Phenotype-limited distributions: short-billed birds move away during times that prey bury deeply

In our seasonal world, animals face a variety of environmental conditions in the course of the year. To cope with such seasonality, animals may be phenotypically flexible, but some phenotypic traits are fixed. If fixed phenotypic traits are functionally linked to resource use, then animals should redistribute in response to seasonally changing resources, leading to a ‘phenotype-limited’ distribution. Here, we examine this possibility for a shorebird, the bar-tailed godwit (Limosa lapponica; a long-billed and sexually dimorphic shorebird), that has to reach buried prey with a probing bill of fixed length. The main prey of female bar-tailed godwits is buried deeper in winter than in summer. Using sightings of individually marked females, we found that in winter only longer-billed individuals remained in the Dutch Wadden Sea, while the shorter-billed individuals moved away to an estuary with a more benign climate such as the Wash. Although longer-billed individuals have the widest range of options in winter and could therefore be selected for, counterselection may occur during the breeding season on the tundra, where surface-living prey may be captured more easily with shorter bills. Phenotype-limited distributions could be a widespread phenomenon and, when associated with assortative migration and mating, it may act as a precursor of phenotypic evolution

Genetic structure in the nonbreeding range of <i>rufa</i> Red Knots suggests distinct Arctic breeding populations

An understanding of the migratory connectivity between breeding and nonbreeding areas is fundamental to the management of long-distance migrants under pressure from habitat change along their flyways. Here we describe evidence for genetic structure within the nonbreeding range of the endangered Arctic-Canadian rufa subspecies of Red Knots (Calidris canutus). Using blood and tissue samples from the major nonbreeding regions in Argentina (Tierra del Fuego and Río Negro), northern Brazil (Maranhão), and southeastern USA (Florida), we estimated genetic structure in 514 amplified fragment length polymorphism (AFLP) loci, applying cluster assignment analyses in DAPC, assignPOP, and STRUCTURE. Using a priori location information, individuals could be correctly re-assigned to their nonbreeding regions, which validated that the assignment accuracy of the data was sufficient. Without using a priori location information, we detected 3–5 genotype clusters, and posterior assignment probabilities of samples to these genotype clusters varied among the three regions. Lastly a chi-square test confirmed that allele frequencies varied significantly among nonbreeding regions, rejecting the hypothesis that samples were drawn from a single gene pool. Our findings hint at undescribed structure within the Red Knot rufa breeding range in the Canadian Arctic and indicate that each rufa nonbreeding area in this study hosts a different subsample of these breeding populations. The observation that nonbreeding sites of rufa Red Knots contain different genetic pools argues for separate conservation management of these sites

Body shrinkage due to Arctic warming reduces red knot fitness in tropical wintering range

Reductions in body size are increasingly being identified as a response to climatewarming. Here we present evidence for a case of such body shrinkage, potentially dueto malnutrition in early life. We show that an avian long-distance migrant (red knot,Calidris canutus canutus), which is experiencing globally unrivaled warming rates at itshigh-Arctic breeding grounds, produces smaller offspring with shorter bills duringsummers with early snowmelt. This has consequences half a world away at their tropicalwintering grounds, where shorter-billed individuals have reduced survival rates. This isassociated with these molluscivores eating fewer deeply buried bivalve prey and moreshallowly buried seagrass rhizomes. We suggest that seasonal migrants can experiencereduced fitness at one end of their range as a result of a changing climate at theother end

Do ditch‐side electric fences improve the breeding productivity of ground‐nesting waders?

1. Insufficient reproduction as a consequence of predation on eggs and chicks is a major determinant of population decline in ground-nesting birds, including waders. For many populations, there is an urgent need to maintain breeding populations at key sites, and conservation practitioners need to find viable management solutions to reduce predation. 2. One tool available to the practitioner is fences that exclude key predators from areas containing breeding birds. Temporary electric fencing is an increasingly popular predator exclusion intervention, but such fences have costs associated with purchase and the time needed to erect and maintain them. Their effectiveness and optimal application are also frequently questioned. 3. We evaluate the use of temporary ditch-side four-strand electric fences in lowland grasslands in two countries, The Netherlands and England, in areas containing high densities of breeding waders. 4. In both countries and in all years, godwit and lapwing nest survival was significantly higher within areas enclosed by ditch-side electric fences. Brood survival, assessed for godwits in The Netherlands, was also higher within fenced areas in all years. This demonstrates that using temporary electric fences to enclose ground-nesting birds can be an effective tool for improving breeding productivity. 5. In our study, closely managed electric fences were effective at excluding red foxes Vulpes vulpes, but not avian and other mammalian predators. The positive effect that electric fencing had on nest and brood survival therefore likely results from a reduction in the total number of visits by mammalian predators, and especially visits by foxes. 6. Although it requires a substantial time investment throughout the period of use, our temporary electric fence design provides flexibility compared to other fence designs when it comes to enclosing different areas within a season and between years, as the targets for protection change or as land and flood management dictate. This conservation intervention can help buy the time required to develop and implement longer term solutions for application at larger scales

Data presented in the paper: Colony-breeding Eurasian Spoonbills in the Netherlands: Local limits to population growth with expansion into new areas

The dataset contains three files, all relating to spoonbill breeding colonies in the Netherlands. We used this dataset to assess population growth of Spoonbills in the Netherlands, and especially in the Wadden Sea. The first file contains yearly breeding colony sizes, which were obtained by counting in each of the colonies in each year the number of breeding pairs. This was done mostly by local nature management teams. The second file contains for several colonies in the Wadden Sea area the average yearly breeding success. This number was obtained by counting the number of fledglings in the end of the breeding season. This was also done mainly by local nature management teams. The last file contains data on the condition of individual chicks in several colonies. These were obtained by researchers from the University of Groningen and NIOZ, and by several Staatsbosbeheer officers

Data from: Migration tendency delays distributional response to differential survival prospects along a flyway

This datafile (plain textfile to be imported in program E-Surge) contains the encounter histories of 2095 adult (>3cy) Eurasian spoonbills, born between 1988 and 2007 and resighted between summer 1994 and summer 2010. Two resighting periods per year are defined (summer = March-September, winter = December-January for France and Iberia and October-February for Mauritania & Senegal). Events are coded as: (0) not resighted, (1) resighted in summer in The Netherlands, (2) resighted in winter in France, (3) resighted in winter in Iberia, (4) resighted in winter in Mauritania & Senegal. Columns refer to encounter history (H:), sample size (S:) and 'standardized' year of birth (COV:yb), calculated as ([year of birth]-2000)/10

Dataset: Sanderlings (Calidris alba) of two different age classes at the moment of individual colour-marking at four non-breeding sites that were or were not observed during migration following the capture

The data file contains data of Sanderlings (Calidris alba) of two different age classes at the moment of capture and individual colour-marking at one of four wintering areas that were or were not observed during migration following the capture. Each individual is indicated with a unique number in column “BirdID”. The column “country” indicates which of the four wintering areas (as depicted in Fig. 1 in the manuscript), with GB indicating England, PT indicating Portugal, MR indicating Mauritania and GH indicating Ghana. The “age” of each bird was either juvenile (1 year old). Whether an individual was observed during migration, i.e. at least 2 latitudinal degrees north of its average winter location between 15 March – 15 October, in the migration period following capture is indicated with a 0 (not observed) or 1 (observed) in the column “observed”. Further details can be found in the methods section in the manuscript