Migratory Ruffs have prolonged stopovers in spring (original) (raw)

Migrating Birds Stop Over Longer Than Usually Thought: An Improved Capture–Recapture Analysis

Ecology, 2001

Migrating animals often divide their journey into alternating phases of migration bouts and stopping over. For investigating many questions of migration ecology it is crucial (1) to estimate the duration of stopover phases, and (2) to test whether animals of different groups differ in their stopover behavior. Using recent advances in capturerecapture statistics, we show how total stopover duration can be estimated from capturerecapture data. The probabilities of immigration are estimated and modeled by recruitment analysis and are converted into the time the animals spent at the stopover place before capture; the probabilities of emigration are estimated and modeled by survival analysis and are converted into the time the animals spent at the stopover place after capture. The sum of the two parts is the total stopover duration. Tests for differences between groups can be addressed by an appropriate model selection procedure. Two examples of migrating passerine birds at a stopover site in Switzerland illustrate this method. Mean total stopover duration was 12.3 d for Reed Warblers and 7.1 d for Reed Buntings. This was considerably higher than values obtained by the minimum stopover duration estimation (6.0 and 4.4 d, respectively). Because of the fundamental weaknesses of the minimum stopover duration estimation, which has been widely used in migration ecology, many findings obtained by this method need to be reconsidered.

Chapter 7 7 Individual and population-level evidence for a large-scale, within-generation shift in a shorebird migration route

In most migrant birds, young perform their first migration independently of adults. The presumed dearth of learning opportunities has been linked to a lack of fast adaptive change in migration routes. Here we describe the first example of an adaptive route change within a generation of a migratory bird. Ruffs (Philomachus pugnax) migrating from West Africa to Fennoscandinavia and Russia via The Netherlands, shifted to alter-native staging areas, after staging performance was compromised. Between 2004-08, 4,363 males were tracked by individual colour-ringing and partly, by radio-tags. Between 2004-08, 145 individuals previously colour-ringed in The Netherlands occurred increasingly eastwards, as far as the next major staging site, 1500 km east in Belarus. This individual flexibility correlated with a new April cohort of 20,000 migrants appearing in Belarus. Capture-resighting methods revealed that individual length of stay of the Dutch migrants declined from 23 to 19 days between 200...

Stopover ecology and population dynamics of migratory shorebirds

2019

Migratory animals are declining worldwide, and for many species there are multiple threats to population stability from throughout the annual cycle. Animals performing longdistance migrations use stopover sites en route to replenish fat stores, and the congregation of individuals at migratory stopover sites affords an opportunity to track population health,

Spring migration of ruffs Philomachus pugnax in Fryslân: estimates of staging duration using resighting data

Ardea, 2010

Seasonal bird migration involves long flights, but most time is actually spent at intermediate staging areas. The duration of stay at these sites can be evaluated with mark–recapture methods that employ day-to-day local encounters of individually marked birds. Estimates of staging duration are based on two probabilities: the immigration probability, the complement of a bird’s seniority to an area, and the emigration probability, the complement of the staying probability. Estimating total staging duration from seniority and staying probabilities requires validation for resighting data and here we compare three data categories of Ruffs Philomachus pugnax passing through The Netherlands during northward migration: (1) newly colour-ringed, (2) previously colour-ringed and (3) radio-tagged Ruffs (recorded by automated receiving stations). Between 2004 and 2008, 4363 resighting histories and 95 telemetry recording histories were collected. As sample sizes for females were low, only data for males were analysed. Possible catching effects affecting estimates of staging duration were explored. Staying probability was estimated for all data. Seniority however, could not be estimated for newly marked Ruffs; the assumption of equal ‘capture’ probability for reverse-time models applied to estimate seniority is violated for seasonal resighting histories starting with a catching event. Therefore, estimates of total staging duration were based on resightings of previously colourmarked birds only. For radio-tagged birds a minimal staging duration (time between tagging and last recording) was calculated. Modelling indicated that newly colour-ringed birds had a higher staying probability than previously colour-ringed birds, but the difference translated to a prolonged staging duration in newly ringed birds of only 0.4–0.5 d, suggesting a very small catching effect. The minimal staging duration of radio-tagged birds validated estimates of staging duration for colour-ringed birds in 2007 but not in 2005. In 2005 a low resighting probability resulted in underestimates of staging duration. We conclude that (1) estimates of staying probability can be affected by catching although effects on staging duration might be small, and that (2) low resighting probabilities can lead to underestimates in staging duration. In our study previously ringed Ruffs resighted in 2006–08 yielded reliable estimates of staging duration as data had sufficiently high resighting probabilities. Average staging durations varied between 19 d in 2008 and 23 d in 2006.

Comparing population trend estimates of migratory birds from breeding censuses and capture data at a spring migration bottleneck

Ecology and Evolution, 2020

Europe has a well‐established network of breeding bird monitoring that is used to produce supranational indices of population trends for many species. However, a comparison of breeding bird censuses with other methods may be beneficial to confirm the validity of such indices. The aim of this study was to assess the value of standardized capture data of migratory birds at migration bottlenecks as an indicator of the effective breeding populations. One limitation to this method is that several populations are co‐occurring at these bottlenecks and their catchment areas need to be clearly identified to allow extrapolation of population indices. Here, we used standardized trends in capture numbers of 30 species on the island of Ponza, a migration bottleneck in the central Mediterranean, and compared them to population trends estimated in the putative catchment breeding areas between 2005 and 2016. The catchment areas were identified through the analysis of ring recoveries during the bree...

Examining the total arrival distribution of migratory birds

Global Change Biology, 2005

This paper reports on the total distribution of spring migration timing of willow warbler, chiffchaff and pied flycatcher at locations in the UK, Germany, Russia and Finland. This is the first time that high-quality data based on known-effort monitoring has been examined on a continental scale. First arrival dates, commonly reported in the literature, were positively correlated with mean arrival dates although they would not make good predictors of the latter. At all locations, at least one aspect of the arrival distribution of each species had got significantly earlier in recent years. The trend towards earliness was associated with warmer local temperatures and more positive winter North Atlantic Oscillation index. In years that were early, the arrival distribution became more elongated and skewed. Researchers should now investigate the consequences of earlier arrival on current and future bird populations.

Estimating shorebird numbers at migration stopover sites

The Condor, 2006

We describe a method for estimating the total number of shorebirds that use a migration stopover site during spring and fall migration. We combined weekly shorebird counts with parameter estimates for detection probability, sampled proportion, and length of stay on the Squaw Creek National Wildlife Refuge. Double sampling was used to determine detection probability and estimated values varied among wetland units from a low of 0.07 to a high of 0.82. The sampled proportion of most wetland units was 100% but was lower in some of the larger units. Length of stay (measured for Pectoral [Calidris melanotos] and Least Sandpipers [C. minutilla] combined) averaged 10.0 days in spring and 3.7 days in fall. Spring shorebird numbers were approximately five times greater than fall numbers on the Refuge. Annual shorebird numbers varied among years from an estimated low in 2003 of 15 734 to a high in 2002 of 69 570. Peak daily counts during study years averaged only 12% of estimated spring totals and 4% of fall totals. An estimate of shorebird numbers based on summing weekly counts, not corrected for detection probability or sampled proportion, would have been only 21% (spring) to 31% (fall) of the total number of birds. These results reveal that peak counts and nonadjusted counts can significantly underestimate the number of shorebirds that use migration stopover sites in the midcontinent of North America.

UTILITY OF OPEN POPULATION MODELS: LIMITATIONS POSED BY PARAMETER ESTIMABILITY IN THE STUDY OF MIGRATORY STOPOVER

The Wilson Journal of Ornithology, 2006

Open population models using capture-mark-recapture (CMR) data have a wide range of uses in ecological and evolutionary contexts, including modeling of stopover duration by migratory passerines. In using CMR approaches in novel contexts there is a need to determine the conditions under which open population models may be employed effectively. Our goal was to determine whether there was a simple a priori mechanism of determining the conditions under which CMR models could be used effectively in the study of avian stopover ecology. Using banding data (n ϭ 188 capture histories), we examined the challenges of using CMR-based models due to parameter inestimability, adequacy of descriptive power (Goodness-of-Fit, GOF), and parameter uncertainty. These issues become more apparent in studies with limited observations in a capture history, as is often the case in studies of avian stopover duration. Limited sample size and sampling intensity require an approach to reducing the number of fitted parameters in the model. Parameter estimability posed the greatest restriction on the utility of open population models, with high parameter uncertainty posing a lesser challenge. Results from our study also indicate the need for Ͼ10 observations per estimated parameter (approximately 3 birds captured or recaptured per day) to provide a reasonable chance of successfully estimating all model parameters.

A global population redistribution in a migrant shorebird detected with continent‐wide qualitative breeding survey data

Diversity and …, 2010

Aim: Over the last two decades, thousands of northward migrating ruffs (Philomachus pugnax) have disappeared from western European staging sites. These migratory ruffs were partly temperate breeding birds, but most individuals head towards the Eurasian Arctic tundras where 95% of the global population breeds. This regional decline may represent either: (1) local loss of breeding birds in western Europe, (2) a global decline, (3) shift(s) in distribution or (4) a combination of these. Location: Northern Eurasia. Methods: To put the declines in western Europe in context, we analysed Arctic monitoring data from the last two decades (Soloviev & Tomkovich, 2009) to detect changes in regional breeding densities across northern Eurasia. We used a novel approach applying generalized additive modelling (GAM) and generalized estimations equations (GEE). Results: We show that the global breeding population of ruffs has made a significant eastwards shift into the Asian part of the breeding range. In the European Arctic, ruffs decreased during the last 18 years. At the same time, in western Siberia, ruffs increased. In eastern Siberia, no significant population changes could be detected. These changes corroborate the finding that during northward migration, growing numbers of ruffs avoided staging areas in the Netherlands and Sweden and started migrating along a more easterly route leading into western Siberia. Main conclusions: We detected an unprecedented large-scale population redistribution of ruffs and suggest that this is a response to loss of habitat quality at the traditional staging site in the Netherlands.

Understanding the Stopover of Migratory Birds: A Scale Dependent Approach

The development of comprehensive conservation strategies and management plans for migratory birds depends on understanding migrant-habitat relations throughout the annual cycle, including the time when migrants stopover en route. Yet, the complexity of migration makes the assessment of habitat require- ments and development of a comprehensive conser- vation strategy a difficult task. We emphasize that development of a comprehensive conservation strategy depends on understanding that migrant-habitat relations during passage are scale dependent, and we outline a practical framework for the study of migrants during stopover that reflects spatial scale and allows us to draw stronger inferences about the behavior, ecology and conservation of migratory birds. This framework is organized into four components, each providing an increasing degree of resolution and information at dif- ferent ecological scales from gross patterns of habitat availability and use by groups of migrants to finer- ...