Re-encounter Data Research Articles

Dispersal in Kentish Plovers (Charadrius alexandrinus): adult females perform furthest movements

Dispersal is an important behavioral process that plays a significant role in, among others, speciation, population viability, and individual fitness. Despite progress in avian dispersal research, there are still many knowledge gaps. For example, it is of interest to study how dispersal propensity relates to age- and/or sex-specific patterns. Here, we investigated the role of sex and life stage on natal (i.e., movement from birth site to first breeding site) and breeding dispersal (i.e., movement between sequential breeding sites) in the Kentish Plover (Charadrius alexandrinus) for dispersal events of more than 10 km. This small and inconspicuous wader is characterized by flexible mating behavior that includes monogamy, and serial polygynandry. Using a continent-wide dataset of ringing and re-encounter data throughout the species’ range in Europe, we found that adult females generally dispersed further than adult males between seasons, but we detected no sex difference in natal dispersal distances and no general difference between natal and breeding dispersal distances. Furthermore, females were the main group exhibiting ‘long-distance’ breeding dispersal, which we defined as dispersal greater than ≥ 108 km, i.e., the upper 10% percentile of our dataset. The data set included dispersal of two females that first bred in the Mediterranean before being detected breeding at the North Sea in the subsequent year, having dispersed 1290 and 1704 km, respectively. These observations represent the longest breeding dispersal observed within the genus Charadrius. Our long-distance dispersal records are consistent with low genetic differentiation between mainland populations shown in previous work. The dispersal of the Kentish Plover is likely linked to its breeding behavior: polyandrous females exhibit extensive mate searching and habitat prospecting. We recommend that the dispersal traits of Kentish Plover be incorporated into the species’ conservation and management planning to more accurately inform models of population connectivity and metapopulation dynamics.

Zero-inflated count distributions for capture-mark-reencounter data.

The estimation of demographic parameters is a key component of evolutionary demography and conservation biology. Capture–mark–recapture methods have served as a fundamental tool for estimating demographic parameters. The accurate estimation of demographic parameters in capture–mark–recapture studies depends on accurate modeling of the observation process. Classic capture–mark–recapture models typically model the observation process as a Bernoulli or categorical trial with detection probability conditional on a marked individual's availability for detection (e.g., alive, or alive and present in a study area). Alternatives to this approach are underused, but may have great utility in capture–recapture studies. In this paper, we explore a simple concept: in the same way that counts contain more information about abundance than simple detection/non‐detection data, the number of encounters of individuals during observation occasions contains more information about the observation process than detection/non‐detection data for individuals during the same occasion. Rather than using Bernoulli or categorical distributions to estimate detection probability, we demonstrate the application of zero‐inflated Poisson and gamma‐Poisson distributions. The use of count distributions allows for inference on availability for encounter, as well as a wide variety of parameterizations for heterogeneity in the observation process. We demonstrate that this approach can accurately recover demographic and observation parameters in the presence of individual heterogeneity in detection probability and discuss some potential future extensions of this method.

Integrating data types to estimate spatial patterns of avian migration across the Western Hemisphere.

For many avian species, spatial migration patterns remain largely undescribed, especially across hemispheric extents. Recent advancements in tracking technologies and high-resolution species distribution models (i.e., eBird Status and Trends products) provide new insights into migratory bird movements and offer a promising opportunity for integrating independent data sources to describe avian migration. Here, we present a three-stage modeling framework for estimating spatial patterns of avian migration. First, we integrate tracking and band re-encounter data to quantify migratory connectivity, defined as the relative proportions of individuals migrating between breeding and nonbreeding regions. Next, we use estimated connectivity proportions along with eBird occurrence probabilities to produce probabilistic least-cost path (LCP) indices. In a final step, we use generalized additive mixed models (GAMMs) both to evaluate the ability of LCP indices to accurately predict (i.e., as a covariate) observed locations derived from tracking and band re-encounter data sets versus pseudo-absence locations during migratory periods and to create a fully integrated (i.e., eBird occurrence, LCP, and tracking/band re-encounter data) spatial prediction index for mapping species-specific seasonal migrations. To illustrate this approach, we apply this framework to describe seasonal migrations of 12 bird species across the Western Hemisphere during pre- and postbreeding migratory periods (i.e., spring and fall, respectively). We found that including LCP indices with eBird occurrence in GAMMs generally improved the ability to accurately predict observed migratory locations compared to models with eBird occurrence alone. Using three performance metrics, the eBird + LCP model demonstrated equivalent or superior fit relative to the eBird-only model for 22 of 24 species-season GAMMs. In particular, the integrated index filled in spatial gaps for species with over-water movements and those that migrated over land where there were few eBird sightings and, thus, low predictive ability of eBird occurrence probabilities (e.g., Amazonian rainforest in South America). This methodology of combining individual-based seasonal movement data with temporally dynamic species distribution models provides a comprehensive approach to integrating multiple data types to describe broad-scale spatial patterns of animal movement. Further development and customization of this approach will continue to advance knowledge about the full annual cycle and conservation of migratory birds.

Representing migration routes from re-encounter data: a new method applied to ring recoveries of Barn Swallows (Hirundo rustica) in Europe

Bird ringing was established more than a century ago to gather information on bird movements. Since then, ornithologists have systematically collected huge databases of records of birds ringed and subsequently re-encountered, but, to date, there have been few quantitative attempts to identify migratory routes from ringing data. Here, we develop a novel, quantitative method for describing migration routes using ringing data and we applied it to a dataset of 72,827 ring recoveries of the Barn Swallow (Hirundo rustica) through western and central Europe from the EURING and SAFRING databanks spanning 1908–2011. We considered movements of 332 individuals during spring migration and 1509 during autumn migration. The results indicate that, in spring, Barn Swallows enter western Europe through Gibraltar or by crossing the Mediterranean Sea through the Balearic Islands, Sardinia, and the Italian peninsula. They then spread over a wide front. In northern France, Belgium and the Netherlands routes diverge, pointing toward either the British Isles or Denmark and Scandinavia. Autumn migration routes are similar to those in spring. The general migration pattern that emerged from the analyses was consistent with previous descriptions of migratory movements of this well-known species. However, this analysis also revealed some previously undocumented migration patterns. For instance, in spring, some migrants moved from the Balearic Islands to Corsica and Italy, thus making a rather long eastward crossing of the Mediterranean Sea. In autumn, some migrants moved from the Balkan Peninsula westwards toward Italy. Analyses restricted to recoveries within the same spring or the same autumn and to birds found dead showed similar patterns. Our procedure was, therefore, able to identify migration patterns over a large geographical area, and may be extended to those species for which large datasets of ring recoveries or sight-resight data are available.

A comparison of migratory strategies of partial migratory raptors from Germany

The phenomenon of partial migration in birds in which some individuals of a population are migratory while others stay in the breeding area is of increasing scientific interest. The strategies of partial migratory raptors from Central Europe are, however, unclear for most species. We analysed ring re-encounter data of Eurasian Sparrowhawks Accipter nisus and Common Buzzards Buteo buteo ringed in Germany in terms of distances and directions between ringing and re-encounter sites. We investigated possible differences between sexes (only in Sparrowhawks) and age classes, as well as effects of ringing region, seasonal weather (in the form of North Atlantic Oscillation indices) and long-term temporal changes (including climate change) on migratory strategies by means of generalized linear models. We found that, in both species, migration is mostly conducted by juveniles, although migratory adults were also found. In general, male Sparrowhawks tend to migrate less than females. Sparrowhawks from different regions showed no differences in migration activity and no responses to long-term temporal changes. They did not respond to seasonal weather either. Buzzards showed strong responses to winter weather (‘winter escapes’) predominantly in highland regions, and a reduction of migratory intensity probably due to global warming. We compared our results to ones for Common Kestrels Falco tinnunculus and found most similarities between Kestrels and Sparrowhawks.

The integration of mark re-encounter and tracking data to quantify migratory connectivity

Animals which spend subsequent seasons in different areas connect geographical regions. The connection between breeding and non-breeding grounds is defined as migratory connectivity. The quantification of such connectivity is important, because movements between different locations can have strong consequences for the moving animal as well as the encountered habitats or ecosystems. Connectivity is usually investigated either on the basis of (few unsystematic) re-encounters of (often large numbers of) marked individuals or by observations of a few individuals tracked by remote sensing techniques, i.e. GPS or geolocation. The combination of qualitatively different data sets can reduce the limitations of each type of data and thus improve the accuracy of the estimated connectivity parameters considerably.We formally combine individual tracking data and mark re-encounter data in a probabilistic model framework for quantifying connectivity. In a first example, we quantify migratory connectivity of a long-distance passerine migrant based on ring re-encounter and geolocator data. As a second example, we combine re-encounter data of ear-tagged wild boars with GPS tracking data to estimate the spatial distribution of wild boars during the hunting and the non-hunting seasons. These two examples illustrate the use of the model in two different framework: 1) long-distance migration and, 2) seasonal (e.g. hunting induced) non-migratory movements.Results from the integrated analyses provided more information than the informal comparison of the results from independent analyses on each data set separately. Parameter estimates were more precise in the integrated analyses compared to the separate analyses and stronger conclusions could be drawn.The integration of mark re-encounter and tracking data reduces sampling bias and increases the value of both data sets but the weighting of each data set needs further investigation.

RoseateTern breeding dispersal and fidelity: responses to two newly restored colony sites

AbstractWe used 22 yr of capture–mark–reencounter (CMR) data collected from 1988 to 2009 on about 12,500 birds at what went from three to five coastal colony sites in Massachusetts, New York, and Connecticut, United States, to examine spatial and temporal variation in breeding dispersal/fidelity rates of adult Roseate Terns (Sterna dougallii). At the start of our study, Roseate Terns nested at only one site (Bird Island) in Buzzards Bay, Massachusetts, but two more sites in this bay (Ram and Penikese Islands) were subsequently recolonized and became incorporated into ourCMRmetapopulation study. We examined four major hypotheses about factors we thought might influence colony‐site fidelity and movement rates in the restructured system. We found some evidence that colony‐site fidelity remained higher at long‐established sites compared with newer ones and that breeding dispersal was more likely to occur among nearby sites than distant ones. Sustained predation at Falkner Island, Connecticut, did not result in a sustained drop in fidelity rates of breeders. Patterns of breeding dispersal differed substantially at the two restored sites. The fidelity of Roseate Terns at Bird dropped quickly after nearby Ram was recolonized in 1994, and fidelity rates for Ram soon approached those for Bird. After an oil spill in Buzzards Bay in April 2003, hazing (deliberate disturbance) of the terns at Ram prior to the start of egg‐laying resulted in lowering of fidelity at this site, a decrease in immigration from Bird, and recolonization of Penikese by Roseate Terns. Annual fidelity rates at Penikese increased somewhat several years after the initial recolonization, but they remained much lower there than at all the other sites throughout the study period. The sustained high annual rates of emigration from Penikese resulted in the eventual failure of the restoration effort there, and in 2013, no Roseate Terns nested at this site.

Partial Migration in a Central European Raptor Species: An Analysis of Ring Re-Encounter Data of Common KestrelsFalco tinnunculus

In partially migratory bird species, some individuals of a population migrate while others stay in the breeding area. Although Common Kestrels Falco tinnunculus are defined as partial migrants, their migratory strategies are still not well described. We investigated ringing and re-encounter data of Kestrels marked as nestlings between 1924 and 2011 in Germany. We defined four populations corresponding to the natural regions of Germany. Although both migratory and resident individuals were found independently of sex or age class at the time of recovery, in general, females and juveniles travelled larger distances than males and adults, respectively. We illustrated the initiation of migratory movements in contrast to dispersal by combining distances and directions in two levels (< 100 km and ≥ 100 km), showing that migration is initiated mostly in September/October, while in August movements seem to mostly reflect dispersal. The NAO Index as well as age class, region and re-encounter period (1950–1970, 1971–1990 or > 1990 as indicator of responses to climate change) of birds in autumn and winter were integrated into Generalized Linear Models. We found that in autumn and winter a tendency to migrate is primarily shown by juveniles and it was significantly higher in years before 1971 than in recent decades. In addition, a higher NAO Index in summer is linked with decreased proportion of birds re-encountered far (> 100 km) from their natal sites in winter, whereas a higher NAO Index in autumn is linked with increased proportion of high-distance re-encounters (> 100 km).

Estimating migratory connectivity of birds when re-encounter probabilities are heterogeneous.

Understanding the biology and conducting effective conservation of migratory species requires an understanding of migratory connectivity – the geographic linkages of populations between stages of the annual cycle. Unfortunately, for most species, we are lacking such information. The North American Bird Banding Laboratory (BBL) houses an extensive database of marking, recaptures and recoveries, and such data could provide migratory connectivity information for many species. To date, however, few species have been analyzed for migratory connectivity largely because heterogeneous re-encounter probabilities make interpretation problematic. We accounted for regional variation in re-encounter probabilities by borrowing information across species and by using effort covariates on recapture and recovery probabilities in a multistate capture–recapture and recovery model. The effort covariates were derived from recaptures and recoveries of species within the same regions. We estimated the migratory connectivity for three tern species breeding in North America and over-wintering in the tropics, common (Sterna hirundo), roseate (Sterna dougallii), and Caspian terns (Hydroprogne caspia). For western breeding terns, model-derived estimates of migratory connectivity differed considerably from those derived directly from the proportions of re-encounters. Conversely, for eastern breeding terns, estimates were merely refined by the inclusion of re-encounter probabilities. In general, eastern breeding terns were strongly connected to eastern South America, and western breeding terns were strongly linked to the more western parts of the nonbreeding range under both models. Through simulation, we found this approach is likely useful for many species in the BBL database, although precision improved with higher re-encounter probabilities and stronger migratory connectivity. We describe an approach to deal with the inherent biases in BBL banding and re-encounter data to demonstrate that this large dataset is a valuable source of information about the migratory connectivity of the birds of North America.

Departure directions, migratory timing and non-breeding distribution of the Red-backed Shrike Lanius collurio: do ring re-encounters and light-based geolocator data tell the same story?

This study explores differences and consistencies between ring re-encounter and light-based geolocator data from Red-backed Shrike when used for studying three aspects of bird migration: departure direction and its relationship with longitude and latitude, non-breeding distribution, and timing of migration. Departure directions were consistent between the two methods. They indicate a funnel-shaped migration with individuals from southwest Europe taking a detour via the eastern Mediterranean rather than migrating via Gibraltar. This indicates that an original migration route has been retained after colonisation of the breeding range. Non-breeding distributions differed substantially between birds ringed and re-encountered and birds tracked by geolocators. This difference may be due to spatio-temporal heterogeneity in ring re-encounter probability and/or due to the two samples of birds belonging to different populations. The monthly average ring re-encounter location moved later southward during autumn and earlier northward during spring migration than the geolocator positions, because of an over-representation of re-encounters in the north. The results emphasise the importance of combining different sources of data when analysing migration patterns of animals that are difficult to track.

Fidelity and Interseasonal Movements of Purple Finches (Carpodacus purpureus (Gmelin)): Analysis of Band Re-encounter Data

The Purple Finch (Carpodacus purpureus (Gmelin)) is a migratory fringillid breeding across the northern co- niferous forests of North America. Although irruptions occur, little information has been gathered on the movements of individual birds. We used the 19,893 re-encounters of banded birds in the Bird Banding Laboratory database to identify patterns of movements and to examine wintering and breeding site fidelity. After normalizing the data for banding effort, we found that birds banded in the northeastern United States tended to move along the Atlantic Seaboard. Most birds banded in the upper Mid-west also moved along a north-south axis. Purple Finches west of the Sierra Nevada and Cascade Mountains in the far west rarely move east of those mountains. Throughout the range of the species, most movements tend to be along the north-south axis. The re-encounter data indicated a strong level of breeding site and wintering site fidelity with evidence of some year-round fidelity. Analysis of re-encounters as a function of season of banding and season of re- encounter demonstrated that birds stayed close to their breeding grounds during the fall before leaving for their wintering areas. Birds departed from the wintering areas early in the spring.

Migratory connectivity derived from sparse ring reencounter data with unknown numbers of ringed birds

The large databases on ring reencounters, e.g. Euring database, contain extant information on the spatial distribution and potentially, on migratory connectivity of birds. However, reencounter data are normally sparse due to low reencounter probability. Further, to extract unbiased information about the spatial distribution of birds, spatial variation in reencounter probability has to be corrected for. To do so, knowledge of the total numbers of ringed birds is crucial but often not available. We present a general, combined statistical model to estimate population specific migration patterns based on the European reencounter data for which the number of ringed birds is unknown. Our approach combines a Cormack–Jolly–Seber model with a multinomial model. We present, for the first time, estimates and credible intervals of the spatial distribution of different populations of a migrant bird during the non-breeding period based on imperfect ringing data. Here, we used the Common Nightingale (Luscinia megarhynchos) as a representative long-distance migrant. The model allowed estimation of which proportions of the different breeding populations use a western, central or eastern flyway. Sensitivity analysis based on simulated data showed that most of these estimates were robust against violation of the most important model assumptions, i.e. homogeneity in recapture probability, homogeneity in breeding area return probability, and in reencounter probability within the flyways. We provide a general technique to account for spatial variation in reencounter probability when analysing migratory connectivity based on ring reencounter data with unknown numbers of ringed individuals. It is applicable for almost all migrating species with reencounter data.

Survival probabilities of loggerhead sea turtles (&lt;i&gt;Caretta caretta&lt;/i&gt;) estimated from capture-mark-recapture data in the Mediterranean Sea

Survival probabilities of loggerhead sea turtles ( Caretta caretta ) are estimated for the first time in the Mediterranean by analysing 3254 tagging and 134 re-encounter data from this region. Most of these turtles were juveniles found at sea. Re-encounters were live resightings and dead recoveries and data were analysed with Barker’s model, a modified version of the Cormack-Jolly-Seber model which can combine recapture, live resighting and dead recovery data. An annual survival probability of 0.73 (CI 95% = 0.67-0.78; n=3254) was obtained, and should be considered as a conservative estimate due to an unknown, though not negligible, tag loss rate. This study makes a preliminary estimate of the survival probabilities of in-water developmental stages for the Mediterranean population of endangered loggerhead sea turtles and provides the first insights into the magnitude of the suspected human-induced mortality in the region. The model used here for the first time on sea turtles could be used to obtain survival estimates from other data sets with few or no true recaptures but with other types of re-encounter data, which are a common output of tagging programmes involving these wide-ranging animals.