Pedro M. Lourenço

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.

Stopover ecology of Black-tailed Godwits Limosa limosa limosa in Portuguese rice fields : a guide on where to feed in winter

Capsule Conservation management of rice fields may be necessary to guarantee the availability of high quality stopover habitats. Aims To analyse habitat selection and quantify the diet composition of birds. Methods Using water level and agricultural management of the fields as variables, habitat selection was analysed by compositional analysis. Godwit diet composition was quantified by faecal analysis, and food abundance was sampled to explain the observed habitat selection. Results We found evidence of higher use of flooded and ploughed paddies than expected from their relative abundance. These fields have the highest densities of buried rice kernels, which seem to be the main food source for Black-tailed Godwits. Conclusion Currently, godwits find good foraging areas in Portuguese rice fields, feeding primarily on rice kernels that are mostly found in flooded ploughed fields. Changes in rice farming, late ploughing and predicted decreases in rainfall may lead to loss of this habitat. However, because of the man-made nature of their requirements, it should be possible to install relevant land-use practices that guarantee the availability of high quality stopover habitats.

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.

Management of Rice Fields for Birds during the Non-growing Season

Abstract. Fields planted with rice (Oryza sativa) are used by a wide variety of bird species during the non-growing season and play an important conservation role in many parts of the world. Management of fields affects the variety and number of birds that use them, and a thorough understanding of these issues could improve the conservation value of rice farming. The challenge for conservation practitioners is identifying management actions that provide benefits, without adverse impacts on crop production. Harvest method, post-harvest straw management, winter flooding, food supplementation and hunting all influence bird populations. Also, field preparation methods, organic farming and the management of field margins and drainage ditches, probably influence the conservation value of rice agriculture but have received less attention. Current knowledge of these issues is reviewed in order to identify management practices thought to have conservation benefits and highlight topics that warrant additional research.

Long-term declines of wader populations at the Tagus estuary, Portugal : a response to global or local factors?

Summary Migratory wader populations face global threats, mainly related to increasing rates of habitat loss and disturbance driven by human activities. To a large extent, the long-term survival of these populations requires the conservation of networks of sites along their migratory flyways. The Tagus estuary, Portugal, is among the most important wetlands for waders in the East Atlantic Flyway. Annual winter wader counts have been carried in this wetland since 1975 and a monthly roost-monitoring programme was implemented in 2007. Wintering populations of three out of the five most abundant species, Dunlin Calidris alpina, Grey Plover Pluvialis squatarola and Redshank Tringa totanus, showed significant population declines over the past three decades, which are most likely due to the loss and degradation of roost sites as a result of increasing human activity. The situation is unlikely to improve, as a high proportion of the wintering waders use roost sites that are situated in highly urbanised areas with no legal protection. The use of different roost sites by waders is highly variable both temporally and spatially, thus emphasizing the need for a network of good quality roost sites. Additionally, during migration, 60–80% of all the waders of the Tagus estuary concentrate at a single refuge, thus increasing the risk for wader populations during these periods.

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.

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.

Population overlap and habitat segregation in wintering Black-tailed Godwits Limosa limosa

Capsule Distinct breeding populations of migratory species may overlap both spatially and temporally, but differ in patterns of habitat use. This has important implications for population monitoring and conservation. Aims To quantify the extent to which two distinct breeding populations of a migratory shorebird, the Black‐tailed Godwit Limosa limosa, overlap spatially, temporally and in their use of different habitats during winter. Methods We use mid‐winter counts between 1990 and 2001 to identify the most important sites in Iberia for Black‐tailed Godwits. Monthly surveys of estuarine mudflats and rice‐fields at one major site, the Tejo estuary in Portugal in 2005–2007, together with detailed tracking of colour‐ringed individuals, are used to explore patterns of habitat use and segregation of the Icelandic subspecies L. l. islandica and the nominate continental subspecies L. l. limosa. Results In the period 1990–2001, over 66 000 Black‐tailed Godwits were counted on average in Iberia during mid‐winter (January), of which 80% occurred at just four sites: Tejo and Sado lower basins in Portugal, and Coto Doñana and Ebro Delta in Spain. Icelandic Black‐tailed Godwits are present throughout the winter and forage primarily in estuarine habitats. Continental Black‐tailed Godwits are present from December to March and primarily use rice‐fields. Conclusions Iberia supports about 30% of the Icelandic population in winter and most of the continental population during spring passage. While the Icelandic population is currently increasing, the continental population is declining rapidly. Although the estuarine habitats used by Icelandic godwits are largely protected as Natura 2000 sites, the habitat segregation means that conservation actions for the decreasing numbers of continental godwits should focus on protection of rice‐fields and re‐establishment of freshwater wetlands.

Space use by Black-tailed Godwits Limosa limosa limosa during settlement at a previous or a new nest location

Capsule Black-tailed Godwits first return to the nest location of the previous year, even when moving to a different nest location later that season. Aims To examine the use of space by Black-tailed Godwits during the two months before egg-laying to two weeks afterwards. Methods We compare the spatial distribution of sightings of eventually site-faithful birds with birds that changed nest location, and relate this to the change of the distance to their previous years and current nest-site in the period until egg-laying. Using a log-likelihood model we establish how the differences in distance to the respective nests change over the course of the season. Results All birds were observed first near their previous years nest-site, and remained there for most of the pre-laying period. Birds that subsequently changed nest location made the move only about five days before egg-laying and were more wide-ranging earlier on. Conclusion The return to the previous nest-site suggests that a decision to move is made only after considerable time investment near the previous nest-site. This indicates that site-faithfulness in Black-tailed Godwits is conditional on experiences after return to the nesting area.