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As is the case for most avian species, there is considerable variation in the egg size of Continental Black-tailed Godwits Limosa l. limosa breeding in The Netherlands. It is interesting that egg size has costs and benefits yet varies considerably at the population level. To better understand this variation in egg size, we tested its relationship to a suite of individual and environmental factors. We found that egg size can decrease up to 2.8% throughout a breeding season and that egg size increases with clutch size by 1.4% with each additional egg in the clutch. Female body mass and body size explained 5% of the total variation in egg size observed across the population. Furthermore, females wintering south of the Sahara laid 3% smaller eggs than those wintering north of the Sahara. We also found that egg size increases with age, which may indicate age-related differences in the endogenous and/or exogenous conditions of females. The variation in egg size was, however, mostly the result of consistent differences among individuals across years (repeatability = 0.60). A comparison of daughters with mothers suggested that most of this individual repeatability reflects heritable variation (heritability = 0.64). The actual individual traits that underlie this heritable variation among individuals remain mostly undetermined. Smaller eggs did have a slightly lower chance of hatching, but we found no relationship between egg size and chick survival. Finally, nest and chick survival were strongly correlated with lay date. Thus, in Black-tailed Godwits, lay date may actually reflect a female's endogenous and/or exogenous condition at the moment of egg-laying. This finding may be general across birds, since food supplementation experiments usually result in advanced laying and larger clutch sizes rather than in larger eggs. [ABSTRACT FROM AUTHOR]

The miniaturization of tracking devices is now rapidly increasing our knowledge on the spatiotemporal organization of seasonal migration. So far, most studies aimed at understanding within- and between-individual variation in migratory routines focus on single populations. This has also been the case for continental Black-tailed Godwits Limosa l. limosa (hereafter Godwits), with most work carried out on individuals from the Dutch breeding population, migrating in relatively large numbers in the westernmost part of the range. Here we report the migratory timing and routes of four adult individuals of the same subspecies from the low-density population in eastern Poland and compare this with previously published data on Godwits breeding in The Netherlands. During northward migration, the birds from Poland departed and arrived later from their wintering and breeding grounds. However, on southward migration the Polish breeding Godwits departed earlier, but arrived one month later than the Dutch birds on their wintering grounds in sub-Saharan Africa. Despite the small sample size of tracked birds from Poland, we find a significantly higher between-individual variation in timing during southward migration in Polish Godwits as compared to the Dutch Godwits. Furthermore, not only did migratory routes differ, but the few Polish Godwits tracked showed a higher level of between- and within-individual variation in route choice during both southward and northward migration. To explain this remarkable discrepancy, we propose that the properties of transmission of social information may be different between Godwits from a high-density population (i.e. the one in The Netherlands) and a low-density population (in Poland) and that this leads to different levels of canalization. To examine this hypothesis, future studies should not only follow individuals from an early age onwards, but also quantify and experimentally manipulate their social environments during migration. [ABSTRACT FROM AUTHOR]

In many bird species intraspecific variation in migration strategies is related to sex or size. The Eurasian Bittern Botaurus stellaris is a sexually size-dimorphic heron species with a vast breeding and wintering range spanning a range of climates. Ringing data show that Bitterns from northern populations migrate westwards or southwards over thousands of kilometres, while Bitterns from southern or temperate breeding areas migrate much shorter distances or remain resident. So far, any differences in the migrations of males and females have remained unstudied. In temperate climates, relatively benign winters alternate with the occasional harsh winter, and under these conditions, males as the larger sex might take the risk to stay rather than show seasonal migration. In the years 2010–2012 we equipped three females and three males from breeding areas in The Netherlands with a tracking device, recording their movements over periods of 2–5 years. All three males and one female stayed within or near the breeding area during the non-breeding season, but two females moved to distant wintering sites. One female migrated 4900 km to The Gambia providing the first direct evidence for trans-Saharan migration in this species. Another female migrated 700 km to winter in Devon, UK, for five consecutive years. The Bitterns were site-faithful to their breeding area and, mostly, to their wintering areas as well, although one male and one female progressively wintered closer to the breeding area in three successive years. Our results suggest that larger males from The Netherlands, a breeding area with fluctuating winter conditions, are predominantly resident, while the females are partial migrants with individually different and flexible strategies. [ABSTRACT FROM AUTHOR]

The article focuses on a study which investigates the diversity of nuptial plumage variants observed in male Ruffs Philomachus pugnax. Topics discussed include combinations like white ruff with black head tufts, a black ruff with white head tufts, and a regular ruff pattern with an irregular pattern, diversity of nuptial plumages among individuals,in the light of development, genetics and function and seasonal development of breeding plumages in Ruffs.

The article discusses a study of the flight behavior and use of stopover areas by Dutch-breeding Black-tailed Godwits (BG) in the Netherlands. The researchers used satellite telemetry and geolocation methods to monitor the migratory timing, use of stopover and nonbreeding sites, and routes of BG during the spring of 2009. They found that BG have different migration patterns in using stopover and nondreeding sites.

The article discusses a study of the effect of the length of long-distance flights on the frequency of inner flight replacement in tundra plovers, Pluvialis. The researchers collected data on moult patterns (MP) of Pacific Golden Plovers (PGP), American Golden Plovers, and Grey Plovers (GP) from the breeding, staging and wintering areas. Similar MP were observed on PGP and GP. They also found a correlation between the annual replacement of secondaries and the migration distance.

The article discusses the results of a study that examined the molecular variation of the subspecies status of Eurasian Spoonbills Platalea leucorodia balsaci in Mauritania. The study shows a significant variation between Spoonbills breeding in Mauritania and the wintering conspecifics breeding in the Dutch Wadden Sea. Among the 130 individuals, 6.3 percent of the total genetic variation is attributable to variation between the two breeding areas. Extensive dispersal within northwest Europe is noted following field observations on individually colour-marked birds from the Netherlands.

This article discusses a study which examined the decline in the food stocks of Afro-Siberian Red Knots in the western Dutch Wadden Sea. Particular focus is given to the boundaries of the western Dutch Wadden Sea, which was surveyed from 1996-2005. Between July and early September, annual sampling of intertidal macrozoobenthic prey were performed. An optimal diet model was used in this study to predict the intake rate of Red Knots. Results of the study showed that there were changes in the extent of intertidal mudflats that fulfilled the minimum intake needs of Red Knots. From 1996-2005, the study found an 86% drop in suitable foraging area. It also found a decline in the proportion of Red Knots without primary moult.

The article provides information on a study which analyzed the phenology, dynamics of the stopover and size of the Portuguese staging and western limosa population. The study described the phenology in comparison with the situation in the early 1990s and estimated staging duration of individual godwits and the total number of godwits using this staging area. The research argues that processes in Iberia are not likely to have contributed to the population decline as the area of rice cultivation has increased.

The article provides information on a study which estimated the total staging duration of Ruffs Philomachus pugnax in Fryslân from seniority and its staying probabilities. The research validated bird resighting data and compared three data categories of Ruffs Philomachis pugnax passing through the Netherlands during northward migration. The categories are newly colored-ringed, previously color-ringed and radio-tagged Ruffs. One of the study's findings was that the estimates of staying probability can be affected by catching although effects on staging duration might be small.

The article focuses on a study which examined the role of predation minimization in the stopover ecology of two Bar-tailed Godwit subspecies. This study collected data from the tidal flats and inland coastal meadows of the Dutch Wadden Sea island Terschelling. To estimate the body condition of the birds, the study analyzed their abdominal profiles, while soil samples were taken to examine food availability of the tidal areas. Results of the study showed that only colour-ringed lapponica individuals were seen from March to mid-April 2007, while the influx of colour-ringed taymyrensis started on April 22. Also included are information on the foraging behaviour of the taymyrensis and lapponica subspecies.