Productivity indices and survival rate estimates from MAPS,a continent-wide programme of constant-effort mist-netting in North America

The Monitoring Avian Productivity and Survivorship (MAPS) programme is a cooperative effort to provide annual regional indices of adult population size and post-fledging productivity and estimates of adult survival rates from data pooled from a network of constant-effort mist-netting stations across North America. This paper provides an overview of the field and analytical methods currently employed by MAPS, a discussion of the assumptions underlying the use of these techniques, and a discussion of the validity of some of these assumptions based on data gathered during the first 5 years (1989-1993) of the programme, during which time it grew from 17 to 227 stations. Ageand species-specific differences in dispersal characteristics are important factors affecting the usefulness of the indices of adult population size and productivity derived from MAPS data. The presence of transients, heterogeneous capture probabilities among stations, and the large sample sizes required by models to deal effectively with these two considerations are important factors affecting the accuracy and precision of survival rate estimates derived from MAPS data. Important results from the first 5 years of MAPS are: (1) indices of adult population size derived from MAPS mist-netting data correlated well with analogous indices derived from point-count data collected at MAPS stations; (2) annual changes in productivity indices generated by MAPS were similar to analogous changes documented by direct nest monitoring and were generally as expected when compared to annual changes in weather during the breeding season; and (3) a model using between-year recaptures in Cormack-Jolly-Seber (CJS) mark-recapture analyses to estimate the proportion of residents among unmarked birds was found, for most tropical-wintering species sampled, to provide a better fit with the available data and more realistic and precise estimates of annual survival rates of resident birds than did standard CJS mark-recapture analyses. A detailed review of the statistical characteristics of MAPS data and a thorough evaluation of the field and analytical methods used in the MAPS programme are currently under way.     

Uses of ringing data for the conservation and management of bird populations: A ringing scheme perspective

This review considers current and potential uses of ring-recovery and mark-recapture methods for conservation-oriented research by European ringing schemes. These schemes are concerned mainly with large-scale studies of the demography and movements of widespread species, much of the data being gathered by volunteers. The data holdings and data-gathering potential of the 33 European ringing schemes are outlined. Over 110 million birds have been ringed in Europe giving rise to 1.8 million recoveries. Some 64% of these recoveries are held in the computerized EURING data bank. Passerines comprise 43% of all recoveries and only 15% are of waterfowl. Currently, about 4 million birds are ringed each year and 90 000 recoveries are reported. Ringing effort is much higher in northern and western Europe than in southern and eastern Europe. Most schemes have recorded the ringing and recovery details of birds that have been recovered in computer files but most ringing data are held only on paper. These ringing data must be computerized for rigorous analyses of survival or movements. Without such computerization, future widespread ringing will be of little value. Five key areas of conservation-oriented research using data from European ringing schemes are identified; monitoring, investigating the causes of population declines, impacts of hunting, flyway networks and seabird studies. Current work and future research opportunities in these areas are discussed, and conservation priorities are identified. Demographic studies for monitoring and identifying the causes of declines are developing well, and are likely to be enhanced further by more gathering of mark-recapture data from standardized projects (such as constant effort sites), by improved access to computerized ringing data and by the development of more flexible, user-friendly software for ring-recovery analysis. Interest in studies of movements is reviving, with quantitative methods starting to be applied to population turnover at migratory stop-over sites (Jolly-Seber models) and to movements between sites (multi-state models). Future planned ringing studies will be important for testing ideas about the dynamics of meta-populations. European ringing schemes have the opportunity to enhance greatly their contribution to conservation over the next decade. This will require better access to computerized data and the development of more planned, cooperative projects at European and national scales. The close collaboration of biologists and statisticians in the analysis of previously collected data should be extended to the review of existing sampling strategies and to the development of new projects.     

Estimating age-specific survival rates of tawny owls--recaptures versus recoveries

We compared estimates of annual survival rates of tawny owls ( Strix aluco ) ringed in southern Finland from several different sampling methods: recoveries of birds ringed as young; recaptures of birds ringed as young; recoveries of birds ringed as adults as well as young; combined recoveries and recaptures of birds ringed as young, and combined recoveries and recaptures of birds ringed as adults and young. From 1979 to 1998, 18 040 young owls were ringed, of which 983 were recaptured as breeders in subsequent years during this period, and 1764 were recovered dead at various locations. In addition, 1751 owls were ringed as adults, of which 612 were later recaptured and 199 were recovered dead. First-year survival rates estimated using only recoveries of birds ringed as young averaged 48%, while apparent survival rates estimated using only recaptures from birds ringed as young averaged 10-13%. Use of combined recapture-recovery models, or supplementary information from recoveries of birds ringed as adults, produced survival estimates of 30-37%. Survival estimates from young-recoveries-only models were biased high, because of violation of the assumption of constant recovery rates with age: birds dying in their first-year were one-third less likely to be found and reported than older birds. In contrast, recaptures-only models confounded emigration with mortality. Despite these differences in mean values, annual fluctuations in estimated first-year survival rates were similar with all models. Estimates of adult survival rates were similar with all models, while those for second-year birds were similar for all models except recaptures-only. These results highlight the potential biases associated with analysing either recaptures or recoveries alone of birds ringed as young, and the benefits of using combined data.     

Investigating the effects of hunting on the survival of British pigeons and doves by analysis of ringing recoveries

Recent changes in British hunting legislation have protected the stock dove Columba oenas since 1 October 1982, and removed protection from the collared dove Streptopelia decaocto after 1 April 1977; the woodpigeon Columba palumbus has remained legal quarry throughout. Ringing recoveries offer a means of comparing annual survival rates before and after the change in legislation. Care is needed in the construction of the recovery matrices to remove inhomogeneities in the data and ensure that each 'year' runs from the day of legislative change. Annual survival rates were estimated by maximum likelihood using multinomial models conditioned on the recoveries; there was no evidence of age- or time-related variation in reporting rates. The annual survival rate of the stock dove was constant, at 54 +/- 3%. For both the collared dove and the woodpigeon, estimates of survival rates in the first year after ringing were not consistent between birds ringed as young and those ringed as adults, but nevertheless averaged less before 1977 than after 1977; annual survival rates of birds that survived the first year after ringing did not differ between time periods, and were 64 +/- 2% for the collared dove and 61 +/- 2% for the woodpigeon. The proportion of recoveries reported shot or trapped was only 14% for the collared dove, compared with 79% for the woodpigeon, and remained constant before and after 1977 for both species; in the case of the stock dove, the proportion reported shot or trapped before and after 1982 fell from 70% to 34%. The change in quarry status had no effect on annual survivorship or population size of either the stock dove or the collared dove, while the woodpigeon has increased regularly in abundance despite heavy shooting.     

Estimating avian dispersal distances from data on ringed birds

Data from birds ringed as chicks and recaptured during subsequent breeding seasons provide information on avian natal dispersal distances. However, national patterns of ring reports are influenced by recapture rates as well as by dispersal rates. While an extensive methodology has been developed to study survival rates using models that correct for recapture rates, the same is not true for dispersal. Here, we present such a method, showing how corrections for spatial heterogeneity in recapture rate can be built into estimates of dispersal rates if detailed atlas data and ringing totals can be combined with extensive data on birds ringed as chicks and recaptured as breeding adults. We show how the method can be implemented in the software package SURVIV (White, 1992).     

Modelling postfledging survival and age-specific breeding probabilities in species with delayed maturity: A case study of Roseate Terns at Falkner Island,Connecticut

We modelled postfledging survival and age-specific breeding probabilities in endangered Roseate Terns ( Sterna dougallii ) at Falkner Island, Connecticut, USA using capture-recapture data from 1988-1998 of birds ringed as chicks and as adults. While no individuals bred as 2-year-olds during this period, about three-quarters of the young that survived and returned as 3-year-olds nested, and virtually all surviving birds had begun breeding by the time they reached 5 years of age. We found no evidence of temporal variation age of first breeding of birds from different cohorts. There was significant temporal variation in the annual survival of adults and the survival over the typical 3-year maturation period of prebreeding birds, with extremely low values for both groups from the 1991 breeding season. The estimated overwinter survival rate (0.62) for adults from 1991-1992 was about three-quarters the usual rate of about 0.83, but the low survival of fledglings from 1991 resulted in less than 25% of the otherwise expected number of young from that cohort returning as breeding birds; this suggests that fledglings suffered a greater proportional decrease in survival than did adults. The survival estimates of young from 1989 and 1990 show that these cohorts were not negatively influenced by the events that decimated the young from 1991, and the young from 1992 and 1993 had above-average survival estimates. The apparent decrease since 1996 in development of fidelity of new recruits to this site is suspected to be due mainly to nocturnal disturbance and predation of chicks causing low productivity.     

Estimating rates of population change for a neotropical parrot with ratio,mark-recapture and matrix methods

Robust methods for estimating rates of population change ( u ) are necessary for applied and theoretical goals in conservation and evolutionary biology. Traditionally, u has been calculated from either ratios of population counts (observed u or u obs ), or population models based on projection matrices (asymptotic u or u asy ,). New mark-recapture methods permit calculation of u from mark-resighting information alone (realized u or u rea ), but empirical comparisons with other methods are rare. In this paper, rates of population change were calculated for a population of green-rumped parrotlets ( Forpus passerinus ) that have been studied for more than a decade in central Venezuela. First, a ratio method based on counts of detected birds was used to calculate u obs. Next, a temporal symmetry method based on mark-recapture data (i.e. the u -parameterization introduced by Pradel, 1996) was used to calculate u rea . Finally, a stage-structured matrix model based on state-specific estimates of fecundity, immigration, local survival, and transition rates was used to calculate u asy . Analyses were conducted separately for females and males. Overall values of u from the three methods were consistent and all indicated that the finite rate of population change was not significantly different from 1. Annual values of u from the three methods were also in general agreement for a majority of years. However, u rea from the temporal symmetry method had the greatest precision, and apparently better accuracy than u asy . Unrealistic annual values of u asy could have been due to poor estimates of the transitional probability of becoming a breeder ( é ) or to a mismatch between the actual and the asymptotic stable stage distribution. In this study, the trade-off between biological realism and accuracy was better met by the temporal symmetry than the matrix method. Our results suggest that the temporal symmetry models can be applied with confidence to populations where less information may be available.     

Survival rates of Hungarian sand martins and their relationship with Sahel rainfall

Since 1986, I have carried out an intensive field survey of 10 000-30 000 pairs of a sand martin ( Riparia riparia ) population. Direct survey of the size and distribution of the breeding population and estimation of adult survival rates by SURGE, based on extensive ringing data sets, allow us to analyze the effects of different environmental factors with high precision. The model selection showed that the S s+t , P t model, in which the survival rates differ by sex for adults and vary in parallel by year and the capture rate varies by year, fits the data. The adult females had a lower survival rate compared to the males. The capture rate could be modelled as a quotient of the number of captured birds and the number of breeding birds along the upper part of the river Tisza. The survival rates of adults were related to the rainfall of the southern Sahel, which has an important role in the extension of the winter foraging habitat in the Sahel. Although the severe decrease in the population size, which may reach 50%, coincided with a large decline in the adult survival rate, there was not a significant relation between the adult survival rate and population size during the studied period. The population recruitment by first breeders and immigrant-emigrant adults could have a key role in the determination of population size. In the case of the studied subpopulation along the river, which is a core of the Carpathian Bend population, the immigration-emigration of adults had an important effect on the population size. The significant difference between juvenile male and female dispersal indicates the importance of separate estimation of juvenile survival for the sexes in further studies.     

Estimating survival rates from recoveries of birds ringed as young: A case study

Models for analysis of survival rates from recoveries of birds ringed as young were evaluated for lesser snow geese ringed on the breeding grounds at La Perouse Bay, Manitoba from 1970 to 1992. Analyses of birds ringed as adults and young indicate recovery rates were lower for young than for older birds and varied independently in the two age classes. Adult survival increased over the study, while that of immatures decreased. Using only recoveries of birds ringed as young, models incorporating observed variation in recovery rates were not identifiable. Many sets of constraints could be selected to make the model identifiable, but there was no objective way to distinguish among them, and each could lead to different conclusions. The observed changes in survival rates could not be estimated. Previous analyses have shown that models for birds ringed as young can be used to test even complex variation in survival rates, provided that recovery rates do not vary with age. Unfortunately, as shown by the geese, this assumption may often be violated and can only be tested with additional data, preferably from birds recaptured or ringed as sub-adults or adults.     

Estimating survival rates from recoveries of birds ringed as young: a case study

Models for analysis of survival rates from recoveries of birds ringed as young were evaluated for lesser snow geese ringed on the breeding grounds at La Perouse Bay, Manitoba from 1970 to 1992. Analyses of birds ringed as adults and young indicate recovery rates were lower for young than for older birds and varied independently in the two age classes. Adult survival increased over the study, while that of immatures decreased. Using only recoveries of birds ringed as young, models incorporating observed variation in recovery rates were not identifiable. Many sets of constraints could be selected to make the model identifiable, but there was no objective way to distinguish among them, and each could lead to different conclusions. The observed changes in survival rates could not be estimated. Previous analyses have shown that models for birds ringed as young can be used to test even complex variation in survival rates, provided that recovery rates do not vary with age. Unfortunately, as shown by the geese, this assumption may often be violated and can only be tested with additional data, preferably from birds recaptured or ringed as sub-adults or adults.     

Transient animals in a resident population of snow geese: Local emigration or heterogeneity?

The estimation of survival rates from analysis of recapture of individually marked animals assumes that all individuals are equally likely to be re-encountered. This assumption is frequently violated in natural populations due to movements to and from the sampling area. We evaluated potential sources of heterogeneity using data from recaptures of 36000 individually marked female lesser snow geese, Anser c. caerulescens , from an expanding population in northern Manitoba, Canada. By stratifying individuals according to marking age and origin (hatched at the colony or not), we assessed the degree to which variation in apparent survival reflected permanent or temporary differences in emigration and effects of handling. In general, for birds ringed as adults, estimated apparent survival rates were significantly lower during the first year after ringing than in subsequent years. By comparing birds ringed as adults (classified by origin) with those ringed as goslings, we were able to demonstrate that these differences are not due to permanent emigration from the colony by transient individuals or heterogeneity of individual capture probability, but more likely reflect differences among individuals in their response to initial marking. Approximately 25% of birds permanently emigrate from the sampling area following marking.     

Transient animals in a resident population of snow geese: local emigration or heterogeneity?

The estimation of survival rates from analysis of recapture of individually marked animals assumes that all individuals are equally likely to be re-encountered. This assumption is frequently violated in natural populations due to movements to and from the sampling area. We evaluated potential sources of heterogeneity using data from recaptures of 36000 individually marked female lesser snow geese, Anser c. caerulescens , from an expanding population in northern Manitoba, Canada. By stratifying individuals according to marking age and origin (hatched at the colony or not), we assessed the degree to which variation in apparent survival reflected permanent or temporary differences in emigration and effects of handling. In general, for birds ringed as adults, estimated apparent survival rates were significantly lower during the first year after ringing than in subsequent years. By comparing birds ringed as adults (classified by origin) with those ringed as goslings, we were able to demonstrate that these differences are not due to permanent emigration from the colony by transient individuals or heterogeneity of individual capture probability, but more likely reflect differences among individuals in their response to initial marking. Approximately 25% of birds permanently emigrate from the sampling area following marking.     

Test for age-specificity in survival of the common tern

Much effort in life-history theory has been addressed to the dependence of life-history traits on age, especially the phenomenon of senescence and its evolution. Although senescent declines in survival are well documented in humans and in domestic and laboratory animals, evidence for their occurrence and importance in wild animal species remains limited and equivocal. Several recent papers have suggested that methodological issues may contribute to this problem, and have encouraged investigators to improve sampling designs and to analyse their data using recently developed approaches to modelling of capture-mark-recapture data. Here we report on a three-year, two-site, mark-recapture study of known-aged common terns (Sterna hirundo) in the north-eastern USA. The study was nested within a long-term ecological study in which large numbers of chicks had been banded in each year for > 25 years. We used a range of models to test the hypothesis of an influence of age on survival probability. We also tested for a possible influence of sex on survival. The cross-sectional design of the study (one year's parameter estimates) avoided the possible confounding of effects of age and time. The study was conducted at a time when one of the study sites was being colonized and numbers were increasing rapidly. We detected two-way movements between the sites and estimated movement probabilities in the year for which they could be modelled. We also obtained limited data on emigration from our study area to more distant sites. We found no evidence that survival depended on either sex or age, except that survival was lower among the youngest birds (ages 2-3 years). Despite the large number of birds included in the study (1599 known-aged birds, 2367 total), confidence limits on estimates of survival probability were wide, especially for the oldest age-classes, so that a slight decline in survival late in life could not have been detected. In addition, the cross-sectional design of this study meant that a decline in survival probability within individuals (actuarial senescence) could have been masked by heterogeneity in survival probability among individuals (mortality selection). This emphasizes the need for the development of modelling tools permitting separation of these two phenomena, valid under field conditions in which the recapture probabilities are less than one.     

Use of the Barker model in an experiment examining covariate effects on first-year survival in Ross's Geese ( Chen rossii ): A case study

The Barker model provides researchers with an opportunity to use three types of data for mark-recapture analyses - recaptures, recoveries, and resightings. This model structure maximizes use of encounter data and increases the precision of parameter estimates, provided the researcher has large amounts of resighting data. However, to our knowledge, this model has not been used for any published ringing studies. Our objective here is to report our use of the Barker model in covariate-dependent analyses that we conducted in Program MARK. In particular, we wanted to describe our experimental study design and discuss our analytical approach plus some logistical constraints we encountered while conducting a study of the effects of growth and parasites on survival of juvenile Ross's Geese. Birds were marked just before fledging, alternately injected with antiparasite drugs or a control, and then were re-encountered during migration and breeding in following years. Although the Barker model estimates seven parameters, our objectives focused on annual survival only, thus we considered all other parameters as nuisance terms. Therefore, we simplified our model structures by maintaining biological complexity on survival, while retaining a very basic structure on nuisance parameters. These analyses were conducted in a two-step approach where we used the most parsimonious model from nuisance parameter analyses as our starting model for analyses of covariate effects. This analytical approach also allowed us to minimize the long CPU times associated with the use of covariates in earlier versions of Program MARK. Resightings made up about 80% of our encounter history data, and simulations demonstrated that precision and bias of parameter estimates were minimally affected by this distribution. Overall, the main source of bias was that smaller goslings were too small to retain neckbands, yet were the birds that we predicted would have the lowest survival probability and highest probability for parasite effects. Consequently, we considered our results conservative. The largest constraint of our study design was the inability to partition survival into biologically meaningful periods to provide insight into the timing and mechanisms of mortality.     

Separation of hunting and natural mortality using ring-return models: An overview

Ring-recovery methodology has been widely used to estimate survival rates in multi-year ringing studies of wildlife and fish populations (Youngs & Robson, 1975; Brownie et al. , 1985). The Brownie et al. (1985) methodology is often used but its formulation does not account for the fact that rings may be returned in two ways. Sometimes hunters are solicited by a wildlife management officer or scientist and asked if they shot any ringed birds. Alternatively, a hunter may voluntarily report the ring to the Bird Banding Laboratory (US Fish and Wildlife Service, Laurel, MD, USA) as is requested on the ring. Because the Brownie et al. (1985) models only consider reported rings, Conroy (1985) and Conroy et al. (1989) generalized their models to permit solicited rings. Pollock et al. (1991) considered a very similar model for fish tagging models which might be combined with angler surveys. Pollock et al. (1994) showed how to apply their generalized formulation, with some modification to allow for crippling losses, to wildlife ringing studies. Provided an estimate of ring reporting rate is available, separation of hunting and natural mortality estimates is possible which provides important management information. Here we review this material and then discuss possible methods of estimating reporting rate which include: (1) reward ring studies; (2) use of planted rings; (3) hunter surveys; and (4) pre- and post-hunting season ringings. We compare and contrast the four methods in terms of their model assumptions and practicality. We also discuss the estimation of crippling loss using pre- and post-season ringing in combination with a reward ringing study to estimate reporting rate.     

Separation of hunting and natural mortality using ring-return models: an overview

Ring-recovery methodology has been widely used to estimate survival rates in multi-year ringing studies of wildlife and fish populations (Youngs & Robson, 1975; Brownie et al. , 1985). The Brownie et al. (1985) methodology is often used but its formulation does not account for the fact that rings may be returned in two ways. Sometimes hunters are solicited by a wildlife management officer or scientist and asked if they shot any ringed birds. Alternatively, a hunter may voluntarily report the ring to the Bird Banding Laboratory (US Fish and Wildlife Service, Laurel, MD, USA) as is requested on the ring. Because the Brownie et al. (1985) models only consider reported rings, Conroy (1985) and Conroy et al. (1989) generalized their models to permit solicited rings. Pollock et al. (1991) considered a very similar model for fish tagging models which might be combined with angler surveys. Pollock et al. (1994) showed how to apply their generalized formulation, with some modification to allow for crippling losses, to wildlife ringing studies. Provided an estimate of ring reporting rate is available, separation of hunting and natural mortality estimates is possible which provides important management information. Here we review this material and then discuss possible methods of estimating reporting rate which include: (1) reward ring studies; (2) use of planted rings; (3) hunter surveys; and (4) pre- and post-hunting season ringings. We compare and contrast the four methods in terms of their model assumptions and practicality. We also discuss the estimation of crippling loss using pre- and post-season ringing in combination with a reward ringing study to estimate reporting rate.     

POPAN-4: Enhancements to a system for the analysis of mark-recapture data from open populations

We describe recent developments in the POPAN system for the analysis of mark-recapture data from Jolly-Seber type experiments. The previous versions (POPAN-3 for SUN/OS workstations and POPAN-PC for IBM-PC running DOS or Windows) included general statistics gathering and testing procedures, a wide range of analysis options for estimating population abundance, survival and birth parameters, and a general simulation capability. POPAN-4 adds a very general procedure for fitting constrained models based on a new unified theory for Jolly-Seber models. Users can impose constraints on capture, survival and birth rates over time and/or across attribute groups (e.g. sex or age groups) and can model these rates using covariate models involving auxiliary variables (e.g. sampling effort).     

POPAN-4: enhancements to a system for the analysis of mark-recapture data from open populations

We describe recent developments in the POPAN system for the analysis of mark-recapture data from Jolly-Seber type experiments. The previous versions (POPAN-3 for SUN/OS workstations and POPAN-PC for IBM-PC running DOS or Windows) included general statistics gathering and testing procedures, a wide range of analysis options for estimating population abundance, survival and birth parameters, and a general simulation capability. POPAN-4 adds a very general procedure for fitting constrained models based on a new unified theory for Jolly-Seber models. Users can impose constraints on capture, survival and birth rates over time and/or across attribute groups (e.g. sex or age groups) and can model these rates using covariate models involving auxiliary variables (e.g. sampling effort).     

Modelling age variation in survival and reporting rates for recovery models

In this paper, we focus on models for recovery data from birds ringed as young. In some cases, it is important to be able to include in these models a degree of age variation in the reporting probability. For certain models this has been found, empirically, to result in completely flat likelihood surfaces, due to parameter redundancy. These models cannot then be fitted to the data, to produce unique parameter estimates. However, empirical evidence also exists that other models with such age variation can be fitted to data by maximum likelihood. Using the approach of Catchpole and Morgan (1996b), we can now identify which models in this area are parameter-redundant, and which are not. Models which are not parameter-redundant may still perform poorly in practice, and this is investigated through examples, involving both real and simulated data. The Akaike Information Criterion is found to select inappropriate models in a number of instances. The paper ends with guidelines for fitting models to data from birds ringed as young, when age dependence is expected in the reporting probability.     

Modelling age variation in survival and reporting rates for recovery models

In this paper, we focus on models for recovery data from birds ringed as young. In some cases, it is important to be able to include in these models a degree of age variation in the reporting probability. For certain models this has been found, empirically, to result in completely flat likelihood surfaces, due to parameter redundancy. These models cannot then be fitted to the data, to produce unique parameter estimates. However, empirical evidence also exists that other models with such age variation can be fitted to data by maximum likelihood. Using the approach of Catchpole and Morgan (1996b), we can now identify which models in this area are parameter-redundant, and which are not. Models which are not parameter-redundant may still perform poorly in practice, and this is investigated through examples, involving both real and simulated data. The Akaike Information Criterion is found to select inappropriate models in a number of instances. The paper ends with guidelines for fitting models to data from birds ringed as young, when age dependence is expected in the reporting probability.