Ring Recovery Data Research Articles

Winter site-fidelity and survival of Redshank Tringa totanus at Cardiff, south Wales

The site-fidelity of adult Redshank Tringa totanus was investigated using colour-ringing and radiotracking at Cardiff Bay, a wintering site in south Wales, in 1996/97 and 1997/98. Between 7 and 20% of colour-ringed adults were seen away from the bay in winter, although only at a distance of 4 km. Radiotracking also suggested that adults were largely faithful either to the bay or to this neighbouring site. Return rates of 89% and 83% were estimated over two successive summers, indicating site-fidelity between winters. Survival rates of 91% and 100% were estimated over the two preceding (four-month) winter periods. Annual survival rates, calculated as the product of the winter survival and over-summer return rates, were therefore 81% and 83%. These estimates are comparable to those previously obtained for Redshank, in studies both on breeding and wintering grounds. Analyses of ring recovery data from throughout the UK complemented the colour-ringing and radiotracking studies in showing that the majority of Redshank are site-faithful both within and between winters. Ring recovery analyses also indicated that first-year Redshank had similar recovery patterns to adults.

Conservation value of ringing seabirds in Britain and Ireland

Large numbers of seabirds have been ringed in Britain and Ireland by volunteers and, to a lesser extent, professional ornithologists. At present, the species with about 5,000 or more ringed per year are Guillemot, Storm Petrel, Herring Gull, Puffin, Arctic Tern and Lesser Black‐backed Gull. Storm Petrel, Cormorant, Shag, Herring and Lesser Black‐backed Gulls and Guillemot provide in excess of 200 recoveries per annum per species. The wintering grounds and general migration routes of most British and Irish seabirds are known but most analyses are rather dated. This might hinder the prediction of effects of threats to British and Irish Seabirds arising away from colonies. Recoveries have proved extremely useful in highlighting seabird conservation issues, such as the killing of terns in West Africa and the drowning of auks in fishing nets. The finding of long‐term population studies of colour‐ringed seabirds is under threat. In future we may have to rely more on analyses of metal ring recoveries for obtaining the demographic data that are essential if the United Kingdom and Republic of Ireland are to conserve their internationally important seabird populations and meet their international obligations. Ringing studies have shown that seabirds are less philopatric than once thought. This may lessen the effect of a local disaster at a colony, but, conversely, other colonies could be influenced by such a disaster. A recent atlas of recoveries of Guillemots ringed in Scotland shows how such maps can be used to assess the seabird colonies that are at risk in a major disaster. Another analysis indicates how recoveries can be used to assess the effects of an unusually severe mortality event on a breeding population. Few papers using the results of seabird ringing have been published in the last five years. Ringing coverage should be maintained at near the current level and a formal review of sample sizes should be undertaken to determine targets for different analytical purposes. More ringing of gulls should be undertaken in Scotland, cliff‐nesting species in England and all species in Ireland. Ringers should be encouraged to ring more adult seabirds and to collect retrap data. Many more analyses of existing data should be undertaken, and published, especially to determine whether the demographic information currently obtained by detailed population studies could be obtained from ring recovery data. Ring subsidies to encourage the ringing of certain species continue to be a useful way of targeting ringing effort towards species of conservation priority.

Value of ringing information for bird conservation in Europe

After a century of existence, scientific bird ringing is still a highly versatile and extremely useful research technique. It allows information on bird ecology and behaviour that is critical for conservation strategies to be gathered. EURING has now existed for more than 30 years, so that the availability of ring recovery data for scientific and conservation purposes is ensured through a network of National Ringing Schemes and a unique central computerised Data Bank. So far, around 115 million birds have been ringed in Europe, producing recoveries that have enabled ornithologists to unravel migration routes, wintering areas and the network of staging areas used by populations of European birds. Aspects of stopover ecology have been investigated using data on the physical condition of staging migrants collected by ringers, providing crucial information on habitats and sites of conservation priority. Bird movements between sites in response to cold spells within the same winter have suggested the need for the creation of networks of protected wetlands. Analyses of the survival rates of long‐distance migrants have indicated that ecological conditions experienced in the African winter quarters are the main factors limiting European breeding populations. Long‐term ringing projects greatly contribute to population monitoring, including the provision of data for species originating from remote breeding areas from where only scanty information is available. With the increasing need for accurate monitoring of European bird populations, ringing represents the best way to obtain estimates of critical demographic parameters (eg annual productivity and survival rates). These are also of the utmost importance for improved internationally co‐ordinated management policies for game species. The ever increasing standards of more than 10,000 European ringers are ensured through EURING. Large‐scale ringing projects in Europe will provide unique and crucial information for future integrated conservation policies.

The scientific strategy of the BTO ringing scheme

1. This strategy aims to increase the contribution which ringing makes to conservation science and ornithological research, recognising that the primary outputs of the scheme are scientific publications based on data gathered by volunteer ringers. The strategy envisages a greater involvement of ringers in planned projects that are designed to provide specific types of information. Clear advice on priority species and categories of birds (eg age classes, seasons of ringing, breeding vs roosting) to be ringed and recaptured will be given to those ringing outside centrally organised projects. 2. The research programme will focus on two main topics, population dynamics and migration and movements. In addition research on life‐histories, moult and condition should be conducted when opportunities allow. 3. The Ringing Scheme makes a vital contribution to studies of population dynamics by providing data on survival rates and productivity, and sometimes also on numbers. Popidation dynamics models based on such da...

Joint analysis of mark—recapture, resighting and ring-recovery data with age-dependence and marking-effect

Using the joint analysis of live-recapture and ring-recovery data described by Burnham in 1993, we generalize it to the case where resightings of live birds are also reported between capture periods. Explicit estimators under 'random' temporary emigration correspond to those suggested by Jolly in 1965. The model is further generalized to admit age-dependence and a temporary marking effect. Explicit maximum-likelihood estimators under random emigration are reported and also contingency table tests for age-dependence and temporary marking effect. The new analysis is illustrated using a five-year subset of data from a 25-year ringing programme for Goldeneye Ducks Bucephala clangula¸. Alternative forms of emigration from the study area are also discussed.

Modelling the survival of British Lapwings Vanellus vanellus using ring-recovery data and weather covariates

Two sets of data are considered. One describes recovery data from Lapwings ringed as young in Britain in 1963–¸92. The other provides several weather covariates for the same period, and our objective is to try to relate these two data sets. We use score tests, provided by the computer package Eagle, to build a simple model which describes the data well. We first establish a need for time variation in the three basic elements of the model: first-year annual survival probability, adult annual survival probability and reporting probability. We then investigate the direct incorporation of covariates, using score tests, to give a limited set of models to compare. The final choice between these models is based on the Akaike information criterion (Arc). We find that adult annual survival is negatively related to measures of winter weather severity. In contrast to previous work, we have found a pronounced decline of reporting rate with time. Our methods produce appreciably higher estimates of adult survival than those previously obtained using methods which assumed reporting rates to be constant over time.

Use of ring recoveries to monitor long-term changes in the survival rates of British and Irish Cormorants Phalacrocorax carbo

Ring recovery data were used to assess changes in the survival rates of Cormorants in Britain and Ireland between 1965 and 1994. It was found that 99% were ringed as nestlings, thus necessitating an assumption of constant reporting rate across age-classes. The wide geographical spread of ringing effort since 1965 produced sufficient recoveries to enable analyses of trends in survival and reporting rates, but regional subdivisions of the data resulted in high sampling correlations between survival estimates. The assumption of a constant reporting rate across age-classes may be violated for British and Irish Cormorants, because first-year birds are more likely to be shot or caught in fishing nets than older birds and they have a differing seasonal pattern of recoveries. A simple simulation showed that first-year, but not adult, survival estimates were particularly sensitive to age-specific variation in reporting rates. However, the observed trend in first-year survival appeared robust to the assumption of constant reporting rates across age-classes. Declining reporting rates in Britain and Ireland imply that larger numbers of Cormorants will need to be ringed in order to monitor future changes in survival. Regional colour marking schemes for Cormorants have the potential to provide high quality survival information, to supplement that provided by dead recoveries and to offset the observed decline in reporting rates.

Variation in the survival rates of some British passerines with respect to their population trends on farmland

To identify the environmental changes responsible for population trends, it is useful first to determine the demographic mechanisms through which they have acted. We present new analyses of survival rates, using British ring-recovery data from 1962 to 1995, for 31 farmland passerine species. Separate estimates of the survival rates of adults and first-years and, where possible, males and females, are calculated specific to periods of increase, stability and decline identified objectively from each species' Common Birds Census (CBC) index trend. The differences between these estimates are assessed for statistical significance by comparing models allowing age-, sex- and trend-specific variation with models constraining these parameters. The variations in survival with respect to CBC trend direction show whether effects on survival have occurred which are consistent with their being an important mechanism mediating the effects of the environment on abundance. Adults generally had significantly higher survival rates than first-years and there was a common trend for male survival to be higher than that of females, although sex-specific variation was not significant for most species. Variations in survival appear to have contributed to the interactions between environmental change and abundance for at least 13 of the species studied.

The effect on the woodpigeon ( Columba palumbus) of the introduction of oilseed rape into Britain

The production of oilseed rape on a large scale in Britain began in 1973 and the woodpigeon ( Columba palumbus) quickly became a major pest of this crop. This paper uses ringing recovery data to examine the effects of the introduction of oilseed rape upon the movements and survival of the woodpigeon, and observational data to investigate changes in foraging behaviour. The mean distance travelled between ringing and recovery sites decreased in areas of high oilseed production but increased where little oilseed rape was grown. In good arable areas, the introduction of oilseed rape did not affect woodpigeon survival but it increased woodpigeon mortality in poor arable areas, probably as a result of increased shooting pressure. Oilseed rape is the preferred winter food of woodpigeons and they forage more efficiently on oilseed rape fields than pastures, the main alternative source of food in winter. After the widespread cultivation of oilseed rape, the average weight loss in a woodpigeon over the winter months became significantly less. Following the introduction of oilseed rape into Britain, overwinter mortality from starvation declined and the number of young produced each summer now has a more important effect upon woodpigeon population size.

Orientation Cage Experiments with Dunlins during Autumn Migration in Iceland

Migratory orientation of Dunlins Calidris alpina at sunset was studied by using orientation cages, during autumn migration in SW Iceland. The aim of the experiments was to examine whether orientation funnels can be used to record the directional behaviour of shorebirds. The results clearly demonstrate that Dunlins are capable of expressing their preferred migratory direction in funnels. Unmanipulated Dunlins showed a well-oriented mean direction towards geographical SSE which is in excellent agreement with available ringing recovery data on Dunlins linked to Iceland. This opens up the possibility to perform carefully controlled experiments to investigate the orientation and navigation mechanisms of migrating waders.

Model Selection in Ring-Recovery Models Using Score Tests

A strategy is outlined for selecting models for ring-recovery data using score tests. The approach is particularly valuable in avoiding unnecessary fitting of complicated, multiparameter models to data that do not require models of such complexity. Difficulties of convergence of iterative methods and potential boundary-estimation problems are thereby reduced. Data analyzed in Freeman and Morgan (1992, Biometrics 48, 217-236) are reanalyzed using score tests. These tests are repeated using both numerical and symbolic differentiation and also using both observed and expected information. We recommend using the expected information, and find that numerical differentiation is as good as symbolic differentiation. Motivated by the need to-describe a wide range of models succinctly, we also provide a new general notation for ring-recovery models.

MATLAB: An environment for analyzing ring-recovery and recapture data

The programming environment provided by MATLAB makes it easy to write code for the interactive analysis of data from ring-recovery and recapture studies. In particular, it is simple to write down a log-likelihood for any given model, to maximize this log-likelihood to estimate the parameters of the model and calculate their standard errors, to perform likelihood ratio and score test comparisons of models, and to compute goodness-of-fit statistics and examine residuals. Eagle is a package of simple MATLAB programs that provides an interactive environment for the analysis of ring-recovery data. Eagle will cope with any model of the Freeman-Morgan kind, where the survival and recovery probabilities may be specified as constant, time- or age-dependent, or as depending on one or more external covariates. This will be extended to handle data from recapture studies and from combined recovery and recapture studies. The package may also be used to analyze arbitrary models, at the expense of a small amount of extra MATLAB programming. A demonstration is given of use of Eagle to analyze data from a ring-recovery study on grey herons ( Ardea cinera ), with and without covariates. The use of the MATLAB programming environment is illustrated by fitting a simple model to some recapture data on herring gulls ( Larus argentatus ).

Do all Blackcaps Sylvia atricapilla show winter site fidelity?

Fidelity to previous wintering areas (i.e. site fidelity) has important ecological and evolutionary implications. However, since the percentage of recaptures of ringed birds at the same wintering area in subsequent years does not allow the estimation of the proportion of birds alive that exhibit site fidelity, previous studies on different passerine species have failed to show the true extent of this site fidelity. Here we use a recent approach, based on the comparison of survival rate estimates from capture‐recapture data at single field stations with recovery data from a much larger area. The idea is to determine the proportion of birds still alive that return to the area. The study was carried out on the Blackcap Sylvia atricapilla, comparing the capture‐recapture data of two field stations (Pilas [SW] and Tiana [NE]) situated 1000 km apart in Spain with the complete winter recovery data of the Spanish Ringing Office. Totals of 1936 and 3976 Blackcaps were ringed at Pilas (1981–1986) and Tiana (1975–1986), respectively, and the numbers of recaptures in subsequent winters were 94 and 34. The pooled annual survival rate estimation based on the two sites is 0.40 (s.e. = 0.05). The annual survival rate estimated from the Spanish ringing recovery data was 0.48 (s.e. = 0.08), which is not significantly different. We can conclude, therefore, that migrant Blackcaps in Spain, if alive, tend to return year after year to the previous wintering site.

On the Augmentation of Ring Recovery Data with Field Information

1. It is well-known that the Cormack-Seber model (Cormack 1970; Seber 1971) for ring-recovery data from birds ringed as nestlings does not provide unique maximum-likelihood estimates of the parameters without the addition of a constraint. Lakhani & Newton (1983) pointed out that the use of a constraint might yield misleading estimates. Unique estimates do result from the addition of separate information on one of the parameters; Lakhani (1987) suggested the possibility of the survival of first-year birds being based on observed deaths of radio-marked birds. 2. We show here that the estimate of the survival probability for first-year birds, obtained from radio-marked birds alone, may not correspond to the overall maximum-likelihood estimate of this probability. 3. We explain how such a discrepancy may arise, and show that, in this case, one of the other parameters in the model is estimated on a boundary to the parameter space, i.e. is either 0 or 1. 4. A small simulation study is carried out to explore the implications of this finding for the bias of the parameter estimators. We see that if the radio-marking does not affect first-year survival, then the most serious bias is for the survival probability phi(k), where k is the number of years' duration of the ringing study. For other parameters, bias will be lower, and possibly of the order of 10%, though this depends on the size of the radio-tracking study. This bias might well be less than the possibly unknown bias in the absence of any augmentation, as claimed by Lakhani (1987). 5. If radio-marked birds experience a reduced probability of survival then more serious bias may extend to all parameters. In this situation, bias increases as the size of the radio-tracking study increases. 6. When a discrepancy of the kind described in (2) above arises, repeating the radio-tracking experiment is advisable only if survival is not expected to be impaired by radio-marking, and if a large radio-marking experiment may be carried out. 7. Lakhani (1987, 1990) has suggested further improvements to the simple radio-tracking scheme examined here. Morgan & Freeman (1989) have discussed a model with first-year variation in survival rates which allows the estimation of model parameters, without the need of any constraints. The possibility of combining this modelling development with further field information is discussed.

The hunting of migratory birds in Europe: a ringing recovery analysis

The hunting of 20 species of migratory birds in Europe and countries bordering the Mediterranean Sea was investigated using ringing recovery data. The intensity of the hunting of birds in each country was measured by the calculation of an index which controls for ringing effort and reporting rates. The hunting of birds was shown to be consistently high in western Mediterranean countries, particularly in southern France, northern and southwestern Iberia, northern Italy and in northwest Africa. Geographical patterns in the relative magnitude of hunting indices for different breeding populations were species‐specific. In Europe most birds are taken during autumn and winter but in North Africa hunting is almost equally prevalent in spring. All species investigated, other than those that remain legitimate quarry species, showed a general reduction in index values after 1980. Analysis of long‐term trends in index values since 1950 indicated a statistically significant overall decrease in the hunting of the majority of species. These changes are thought to be at least partly attributable to a real decline in the taking of birds but they may also reflect changed attitudes to reporting the hunting of species which are now protected. This analysis provides the first quantitative Europe‐wide assessment of geographical and temporal trends in the hunting of migratory birds.

The dispersal and philopatry of great skuas from foula, Shetland

Ring recovery data were used to describe the dispersal of Great Skuas from Foula, Shetland, from 1963 to 1990. In general, the dispersal patterns and causes of recoveries had not changed since they were first described by Furness (1978) up to 1977. However, recoveries of 1–4year‐olds had increased since 1977 and recoveries of first‐year birds were greater after 1986 than for all previous years combined. Ring recovery data and observations of individually colour‐ringed birds provided several lines of evidence suggesting that levels of immigration and emigration in the Great Skua population on Foula were very low. Great Skuas also displayed a high degree of micro‐philopatry, generally choosing clubs and breeding sites within areas on the island from which they originated.

A Note on Seber's Model for Ring-Recovery Data

We provide simple explicit maximum-likelihood estimates for Seber's (1971) model for ring-recovery data, obtaining both the general solution, and the particular estimate satisfying Seber's constraint.

A note on Seber's model for ring-recovery data

SUMMARY We provide simple explicit maximum-likelihood estimates for Seber's (1971) model for ringrecovery data, obtaining both the general solution, and the particular estimate satisfying Seber's constraint.

A Model with First-Year Variation for Ring-Recovery Data

A probability model is proposed for ring-recovery data in which the survival probability for first-year birds is allowed to vary with calendar year. This model may be fitted to data by maximum likelihood without the customary arbitrary additional constraint when only young birds have been ringed. The approach is illustrated on simulated data and two real examples. Profile log-likelihoods reveal the possibility of substantial differences between alternative methods for estimating confidence intervals. More parsimonious versions of the model may be obtained, for example, through regressing the firstyear survival probabilities on covariates if that is feasible. Additionally, the ring-reporting probability may also be made year-dependent, and any variation can be tested by likelihood ratio tests.

Efficient Estimation of Age-Specific Survival Rates from Ring Recovery Data of Birds Ringed as Young, Augmented by Field Information

Efficient Estimation of Age-Specific Survival Rates from Ring Recovery Data of Birds Ringed as Young, Augmented by Field Information