A brief history of the many faces of detection in ecology and wildlife management

In the early years of the development of ecological methods, detection was considered a relatively simple parameter to estimate. The early closed population estimation techniques of Lincoln and Petersen and the more sophisticated open population models of Leslie, Chitty, Chitty and Jolly, and Seber assumed a relative ease of estimating the detection probability. Wildlife ecologists who knew their animals were always concerned about unequal catchability, and fisheries biologists like Ricker provided models to compensate for unequal catchability in fishery estimation, but it was not until the Colorado mafia published their monograph in 1978 on a series of models that allowed for certain classes of unequal detection that the problem was formalized for closed populations in Program CAPTURE. From the mid-1970s there was a groundswell of publications and a generation of cooperation between mathematicians and ecologists to attack the problem of detection, not only for population estimation but more importantly for disease analysis and pest management. This new synthesis of mathematical and statistical power with ecological insights of the clever ways that animals and plants avoid detection has produced a series of methods that recognised as a critical part of wildlife management in this century.     

Capture probability of fishes in Central European (Hungary) wadeable lowland streams

Neglect of imperfect capture efficiency leads to biased inferences on population abundance, and correspondingly, seriously affects ecological research, bioassessment, conservation, and fisheries management. To date, many research studies have studied capture efficiency of salmonid fishes, but the catchability of fishes living in non-salmonid streams has received much less attention. This paper estimates capture probability for seven fish species in densely vegetated lowland streams by using double-pass electrofishing data and an N-mixture removal model. Results show that capture probability can vary among species, and between-stream differences have a stronger influence on the abundance and the catchability than within-stream variability. Estimation uncertainty decreases with observed abundance, and the mean catchability tends to be the highest for the medium abundant species. These findings suggest that relative abundances from single-pass data are biased to a species- and habitat-specific degree. Therefore, plausible estimation of capture probability from double-pass electrofishing requires data collected from numerous sites that cover a wide range of the environmental gradient in lowland streams.     

Size and overlap of home range inCalomys musculinus (Muridae: Sigmodontinae)

Home range size and overlap ofCalomys musculinus (Thomas, 1913) was examined in relation to sex and breeding periods. The study was carried out in four 0.25 ha enclosures, in a natural pasture, between October 2002 and July 2003. The four enclosures functioned as independent populations and each was considered a replicate. The capture, mark and recapture method was used. Home range size and overlap inC. musculinus depended on sex and period. Home range size of males was always larger than that of females. Females showed a small degree of intra-sexual home range overlap during the breeding period. In general, male home ranges overlapped with females. We conclude that differences in home range size inC. musculinus is determined by sex and breeding period. Moreover, the degree of inter- and intra-sexual home range overlap during the breeding period suggests that both males and females ofC. musculinus use space differently. Females did not share their home range with other females, while males fully shared it with both sexes, and male spacing is influenced by the distribution of females. A promiscuous-polygynous mating system is suggested forC. musculinus.     

A field study of the effect of prebaiting on censusing by the capture-recapture method in a vole population

Populations of the vole, Clethrionomys rufocanus, in a lowland woodlot of Hokkaido were studied for the presence of effects of prebaiting on censusing by the capture-recapture method. A grid of 121 live-traps, spaced 5 m apart, was laid out on each of two plots, one of which alone was prebaited three days long. Owing to very high densities and great trap-efficiency, sufficient and favourable samples could be available for statistical analysis, except the trend of delayed catch for young in sampling. The population on either plot, however, proved to be markedly variable in catchability of unmarked animals in the course of trapping; while the probability of recapture was counted as invariable on the average from day to day, the recapture frequency was different between juveniles, subadults and adults. Needless to say, the catchability was distinctly greater for marked voles than for unmarked ones, whether prebaited or not, through the trapping period, except that the first-day catchability for unmarked ones on the prebaited plot seems not to be significantly lower than that for marked ones. Consequently, it turns out that the prebaiting has almost never helped to eliminate the important bias induced by differential trap-response of marked and unmarked animals; its contribution is only that the catchability for unmarked ones is slightly higher on the part of the prebaited plot on earlier days of the period. In accordance with the heterogeneous catchability, the Γ-form distribution analogous to the geometric could be applied with thorough fitness to the capture frequency in order to estimate the whole populations. The fact that the estimates are reliable, being not at any rate underestimates, was further confirmed by the result of a follow-up work conducted by means of the removal method with wider trap-spacing which brought forth distinct underestimation chiefly referable to unexposure to traps of the partial populations. The subject of unexposure was discussed by laying stress on the relation between minimum range length and trap-spacing.     

Acquired hook-avoidance in the pike Esox lucius L. fished with artificial and natural baits

Tagged pike Esox lucius L. in a drainable pond were fished by hook and line, using either a spinner or a small live fish as bait. Catch per unit effort could be used as a measure for catchability because all captured pike were immediately returned to the pond and mortality was low.
Catchability to spinner fishing decreased to very low levels after about half of the population had been caught in this way. Catchability to live bait fishing remained unaffected both by intensive spinner and live bait fishing.
It was difficult to capture pike more than once by spinning. In live bait fishing, on the other hand, the number of recaptures closely matched the number expected if catchability remains unaffected by earlier capture.
The advantages are discussed of the use of artificial baits over live baits in hook and line fishing for pike.     

Behaviour and stress response during capture and handling of the red-billed chough Pyrrhocorax pyrrhocorax (Aves: Corvidae)

We studied the effect of capture and handling on free-living red-billed choughs Pyrrhocorax pyrrhocorax . We analysed the association between bird behavioural response and individual health, breeding status, sex, and age. Active responses (aggression towards the ringer, screaming) were more common in the breeding period, and in individuals with a high heterophils to lymphocytes ratio, indicating poor physiological condition and/or high chronic stress. Adults were more aggressive than juveniles and yearlings, and females were more aggressive than males. Sex, age, and condition differences were also recorded in the spectrotemporal output of distress calls. Birds with a screaming/active response appeared to be more stress-susceptible than passive and silent individuals, and this response was stronger during the energy demanding period of reproduction. The results obtained suggest that the response of the red-billed chough during capture might primarily reflect stress-susceptibility, although a number of potential alternative explanations are discussed.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 846–855.     

Changes in body mass and feeding behaviour in male harbour seals, Phoca vitulina, in relation to female reproductive status

Loss of body mass has been used as an index of the cost of reproductive effort in mammals. We studied changes in body mass of male harbour seals, Phoca vitulina , during the breeding season on Sable Island, Nova Scotia, Canada. Individually marked subadult ( n = 21) and adult ( n = 22) males were captured at approximately six-day intervals throughout the breeding season. Adult males weighed an average of 108 kg ± 5·6 (S.E.) at initial capture, whereas subadults weighed an average of 76 ± 6·6 kg. The rate of mass loss by adult males did not differ from zero during the pre-mating period (i.e. the period without receptive females), but differed significantly from zero (-0·91 ± 0·007 kg/day) during the mating period (i.e. the period with receptive females). By contrast, the rate of mass change of subadults did not differ from zero in either period, indicating that food availability was unlikely to be responsible for the observed changes in adults. Adult males lost up to 24% of body mass during the breeding season. Examination of sera for the presence of chylomicrons (i.e. evidence of recent feeding) also suggested that adults stopped feeding during the mating period, while subadults did not. These results suggest that reproduction represents a significant energetic cost to adult male harbour seals.     

Sex ratio of North Island kaka (

The sex ratio of the kaka population inhabiting the Waihaha Ecological Area, Pureora Forest Park was estimated between late October 1994 and January 1995. The observed sex ratio estimate was three males to one female compared to a capture rate (using mist nets) of six to one in the same area between January and June 1994. Females appeared to be less susceptible to capture than males. The skewed sex ratio toward male kaka was significant and suggests that female kaka suffer higher mortality (probably due to predation at the nest) than males. The slow breeding rate of kaka combined with a high loss of breeding females is a serious threat to the long term survival of the kaka population within the Waihaha Ecological Area.     

Reconstruction of paternal genotypes over multiple breeding seasons reveals male green turtles do not breed annually

For species of conservation concern, knowledge of key life-history and demographic components, such as the number and sex ratio of breeding adults, is essential for accurate assessments of population viability. Species with temperature-dependent sex determination can produce heavily biased primary sex ratios, and there is concern that adult sex ratios may be similarly skewed or will become so as a result of climate warming. Prediction and mitigation of such impacts are difficult when life-history information is lacking. In marine turtles, owing to the difficultly in observing males at sea, the breeding interval of males is unknown. It has been suggested that male breeding periodicity may be shorter than that of females, which could help to compensate for generally female-biased sex ratios. Here we outline how the use of molecular-based paternity analysis has allowed us, for the first time, to assess the breeding interval of male marine turtles across multiple breeding seasons. In our study rookery of green turtles (Chelonia mydas), 97% of males were assigned offspring in only one breeding season within the 3-year study period, strongly suggesting that male breeding intervals are frequently longer than 1year at this site. Our results also reveal a sex ratio of breeding adults of at least 1.3 males to each female. This study illustrates the utility of molecular-based parentage inference using reconstruction of parental genotypes as a method for monitoring the number and sex ratio of breeders in species where direct observations or capture are difficult.     

Seasonal variation of mortality,detectability, and body condition in a population of the adder (Vipera berus)

We analyzed seasonal variation in mortality rates in adult males and females of the European adder (Vipera berus), using data collected during a 13‐year capture–recapture study (2005–2017) in a large population. We concurrently obtained quantitative information on the seasonal variation in the detectability and body condition of adders. Our results show strong seasonality in body condition, encounter, and capture rates of adult adders, and these patterns differ markedly between sexes and between breeding and nonbreeding females. Seasonal variation in mortality rates was however virtually nonexistent in males and moderately low in both breeding and nonbreeding females. In addition, we found no evidence for among‐year differences in the seasonal mortality schedules of males and females. During periods of intensive basking, both males and pregnant females are highly visible for humans, but are not subject to strong natural mortality. This low susceptibility to predation is presumably induced by various factors, including the limitation of overt exposure to short periods of time and specific microhabitats, the dorsal coloration pattern that provides cryptic protection and possibly also an aposematic warning signal, and presumed seasonal differences in the foraging behavior and food requirements of natural predators. Our data provide some evidence that female adders, but not males, are relatively vulnerable to predation during the seasonal migrations between the hibernation and feeding habitats. Mortality in the females was not much elevated during their breeding years, but was notably highest in the spring of the ensuing nonbreeding year. After giving birth, reproductive females are extremely emaciated and have a weakened general condition. They then run the risk of dying from starvation either before, during, or after hibernation. The higher mortality after giving birth, that is sustained over a period of ca. 9 months, should be considered as an indirect and delayed survival cost of reproduction.     

Environmental and seasonal adaptations of the adrenocortical and gonadal responses to capture stress in two populations of the male garter snake, Thamnophis sirtalis

Stress and reproduction are generally thought to work in opposition to one another. This is often manifested as reciprocal relationships between glucocorticoid stress hormones and sex steroid hormones. However, seasonal differences in how animals respond to stressors have been described in extreme environments. We tested the hypothesis that garter snakes, Thamnophis sirtalis, with limited reproductive opportunities will suppress their hormonal stress response during the breeding season relative to conspecifics with an extended breeding season. The red-sided garter snake, T.s. parietalis, of Manitoba, Canada, has a brief breeding season during which males displayed no change in either plasma levels of testosterone or corticosterone, which were both elevated above basal levels, in response to capture stress. During the summer, capture stress resulted in increased plasma corticosterone and decreased testosterone. During the fall, when mating can also occur, males exhibited a significant decrease in testosterone but no increase in corticosterone in response to capture stress. The red-spotted garter snake, T.s. concinnus, of western Oregon, has an extended breeding season during which males displayed a stress response of increased plasma corticosterone and decreased testosterone levels. The corticosterone response to capture stress was similar during the spring, summer, and fall. In contrast, the testosterone response was suppressed during the summer and fall when gametogenesis was occurring. These data suggest that male garter snakes, in both populations, seasonally adapt their stress response but for different reasons and by potentially different mechanisms. J. Exp. Zool. 289:99-108, 2001.     

Plasma glucocorticoid concentrations in free-ranging platypuses (Ornithorhynchus anatinus): response to capture and patterns in relation to reproduction

Energy demands in the platypus are likely to increase in the breeding season, which occurs from winter to early spring. Glucocorticoids, which play a major role in energy mobilisation, were measured in consecutive blood samples from free-ranging adults at approximately monthly intervals throughout the year. Glucose and free fatty acids were also measured in some samples. Plasma concentrations of glucocorticoids rose significantly during the first 30 min after capture, accompanied by a rise in free fatty acids, but no corresponding increase in glucose concentrations. We observed a strong pattern in plasma glucocorticoids in samples collected within 15 min of capture (indicative of pre-disturbance concentrations) in different phases of the annual reproductive cycle, with significantly higher levels in both males and females in the breeding season compared to the non-breeding season. These data, and the decline in tail fat stores that occur towards the end of the mating period (around October), suggest that platypus experience high-energy demands during this phase of reproduction. Plasma glucocorticoid concentrations in females sampled during the lactation period (October-February) were relatively low, and similar to those in females sampled in the non-breeding, non-lactation period (March-June). The latter requires further investigation as results may have been influenced by sampling limitations.     

Metabolic changes in male snakes, Thamnophis melanogaster, during a breeding period

1. Daily basking periods were lengthened substantially during a breeding period in a natural population of the snake, Thamnophis melanogaster. 2. In the laboratory, oxygen consumption of male T. melanogaster significantly increased during a breeding period, compared to pre- and post-breeding levels in the same males. 3. In both laboratory and field males, serum lipid increased initially and then decreased during the breeding period. 4. Serum protein of laboratory males decreased significantly following the breeding period. 5. Serum glucose did not change significantly in laboratory males, but increased significantly during the breeding period in field males. 6. Changes in oxygen consumption and nutrient distribution may reflect changing energy demands attendant with gonadal recrudescence in this snake.     

Lack of consistent hormonal responses to capture during the breeding season of the bearded dragon, Pogona barbata

The bearded dragon (Pogona barbata: Agamidae) is a diurnal, oviparous, multi-clutching lizard from Australia. We examined plasma hormonal responses to capture in males and females during the spring breeding season. Corticosterone concentrations at capture (0 h; < or =3 min after capture) were low (males: 1.81+/-0.63 ng/ml; females 2. 23+/-0.47 ng/ml) and within sexes were unrelated to the time of the day, snout-vent length or, in females, reproductive condition (vitellogenic, gravid, assumed spent). Corticosterone concentrations at capture were significantly and inversely correlated with body condition in males, but not in females. Unexpectedly, neither sex showed significant changes in mean concentrations of corticosterone at 3.5 or 24 h after capture compared with 0 h values. Corticosterone concentrations at 3.5 h after capture did not differ between dragons bled at capture or not. Concentrations of progesterone in both the sexes did not change between 0 h and 3.5 or 24 h after capture. Testosterone concentrations in males at capture were moderate (10.1+/-2.2 ng/ml), and unchanged at 3.5 h after capture. The adrenocortical axis of adult bearded dragons in the breeding season seems remarkably unresponsive to capture compared with many other reptiles. Low adrenocortical responses to capture may be a feature of reptiles known to adjust well to captivity.     

Seasonal and Acute Changes in Adrenocortical Responsiveness in an Arctic-Breeding Bird

The Lapland longspur,Calcarius lapponicus,times its breeding season so that chicks hatch coincident with the brief period of food abundance in the high arctic. This synchronization requires that all reproductive activities occur in over a much shorter period than at lower latitudes. Because of the known influence of stress hormones on delaying breeding in temperate-zone birds and the detrimental effects of such delays in the arctic, we expected the performance of the hypothalamic–pituitary–adrenal (HPA) axis of arctic-breeding birds to show less sensitivity to environmental stress than their mid-latitude counterparts. We found that adrenocortical responsiveness to the standardized stress of capture and handling, measured by taking five serial blood samples for corticosterone during the course of a 1-hr period, was similar to many temperate passerines and was also similar both between male and female longspurs and between the migratory and reproductive phases. However, the profile of plasma corticosterone during capture stress was significantly damped in longspurs sampled as they began their postnuptial molt. In addition, we had the opportunity to examine endocrine responses to a natural environmental stress in 1989 during a 3-day snowstorm which concealed available food resources. During this storm longspurs formed progressively larger flocks each day, with females abandoning incubation duties by the third day. Birds captured during the storm showed highly significant increases in both the rate of plasma corticosterone increase during capture and the peak postcapture level compared with birds sampled before the storm. This increased adrenal potential suggests increased activity of the HPA axis in response to severe conditions and is reminiscent of the response to fasting. Although the storm occurred during incubation, and reproductive hormone levels had begun to decline, we measured significant reductions in luteinizing hormone in both males and a subset of females captured during the storm.     

Lek fidelity and movement among leks by male Greater Sage‐grouse Centrocercus urophasianus: a capture‐mark‐recapture approach

Males in lek mating systems tend to exhibit high fidelity to breeding leks despite substantial evidence of skewed mating success among males. Although movements between leks are often reported to be rare, such movements provide a mechanism for an individual to improve lifetime fitness in response to heterogeneity in reproductive conditions. Additionally, estimates of apparent movements among leks are potentially biased due to unaccounted variation in detection probability across time and space. We monitored breeding male Greater Sage‐grouse Centrocercus urophasianus on 13 leks in eastern Nevada over a 10‐year period, and estimated movement rates among leks using capture‐mark‐recapture methods. We expected that male movement rates among leks would be low, despite predictions of low breeding success for most males, and that detection rates would be highly variable among leks and years. We used a robust design multistate analysis in Program mark to estimate probability of movements among leks, while accounting for imperfect detection of males. Male Sage‐grouse were extremely faithful to their leks; the annual probability of a male moving away from its original lek of capture was approximately 3% (se = 0.01). Detection probabilities varied substantially among leks (range = 0.21–0.95), and among years (range = 0.30–0.76), but remained relatively constant within years at each lek. These results suggest that male Sage‐grouse dispersal is either rare, or consists primarily of dispersal of sub‐adults from their natal areas prior to the breeding season. The study highlights the benefits of robust design multistate models over standard ‘live‐encounter’ analyses, as they not only permit estimation of additional parameters, such as movement rates, but also allow for more precise parameter estimates that are less sensitive to heterogeneity in detection rates. Additionally, as these data were collected using capture‐mark‐recapture methods, our approach to estimating movement rates would be beneficial in systems where radiotagging is detrimental to the study organism.     

Catchability: a key parameter for fish stock assessment

Summary Catchability is a concept in fishery biology which reflects the efficiency of a particular fishery. Its quantitative magnitude is expressed by the catchability coefficient, which relates the biomass abundance to the capture or fishing mortality. This paper is a comprehensive review of catchability including the development of our knowledge, interpretation and estimation.Catchability patterns indicate that the catchability coefficient has been used in two main lines: (a) increased efficiency of fishing effort and (b) its relation to population fishery processes for assessment and management purposes. It involves various aspects of the fishery, such as individual and population biology, characteristics of the fishing gear, amount of fishing, fishing strategies, and environmental fluctuation, among others.The concept is proposed of an integrated model of the catchability coefficient, which incorporates various of the aspects mentioned above. It is illustrated with two examples of its application: the red grouper (Epinephelus morio) fishery from the Campeche Bank, Gulf of Mexico, and the sardine (Sardinops caeruleus) fishery from the Gulf of California.     

Is heterogeneity of catchability in capture–recapture studies a mere sampling artifact or a biologically relevant feature of the population?

The heterogeneity of catchability (HC) among the individuals encountered during a capture–recapture study has long been regarded as a liability. However, heterogeneous capture probabilities may reflect interesting but hidden features of the population, such as social status. The difficulty is to distinguish between this intrinsic heterogeneity and the extrinsic heterogeneity induced by the study itself. So far, population ecologists have not been able to distinguish between these two sources of variation in capture heterogeneity because, in the presence of heterogeneity of capture in the data, they have frequently used a too simple approach. This traditional approach, which consists of incorporating two common sources of lack of fit (transience and trap-dependence), does not directly model the HC and thus cannot investigate its biological meaning. In this context, we propose, for open populations, to directly model the HC by employing multievent models. Multievent models make it possible to break HC into two classes of catchability viewed as uncertain states. With the introduction of a coefficient of heterogeneity to model proportional probabilities of capture over time in the two classes, our approach allows the investigation of HC in a parsimonious way. In this paper, we apply both this new approach and the traditional approach to a long-term data set of male deer mice Peromyscus maniculatus. We then compare 13 candidate models separately for each approach. Our results indicate that the new approach is superior to the traditional approach. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The implications of stress on male mating behavior and success in a sexually dimorphic polygynous mammal, the grey seal

Studies on primates and other taxa have shown that the physiological response of an individual to stress reflects their social status. We combined behavioral observations with measures of stress to test the hypothesis that stress is an important physiological determinant of mating behavior and success in the male grey seal. Known-age males (N=19) were studied during the breeding seasons of 2004 and 2005 at Sable Island, Canada. The stressor was a capture and restraint period of 35 min and serial samples of cortisol and testosterone were taken as measures of stress. The mean baseline concentrations of cortisol and testosterone were 9.7+/-0.5 ug/dl and 6.2+/-0.6 ng/mL, respectively. The baseline cortisol concentration was negatively correlated with the duration of time a male spent at a site (r=-0.507, P=0.027), which was a strong correlate of mating success (r=0.659, P=0.002). All males experienced an increase in the concentration of cortisol during the restraint period (79.1+/-8.4%; CV=46.1%). The percentage rise in cortisol during restraint was correlated with the mean duration of time spent at a site (r=0.544, P=0.016) and thus success. The concentration of testosterone also increased during the restraint period (32.8+/-9.7%). This might be an adaptive response to maintaining the ability to reproduce while under stress. Our study indicates that stress is an important determinant of success in male grey seals. More successful males might exhibit an adaptive response to stress by maintaining low concentrations of cortisol during breeding.     

Distribution and reproductive success of the Pied Flycatcher Ficedula hypoleuca in relation to forest patch size and vegetation characteristics; the effect of scale

We studied habitat choice, distribution and reproductive success in the Pied Flycatcher Ficedula hypoleuca in relation to the spatial structure of a fragmented forest area. Two hierarchical levels of forest habitat structure were used: (1) forest patch size (macrohabitat) and (2) vegetative structure within forest patches (microhabitat). In spring, both males and females settled preferentially in large and medium-sized forest stands (>1 ha) where breeding density was also higher than in small stands (<1 ha). Stands <5 ha were occupied later, and the proportion of unpaired males was higher there than in large stands (>5 ha). The known age distributions of breeding birds and breeding success were independent of forest patch size. Nest predation rate was not associated with stand size or nest distance from the forest edge. The preference of breeding birds for large forest patches was presumably related to the higher amount of resources (nest sites, mates, food) a large patch can offer for reproduction compared with a small patch. At the microhabitat level, territories of old males were characterized by relatively more deciduous trees that contained more invertebrate food than coniferous tree-dominated territories of yearling males. The reproductive success of old males, as measured by the number of fledged young per male, was higher than that of yearling males. This suggests that the larger body size and blacker plumage of old males possibly contributed to male dominance and that old males excluded younger males from preferred habitats through territorial behaviour. Our results suggest that habitat choice of the Pied Flycatcher was affected by both micro- and macrohabitat. On the basis of settlement pattern, density and reproductive success, the distribution of Pied Flycatchers across forest stands of different sizes followed the ideal-free distribution model, whereas at the microhabitat level, age-related unequal distribution of males followed the ideal-despotic model of Fretwell and Lucas.