SURVIVAL ESTIMATES FOR FLORIDA MANATEES FROM THE PHOTO-IDENTIFICATION OF INDIVIDUALS

We estimated adult survival probabilities for the endangered Florida manatee ( Trichechus manatus latirostris ) in four regional populations using photoidentification data and open-population capture-recapture statistical models. The mean annual adult survival probability over the most recent 10-yr period of available estimates was as follows: Northwest - 0.956 (SE 0.007), Upper St. Johns River - 0.960 (0.011), Atlantic Coast - 0.937 (0.008), and Southwest - 0.908 (0.019). Estimates of temporal variance independent of sampling error, calculated from the survival estimates, indicated constant survival in the Upper St. Johns River, true temporal variability in the Northwest and Atlantic Coast, and large sampling variability obscuring estimates for the Southwest. Calf and subadult survival probabilities were estimated for the Upper St. Johns River from the only available data for known-aged individuals: 0.810 (95% CI 0.727–0.873) for 1st year calves, 0.915 (0.827–0.960) for 2nd year calves, and 0.969 (0.946–0.982) for manatee 3 yr or older. These estimates of survival probabilities and temporal variance, in conjunction with estimates of reproduction probabilities from photoidentification data can be used to model manatee population dynamics, estimate population growth rates, and provide an integrated measure of regional status.     

Survival, movement, and resource use of the butterfly Parnassius clodius

Abstract.  1. A mark–recapture study was conducted on the American Apollo butterfly Parnassius clodius Menetries during three field seasons (1998–2000) to examine its movement patterns over the course of a season within a sagebrush meadow in Grand Teton National Park, Wyoming, U.S.A. The study examined how resources affected butterfly distribution patterns and used mark–recapture data to gain insight into movement differences between sexes and over time.
2. The average straight-line movement of P. clodius was 202 m day⁻¹, adjusted for sampling effort at different distances. Movement estimates in all 3 years were highly correlated with the average distance between plots sampled.
3. Butterfly abundance was correlated positively with per cent cover of its host plant Dicentra uniflora , but this relationship decreased in importance during the peak of the flight period when individuals may be more interested in finding mates. There was a weak, positive correlation between butterfly abundance and the abundance of its primary nectar source, Eriogonum umbellatum in 1999, but no relationship in 2000.
4. Survival, recapture, and transition probabilities were estimated using open population, capture–recapture models. Survival and recapture probability decreased over the course of each season, while the probability of moving between plots increased. Recapture probability was significantly lower for females than for males among all 3 years, but there was no difference between the sexes in survival rate.     

ESTIMATION OF AGE-SPECIFIC PROBABILITIES OF FIRST RETURN AND ANNUAL SURVIVAL RATES FOR THE MALE GRAY SEAL (HALICHOERUS GRYPUS) ON SABLE ISLAND FROM CAPTURE-RECAPTURE DATA

We used a longitudinal capture-recapture study to estimate the age-specific probabilities of first return to the breeding colony and annual survival rates for male gray seals ( Halichoerus grypus ), based on resightings of seals branded as young on Sable Island. We estimated that the average age of first returns for seals born in 1969–1970 to be 9.1 (SE 0.4) yr; for seals born in 1973–1974 it is estimated to be 9.8 (SE 0.2) yr. The estimated annual survival rate of these males was estimated to be 0.976 (SE 0.003).     

Estimating age‐dependent survival when juveniles resemble females: Invasive ring‐necked parakeets as an example

Many species only show sexual dimorphism at the age of maturity, such that juveniles typically resemble females. Under these circumstances, estimating accurate age‐specific demographic parameters is challenging. Here, we propose a multievent model parameterization able to estimate age‐dependent survival using capture–recapture data with uncertainty in age and sex assignment of individuals. We illustrate this modeling approach with capture–recapture data from the ring‐necked parakeet Psittacula krameri. We analyzed capture, recapture, and resighting data (439 recaptures/resightings) of 156 ring‐necked parakeets tagged with neck collars in Barcelona city from 2003 to 2016 to estimate the juvenile and adult survival rate. Our models successfully estimated the survival probabilities of the different age classes considered. Survival probability was similar between adults (0.83, 95% CI = 0.77–0.87) and juveniles during their second (0.79, 95% CI = 0.58–0.87) and third winter (0.83, 95% CI = 0.65–0.88). The youngest juveniles (1st winter) showed a slightly lower survival (0.57, 95% CI = 0.37–0.79). Among adults, females showed a slightly higher survival than males (0.87, 95% CI = 0.78–0.93; and 0.80, 95% CI = 0.73–0.86, respectively). These high survival figures predict high population persistence in this species and urge management policies. The analysis also stresses the usefulness of multievent models to estimate juvenile survival when age cannot be fully ascertained.     

Estimating Survival for Elusive Juvenile Pond-Breeding Salamanders

Juvenile vital rates have important effects on population dynamics for many species, but this demographic is often difficult to locate and track. As such, we frequently lack reliable estimates of juvenile survival, which are necessary for accurately assessing population stability and potential management approaches to conserve biodiversity. We estimated survival rates for elusive juveniles of 3 species, the ringed salamander (Ambystoma annulatum), spotted salamander (A. maculatum), and small-mouthed salamander (A. texanum), using 2 approaches. First, we conducted an 11-month (2016–2017) mark-recapture study within semi-natural enclosures and used Bayesian Cormack-Jolly-Seber models to estimate survival and recapture probabilities. Second, we inferred the expected annual juvenile survival rate given published vital rates for pre-metamorphic and adult ambystomatids assuming stable population growth. For all 3 species, juvenile survival probabilities were constant across recapture occasions, whereas recapture probability estimates were time-dependent. Further, survival and recapture probabilities among study species were similar. Post-study sampling revealed that the initial study period median estimate of annual survival probability (0.39) underestimated the number of salamanders known alive at 11 months. We therefore appended approximately 1 year of opportunistic data, which produced a median annual survival probability of 0.50, encompassing salamanders that we knew to have been alive. Calculation from literature values suggested a mean annual terrestrial juvenile ambystomatid survival probability of 0.49. Similar results among our approaches indicated that juvenile survival estimates for the study species were robust and likely comparable to rates in nature. These estimates can now be confidently applied to research, monitoring, and management efforts for the study species and ecologically similar taxa. Our findings indicated that similarly robust vital rate estimates for subsets of ecologically and phylogenetically similar species can provide reasonable surrogate demographic information that can be used to reveal key factors influencing population viability for data-deficient species. © 2020 The Wildlife Society.     

Influence of maternal characteristics and oceanographic conditions on survival and recruitment probabilities of Weddell seals

For long‐lived animals, maternal age and breeding experience can vary widely and affect offspring survival and recruitment probabilities. In addition, these vital rates may be influenced by annual variation in environmental conditions. We evaluated various hypotheses regarding how offspring survival and recruitment probabilities vary as functions of maternal characteristics and oceanographic conditions, using 25 years of data from a study of individually‐marked Weddell seals in Erebus Bay, Antarctica. We predicted that survival and recruitment would be positively related to maternal age and experience up to some threshold value and considered three hypothesized shapes for the relationship beyond the threshold age (steadily increasing, pseudo‐threshold, or decreasing). We predicted an inverse relationship between maternal age at first reproduction and offspring survival and recruitment probabilities. We predicted that sea‐ice extent, which positively influences primary productivity, would be positively related to annual recruitment probabilities. Results revealed contrasting influences of maternal age on probabilities of survival and recruitment of young. Survival rate was best modeled by a pseudo‐threshold relationship with maternal age, e.g. in 1999, survival rate was estimated as 0.61, 0.69 and 0.72, respectively, for seals born to 6‐, 14‐ and 22‐yr‐old mothers. In contrast, estimated recruitment probability was highest for seals born to young mothers, e.g. recruitment probability for a 7‐yr‐old who had not yet had a pup was estimated as 0.51 vs 0.30, respectively, if she was born to a 6‐ versus a 14‐yr‐old mother. The combined results for offspring survival and recruitment suggest countervailing selection where genotypes favored for reproductive success are generally selected against as juveniles, resulting in high recruitment probabilities for individuals that had low juvenile survival rates. Finally, we found support for our prediction that oceanographic conditions affected annual recruitment rates, but not survival rates. Specifically, annual recruitment probability was positively related to the sea‐ice extent in September of the previous year.     

Abundance and Survival Rates of the Hawai’i Island Associated Spinner Dolphin (Stenella longirostris) Stock

Reliable population estimates are critical to implement effective management strategies. The Hawai’i Island spinner dolphin (Stenella longirostris) is a genetically distinct stock that displays a rigid daily behavioural pattern, foraging offshore at night and resting in sheltered bays during the day. Consequently, they are exposed to frequent human interactions and disturbance. We estimated population parameters of this spinner dolphin stock using a systematic sampling design and capture–recapture models. From September 2010 to August 2011, boat-based photo-identification surveys were undertaken monthly over 132 days (>1,150 hours of effort; >100,000 dorsal fin images) in the four main resting bays along the Kona Coast, Hawai’i Island. All images were graded according to photographic quality and distinctiveness. Over 32,000 images were included in the analyses, from which 607 distinctive individuals were catalogued and 214 were highly distinctive. Two independent estimates of the proportion of highly distinctive individuals in the population were not significantly different (p = 0.68). Individual heterogeneity and time variation in capture probabilities were strongly indicated for these data; therefore capture–recapture models allowing for these variations were used. The estimated annual apparent survival rate (product of true survival and permanent emigration) was 0.97 SE±0.05. Open and closed capture–recapture models for the highly distinctive individuals photographed at least once each month produced similar abundance estimates. An estimate of 221±4.3 SE highly distinctive spinner dolphins, resulted in a total abundance of 631±60.1 SE, (95% CI 524–761) spinner dolphins in the Hawai’i Island stock, which is lower than previous estimates. When this abundance estimate is considered alongside the rigid daily behavioural pattern, genetic distinctiveness, and the ease of human access to spinner dolphins in their preferred resting habitats, this Hawai’i Island stock is likely more vulnerable to negative impacts from human disturbance than previously believed.     

Who are we sampling? Apparent survival differs between methods in a secretive species

Survival is a fundamental parameter in population dynamics with increasing importance in the management and conservation strategies of wildlife populations. Survival probability in vertebrates is usually estimated by live‐encounter data obtained by means of physical mark–capture–recapture protocols. Non‐invasive acoustic marking relying on individual‐specific features of signals has been alternatively applied as a marking technique, especially in secretive species. Nevertheless, to date no research has compared survival rate estimates obtained by acoustic and physical marking. We estimated half‐yearly and annual survival and recapture rates of a secretive and threatened passerine, the Dupont's lark Chersophilus duponti, using two separate live‐encounter data sets of males collected simultaneously by physical and acoustic marking in the same study area. The separate analysis of both methods led to different model structures, since transient individuals had to be accounted for in the acoustic marking but not in the physical marking data set. Furthermore, while reencounter probabilities did not differ between methods, survival estimates employing physical marking were lower than those obtained acoustically, especially between the postbreeding and the breeding period when the apparent survival of colour‐banded birds was twice as low as for acoustic marking. The combination of marking methods suggested the existence of different subsets of individuals differentially sampled within the population: whereas colour‐banded males seemed to represent the territorial fraction of the population, both resident and floater individuals were probably detected by acoustic marking. Using traditional mark–recapture methods exclusively could have misled our estimates of survival rates, potentially affecting prospective predictions of population dynamics. Acoustic marking has been poorly applied in mark–recapture studies, but might be a powerful complement to obtain accurate estimates of fundamental demographic parameters such as survival and dispersal.     

Nasal Discs and the Vital Rates of Lesser Scaup

Nasal discs have been used to identify ducks in studies of survival and reproduction. To date, there has not been a comprehensive assessment of nasal-disc effects on the vital rates of wild ducks. We applied nasal discs to 603 juvenile and 784 adult lesser scaup (Aythya affinis) females from a population breeding in southwest Montana, USA, and released 1,399 juvenile and 71 adult females wearing only metal leg bands between June 2005 and September 2016. Using resighting, recapture, and hunter-recovery data collected from those individuals, we estimated survival and recovery probability with multistate capture-recapture models in Program MARK. We also assessed if recovery distance from our study site and pre-breeding and brood-rearing body condition were diminished for females wearing nasal discs. Model-averaged survival probabilities were 0.231 ± 0.035 (SE) for juveniles and 0.482 ± 0.019 for adults released with nasal discs. Survival was 1.8–3.4 times higher for females released with metal leg bands when compared to those released with nasal discs; survival of these juveniles was 0.433 ± 0.049 and 0.693 ± 0.039 for adults. We did not find evidence for recovery probability or recovery distance varying between females that wore nasal discs and those that did not. During the pre-breeding and brood-rearing seasons, we did not find females wearing nasal discs to be in lower body condition when compared to unmarked females. Our comprehensive assessment of nasal discs on wild lesser scaup suggests that survival probabilities estimated from nasal-marked study populations should be cautiously interpreted as minimum estimates. © 2021 The Wildlife Society.     

Survival rate, abundance, and residency of long-finned pilot whales in the Strait of Gibraltar

Long-finned pilot whales in the Strait of Gibraltar are distributed over the main shipping routes. This exposes them to risks of collisions and probable acoustic and physical disturbance. This species is also the target of whale-watching operations. The aim of this study was to estimate the annual population size, survival rate, and population growth rate of pilot whales occurring in the Strait and their inter-annual variation using photo-identification. A robust design was used to estimate all three parameters. A total of 10,784 individual pilot whale fins were photographed and analyzed. The population size estimation in summer ranged from a low of 147 individuals in 1999 to a high of 265 individuals in 2003. The annual population growth rate was estimated from mark recapture models to be 5.5%. The survival rate of adults was estimated at 0.982 (95% CI: 0.955–0.993). The same individuals have been observed between years. This suggests that this population is resident in the Strait, at least during summer. This study provides baseline knowledge prior to a predicted increase in shipping traffic throughout the main foraging area due to the opening in 2007 of a major shipping harbor along the Moroccan coast of the Strait.     

Estimating demographic parameters for loggerhead sea turtles using mark–recapture data and a multistate model

The survival for adult loggerhead sea turtles from a saturation tagging study on Bald Head Island, NC, USA, was estimated using a multistate model with unobservable states to relax assumptions that are violated when survival is estimated from multistate models and produce more accurate estimates of survival, recapture, and breeding transition probabilities. The influence of time, trap dependence, and low site fidelity to the study nesting beach on survival and recapture were examined. The best model given the data included an imprecise site-fidelity effect on survival, constrained the reproductive cycle to 4 years, and contained a time effect on recapture rates. The estimate of annual survival for adult females was of 0.85, producing the highest estimate in the literature for loggerhead sea turtles. Multistate models should be applied to other nesting beach data for sea turtles to improve survival estimates and in turn the ability to model and manage populations.     

Annual survival rates of adult Red-necked Nightjars Caprimulgus ruficollis

Nothing is known about the survival rates of Nightjars. Here we estimate annual survival rates of adult Red-necked Nightjars Caprimulgus ruficollis in and around the Donana National Park, southwest Spain. During the period 1989-95, 557 adults were marked and 19.7% of them were recaptured at least once in subsequent years. Capture-recapture models were built to estimate separately survival and recapture probabilities. The final selected model showed that probabilities of recapture differed between years (0.06-0.30) but not between sexes, and were independent of recapture effort. Survival was dependent on the interaction between sex and rainfall, this effect being negative for females and positive for males. However, it is not clear why rainfall influences the survival of males and females differentially due to the lack of accurate information on other life history traits. Average adult survival for the whole period was 0.74 for males (95% CI: 0.63-0.82) and 0.64 for females (95% CI: 0.56-0.72).     

Resident and transient dynamics, site fidelity and survival in wintering Blackcaps Sylvia atricapilla: evidence from capture–recapture analyses

In their winter quarters, migrant birds may either remain within a small area (resident strategy) or move frequently over a large area looking for locally abundant food (transient strategy). It has been suggested that both strategies could simultaneously occur in the same population. We used time-since-marking capture–recapture models to infer the coexistence of these two behavioural strategies (transient and resident) among wintering Blackcaps Sylvia atricapilla using weekly recapture data over a 7-year period. A related question is whether Blackcaps, if surviving to the next winter, always return to the same wintering area, so we also used this approach to analyse winter site fidelity and to estimate annual survival probabilities. Model selection supported the existence of heterogeneity in survival estimates for both the within-season and the interannual survival probabilities, i.e. there was evidence for the existence of transients. It was estimated that 26% of the Blackcaps were resident during the winter. Mean apparent annual survival probability was 0.46 (se = ±0.11). However, there was some evidence suggesting that not all individuals showed winter site fidelity. The estimated proportion of individuals that, if alive, returned to the wintering area was 28%. This is the first study to show the existence of these two behavioural strategies (residence and transience) among wintering Blackcaps, and the first confirming this pattern using capture–recapture models. These models considering transient and resident dynamics may become an important tool with which to analyse wintering strategies.     

MULTISITE MARK-RECAPTURE FOR CETACEANS: POPULATION ESTIMATES WITH BAYESIAN MODEL AVERAGING

Mark-recapture techniques are widely used to estimate the size of wildlife populations. However, in cetacean photo-identification studies, it is often impractical to sample across the entire range of the population. Consequently, negatively biased population estimates can result when large portions of a population are unavailable for photographic capture. To overcome this problem, we propose that individuals be sampled from a number of discrete sites located throughout the population's range. The recapture of individuals between sites can then be presented in a simple contingency table, where the cells refer to discrete categories formed by combinations of the study sites. We present a Bayesian framework for fitting a suite of log-linear models to these data, with each model representing a different hypothesis about dependence between sites. Modeling dependence facilitates the analysis of opportunistic photo-identification data from study sites located due to convenience rather than by design. Because inference about population size is sensitive to model choice, we use Bayesian Markov chain Monte Carlo approaches to estimate posterior model probabilities, and base inference on a model-averaged estimate of population size. We demonstrate this method in the analysis of photographic mark-recapture data for bottlenose dolphins from three coastal sites around NE Scotland.     

Demographic parameters of a free-ranging deep-diving cetacean,the long-finned pilot whale

Demographic parameters provide baselines to estimate future population trajectories which can then be used in management decisions. The aim here was to estimate demographic parameters of long-finned pilot whale (Globicephala melas) from the Strait of Gibraltar by fitting mark-recapture models to photo-identification data of primary and secondary marked individuals. These parameters were used to forecast the future population trajectories in a population viability analysis (PVA) given different scenarios of demographic rates. Survival rate increased with age from 0.629, 95% CI [0.409, 0.805] for calves, 0.869, 95% CI [0.758, 0.934] for juveniles, to 0.972, 95% CI [0.953, 0.983] for adults. A preliminary mean observed interval of viable calves was 4.5 years. The PVA estimated the population would persist over 100 years with a 100% probability for all scenarios except those with lower 95% CI survival values, for which the probability of extinction reached 100%. Population growth rate was negative in all scenarios except those with 95% CI upper survival values. Interbirth interval and juvenile survival were found most influential and depended on the correct identification of secondary marked (e.g., calves and juveniles) individuals on a long-term basis. This population was found in a precarious state prior to a morbillivirus outbreak that might even more endanger its long-term viability.     

Male mating success in an aquatically mating pinniped, the harbour seal (Phoca vitulina), assessed by microsatellite DNA markers

Similar to many other pinniped species, harbour seals ( Phoca vitulina ) mate exclusively at sea. Here we present the first attempt to measure male mating success in an aquatically mating pinniped. Male mating success was estimated by paternity analysis in two cohorts of pups born at Sable Island, Nova Scotia, Canada, using microsatellite DNA markers. The genotypes of 275 pups born in 1994 and 1995 were compared to those of 90 candidate males at six microsatellite loci using a likelihood approach to resolve paternity. Paternity could be assigned for two, 22, 40 and 85 pups at confidence levels of 95, 80, 65 and 50%, respectively. Most successful males were assigned the paternity of a single offspring, suggesting a low variance in male mating success relative to most pinniped species. The proportion of paternal half sibs within cohorts and between maternally related sibs estimated by maximum likelihood were not significantly different from zero. It is thus unlikely that most offspring were sired by a small number of highly successful unsampled males, and that female harbour seals do not usually exhibit fidelity to the same male in sequential breeding seasons. A low level of polygyny in Sable Island harbour seals is consistent with predictions based on their breeding ecology, as females are highly mobile and widely dispersed in the aquatic mating environment at Sable Island.     

Mark-resight estimates of seasonal variation in harbor seal abundance and site fidelity

Monitoring trends in abundance of pinnipeds typically involves counting seals at terrestrial haul-out sites during the breeding season. Counts of seals made at other times of the year are typically lower; however, it is often unknown whether this is because fewer animals are present or whether lower counts simply reflect a reduction in haul-out probability. Here we illustrate how photo-identification data from an individual-based study of harbor seals (Phoca vitulina) can be used to estimate seasonal variation in abundance and site fidelity. Monthly data collected over a two-year period were analyzed using a mark-recapture mark-resight model accounting for individuals transitioning between observable and unobservable states. Levels of site fidelity were high throughout the year and abundance estimates showed no seasonal pattern. This suggests that individual seals used haul-out sites to the same extent throughout the year, and that peaks in counts during the breeding season are a result of seasonal changes in haul-out probability. The results of this study have implications for understanding population sub-structuring, gene flow and disease spread.     

Effects of flipper bands and injected transponders on the survival of adult Little Penguins Eudyptula minor

Tagging is essential for many types of ecological and behavioural studies, and it is generally assumed that it does not affect the fitness of the individuals being examined. However, the tagging of birds has been shown to have negative effects on some aspects of their lives. Here we investigate the influence of tagging on apparent survival. We examined the effects of flipper bands and injected transponders on the apparent survival of adult Little Penguins by comparing the survival probabilities of 2483 Little Penguins marked at Phillip Island, Australia, between 1995 and 2001 in one of three ways: with bands, with transponders or with both. The design of the study and our method of analysis allowed us to estimate tag loss and ensured that tag loss did not bias the survival estimates. Birds marked with flipper bands had lower survival probabilities than those marked with transponders (with apparent survival probabilities in the first year after tagging of 75% for banded birds and 80% for birds fitted with transponders, and in subsequent years of 87% for banded birds and 91% for birds fitted with transponders). We estimated both band and transponder loss probabilities for the first time, and found that transponder loss probabilities were substantially higher than band loss probabilities, particularly in the first year after marking when the tag loss probability was 5% for transponders and 0.7% for bands. Survival probabilities were lower in the first year after marking than in subsequent years for all birds. Studies of penguins that have used flipper bands to identify individuals may have underestimated annual adult survival probabilities, as banded penguins were likely to have lower than average survival probabilities than those of unbanded birds. The higher annual survival probabilities of individuals marked with transponders indicate that this should be the preferred marking technique for Little Penguins. However, future studies will, like ours, need to consider the higher rates of transponder loss when estimating survival, possibly by double‐tagging some birds.     

The World’s Northernmost Harbour Seal Population–How Many Are There?

This study presents the first abundance estimate for the world’s northernmost harbour seal (Phoca vitulina) population, which resides in Svalbard, Norway, based on three digital stereoscopic photographic surveys conducted in 2009 and 2010. The counts from these high resolution 3D images were combined with a novel method for estimating correction factors for animals that were in the water at the time of the surveys, in which extensive behavioural data from radio-tagged harbour seals were used together with age distribution data to estimate the proportion of seals of various age and sex classes hauled out at the times of the surveys. To detect possible seasonal shifts in age distribution between surveys, lengths of hauled out seals were measured from the stereoscopic images. No body-length differences were detected between the surveys; but, this may be due to a high degree of sexual dimorphism exhibited in this population. Applying the modelled correction factors, a total of 1888 (95% CI: 1660–3023), 1742 (1381–3549) and 1812 (1656–4418) harbour seals were estimated for the surveys flown on 01 August 2009, 01 August 2010 and 19 August 2010, respectively. The similarity between the three survey estimates (despite significant differences in the number of animals actually counted on the photos from each survey effort) suggests that the variation in numbers of hauled out seals is reasonably accurately adjusted for by the haul-out probability model. The low population size, the limited spatial distribution of the population and its reduced genetic diversity make this population vulnerable to chance events, such as disease epidemics.     

Capture–recapture models with heterogeneity to study survival senescence in the wild

Detecting senescence in wild populations and estimating its strength raise three challenges. First, in the presence of individual heterogeneity in survival probability, the proportion of high‐survival individuals increases with age. This increase can mask a senescence‐related decrease in survival probability when the probability is estimated at the population level. To accommodate individual heterogeneity we use a mixture model structure (discrete classes of individuals). Second, the study individuals can elude the observers in the field, and their detection rate can be heterogeneous. To account for detectability issues we use capture–mark–recapture (CMR) methodology, mixture models and data that provide information on individuals’ detectability. Last, emigration to non‐monitored sites can bias survival estimates, because it can occur at the end of the individuals’ histories and mimic earlier death. To model emigration we use Markovian transitions to and from an unobservable state. These different model structures are merged together using hidden Markov chain CMR models, or multievent models. Simulation studies illustrate that reliable evidence for survival senescence can be obtained using highly heterogeneous data from non site‐faithful individuals. We then design a tailored application for a dataset from a colony of black‐headed gull Chroicocephalus ridibundus. Survival probabilities do not appear individually variable, but evidence for survival senescence becomes significant only when accounting for other sources of heterogeneity. This result suggests that not accounting for heterogeneity leads to flawed inference and/or that emigration heterogeneity mimics survival heterogeneity and biases senescence estimates.