Conservation of migrants on their breeding grounds

This paper addresses the question of how to diagnose the causes of a population decline of a migratory bird so that conservation action can be taken. Diagnosis may be through study of habitats or population factors. Different approaches are illustrated with examples from the more threatened migratory species which breed in Europe. Gaps in knowledge of how to make conservation diagnoses and of the circumstances of some of Europe's few migratory and globally endangered birds are shown.     

Incubation in uni-parental Arctic breeding waders

Bruinzeel, L., Tulp, I., Jukema, J. & Stepanova, O. 2000. Incubation in mi-parental arctic breeding waders. Ostrich 71 (1 & 2): 345.

Little Stints Calidris minuta are amongst the smallest breeding waders. This, in combination with the fact that they have a peculiar breeding system, in which each adult takes care of her/his own nest and young, puts high demands during incubation. Due to uni-parental feeding system, feeding time is limited. The accumulation of he1 stores prior to breeding may be crucial to get through the 21-day incubation period. Incubation rhythms, body mass dynamics and energy expenditure of Little Stints was studied at Medusa Bay, Western Taimyr in the summer of 1996. Repeated body mass measurements during incubation were taken by catching the birds on the nest. Concurrently, we measured nest attentiveness, using Tiny Talk dataloggers and temperature sensitive probes, which were placed in the nests. Arthropod availability was measured to estimate food availability. In comparison, body mass dynamics were also studied in Curlew Sandpiper, another uni-parental breeder, but three times bigger. The first (preliminary) results of this study were presented.     

Varying response of breeding waders to experimental manipulation of their habitat and predators

Many ground-nesting bird species including waders are of conservation concern across Europe. Population declines of Eurasian Curlew Numenius arquata (hereafter Curlew), a globally Near-threatened wader, exemplify this and are driven by low breeding success due to predation, and loss and degradation of breeding habitat. We tested whether the combined delivery of vegetation management and lethal control of Red Foxes Vulpes vulpes and Carrion Crows Corvus corone and Hooded Crows C. cornix improved Curlew nesting success and breeding abundance across UK study sites over five years. On trial sites, vegetation management improved habitat condition and Curlew distributions shifted towards managed areas. However, changes in predator abundances, Curlew nesting success and Curlew breeding abundance did not differ between trial and reference sites. Northern Lapwing Vanellus vanellus numbers increased on trial sites and decreased on reference sites, whilst Common Snipe Gallinago gallinago numbers showed no treatment response. Some of these outcomes were associated with additional environmental variables added to Treatment:Year terms in three-way interactions (changes in fox abundance associated with abundance of non-native gamebirds; changes in Crow abundance associated with gamebirds and woodland area; changes in Curlew nesting success associated with crow abundance), highlighting that outcomes depend on site-specific contexts, and consistent responses to interventions cannot be assumed. The difficulty in increasing Curlew nesting success likely relates to underlying mesopredator densities in the UK, which are known to be high in a European context. Our results suggest that a model of delivery like this study, including management of predators using lethal control, at comparable intensities, is highly unlikely to be effective for Curlew or Snipe within agri-environment schemes, but could be for Northern Lapwing. To make progress on wader recovery it is imperative to understand the underlying drivers of high mesopredator densities and address these through landscape-scale intervention and policy changes.     

Testing the effects of recreational disturbance on two upland breeding waders

Previous work has shown that Golden Plovers Pluvialis apricaria guarding chicks utilize heavily disturbed habitat at a lower rate than surrounding areas, but that such rates of avoidance are reduced when the movement of people is restricted to a surfaced footpath. However, there remained some unanswered questions, which are addressed in this paper. First, we examine to what extent habitat avoidance is dependent upon visitor numbers, and find no evidence that Golden Plovers avoided disturbed areas at a site where visitor pressure was half that previously studied. Secondly, we examine whether these relationships between habitat occupancy and disturbance apply to other upland waders and find that Dunlin Calidris alpina habitat utilization in disturbed areas showed a non-significant increase of approximately 50% following the provision of a surfaced footpath, in a manner similar to that observed for Golden Plover. Thirdly, we examine whether the large numbers of visitors (120 per weekend day) using the surfaced footpath impact on Golden Plover breeding success, despite the lack of habitat avoidance. There was no evidence that nest location, clutch survival or chick growth rates were reduced close to the footpath. Together, these results suggest that high levels of disturbance can impact upon habitat usage by upland waders, but only in limited circumstances where visitor pressure is very high (greater than at least 30 visitors per weekend day). However, access to such areas can be permitted for large numbers of visitors without impacting upon wader reproductive performance through the provision of a well-surfaced route.     

Mating system and timing of breeding in Holarctic waders

In passerine birds polygamous species lay eggs later than monogamous species. Yom-Tov has hypothesized that this is because polygamous males do not provision their mates with food, thereby delaying egg-laying. An indirect prediction of this hypothesis is that there should be no difference in laving dates between monogamous and polygamous birds in which mate provisioning does not occur. This prediction was tested by examining egg-laying dates in sympatric wader species that have contrasting mating systems but in which food provisioning of mates does not occur. Polygamous waders laid eggs later than monogamous waders, however, both in a comparison involving only calidridine sandpipers and in a comparison involving sandpipers and plovers. Accounting for phylogeny did not affect the direction of the results, which therefore cast doubt on the validity of the 'mate provisioning' hypothesis and indicated that features common to both passerines and waders were more likely to explain the differences in egg-laying dates between mating systems. Mating system and parental care system were strongly related, with all polygamous species being uniparental and monogamous species being biparental. It is suggested that seasonally early food supplies are of relatively low abundance, constraining species to biparental care and monogamy. By contrast, seasonally late food supplies are more abundant, making uniparental care more successful, thereby creating greater opportunities for mate desertion and polygamy.     

Body condition of shorebirds upon arrival at their Siberian breeding grounds

Arctic breeding shorebirds carry substantial body stores on their long-distance migrations from their non-breeding grounds. Upon arrival at the breeding area the remains of these stores can be used for egg formation, insurance against poor feeding conditions or rebuilding organs. We quantified body condition (body mass, total body water, lean body mass and fat mass estimated using the deuterium dilution method) in seven shorebird species caught upon arrival in the Siberian Arctic. Arrival condition was compared with incubation condition in a subset of species. After correction for structural size, body mass was significantly lower at arrival than during incubation in most of the species (but 3–18% above lean mass). Fat index (fat mass/lean mass) varied between 5.1 and 13.2%. Fat stores were estimated to enable survival for 0.6 days for the smallest and 2.5 days for the largest species. We discuss possible functions of arrival stores: insurance, egg-formation or rebuilding organs. G. H. Visser: Deceased.     

Minimal intra-seasonal dietary overlap of barnacle and pink-footed geese on their breeding grounds in Svalbard

We analysed barnacle Branta leucopsis and pink-footed goose Anser brachyrhynchus summer diets (May–July 2003) based on the proportions of different plant constituents in the faecal material of adult breeding birds in Sassendalen, Svalbard to assess potential inter-specific competition. Diets were highly restricted and overlapped little during pre-nesting and post hatch. During incubation both species showed greatest variety in their diet, reflecting site-specific differences in local food abundance. However, locally the diets of pink-footed and barnacle geese resembled each other most at this time (although still differing significantly). The conflicting needs of nest defence and maintenance of body condition constrains the extent of the feeding resource utilised by nesting pairs and explains slightly greater dietary overlap at this time. Hence, there is little evidence of inter-specific competition (interference or depletion) at present, but this is most likely to be manifest during the incubation period in the future if goose numbers continue to increase. More detailed investigations of the degree of spatial overlap of the two species and their effects on plant structure, quality and community composition are necessary to predict likely outcomes of expected increases in numbers of both goose species.     

Population changes of breeding waders on farmland in relation to agri-environment management

Capsule Population response of breeding waders to agri-environment management varied between management options and species; implementation has been on too small a scale to reverse national population declines.

Aims To test whether numbers of five breeding wader species have shown a more positive response between 1992 and 2005, at sites with appropriate agri-environment management, than at sites that have remained outside such schemes.

Methods Using data from 60 pairs of farmland study areas in Scotland first surveyed in 1992/93, before agri-environment scheme (AES) implementation, and again in 2005, after scheme implementation, we tested at both site and field scales whether changes in the abundance of five breeding wader species were associated with AES management options designed to benefit these species.

Results Changes in breeding wader abundance were more positive on sites in AES, especially for Northern Lapwings Vanellus vanellus and Common Redshanks Tringa totanus, even though management had not been targetted specially at breeding waders on those sites. However, AES management was associated only with modest population increase for Common Redshanks, and a reduction in the magnitude of decline for Northern Lapwings. At the field scale, there was evidence for Northern Lapwings, Common Redshanks and Common Snipe Gallinago gallinago that options which limited grazing and other agricultural activity were associated with more positive outcomes than those which also manipulated water levels.

Conclusions AES management for breeding waders slowed, and in some cases reversed, breeding wader decline at field and farm scales. These benefits were from options that limited grazing and agricultural operations during the breeding season, but not those that also aimed to raise water levels. A possible explanation is that when wetland options are applied to agriculturally marginal fields, grazing reduction or abandonment, and succession to rank vegetation cover then occur over the course of 5-year agreements, with detrimental effects for breeding waders. Verification arrangements need to be robust enough to guard against this. Levels of agri-environment provision in 2005 were too limited and too poorly targeted at remaining key areas for breeding waders to be able to halt or reverse national population declines.     

Vegetation structure influences predation rates of early nests in subarctic breeding waders

Ground-nesting species are vulnerable to a wide range of predators and often experience very high levels of nest predation. Strategies to reduce nest vulnerability can include concealing nests in vegetation and/or nesting in locations in which nests and eggs are camouflaged and less easy for predators to locate. These strategies could have important implications for the distribution of ground-nesting species and the success rates of nests in areas with differing vegetation structure. However, the factors influencing the success of nest concealment and camouflage strategies in ground-nesting species are complex. Here we explore the effects of local vegetation structure and extent of nest concealment on nest predation rates in a range of ground-nesting, sympatric wader species with differing nest concealment strategies (open-nest species: Oystercatcher Haematopus ostralegus, Golden Plover Pluvialis apricaria and Whimbrel Numenius phaeopus; concealed-nest species: Black-tailed Godwit Limosa limosa, Redshank Tringa totanus and Snipe Gallinago gallinago) in south Iceland, in landscapes that comprise substantial variability in vegetation structure at a range of scales. We monitored 469 nests of these six wader species in 2015 and 2016 and ~40% of these nests were predated. Nest predation rates were similar for open-nest and concealed-nest species and did not vary with vegetation structure in the surrounding landscape, but nest-concealing species were ~10% more likely to have nests predated when they were poorly concealed, and the frequency of poorly concealed nests was higher in colder conditions at the start of the breeding season. For concealed-nest species, the reduced capacity to hide nests in colder conditions is likely to reflect low rates of vegetation growth in such conditions. The ongoing trend for warmer springs at subarctic latitudes could result in more rapid vegetation growth, with consequent increases in the success rates of early nests of concealed-nest species. Temperature-related effects on nest concealment from predators could thus be an important mechanism through which climate change affecting vegetation could have population-level impacts on breeding birds at higher latitudes.     

Sharing habitat: Effects of migratory barnacle geese density on meadow breeding waders

• 1.Following targeted conservation actions most goose populations have increased. The growing goose populations caused an increase in human-wildlife conflicts and have the potential to affect nature values. As meadow birds, including meadow-breeding waders, were declining throughout Western Europe, the possible negative effect of rising numbers of foraging barnacle geese on their breeding success has been questioned.
• 2.We used GPS-transmitter data to measure the density of foraging barnacle geese during daylight hours. Using dynamic Brownian Bridge Movement Models (dBBMM), we investigated the effect of barnacle goose density on the territory distribution of five wader species, and on nest success of the locally common Northern lapwing. We used model selection methods to identify the importance of barnacle goose density related to other environmental factors.
• 3.Our results showed an insignificant positive association between barnacle goose density and nest territory density of the Northern lapwing and common redshank. Barnacle goose density had no influence on territory selection of godwit, oystercatcher and ringed plover. We did, however, find a negative correlation between barnacle geese density and the nest success of the Northern Lapwing.
• 4.We infer that either barnacle goose foraging leads to improved territory conditions for some wader species, or that both barnacle geese and waders prefer the same type of habitat for foraging and nesting. Higher barnacle goose density was correlated with fewer Northern lapwing nests being successful.
• 5.Synthesis and application: Experimental research is needed to disentangle the causal chain, but based on our observational findings, we suggest to increase water logging that may attract both barnacle geese and wader species. Further investigation on the effects of barnacle geese on wader species is necessary to identify the cause of the negative correlation between barnacle geese density and nest success of lapwings; nest protection experiments could give further insight.

     

Differences in food abundance cause inter-annual variation in the breeding phenology of High Arctic waders

Previous work has shown that High Arctic waders in Greenland are “income breeders”, i.e. the resources used for egg formation are based almost entirely on biomass obtained on the breeding grounds. Thus, their breeding phenology is expected to be highly sensitive to inter-annual variation in food abundance during the pre-laying period. Early spring snow-cover may also influence timing of egg-laying either directly or mediated through food resources. Here, we report on the inter-annual variation in clutch initiation of three wader species breeding in High Arctic Greenland, Sanderling (Calidris alba), Dunlin (Calidris alpina) and Ruddy Turnstone (Arenaria interpres), in relation to spring snow-cover and spring arthropod abundance over ten breeding seasons at Zackenberg Research Station 1995–2005. Food abundance had the strongest effect on timing of clutch initiation, while the proportion of snow-free land had a weaker but still significant effect, i.e. more food and more snow-free land both result in earlier egg-laying. We hypothesize that food is most important when there is sufficient snow-free land to nest on, while snow-cover is of increasing importance in years with late snowmelt.     

The effect of conservation interventions on the abundance of breeding waders within nature reserves in the United Kingdom

Breeding populations of many wading birds have declined globally, primarily caused by habitat degradation and loss. In the UK, population declines have been particularly notable on lowland wet grasslands. In response, some areas of lowland wet grassland have been restored and are under ongoing management to improve the breeding conditions of target species. Here, we assess the efficacy of management measures using a Bayesian framework and controlling for confounding factors. We focus on four wader species, Northern Lapwing Vanellus vanellus, Eurasian Curlew Numenius arquata, Common Snipe Gallinago gallinago and Common Redshank Tringa totanus, that breed in numbers on wet grassland reserve sites in the UK. We collated annual site-specific climate variables, management information (e.g. the creation of wet features and predator control measures) and bird counts between 1994 and 2018. We found the effects of conservation actions varied between intervention types and species. For Lapwing and Redshank, excluding predators by predator-exclusion fencing, especially in combination with fox control, was generally associated with higher breeding counts. For all study species, sites with longer histories of management were associated with higher breeding numbers, with the effect of site age being particularly notable for management on former arable land. Our findings support the effectiveness of targeted conservation actions to achieve high numbers of breeding waders on lowland wet grassland reserves, and also highlight the value of consistent and reliable monitoring data.     

Fat reserves of migrating passerines at arrival on the breeding grounds in Swedish Lapland

Mist-net capture data taken during 6 years (1988–1990 and 1992–1994) of field work were used to describe the arrival sequences and fat loads of nine species of migratory passerines which breed in a near-Arctic environment in Swedish Lapland. Long-distance migrants arrived with significantly larger mean fat reserves than did medium- and short-distance migrants. Long-distance migrants carried fat loads at arrival which corresponded to potential remaining flight distances between 242 and 500 km. When females and males arrived on the breeding grounds simultaneously, females carried significantly larger energy reserves than did males in seven out of nine species. In contrast, when the sexes showed a significant difference in median arrival date (two out of nine species), there was no difference in mean fat load carried into the breeding area. A relationship was found between the migratory habits and foraging ecology of each species and the amount of fat reserves at arrival, suggesting that species-specific migratory distances and feeding habits determine the amount of fat that is needed during the transition period between migration and onset of breeding. The short growing season in the study area restricts the time available for breeding and moult, and large energy reserves at arrival may speed up the breeding schedule to counteract possible time constraints. Overloading at the last stopover site during spring migration may be an adaptation allowing birds to cope with a restricted time frame for breeding and moult at high latitudes.     

Timing of events on the breeding grounds for five species of sympatric warblers

ABSTRACT On the breeding grounds, migratory birds have limited time to breed and molt before autumn migration. However, few studies of long‐distance migrants have examined the phenology of these events to determine what life‐history trade‐offs might result if these activities overlap. From 2000 to 2007, I used banding data to determine the timing of migration, breeding, and primary molt for Yellow Warblers (Dendroica petechia), Yellow‐rumped Warblers (D. coronata coronata), American Redstarts (Setophaga ruticilla), Ovenbirds (Seiurus aurocapilla), and Canada Warblers (Wilsonia canadensis) at a study site in Alberta, Canada. Hatching date did not differ among species (P= 0.63), with means ranging from 27 June to 3 July. All species began primary molt between 12 July and 18 July, near the expected fledging date of offspring, and therefore all species exhibited overlap between postfledging parental care and molt. The duration of primary molt ranged from 28 d for Canada Warblers to 69 d for Yellow‐rumped Warblers. Yellow Warblers, Yellow‐rumped Warblers, and American Redstarts began autumn migration having completed about 50% of their primary molt. However, Ovenbirds departed when 21% of molt was complete, and Canada Warblers departed 2 d after completing molt. For all five species of warblers, molt did not overlap with nest‐bound breeding activities. However, molt did overlap with both postfledging care and migration. This suggests that initiating migration as soon as possible is important, possibly because earlier arrival on the wintering grounds may improve access to high quality winter habitat. Overall, warblers may maximize individual fitness by combining life‐history events that result in overlapping portions of the breeding cycle, molt, and migration.