Jos C.E.W. Hooijmeijer

The interplay between habitat availability and population differentiation

We present STRUCTURE HARVESTER (available at http://taylor0.biology.ucla.edu/structureHarvester/), a web-based program for collating results generated by the program STRUCTURE. The program provides a fast way to assess and visualize likelihood values across multiple values of K and hundreds of iterations for easier detection of the number of genetic groups that best fit the data. In addition, STRUCTURE HARVESTER will reformat data for use in downstream programs, such as CLUMPP.

Intensified agricultural use of grasslands reduces growth and survival of precocial shorebird chicks

Intensification of agricultural use of grassland habitats has been linked to the declines of many farmland bird species, several of whom have been in decline for multiple decades despite agri-environmental schemes. In the Netherlands, where most grasslands have been transformed into well-drained monocultures managed for maximal dairy production, schemes that aim to protect nests from agricultural activities are the most popular. The cause of the failure of these schemes, however, seems poor recruitment of farmland birds. Using the black-tailed godwit Limosa limosa limosa as our model species, we tested the hypothesis underlying the most popular agri-environmental schemes that there are no differences in condition at hatch, growth, and apparent survival rates between chicks raised on monocultures compared with chicks from herb-rich meadows with high water tables, often managed, for the sake of grassland birds, in traditional ways. We also compare the growth rates from both habitat types with those of chicks from dairy farmland from 1976 to 1985, a time when population declines of godwits first became visible. Hatchling mass did not differ between chicks from herb-rich meadows and grassland monocultures, but chicks hatched on monocultures were on average 1416% lighter at fledging, and had 4% smaller bills than chicks hatched on herb-rich meadows. The growth rates of female chicks hatched on herb-rich meadows were similar to those of chicks measured from 1976 to 1985. Males fledged lighter and smaller than females. Apparent survival during the first year of life for chicks hatched on herb-rich meadows was 2 center dot 5 times higher than that of chicks hatched on grassland monocultures. The apparent survival on herb-rich meadows seems sufficient for a stable population. Synthesis and applications: We found striking differences between chicks hatched on modern grassland monocultures and herb-rich meadows. That chicks hatched on monocultures had lower growth and survival rates than chicks on meadows indicates that these chicks suffer a higher risk of starvation and/or predation. These findings imply that the most often applied agri-environmental schemes (i.e. payments per clutch found and postponed mowing), are not effective. Instead, these schemes could even encourage maladaptive habitat choice. Conservation efforts should thus focus on the provision of herb-rich meadows with high groundwater tables.

Repeatable timing of northward departure, arrival and breeding in Black-tailed Godwits Limosa l. limosa, but no domino effects

When early breeding is advantageous, migrants underway to the breeding areas may be time stressed. The timing of sequential events such as migration and breeding is expected to be correlated because of a “domino effect”, and would be of particular biological importance if timings are repeatable within individuals between years. We studied a colour-marked population of Black-tailed Godwits Limosa l. limosa both on staging areas in Portugal and on breeding areas in The Netherlands. For each individual, we measured the timing of the staging period, the arrival date on the breeding area and the egg laying date. We measured average egg volume as a measure of reproductive investment. The date of departure from the staging areas, the arrival date on the breeding areas, and the egg laying date were repeatable among years in individual Black-tailed Godwits. The arrival dates of paired males and females and the average annual male and female arrival dates were correlated. The dates of departure from Portugal, arrival in The Netherlands, and egg laying were not correlated. Earlier clutches had larger eggs than late clutches. If the length of the individually available pre-laying period is accounted for, early arriving birds spent more time on the breeding grounds before laying than late arriving birds. The repeatability of the itineraries and the correlation between arrival timing of males and females are consistent with observations in other migrants. Despite evidence for early breeding being advantageous, we found no evidence of a “domino effect”.ZusammenfassungLangstreckenzieher stehen unter starkem Zeitdruck wenn ein früher Brutzeitpunkt vorteilhaft ist. Es wird angenommen, dass der Zeitpunkt von Abflug, Ankunft und Eiablage von individuellen Vögeln wiederholbar zwischen den Jahren ist. Deshalb kann man erwarten, dass die Zeitpunkte dieser sequentiellen Ereignisse miteinander korrelieren: der “Dominoeffekt”. We untersuchten eine mit Farbringen markierte Uferschnepfen Population in den Rastgebieten in Portugal und im Brutgebiet in den Niederlanden. Wir wissen für jedes Individuum sowohl den Zeitraum des Aufenthalts im Rastgebiet, den Ankuftszeitpunkt im Brutgebiet, und das Eiablagedatum. Wir verwandten das durchschnittlichen Eivolumen, welches mit dem Bruterfolg korreliert, als Indikation für reproduktive Investition. Innerhalb individueller Vögel waren sowohl Abflugzeitpunkt aus den Rastgebieten, Ankunft im Brutgebiet und Eiablagedatum wiederholbar zwischen den Jahren. Die Ankunftszeitpunkte von später verpaarten Männchen und Weibchen, sowie die durchschnittlichen jährlichen Ankunftszeitpunkte beider Geschlechter waren miteinander korreliert. Abflugszeitpunkt aus den Rastgebieten, Ankunftszeitpunkt im Brutgebiet und Eiablagedatum waren jedoch nicht miteinander korreliert. Frühe Gelege enthielten größere Eier als späte Gelege. Früh ankommende Vögel hielten sich länger im Brutgebiet auf als spät ankommende Vögel, selbst wenn wir für die Dauer des Aufenthaltes korrigierten. Die Wiederholbarkeit des Zugzeitplans und die Korrelation zwischen den Geschlechtern sind im Einklang mit Beobachtungen an anderen Zugvogelarten. Trotz des offensichtlichen selektiven Vorteils eines frühen Eiablagedatums fanden wir keine Hinweise auf einen Dominoeffekt.

Sexual dimorphism in plumage and size in Black-tailed Godwits Limosa limosa limosa

Systematic sex-related differences in size and plumage are informative of sex-specific selection pressures. Here, we present an analysis of sexual dimorphism in body size and plumage of Black-tailed Godwits Limosa limosa limosa from a breeding population in The Netherlands. Molecular methods were used to unambiguously assign the sex of captured birds. To quantify breeding plumage, we developed nine plumage scores. These scores describe the intensity of orange in the breast plumage, the extent of black bars on the belly, the coverage and number of breeding feathers on the back, the conspicuousness of the white eye stripe, the extent of white plumage on the head, the percentage of orange colour in the bill and the percentage of white and black spots covering the neck. Most females were structurally bigger, and had a greater body mass. Nonetheless, we found a greater overlap in bill length between the sexes than expected on the basis of literature data: biometrics alone are not sufficient to correctly discriminate between the sexes. Black-tailed Godwits are sexually dimorphic mostly with respect to the amount of white spots on the neck, females being of lighter colour than males. In addition, females showed fewer black bars and less orange on the breast, had more white in the head and fewer and a smaller extent of breeding feathers on the back. Interestingly, we found a genotypic polymorphism on the sex-related CHD1 gene on the Z chromosome, commonly used for molecular sexing in birds. Males of the less frequent genotype had significantly more white in their plumage and had fewer black bars on their breast, while in females no differences between the two genotypes were found.

When Siberia came to the Netherlands : The response of continental black-tailed godwits to a rare spring weather event

1. Extreme weather events have the potential to alter both short- and long-term population dynamics as well as community- and ecosystem-level function. Such events are rare and stochastic, making it difficult to fully document how organisms respond to them and predict the repercussions of similar events in the future. 2. To improve our understanding of the mechanisms by which short-term events can incur long-term consequences, we documented the behavioural responses and fitness consequences for a long-distance migratory bird, the continental black-tailed godwit Limosa limosa limosa, resulting from a spring snowstorm and three-week period of record low temperatures. 3. The event caused measurable responses at three spatial scales - continental, regional and local - including migratory delays (+19 days), reverse migrations (>90 km), elevated metabolic costs (+8·8% maintenance metabolic rate) and increased foraging rates (+37%). 4. There were few long-term fitness consequences, however, and subsequent breeding seasons instead witnessed high levels of reproductive success and little evidence of carry-over effects. 5. This suggests that populations with continued access to food, behavioural flexibility and time to dissipate the costs of the event can likely withstand the consequences of an extreme weather event. For populations constrained in one of these respects, though, extreme events may entail extreme ecological consequences.

Unexpected diversity in socially synchronized rhythms of shorebirds

The behavioural rhythms of organisms are thought to be under strong selection, influenced by the rhythmicity of the environment. Such behavioural rhythms are well studied in isolated individuals under laboratory conditions, but free-living individuals have to temporally synchronize their activities with those of others, including potential mates, competitors, prey and predators. Individuals can temporally segregate their daily activities (for example, prey avoiding predators, subordinates avoiding dominants) or synchronize their activities (for example, group foraging, communal defence, pairs reproducing or caring for offspring). The behavioural rhythms that emerge from such social synchronization and the underlying evolutionary and ecological drivers that shape them remain poorly understood. Here we investigate these rhythms in the context of biparental care, a particularly sensitive phase of social synchronization where pair members potentially compromise their individual rhythms. Using data from 729 nests of 91 populations of 32 biparentally incubating shorebird species, where parents synchronize to achieve continuous coverage of developing eggs, we report remarkable within- and between-species diversity in incubation rhythms. Between species, the median length of one parent’s incubation bout varied from 1–19 h, whereas period length—the time in which a parent’s probability to incubate cycles once between its highest and lowest value—varied from 6–43 h. The length of incubation bouts was unrelated to variables reflecting energetic demands, but species relying on crypsis (the ability to avoid detection by other animals) had longer incubation bouts than those that are readily visible or who actively protect their nest against predators. Rhythms entrainable to the 24-h light–dark cycle were less prevalent at high latitudes and absent in 18 species. Our results indicate that even under similar environmental conditions and despite 24-h environmental cues, social synchronization can generate far more diverse behavioural rhythms than expected from studies of individuals in captivity. The risk of predation, not the risk of starvation, may be a key factor underlying the diversity in these rhythms.

Reproductive timing and investment in relation to spring warming and advancing agricultural schedules

AbstractAdvances in mowing schedules have led to early and rapid declines in the seasonal food availability for, and survival rates of, chicks of grassland-breeding waders. Concurrently, increased levels of soil fertilization may have improved food abundance for adults. These developments are assumed to have resulted in an advancement of laying during 1930–1976 in several meadowbird species, including Black-tailed Godwits. Despite an apparent selective advantage of early breeding, after 1976 Godwits stopped advancing their laying dates. We have analyzed the timing of breeding and reproductive investment in Dutch Black-tailed Godwits relative to recent changes in agricultural practices and climate during 1976–2007. Early and late spring temperatures and precipitation in March were used as indicators for the timing of fertilizer application and mowing, and also as qualitative measures of relative food availability for adults and chicks. When precipitation was higher in March, Black-tailed Godwits laid earlier. Following warmer winters, the earliest females laid larger eggs, which hatched heavier chicks with a higher survival probability. We suggest that the positive effect of an increasing March precipitation on invertebrate abundance may be constrained by the current policy of rigid control of the water table. This policy prevents Godwits from further advancing laying dates, which would increase their chick’s survival prospects under increasingly early mowing schedules. Policy-makers should, next to delaying mowing schedules, also consider reduced draining in early spring as a tool to help stop the population decline of the Black-tailed Godwit.ZusammenfassungBrutzeitpunkt und Reproduktion von Uferschnepfen in Bezug auf Veränderungen landschaftlicher Aktivitäten und Klimaerwärmung Immer frühere Mahdzeitpunkte führen zu einer immer früheren und schnellen Verringerung der saisonalen Nahrungsverfügbarkeit, und damit auch einer starken Abnahme der Überlebenschancen von Wiesenvogelküken. Im Gegensatz dazu hat die zeitgleiche zunehmende Düngung von Grasland sehr wahrscheinlich die Nahrungsgrundlage für adulte Wiesenvögel verbessert. Dies hatte zur Folge dass gleich mehrere Arten von Wiesevögeln einschließlich der Uferschnepfe zwischen 1930 und 1976 ihre Eiablage immer früher tätigten. Überraschenderweise, und obwohl eine früherer Eiablagezeitpunkt anscheinend einen Selektionsvorteil verschafft, stellten Uferschnepfen das Verfrühen der Eiablage nach 1976 ein. Hier präsentieren wir eine Analyse des Zeitpunktes der Eiablage und der Investition in die Reproduktion von niederländischen Uferschnepfen vor dem Hintergrund der rezenten Veränderungen landwirtschaftlicher Aktivitäten und des Klimas im Zeitraum von 1976–2007. Wir verwenden die mittleren Temperaturen während des frühen und späten Frühjahres sowie die Niederschlagssumme im März als Indikatoren für respektive den Zeitpunkt der Düngung, der Mahd und als qualitatives Maß des relativen Nahrungsangebot für adulte Uferschnepfen und Jungtiere. In Jahren mit feuchterem März legten Uferschnepfen ihre Eier früher. Nach wärmeren Wintern legten frühe Weibchen größere Eier, aus welchen Kücken in besserer Kondition schlüpften, welche eine bessere Überlebenswahrscheinlichkeit hatten. Unsere Resultate suggerieren, dass der positive Effekt, den die Klimaänderung auf den Niederschlag im Frühjahr, und damit auch auf die Nahrungsverfügbarkeit für adulte Uferschnepfen hat, durch die starke Kontrolle des Grundwasserspiegels zunichte gemacht wird. Dies verhindert, dass Uferschnepfen früher legen können, was die Überlebenschancen der Kücken unter immer früheren Mahdterminen deutlich verringert.

Site selection and resource depletion in black‐tailed godwits Limosa l. limosa eating rice during northward migration

1. During migratory stopovers, animals are under strong time stress and need to maximize intake rates. We examine how foragers react to resource depletion by studying the foraging ecology and foraging site selection of black-tailed godwits Limosa l. limosa staging in rice fields during their northward migration stopover (January-March 2007). 2. We analysed godwit abundance and foraging behaviour, sampled the availability of rice in the fields and used the functional response model to predict the giving-up density (GUD) of rice kernels when godwits should give up a rice field. Sightings of individually colour-marked birds were used to verify whether individuals moving between rice fields confirmed the predicted GUD. 3. Black-tailed godwit intake rates at different rice densities fitted Hollings functional response curve. The predicted GUD of rice necessary to balance allometric estimates of daily energy expenditure (DEE) and measured time budgets were confirmed by GUD measured in the field. 4. Individually marked birds moved towards rice fields with higher rather than lower rice densities more often than randomly expected. These birds increased the measured intake rates after this move. 5. Godwit foraging caused a decrease in the rice density of individual fields during the stopover period. Despite this, overall intake rates remained constant as godwits reacted to resource depletion by moving to a new foraging site as soon as their intake rate falls below the required levels to achieve DEE.

A modern landscape ecology of Black-tailed Godwits : Habitat selection in southwest Friesland, The Netherlands

For a long time, agricultural areas had considerable ornithological value, an ecological richness which in The Netherlands was epitomised by the term ‘meadow birds’. However, over the last half century, agricultural intensification has negatively affected the quality of meadow bird habitats. Here we provide a quantitative characterization of agricultural habitats and their use by Blacktailed Godwits Limosa I. limosa in the south-western part of the province of Friesland, The Netherlands, in 2009, to provide a yardstick to evaluate further change. We used groundwater level, vegetation typology, relief in the landscape, the occurrence of foot drains, land use and soil characteristics such as textures and peat to describe the landscape that comprised 43 polders covering 8480 ha. We used a Principal Component Analysis to summarize landscape characteristics and find that much of the habitat variation is explained by a combination of herb richness of the vegetation, the presence or absence of foot drains and groundwater level. The modern agricultural landscape of southwest Friesland consists of 80% of uniform, intensively managed landscape with herb-poor meadows and low groundwater levels, the remaining 20% being taken by remnants of the former herb-rich meadows. The whole study area was searched weekly and Black-tailed Godwits were mapped between arrival and egg-laying. The positive relationship between godwit density and the first PC axis indicates that Black-tailed Godwits preferred herb-rich polders with high groundwater levels and the presence of foot drains. Soil texture was poorly correlated with godwit breeding densities for intensively managed (herb-poor) parcels, but for herb-rich meadows, soils of sandy clay loam and sandy clay harboured the highest densities of godwits. To protect Black-tailed Godwits, areas should have a herb-rich vegetation, contain foot drains and high groundwater tables should be re-established.

Phenology, Stopover Dynamics and Population Size of Migrating Black-Tailed Godwits Limosa Limosa Limosa in Portuguese Rice Plantations

Between 2005/06 and 2008/09 we studied Black-tailed Godwits Limosa I. limosa staging in the rice fields surrounding the Tejo and Sado estuaries, Portugal. Godwits were counted weekly and flocks were scanned for colour-ringed individuals. We analysed phenology, dynamics of the stopover, and estimated the size of the Portuguese staging population as well as the total western limosa population, Godwits started arriving in January. Numbers peaked in the second half of February, after which they quickly departed from the area. Comparison with previous records suggested that numbers have decreased since the early 1990s, and that godwits currently peak later than some 15 years ago. Individual staging durations averaged 22.6 days in 2007 and 25.3 days in 2009, and increased towards the end of the staging period. We estimated that a total 59 200 birds used the area in 2007 and 53 100 in 2009. Using estimates for the proportion of colour-ringed birds in the flocks, we estimated the population size of the western part of the L. l. limosa population at 133 151–140 722 birds. This is higher than previous estimates based on inventories of the breeding population, but accounts for the non-breeding segment of the population. Thus, we estimate that 38–44% of the NW European Black-tailed Godwit population stage in Portugal. It is argued that processes in Iberia are not likely to have contributed to the population decline as the area for rice cultivation has increased. Nevertheless, as godwits staging in Iberia are totally dependent on human-made habitats, changes in rice farming practices could have great impact on the total population size.