the importance of habitat on the breeding grounds used after breeding. Although detailed investigations have shed light on the ecology and population dynamics of a few avian species, knowledge is sketchy for most species. Replication of comprehensive studies is needed for multiple species across a range of areas, Information deficiencies are even greater during the wintering season, when birds require sites that provide security and food resources needed for survival and developing nutrient reserves for spring migration and, possibly, reproduction. Research is needed on many species simply to identify geographic distributions, wintering sites, habitat use, and basic ecology. Studies are complicated, however, by the mobility of birds and by sexual segregation during winter. Stable-isotope methodology has offered an opportunity to identify linkages between breeding and wintering sites, which facilitates understanding the complete annual cycle of birds. The twice-annual migrations are the poorest-understood events in a bird's life. Migration has always been a risky undertaking, with such anthropogenic features as tall buildings, towers, and wind generators adding to the risk. Species such as woodland specialists migrating through eastern North America have numerous options for pausing during migration to replenish nutrients, but some species depend on limited stopover locations. Research needs for migration include identifying pathways and timetables of migration, quality and distribution of habitats, threats posed by towers and other tall structures, and any bottlenecks for migration. Issues such as human population growth, acid deposition, climate change, and exotic diseases are global concerns with uncertain consequences to migratory birds and even less-certain remedies. Despite enormous gaps in our understanding of these birds, research, much of it occurring in the past 30 years, has provided sufficient information to make intelligent conservation efforts but needs to expand to handle future challenges.

Lower predation risk for migratory birds at high latitudes

Quantifying the costs and benefits of migration distance is critical to understanding the evolution of long-distance migration. In migratory birds, life history theory predicts that the potential survival costs of migrating longer distances should be balanced by benefits to lifetime reproductive success, yet quantification of these reproductive benefits in a controlled manner along a large geographical gradient is challenging. We measured a controlled effect of predation risk along a 3350-kilometer south-north gradient in the Arctic and found that nest predation risk declined more than twofold along the latitudinal gradient. These results provide evidence that birds migrating farther north may acquire reproductive benefits in the form of lower nest predation risk.

Breeding habitat preference and nest success of Red-necked Phalaropes on Niglintgak Island, Northwest Territories

Red-necked Phalaropes ( Phalaropus lobatus (L., 1758)) breed throughout arctic and subarctic wetlands. These wetlands provide Red-necked Phalaropes dense graminoid habitat that shelters and conceals nests, and freshwater ponds where phalaropes engage in social interactions and feed on small aquatic invertebrates. We studied breeding habitat preference of Red-necked Phalaropes at multiple scales and determined which, if any, nest-site characteristics influenced hatching success. Red-necked Phalaropes avoided habitat at the meso (home range) scale containing large areas of mud and shrub cover, and selected sites with greater cover of graminoids, aquatic emergents, and open water than that available in the environment. At the micro (nest) scale, phalaropes chose sites dominated by graminoids and water. In 2005, concealed nests experienced higher daily nest survival than exposed nests. In 2006, 40% of nests were destroyed during a summer storm surge and we detected no differences in habitat characteristics between the remaining successful and unsuccessful nests. We suggest that annual differences in the adaptive value of nest-site selection depend on the relative abundance of mammalian and avian predators. A habitat model using data at the meso scale correctly identified phalarope habitat and has the potential to be used broadly across the western Arctic.

Impacts of roads associated with the Ekati Diamond MineTM, Northwest Territories, Canada, on reproductive success and breeding habitat of Lapland Longspurs

We examined the effects of roads associated with the Ekati Diamond MineTM, Nortwest Territories, Canada, on reproductive success and breeding habitat of Lapland Longspurs (Calcarius lapponicus (L., 1758)) by comparing these attributes on study sites located directly beside and at least 5 km away from roads. No significant differences between roads and reference sites were detected for first-egg dates, clutch size, mean nestling mass on the 7th day following hatch, or daily nest survival. We found no evidence that Lapland Longspurs were avoiding nest sites located near roads. Recorded frequencies of male song overlapped with the harmonics of heavy-truck noise. Snow-water equivalent and percent cover of mosses were significantly higher on reference sites, while soil moisture and dust deposition were higher on road sites. Dust suppressant applied midway through the breeding season significantly reduced dust deposition. Lapland Longspur nest sites had significantly higher percent cover of graminoids and of shrubs and forbs, and significantly lower percent cover of lichens than random sites, an effect that occurred both near and distant from roads. Currently, there appears to be no measurable effect of roads associated with the Ekati Diamond MineTM on current territorial choice and reproductive performance of Lapland Longspurs. Observed differences in habitat characteristics between reference plots and road plots suggest that long-term changes in the vegetation community may occur that could affect nest-site selection of Lapland Longspurs.

Do floral syndromes predict specialization in plant pollination systems? An experimental test in an “ornithophilous” African Protea

We investigated whether the "ornithophilous" floral syndrome exhibited in an African sugarbush, Protea roupelliae (Proteaceae), reflects ecological specialization for bird-pollination. A breeding system experiment established that the species is self-compatible, but dependent on visits by pollinators for seed set. The cup-shaped inflorescences were visited by a wide range of insect and bird species; however inflorescences from which birds, but not insects, were excluded by wire cages set few seeds relative to open-pollinated controls. One species, the malachite sunbird (Nectarinia famosa), accounted for more than 80% of all birds captured in P. roupelliae stands and carried the largest protea pollen loads. A single visit by this sunbird species was enough to increase seed set considerably over unvisited, bagged inflorescences. Our results show that P. roupelliae is largely dependent on birds for pollination, and thus confirm the utility of floral syndromes for generating hypotheses about the ecology of pollination systems.

Food-chain chemistry, reproductive success, and foraging behaviour of songbirds in acidified maple forests of central Ontario

We examined the breeding success of two insectivorous bird species, the resident black-capped chickadee (Parus atricapillus) and the Neotropical migrant chestnut-sided warbler (Dendroica pensylvanica), in relation to food-chain chemistry at a healthy and a declining forest site in central Ontario, Canada. The health of sugar maples (Acer saccharum) was poorer and the pH of both soil and throughfall was lower at the declining site than at the healthy site. The calcium and magnesium concentrations and the calcium:aluminum ratio in the soil were also lower at the declining site than at the healthy site. The calcium, magnesium, and phosphorus concentrations and the calcium:aluminum ratio in sugar maple foliage were lower at the declining site than at the healthy site, indicating extensive acid leaching of the soil and foliage at the declining site. Caterpillars (Geometridae) at the declining site had a lower calcium concentration and beetles had a lower magnesium concentration than these groups at the healthy site. The calcium:aluminum ratios in the tissues of insects in both groups were lower at the declining site than at the healthy site, paralleling the foliar and soil chemical differences. There were, however, no differences in clutch or brood sizes, or percent hatch, for either bird species between the healthy and declining sites. Chickadees consistently foraged lower in the canopy at the declining site, a possible compensatory behaviourial response to canopy dieback and (or) lower food quality in the upper canopy.

Intra- and inter-specific interactions of foraging American oystercatchers on an oyster bed

We compared the rates of intraspecific and interspecific kleptoparasitism of foraging American oystercatchers (Haematopus palliatus) on a commercial oyster (Crassostrea virginica) bed during two seasons and between 1979 and 1995. In 1979 most conspecific kleptoparasites were immature oystercatchers and victims were adults. Both intra- and inter-specific parasitism were more common in 1979 than in 1994 or 1995. Kleptoparasitism by conspecifics was more common than by gulls (Larus argentatus, L. marinus) but was not density dependent. Gulls primarily kleptoparasitized oystercatchers foraging on mussels (Geukensia demissa), with their longer handling times. Kleptoparasitism by gulls increased as the number of gulls on the oyster bed increased, and the presence of gulls significantly depressed intake rates and sizes of mussels taken by oystercatchers during autumn. Oystercatchers ate smaller oysters in autumn than in winter in both the presence and absence of gulls. The presence of conspecific and gull kleptoparasites changed the oystercatchers' relative preference for oysters over mussels in their diet. The presence of gulls only partly explained the oystercatchers' lower rates of intake of oysters in autumn than in winter.

Foraging behaviour of American oystercatchers in response to declining prey densities

American oystercatchers (Haematopus palliatus) responded to declines in the density of oysters (Crassostrea virginica) on a commercial oyster bed examined in 1979 and 1995 by increasing the number of species of prey eaten and search times, but not peck rates or handling times. Seasonal changes in foraging behaviour included oystercatchers choosing larger oysters with longer handling times in winter than in autumn, but with subsequently greater profitability and higher intake rates. Time budgets of foraging birds were similar in the two seasons. Oystercatchers ate fewer mussels in winter than in autumn, and fewer mussels than oysters at all times. Search and handling times for mussels were similar in autumn of the 2 years. After a commercial harvest of oysters at a second site, handling times for oysters did not decline; however, search times were significantly more variable, niche breadth was greater, and there was a trend towards longer search times post harvest. The recorded changes in foraging behaviour indicated a close match between search and handling times and prey density and size and behavioural flexibility of foraging birds in response to sometimes drastic changes in their prey base.

Embryonic brain growth in two shorebirds: Charadrius vociferus and Gallinago gallinago

The sizes of six brain regions and of the whole brain were measured for a series of embryonic killdeer, Charadrius vociferus, and common snipe, Gallinago gallinago, to examine (1) the allometric relationship between whole brain and body mass through ontogeny, (2) whether the longer incubation period of the killdeer corresponds to a larger brain at hatch, (3) whether different brain regions grow independently in size through ontogeny, and (4) whether relative size of particular brain regions relates to relative importance of hatching behavior or to the relative importance of behaviors in the adult. Although snipe are generally less precocial at hatch than killdeer, and hence are predicted to have lower allometric coefficients, the allometric relationships between brain and body mass for the two species were not significantly different and were comparable to those for other birds and mammals. The onset of the rapid growth phase of the whole brain, and each region, was very early in the snipe; as a consequence, brain sizes in both species are similar at hatch, despite the shorter incubation period of snipe. In hatchlings of both species, the brain comprises about 7% of body mass. The telencephalon grows most rapidly, the diencephalon and myelencephalon grow more slowly, and the optic tectum grows steadily throughout the embryonic period. The telencephalon of the hatchling snipe is relatively larger than that of hatchling killdeer and exhibits a large nucleus basalis, typical of tactile foragers, although snipe do not forage tactily until adulthood. The relatively large optic tectum of hatchling killdeer corresponds to the highly visual method of foraging of hatchlings. However, the degree to which brain regions grow in the embryonic period, with the exception of the optic tectum and cerebellum in killdeer, appears to relate very closely to their eventual size in adults, with large brain regions growing less in the embryonic period than small brain regions.