Timing of Breeding Site Availability Across the North-American Arctic Partly Determines Spring Migration Schedule in a Long-Distance Neotropical Migrant

Long-distance migrants are under strong selection to arrive on their breeding grounds at a time that maximizes fitness. Many arctic birds start nesting shortly after snow recedes from their breeding sites and timing of snowmelt can vary substantially over the breeding range of widespread species. We tested the hypothesis that migration schedules of individuals co-occurring at the same non-breeding areas are adapted to average local environmental conditions encountered at their specific and distant Arctic breeding locations. We predicted that timing of breeding site availability (measured here as the average snow-free date) should explain individual variation in departure time from shared non-breeding areas. We tested our prediction by tracking American Golden-Plovers (Pluvialis dominica) nesting across the North-American Arctic. These plovers use a non-breeding (wintering) area in South America and share a spring stopover area in the nearctic temperate grasslands, located >1,800 km away from their nesting locations. As plovers co-occur at the same non-breeding areas but use breeding sites segregated by latitude and longitude, we could disentangle the potential confounding effects of migration distance and timing of breeding site availability on individual migration schedule. As predicted, departure date of individuals stopping-over in sympatry was positively related to the average snow-free date at their respective breeding location, which was also related to individual onset of incubation. Departure date from the shared stopover area was not explained by the distance between the stopover and the breeding location, nor by the stopover duration of individuals. This strongly suggests that plover migration schedule is adapted to and driven by the timing of breeding site availability per se. The proximate mechanism underlying the variable migration schedule of individuals is unknown and may result from genetic differences or individual learning. Temperatures are currently changing at different speeds across the Arctic and this likely generates substantial heterogeneity in the strength of selection pressure on migratory schedule of arctic birds migrating sympatrically.

Drought at a coastal wetland affects refuelling and migration strategies of shorebirds

Droughts can affect invertebrate communities in wetlands, which can have bottom-up effects on the condition and survival of top predators. Shorebirds, key predators at coastal wetlands, have experienced widespread population declines and could be negatively affected by droughts. We explored, in detail, the effects of drought on multiple aspects of shorebird stopover and migration ecology by contrasting a year with average wet/dry conditions (2016) with a year with moderate drought (2017) at a major subarctic stopover site on southbound migration. We also examined the effects of drought on shorebird body mass during stopover across 14 years (historical: 1974–1982 and present-day: 2014–2018). For the detailed comparison of two years, in the year with moderate drought we documented lower invertebrate abundance at some sites, higher prey family richness in shorebird faecal samples, lower shorebird refuelling rates, shorter stopover durations for juveniles, and, for most species, a higher probability of making a subsequent stopover in North America after departing the subarctic, compared to the year with average wet/dry conditions. In the 14-year dataset, shorebird body mass tended to be lower in drier years. We show that even short-term, moderate drought conditions can negatively affect shorebird refuelling performance at coastal wetlands, which may carry-over to affect subsequent stopover decisions. Given shorebird population declines and predicted changes in the severity and duration of droughts with climate change, researchers should prioritize a better understanding of how droughts affect shorebird refuelling performance and survival.

Nest-site selection of a subarctic-breeding shorebird: evidence for tree avoidance without fitness consequences

Vegetation communities in the subarctic are at risk of change due to climate-driven tree and shrub encroachment. Vegetation change may lead to unsuitable habitat for arctic-breeding birds, many of whom are declining. Although many possible factors are contributing to their decline, loss of breeding habitat could be a major contributor. We examined nest-site selection in Dunlin (Calidris alpina hudsonia (Todd, 1953)), a shorebird that nests in open fen habitats in the Churchill, Manitoba, Canada, region. Our objective was to determine whether this species avoids treed habitats and the possible fitness consequences for this. We examined the role of vegetative horizontal and vertical concealments on nest-site selection and nest fate. Dunlin selected nest sites with lower densities of trees than present at unused sites (40 m radius). Both horizontal and vertical concealments were significantly greater at nests than at unused sites, and horizontal concealment was greatest in the north. No measure of tree density or height, or concealment, significantly predicted nest fate. Although Dunlin appear to select nest sites that may minimize exposure to northerly winds and that may provide cover against potential predators, the current nest-site characteristics are not reinforced by contemporary selection.

Does prey availability affect the reproductive performance of Barn Swallows (Hirundo rustica) breeding in Ontario, Canada?

Animal populations are often limited by food availability, particularly during the breeding season. In birds, food limitation can impact several components of the reproductive cycle, including the timing of reproduction and reproductive output. Barn Swallows (Hirundo rustica Linnaeus, 1758) have experienced a population decline over the past 40 years in North America that is thought to be related to changes in prey availability. We monitored Barn Swallow reproductive behaviour and prey availability throughout two breeding seasons at 10 sites in Ontario, Canada, to test the hypothesis that limited prey availability during the breeding season affected reproductive behaviour. We found no relationship between food availability and number of eggs laid or number of young fledged. Neither did we observe higher rates of second brooding or more pairs nesting at breeding sites with higher food availability. Barn Swallows did not time their reproductive effort to maximize prey availability during the nesting period, but any mismatch in phenology of prey and bird reproduction at a breeding site was not associated with lower reproductive success. The results of this study did not support our hypothesis and suggest that Barn Swallow reproductive behaviour was not negatively affected by limited prey availability on the breeding grounds.

Spatio-temporal responses of predators to hyperabundant geese affect risk of predation for sympatric-nesting species

The Arctic is undergoing rapid changes, with anthropogenic shifts in climate having important and well-documented impacts on habitat. Populations of predators and their prey are affected by changing climate and other anthropogenic factors, and these changing trophic interactions could have profound effects on breeding populations of Arctic birds. Variable abundance of lemmings (a primary prey of generalist Arctic predators) and increasing abundance of light geese (Lesser Snow and Ross' Geese; a secondary prey) could have negative consequences for numerous sympatric shorebirds (an incidental prey). Using 16 years of predator-prey observations and 13-years of shorebird nest survival data at a site near a goose colony we identify relationships among geese, lemmings, and their shared predators and then relate predator indices to shorebird risk of nest predation. During two years, we also placed time-lapse cameras and artificial shorebird nests at increasing distances from a goose colony to document spatial trends in predators and their effect on risk of predation. In the long-term data, yearly indices of light geese positively influenced indices of gulls and jaegers, and shorebird nest predation rate was negatively correlated with jaeger and fox indices. All three predator indices were highest near the goose colony and artificial nest predation probability was negatively correlated with distance from goose colony, but these effects were less apparent during the second year. Combined, these results highlight the variation in predator-mediated interactions between geese and shorebirds and outline one mechanism by which hyperabundant geese may be contributing to local or regional declines in Arctic-nesting shorebird populations.

Long-distance migratory shorebirds travel faster towards their breeding grounds, but fly faster post-breeding

Long-distance migrants are assumed to be more time-limited during the pre-breeding season compared to the post-breeding season. Although breeding-related time constraints may be absent post-breeding, additional factors such as predation risk could lead to time constraints that were previously underestimated. By using an automated radio telemetry system, we compared pre- and post-breeding movements of long-distance migrant shorebirds on a continent-wide scale. From 2014 to 2016, we deployed radio transmitters on 1,937 individuals of 4 shorebird species at 13 sites distributed across North America. Following theoretical predictions, all species migrated faster during the pre-breeding season, compared to the post-breeding season. These differences in migration speed between seasons were attributable primarily to longer stopover durations in the post-breeding season. In contrast, and counter to our expectations, all species had higher airspeeds during the post-breeding season, even after accounting for seasonal differences in wind. Arriving at the breeding grounds in good body condition is beneficial for survival and reproductive success and this energetic constraint might explain why airspeeds are not maximised in the pre-breeding season. We show that the higher airspeeds in the post-breeding season precede a wave of avian predators, which could suggest that migrant shorebirds show predation-minimizing behaviour during the post-breeding season. Our results reaffirm the important role of time constraints during northward migration and suggest that both energy and predation-risk constrain migratory behaviour during the post-breeding season.

Comment on "Global pattern of nest predation is disrupted by climate change in shorebirds"

Kubelka et al (Reports, 9 November 2018, p. 680) claim that climate change has disrupted patterns of nest predation in shorebirds. They report that predation rates have increased since the 1950s, especially in the Arctic. We describe methodological problems with their analyses and argue that there is no solid statistical support for their claims.

Consistent declines in wing lengths of Calidridine sandpipers suggest a rapid morphometric response to environmental change

A recent study demonstrated that semipalmated sandpiper (Calidris pusilla) wing lengths have shortened from the 1980s to the present-day. We examined alternative and untested hypotheses for this change at an important stopover site, James Bay, Ontario, Canada. We evaluated morphometric patterns in wing length and bill length by age and sex, when possible, and assessed if wing shape has also changed during this time-period. We investigated patterns of morphological change in two additional Calidridine sandpipers, white-rumped sandpipers (Calidris fuscicollis) and least sandpipers (Calidris minutilla), to determine if shorter wing lengths are a widespread pattern in small sandpipers. We also examined allometric changes in wing and bill lengths to clarify if wing length declines were consistent with historical scaling relationships and indicative of a change in body size instead of only wing length change. We found that including sex and wing shape in analyses revealed important patterns in morphometric change for semipalmated sandpipers. Wing lengths declined for both sexes, but the magnitude of decline was smaller and not significant for males. Additionally, semipalmated sandpiper wings have become more convex, a shape that increases maneuverability in flight. Wing lengths, but not bill lengths, declined for most species and age classes, a pattern that was inconsistent with historical allometric scaling relationships. For juvenile semipalmated sandpipers, however, both bill and wing lengths declined according to historical scaling relationships, which could be a consequence of nutritional stress during development or a shift in the proportion of birds from smaller-sized, western breeding populations. Except for juvenile semipalmated sandpipers, we did not find evidence for an increase in the proportion of birds from different breeding populations at the stopover site. Given the wide, hemispheric distribution of these sandpipers throughout their annual cycles, our results, paired with those from a previous study, provide evidence for wide-spread reduction in wing lengths of Calidridine sandpipers since the 1980s. The shorter wing lengths and more convex wing shapes found in this study support the hypothesis that selection has favored more maneuverable wing morphology in small sandpipers.

Diet and prey size selectivity of Semipalmated Plovers (Charadrius semipalmatus) in coastal Georgia

We examined diet of nonbreeding Semipalmated Plovers (Charadrius semipalmatus Bonaparte, 1825) in the Cumberland Island estuary, Georgia, USA, through fecal sample analysis. We also examined prey size selectivity by Semipalmated Plovers for the most common prey item found in the fecal samples, which are polychaetes in the family Nereidae (= Nereididae). We compared the size distribution of polychaetes in Semipalmated Plover fecal samples from salt marshes and mudflats with the size distribution of polychaetes sampled from the two habitats. Semipalmated Plovers foraging on mudflats had less variable diets than those foraging on salt marshes, although the mean number of prey per Semipalmated Plover fecal sample was similar between the two habitats. Size selectivity by Semipalmated Plovers of nereid (= nereidid) polychaetes varied as a function of habitat, with Semipalmated Plovers eating larger polychaetes in salt marshes than in mudflats, although in both habitats Semipalmated Plovers avoided extremely small and (or) large ones. Semipalmated Plovers took fewer of the available prey groups and were more selective in sizes of the dominant prey group on mudflats, where prey densities were the highest. These observations are consistent with predictions from optimal foraging theory.

Human Activity and Habitat Characteristics Influence Shorebird Habitat Use and Behavior at a Vancouver Island Migratory Stopover Site

Pacific Rim National Park Reserve on Vancouver Island, British Columbia, Canada, has 16 km of coastal beaches that attract many thousands of people and shorebirds (S.O. Charadrii) every year. To identify locations where shorebirds concentrate and to determine the impact of human activity and habitat characteristics on shorebirds, we conducted shorebird and visitor surveys at 20 beach sectors (across 20 total km of beach) during fall migration in 2011-2014 and spring migration in 2012 and 2013. Using zero-inflated negative binomial regression and a model selection approach, we found that beach width and number of people influenced shorebird use of beach sectors (Bayesian information criterion weight of top model = 0.69). Shorebird absence from beaches was associated with increasing number of people (parameter estimate from top model: 0.38; 95 % CI 0.19, 0.57) and decreasing beach width (parameter estimate: -0.32; 95 % CI -0.47, -0.17). Shorebirds spent more time at wider beaches (parameter estimate: 0.68; 95 % CI 0.49, 0.87). Close proximity to people increased the proportion of time shorebirds spent moving, while shorebirds spent more time moving and less time foraging on wider beaches than on narrower ones. Shorebird disturbance increased with proximity of people, activity speed, and presence of dogs. Based on our findings, management options, for reducing shorebird disturbance at Pacific Rim National Park Reserve and similar shorebird stopover areas, include mandatory buffer distances between people and shorebirds, restrictions on fast-moving activities (e.g., running, biking), prohibiting dogs, and seasonal closures of wide beach sections.

Effects of geolocators on hatching success, return rates, breeding movements, and change in body mass in 16 species of Arctic-breeding shorebirds

BACKGROUND

Geolocators are useful for tracking movements of long-distance migrants, but potential negative effects on birds have not been well studied. We tested for effects of geolocators (0.8-2.0 g total, representing 0.1-3.9 % of mean body mass) on 16 species of migratory shorebirds, including five species with 2-4 subspecies each for a total of 23 study taxa. Study species spanned a range of body sizes (26-1091 g) and eight genera, and were tagged at 23 breeding and eight nonbreeding sites. We compared breeding performance and return rates of birds with geolocators to control groups while controlling for potential confounding variables.

RESULTS

We detected negative effects of tags for three small-bodied species. Geolocators reduced annual return rates for two of 23 taxa: by 63 % for semipalmated sandpipers and by 43 % for the arcticola subspecies of dunlin. High resighting effort for geolocator birds could have masked additional negative effects. Geolocators were more likely to negatively affect return rates if the total mass of geolocators and color markers was 2.5-5.8 % of body mass than if tags were 0.3-2.3 % of body mass. Carrying a geolocator reduced nest success by 42 % for semipalmated sandpipers and tripled the probability of partial clutch failure in semipalmated and western sandpipers. Geolocators mounted perpendicular to the leg on a flag had stronger negative effects on nest success than geolocators mounted parallel to the leg on a band. However, parallel-band geolocators were more likely to reduce return rates and cause injuries to the leg. No effects of geolocators were found on breeding movements or changes in body mass. Among-site variation in geolocator effect size was high, suggesting that local factors were important.

CONCLUSIONS

Negative effects of geolocators occurred only for three of the smallest species in our dataset, but were substantial when present. Future studies could mitigate impacts of tags by reducing protruding parts and minimizing use of additional markers. Investigators could maximize recovery of tags by strategically deploying geolocators on males, previously marked individuals, and successful breeders, though targeting subsets of a population could bias the resulting migratory movement data in some species.

Habitat selection and nest success of the Upland Sandpiper (

The Upland Sandpiper (Bartramia longicauda) is a grassland shorebird species associated primarily with prairie habitats in central North America. A disjunct and poorly studied population also occurs in Yukon, Canada, and Alaska, United States. We studied habitat selection of nesting Upland Sandpipers in Ivvavik National Park, Yukon, at the scales of microhabitat (1-m radius around nest) and putative home range (11.3-m radius plots at nests and within 50 m of nest). At the microhabitat scale, the Upland Sandpiper selected nest sites with lower visibility from above than that of their home range (median 91.5%, range 70–98% versus median 99.0%, range 85–100%) and less-variable composition of vegetation than at random sites within the home range. Vegetation adjacent to the nest in the eastern quadrat was significantly shorter (mean ± standard error: 10.6 ± 1.55 cm) than that in other directions around the nest (> 13 cm); nest sites and microsites within home ranges were more often hummocky than random sites in the park. At the mesohabitat scale, Upland Sandpipers selected sites within home ranges with fewer trees than random sites within the park (10.3 ± 3.0 trees per 11.3-m-radius plot around nest versus 32.9 ± 5.9 trees per 11.3-m-radius plot in the park) and greater herbaceous cover (70.7% ± 3.0% versus 56.2% ± 3.7%). Despite the disproportionate use of sites with fewer trees, more herbaceous cover, and lower vertical visibility, these factors did not relate to nest success in our sample. Of the 24 nests found in 2010 and 2011, 22 contained four eggs and 2 contained three eggs. Upland Sandpipers at this high latitude site had a nesting success rate of 0.85 ± 0.01 and 0.56 ± 0.01 in 2010 and 2011, respectively, for a 21-day incubation period. Further assessment of the selected characteristics of nesting sites will improve our ability to predict the effects of northward shrub and tree encroachment on this grassland species.

Adult Ovenbirds (Seiurus aurocapilla) show increased stress-responsiveness in logged forests

Forest harvesting is a form of anthropogenic disturbance, yet the effects of such disturbance on the endocrine physiology of wildlife have been infrequently studied. We investigated the effect of two methods of forest harvesting ('intensive' and 'typical' group-selection silviculture) and un-harvested control sites on the glucocorticoid levels of adult Ovenbirds (Seiurus aurocapilla), a forest interior bird species. We collected blood samples from adult males immediately after capture to examine baseline corticosterone, and then following a standardized capture and restraint protocol, to examine stress-induced levels. There was no significant repeatability in either baseline or stress-induced corticosterone levels for eleven individuals measured in both years of study. Despite no differences across harvesting treatments in male body mass or baseline corticosterone levels, males captured in sites subjected to intensive harvesting had significantly higher stress-induced corticosterone levels than males in other treatments. Currently, the mechanism driving differences in stress-reactivity is unknown although we hypothesize that the size of gaps resulting from intensive group-selection silviculture may increase perceived predation risk. In comparison to our previous work on nestling Ovenbirds, adults respond differently to stress from group-selection silviculture.

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.

Brain regions and encephalization in anurans: adaptation or stability?

Relative brain size and the relative size of six brain regions (main olfactory bulbs, accessory olfactory bulbs, telencephalon, optic tectum, cerebellum and brain stem) in ten species of anurans from five habitats were examined to determine whether there was any evidence of adaptation in brain structure. A previously published data set was also reanalysed. Arboreal frogs have larger body-size corrected brains than frogs from other habitats. Arboreal ranid (Platymantis vitiensis) and hylid (Hyla versicolor) possess slightly larger cerebella than the ranids and hylids from other habitats. Platymantis vitiensis lacks an accessory olfactory bulb. The fully-aquatic Xenopus laevis (Pipidae) has a smaller optic tectum and cerebellum than the non-fossorial hylids and ranids. Adaptation to life underground appears to explain the modified brains of two fossorial frogs, Hemisus guineensis (Ranidae) and Rhinophrynus dorsalis (Rhinophrynidae). Both species of fossorial frogs have reduced optic tecta, larger main olfactory and smaller accessory olfactory bulbs, and larger torus semicircularis than non-fossorial species. Our data showed a strong negative correlation between the size of the optic tectum and the size of the main olfactory bulbs. We conclude that, although anuran brains are very similar across taxa in qualitative and general structure, there are some interesting, apparent adaptations, to fossorial and arboreal life.

Movements and hibernation sites of overwintering painted turtles in southern Ontario

Selection of hibernation sites and overwintering movements were examined in a small population of painted turtles (Chrysemys picta), in a pond near Lakefield, Ontario. Turtles emerged from overwintering sites where the water depth, sediment depth, and temperature did not differ from the average for the pond, but were less variable. Turtles overwintered in areas with water depths from 0.2 to 0.48 m, sediment depths from 0.5 to 0.95 m, and sediment temperatures from 3 to 6 °C. Contrary to prediction, turtles did not overwinter in the regions of the pond that were the first to melt in the spring. Four turtles tagged with temperature-sensitive transmitters and followed over the winter maintained carapace surface temperatures between 4 and 6 °C during the period of ice cover. Movements of turtles continued after ice cover but virtually ended once the water became anoxic. All turtles were buried in the mud from January to spring emergence in March.