Natal Site Research Articles

Revealing early life history of brown trout in an impaired watershed through otolith geochemistry

Early life history data are critical for conservation and management of trout species in freshwater river networks and are imperative for planning habitat restoration in degraded watersheds. In this study, we use otolith geochemical signatures to assign natal provenance and determine age of tributary outmigration for fluvial brown trout ( Salmo trutta) in the Upper Clark Fork River watershed, a large impaired river network. Distinct spatial variations in chemical markers allowed for accurate assignment of fish to their stream of origin and often to specific natal sites. All 10 natal tributaries investigated in this study contributed brown trout to the mainstem and most fish migrated from tributaries to the mainstem during age 1. Mainstem natal habitats, previously thought to be limited by pollution, contributed 29% of the total natal production. Our results indicate that trout in the Upper Clark Fork River use spawning and rearing habitats that are spread throughout the basin. Thus, restoration strategies should focus on maintaining and enhancing a broad variety of habitats and life histories to be successful.

High egg retention in Chinook Salmon Oncorhynchus tshawytscha carcasses sampled downstream of a migratory barrier.

Barriers in rivers have the potential to severely decrease functional connectivity between habitats. Failure to pass barriers and reach natal spawning habitat may compromise individual reproductive success, particularly for semelparous, philopatric species that rely on free-flowing rivers to reach natal habitat during their once-in-a-lifetime spawning migrations. To investigate the consequences of in-river barriers on fish spawning success, we quantified egg retention and spawning effort (caudal fin wear) in female Chinook Salmon Oncorhynchus tshawytscha carcasses collected downstream of the Whitehorse Hydro Plant on the upper Yukon River and at a nearby free-flowing tributary (Teslin River) from 2018 to 2020 (~2900 km migrations). Previous studies have demonstrated that a large proportion of fish attempting to reach spawning locations upstream of the hydro plant fail to pass the associated fishway. We estimated nearly all female salmon failing to pass the hydro plant attempted spawning in non-natal habitat downstream, but that these females retained ~34% of their total fecundity compared to ~6% in females from the free-flowing river. Females downstream of the hydro plant also had lower wear on their caudal fin, a characteristic that was correlated with increased egg deposition. Egg retention did not vary across years with different run sizes, and we propose that egg retention downstream of the hydro plant was not driven by density-dependent mechanisms. Findings from this work indicate that female Chinook Salmon can still deposit eggs following failed fish passage and failure to reach natal spawning sites, though egg retention rates are considerably higher and uncertainties remain about reproductive success. We encourage researchers to incorporate carcass surveys into fish passage evaluations for semelparous species to fully account for consequences of failed passage.

The potential function of post-fledging dispersal behavior in first breeding territory selection for males of a migratory bird.

One possible hypothesis for the function of post-fledging dispersal is to locate a suitable future breeding area. This post-fledging period may be particularly important in migratory species because they have a limited period to gather information prior to autumn migration, and in protandrous species, males must quickly acquire a territory after returning from spring migration to maximize their fitness. Here we use color-ring resightings to investigate how the post-fledging dispersal movements of the Cyprus wheatear Oenanthe cypriaca, a small migratory passerine, relate to their first breeding territory the following year when they return from migration. We found that males established first breeding territories that were significantly closer to their post-fledging location than to their natal sites or to post-fledging locations of other conspecifics, but these patterns were not apparent in females. Our findings suggest that familiarity with potential breeding sites may be important for juveniles of migratory species, particularly for the sex that acquires and advertises breeding territories. Exploratory dispersal prior to a migrant's first autumn migration may contribute toward its breeding success the following year, further highlighting the importance of early seasonal breeding on fitness and population dynamics more generally.

Cooperative Behaviors in Group-Living Spider Mites

Cooperative behaviors are evolutionary stable if the direct and/or indirect fitness benefits exceed the costs of helping. Here we discuss cooperation and behaviors akin to cooperation in subsocial group-living species of two genera of herbivorous spider mites (Tetranychidae), i.e., the largely polyphagous Tetranychus spp. and the nest-building Stigmaeopsis spp., which are specialized on grasses, such as bamboo. These spider mites are distributed in patches on various spatial scales, that is, within and among leaves of individual host plants and among individual hosts of single or multiple plant species. Group-living of spider mites is brought about by plant-colonizing foundresses ovipositing at local feeding sites and natal site fidelity, and by multiple individuals aggregating in the same site in response to direct and/or indirect cues, many of which are associated with webbing. In the case of the former, emerging patches are often composed of genetically closely related individuals, while in the case of the latter, local patches may consist of kin of various degrees and/or non-kin and even heterospecific spider mites. We describe and discuss ultimate and proximate aspects of cooperation by spider mites in host plant colonization and exploitation, dispersal, anti-predator behavior, and nesting-associated behaviors and conclude with theoretical and practical considerations of future research on cooperation in these highly rewarding model animals.

First Satellite Telemetry Study of Movement Behavior of Juvenile Golden Eagles from Mexico

ABSTRACT The southern limit of the Golden Eagle's (Aquila chrysaetos) breeding range in North America is Mexico, where the eagle is the national symbol yet designated as a threatened, high priority species for conservation action. Movement information needed for conserving Mexico's Golden Eagles is sparse; knowledge of dispersal from natal areas is essential to understand the eagle's ecology and help provide for its management. Using satellite telemetry data, we analyzed movements of three males and one female from central Mexico during their first year of life; we documented (1) timing and distance of initial dispersal movements, (2) total distance traveled and maximum distance from natal site by month of age following fledging, and (3) size of areas (based on 95% adaptive local convex hulls) across which eagles ranged following initial dispersal. Individual eagles dispersed from their natal areas between mid-September and mid-November, at 6–8 mo of age. Monthly total distance traveled by males reached approximately 350–1350 km at 8–11 mo; the female's peak monthly travel was 3000 km, at age 7 mo. Monthly proximity to natal sites by individuals at ages 8–12 mo was relatively constant, averaging 17.9 km (SD = 5.7) to 129.1 km (SD = 11.3). After dispersal, the monthly ranging areas overall increased during the first year of life for all eagles, especially the female, due mainly to multiple long-distance excursions. Our data suggest that movement behavior of juvenile Golden Eagles from Mexico is mostly similar to that of conspecifics from nonmigratory populations elsewhere. Our study may help serve as a foundation for future work to better understand movement dynamics and resource selection by Mexico's Golden Eagles.

Determinants of nest box local recruitment and natal dispersal in a declining bird population

Recruitment and dispersal are important demographic rates and studying their determinants is particularly important in the current context of global anthropogenic perturbations. In birds, and especially for migratory species, assessing these rates is challenging because of the difficulties involved in tracking individuals beyond fledging. Here we assessed the determinants of nest box local recruitment and natal dispersal distances in a declining aerial insectivore, the tree swallowTachycineta bicolor. We used a 16‐year dataset obtained from the long term monitoring of a population breeding within a 10 200‐km2study system located along a gradient of agricultural intensification in southern Québec, Canada. Yearly nest box local recruitment rates ranged there in between 1.0% and 3.2%. Heavier nestlings who fledged earlier were more likely to recruit. Natal dispersal distances were generally short (mean ± SD = 12.7 ± 13.8 km) in the study system and were influenced by different factors depending on sex. Females dispersed over shorter distances when conspecific occupancy on breeding site was high, while males dispersed farther in the presence of competing house sparrowsPasser domesticusand when their mother was young. Selection of breeding locations appeared to take place at multiple scales and individuals recruited in sites with characteristics similar to their natal sites. Our results provide important information concerning the factors influencing nest box local recruitment and natal dispersal dynamics of this migratory species. These factors should be considered in conservation practices for this species in order to support production of recruits in habitats favorable to their survival.

Evidence of an olfactory imprinting window in embryonic Atlantic salmon

AbstractSalmonid olfactory imprinting during the parr‐to‐smolt transformation (PST) is essential for successful homing to natal spawning sites years later by mature fish. However, in many species, juveniles may move away from spawning sites before the PST, yet home to the natal site as adults, indicating that there may be multiple imprinting windows. To test the hypothesis that olfactory learning can occur prior to the PST, we exposed Atlantic salmon (Salmo salar) to the imprinting odorant L‐arginine at the alevin stage. Odour exposures were conducted in both brook and well water to test whether environmental characteristics of the rearing water affected endocrine and imprinting responses. Changes in thyroid hormone concentration differed over the course of development between water sources (p < .001). In brook water, fish experienced a plateau in thyroxine concentrations coinciding with the L‐arginine exposure, but a continued decline was observed in those kept in well water. In subsequent experiments, migratory stage adults from the brook water‐reared group exposed to L‐arginine spent significantly more time than control fish (p < .04) in the L‐arginine odour arm of a two‐choice maze, whereas the well water‐reared group's responses did not differ from those of the control group. Our findings provide physiological and behavioural evidence supporting the hypothesis that imprinting in Atlantic salmon can occur before the PST. These results indicate that the water source during development may affect the ability to imprint and may have implications for hatchery programmes that often incubate salmonids in well water during the alevin life stage.

Dispersal from the Natal Colony of the Grey Heron Ardea cinerea Nesting in Poland

Natal dispersal is the movement from the natal site to the colony of the first reproduction, while breeding dispersal is the movement from one breeding colony to another within or between breeding seasons. These processes are major determinants of genetic structure and a key component of population dynamics. In this study we investigated whether age of recovered bird (immatures, adults) and/or period (three multi-year periods characterized by various climate change dynamics) of recovery from the breeding season affect distance and direction of dispersal from the natal colony in Grey Herons Ardea cinerea nesting in Central Europe, in Poland. We found that the distance of dispersal from the natal area for Grey Herons ranged from 0 to 392 km with mean ± SD 84.1 ± 99.1 km (N = 72). Independently of periods, individuals recovered as immatures had longer dispersal distance than those recovered as adults. Our study revealed that proportion of recoveries representing strong natal fidelity (within the distance of ≤ 38 km around the natal colony, N = 37, 51.4%) differed significantly between the studied periods with the highest proportion (71%) in 1981–2014 and lower proportions in periods 1932–1939 (35%) and 1940–1980 (27%). We also found that the distance of dispersal from the natal colony was affected significantly by the period, with the distance in 1980–2014 being significantly shorter compared to 1940–1980 and with a tendency to be shorter than in 1932–1939. Direction of dispersal from the natal colony was affected significantly neither by period nor age of recovered birds. On average Grey Herons dispersed with a marked SW directional component. Our results indicate that Central European population of Grey Herons have shortened average distance of dispersal from the natal colony since the 1930s. This observation is concordant with changes reported for other European waterbirds.

Natal dispersal of Whooping Cranes in the reintroduced Eastern Migratory Population.

Natal dispersal is a key demographic process for evaluating the population rate of change, especially for long‐lived, highly mobile species. This process is largely unknown for reintroduced populations of endangered avian species. We evaluated natal dispersal distances (NDD) for male and female Whooping Cranes (Grus americana) introduced into two locations in central Wisconsin (Necedah National Wildlife Refuge, or NNWR, and the Eastern Rectangle, or ER) using a series of demographic, spatial, and life history‐related covariates. Data were analyzed using gamma regression models with a log‐link function and compared using Akaike information criterion corrected for small sample sizes (AICc). Whooping Cranes released in the ER dispersed 261% further than those released into NNWR, dispersal distance increased 4% for each additional nesting pair, decreased about 24% for males as compared to females, increased by 21% for inexperienced pairs, and decreased by 3% for each additional year of age. Natal philopatry, habitat availability or suitability, and competition for breeding territories may be influencing observed patterns of NDD. Whooping Cranes released in the ER may exhibit longer NDD due to fragmented habitat or conspecific attraction to established breeding pairs at NNWR. Additionally, sex‐biased dispersal may be increasing in this population as there are more individuals from different natal sites forming breeding pairs. As the population grows and continues to disperse, the drivers of NDD patterns may change based on individual or population behavior.

Cooperative den maintenance between male Japanese badgers that are delayed dispersers and their mothers

In some vertebrates, sexually mature individuals delay dispersal from their natal sites. Delayed dispersers are known to help their parents in many species; however, few studies have investigated the behavior of delayed dispersers in carnivores. Male offspring of the Japanese badger, Meles anakuma, remain in their natal sites and share setts with their mothers well after reaching sexual maturation. In this study, we investigated the contribution of male delayed dispersers in den maintenance activities of digging and bedding at their setts from September to February between 2010 and 2018. We found that delayed dispersers contributed approximately 60 and 30% of digging and bedding tasks, respectively. Specifically, while digging was constantly performed throughout the surveyed period, efforts in bedding gradually increased from September to February. We also found that delayed dispersers occasionally performed digging and bedding simultaneously with their mothers and siblings. Mothers may allow the male offspring to remain in the natal sites because of their help with den maintenance. It is probably advantageous for the males to remain in a familiar environment and have access to resources until they become large and competitive enough to establish and defend their mates and their own territories. Digital video images related to the article are available at http://www.momo-p.com/showdetail-e.php?movieid=momo210707ma01a, http://www.momo-p.com/showdetail-e.php?movieid=momo210707ma02a, http://www.momo-p.com/showdetail-e.php?movieid=momo210707ma03a, http://www.momo-p.com/showdetail-e.php?movieid=momo210707ma04a, http://www.momo-p.com/showdetail-e.php?movieid=momo210707ma05a, http://www.momo-p.com/showdetail-e.php?movieid=momo210707ma06a and http://www.momo-p.com/showdetail-e.php?movieid=momo210707ma07a.

Northerly dispersal trends in a lowland population of Peregrines Falco peregrinus in southwest England

ABSTRACT Little is known about the post-natal dispersal of Peregrines Falco peregrinus from lowland areas of England. We used the resighting and recovery data from 66 Peregrine nestlings (34 females, 32 males) colour-ringed in the southwest of England to outline their reported dispersal movements. Our results revealed that Peregrines, in particular females, disperse in a north-northeasterly direction, with females being resighted at greater distances than males. Males were resighted a mean of 44 km from their natal site and females significantly further (mean 117 km). Despite more recent local and regional declines in some areas of their UK range, Peregrines have been increasing at a national level in England and extending their breeding range into new areas. Our results indicate that Peregrines have the potential to continue occupying suitable vacant habitats across the UK. Dispersing birds from the southwest of England are potentially helping to increase the breeding population of Peregrines in other areas where they have been absent or scarce for many years.

Calving rates, long-range movements and site fidelity of southern right whales (Eubalaena australis) in south-eastern Australia

Within New Zealand and eastern Australia, over 58,000 southern right whales were harvested by commercial whalers between 1790 and 1980, with approximately 19,000 harvested from south-eastern Australia. Local extirpation is believed to have led to a loss of cultural memory of calving areas, contributing to the limited recovery of the south-eastern Australian population. While the number of whales observed using the south-eastern Australian coastline is increasing, there has been no change over three decades in the annual abundance of cow-calf pairs at Logans Beach in Warrnambool, Victoria, the only established calving ground in the region. Knowledge of life history parameters of the south-eastern Australian population is lacking. Here, we examine sightings and photo-identification data from southern Australia to investigate calving intervals, long range movements and fidelity to the Logans Beach nursery ground. Sightings data revealed at least 93 calves were born at Logans Beach between 1980 and 2018 (an average of 2.6 per year) with a mean calving interval of 3.5 ± 1.0 years (± SE, n = 34). Comparison between photo-identification catalogues compiled for south-eastern and south-western Australian populations shows that southern right whales are wide ranging within southern Australian waters. Females can be sighted at locations as far apart as 3,800 km across seasons and there is overlap in the wintering range of the south-eastern and south-western populations, with at least 7% of whales using both regions. We also provide the first report of an Australian southern right whale female with strong site fidelity to a calving area in one region relocating long-term to a calving area in another region. This work highlights several knowledge gaps, such as; the location of feeding and conception grounds for this population as well as the degree of mixing between the two Australian populations outside their wintering areas. In addition, the proportion of female calves born at Logans Beach returning to their natal site to calve remains unclear. Our work provides the first assessment of calving rates, movement and site fidelity within the south-eastern Australian population, critical for understanding constraints to recovery and informing conservation management of southern right whales in Australia. Targeted, long-term monitoring programs across the south-eastern Australian region are needed to provide demographic information on which to base predictions of the impacts of anthropogenic threats such as noise disturbance, entanglement and vessel strike.

Natal Dispersal of Aplomado Falcons in Chihuahua, Mexico

The persistence of a species throughout its geographic range requires dispersal among its populations. The study of dispersal is particularly relevant for species whose geographic range has contracted, such as the endangered Northern Aplomado Falcon (Falco femoralis septentrionalis). We used Argos 5-g PTT-100 satellite transmitters to determine the movements of two wild Chihuahuan Desert Aplomado Falcons (one female and one male) from fledging to breeding (male), or transmitter failure (female), at 1062 d and 439 d of age, respectively. Both falcons dispersed from their natal territories 2–3 mo after fledging. These falcons then wandered between activity centers near historic breeding territories and some territories recently converted to farmlands. These two falcons also explored areas outside known breeding areas via some long-distance movements to areas of potential breeding habitat being converted to farmland. In 2 yr, movements of the male covered 7412 km2. This falcon nested unsuccessfully with an unbanded female in a vacant breeding territory 15 km from his natal site. His nesting attempt the following year yielded two fledglings. While a breeding bird, the male falcon had a home range of 200 km2. For 17 mo, the female falcon wandered through an area of 12,136 km2. The farthest distance she traveled from her nest site prior to transmitter failure was 154 km.

Production and outmigration of young-of-year northern pike Esox lucius from natural and modified waterways connected to Lower Green Bay, Wisconsin.

Production and outmigration of young-of-year (YOY) northern pike from natal sites in Lower Green Bay, WI, USA, were documented over three consecutive years (2013-2015). We tested the hypothesis that spawning success and outmigration characteristics of YOY northern pike would vary among natural and anthropogenically modified habitats. Sixteen focal study locations were surveyed, including a restored natural wetland, agricultural drainage ditches, a flooded forested wetland and several unimpounded tributaries. We collected 1469 YOY northern pike with most individuals (N= 1163) originating from a flooded forested wetland on the east shore. Most sites produced YOY in all years (range N= 2-1145 individuals among study years). Outmigration ranged between 1 and 40 days during 2013-2015. Greater production and extended outmigration times occurred at most sites in 2014 (range 17-40 days) when the region experienced a late spring with heavy precipitation. In contrast, the lowest production and shortest outmigration period occurred at most sites in 2015 (range 14-23 days) when environmental conditions reflected regional averages. Outmigration began nearly 3 weeks earlier in 2015 (5/8) than in other study years (8 June 2013 and 25 May 2014). Total length (TL) of outmigrating northern pike ranged between 17 and 138 mm. Total length of YOY was significantly different among sites in 2013 and 2014, with the smallest fish (17 mm TL) outmigrating from agricultural ditches in both years. There were no significant variations in size among sites in 2015 (range 21-95 mm TL). Our results indicate significant variation in YOY northern pike outmigration characteristics within Lower Green Bay that may reflect the interplay between adult spawning site selection and annual weather patterns. Our findings highlight the importance of quantifying overlooked habitats in regions of mixed development.

Survival and sexual maturity of sexually propagated Acropora verweyi corals 4 years after outplantation

Most coral reef restoration efforts are carried out over 1–2 years, and few have assessed long‐term (over 3 years) outcomes. Although studies of outplantation of sexually propagated corals have reported promising initial results, few studies have followed outplanted corals to maturity. Here, we monitored sexually propagated Acropora verweyi corals for 4 years post‐outplantation to determine their survival and sexual maturity. These corals were outplanted when 4 months old in two size classes (small = 0.3–0.5 cm; large = 1.0–1.5 cm) at two sites in the northwestern Philippines. Four years after outplantation, the 240 colonies of A. verweyi exhibited 17.9% survival, with mean diameters ranging from 7.48–26.8 cm. Most of the surviving outplants were gravid (81.4% of the 43 colonies) with mean diameters of at least 11.8 cm. Higher survivorship was detected in the initial large size class outplants than in the small ones at the natal site, but not at the other site. However, 4 years after outplantation, there was no significant difference in terms of geometric mean diameter between the initial size classes or between the sites. Results show that 4‐month‐old outplants of sexually propagated corals can survive until sexual maturity and are already capable of contributing gametes for the potential recovery of degraded coral communities at age 4 years.

Juvenile Barn Owl Tyto alba dispersal: a radio-tracking study of roost site selection in relation to landscape features

ABSTRACT Capsule Radio-tracking of 19 juvenile Barn Owls Tyto alba alba in England revealed different spatial patterns for males and females, that tree branches were frequent roost sites, and that altitudinal distribution changed after owls acquired home ranges. Aims To gain new understanding of the natal dispersal of Barn Owls by identifying roost sites and analysing their spatial pattern, site type, altitude, and location in relation to linear features. Methods Diurnal roost sites of 19 juvenile Barn Owls were located by radio-tracking in southwest England. We evaluated the possibility of sex-bias in natal and between-roost dispersal distances and tested for change in the site types used as natal sites and daytime roosts. We tested for differences in the altitude of roosts used during the dispersal phase and those used once the birds acquired a home range, and we analysed the location of roost sites in relation to major roads, railways, and rivers. Results Barn Owls commenced dispersal when they were between 63 and 122 days after hatching (median = 94). Roost sites used by females were more widely scattered than those used by males. Owls roosted most frequently in trees, despite most natal sites being in buildings. The altitude of roost sites during dispersal in elevated landscapes was higher than those on their acquired home range. We could find no evidence that owls followed linear features during dispersal, nor that hills were barriers to dispersal. Conclusion Post-fledging roosting behaviour of female and male Barn Owls differed spatially and was congruent with a wider pattern of sex-bias in avian natal dispersal. Frequent roosting on tree branches had implications for exposure to adverse weather. Some juveniles roosted at altitudes that were higher than subsequent roosts on their acquired home range. We found no evidence to support the proposal that linear landscape features constituted dispersal corridors.

Post-breeding flocks of White Storks Ciconia ciconia in southern Poland: size, age composition and the geographical origin of birds

ABSTRACT Capsule White Storks Ciconia ciconia forming migrating flocks in southern Poland in autumn came from central Poland and eastern Germany, and used ploughed fields and cut meadows to forage before they moved south. Aims The aim of this study was to collect information on the flocking behaviour of the White Stork in southern Poland, with a special focus on the origins of birds forming flocks, flock size, age characteristics of birds, and habitat selection. Methods During a study conducted in 2012–2019 in southern Poland, we recorded the size, age composition and geographic origin of White Storks forming autumn flocks. The collection of the large number of records was made possible by the use of a small aeroplane during the first two years of the study, which enabled us to locate flocks over a large study area. Results In total, 5685 storks were observed, with a median flock size of eight individuals, although flock size varied during the migration period and by time of day. For the 2980 birds for which age could be determined, there was a higher proportion of adults (55.7%) than juveniles (44.3%). Analysis of data from ringed birds showed that the mean (±sd) distance travelled from natal sites was 277.3 ± 245.3 km, with birds coming mainly from southern Poland and eastern Germany. Storks foraged mainly in ploughed fields and cut meadows, and such habitats appear crucial for fuelling before migration. Conclusions Southern Poland provides an important stop-over site for migrating White Storks, which originate from a potentially large area. Hence, ensuring the continued availability of autumn foraging for White Storks in southern Poland benefits not only local birds but also a much larger population.

Site characteristics influence Andean bear natal-den selection in dry forest habitat

Natal dens are critical for reproduction in bears, yet we know virtually nothing of Andean bear (Tremarctos ornatus) denning ecology, nor whether female Andean bears select dens or den sites with specific characteristics. We analyzed data from 2008 to 2013 on characteristics of 8 natal dens (shelter and surroundings within 5 m) and den sites (context at ≥50 m from den) used by 4–5 females, with 21 potential (suitable but unused) natal dens and 30 potential den sites in the equatorial dry forest of Cerro Venado, Lambayeque, Peru. All observed natal dens were preexisting cavities under rocks, <5 m from a cliff. Natal dens had 1–2 entrances that varied in diameter (mean ± SE = 66.3 ± 9.01 cm). Maximum resting dimension within these dens was >2 m (242.3 ± 32.97 cm) and minimum vertical height within the resting area was <1.5 m (71.0 ± 10.93 cm). We found no evidence that female Andean bears preferred natal dens with any of the measured characteristics. Thus, if females in this area are selective when seeking a natal den, they are selective based on den site characteristics. All natal den sites were <50 m from a cliff and at relatively high elevations for this study area (887.8 ± 73.73 m above sea level). Sites were relatively steep (37.4 ± 6.38°), rugged (168.4 ± 26.29), and not obviously close to water (0.9 ± 0.21 km). Variables based on elevation and slope best described female use of natal den sites. Food, water, and solar heating seemed not to affect use of sites. Our results suggest that topographic resistance to travel by humans and other large mammals affects natal den site use in this area, and possibly elsewhere. The relevant topographical characteristics can be evaluated remotely, so conservation planners can model where natal den sites may occur in other habitats.

Breeding dispersal movements of Dupont’s Lark Chersophilus duponti in fragmented landscape

SummaryUnderstanding patterns of dispersal behaviour of threatened species is important in conservation biology and population ecology, especially in fragmented landscapes. Dupont’s Lark Chersophilusduponti is a threatened passerine whose European population has declined by around 40% in the last decade. To study natal and breeding dispersal of the species, we used a long-term mark-recapture dataset (2011–2019) and analysed the records of 32 males (39 dispersal movements) and five females (five dispersal movements) captured during the breeding season at Rincón de Ademuz (Valencia, eastern Spain). Adult birds had a median breeding dispersal of 154 m (Q25-Q75 = 70.0–300.3). Among these captures, two adult males dispersed to a new patch of habitat separated by more than 5,800 m. Only one out of 26 nestlings ringed was trapped as an adult bird, which occurred at a site different from the natal territory (4,500 m). Our results show a low breeding dispersal for the species and are, in essence, in agreement with previous studies carried out in the Ebro Valley metapopulation, one of the core areas for the species in Europe. Nonetheless, unlike in the Ebro Valley, we detected movements of adult birds between habitat patches. The low recovery rate of young birds suggests that they left their natal sites and moved outside the study area or that their survival rate was very low. Future studies focused on the post-fledging survival rate and natal dispersal movements are essential to determine effective conservation measures for the species. Habitat management actions in occupied and potential sites should be carried out close to the areas inhabited by the species to increase the success rate of the interventions and the effective dispersal and therefore population connectivity.

Partitioning maternal and exogenous diet contributions to otolith 87Sr/86Sr in kokanee salmon (Oncorhynchus nerka)

Strontium isotopes (87Sr/86Sr) recorded in the otoliths of Pacific salmon (Oncorhynchus spp.) are commonly used to identify natal origin. For species that migrate at or soon after emergence, the embryonic region of the otolith provides the only record of provenance. However, maternal contribution of Sr from the yolk can confound the isotopic signature of the natal site. We experimentally quantified maternal and exogenous diet contributions to otolith 87Sr/86Sr over embryonic development in kokanee salmon (Oncorhynchus nerka). Eggs from two populations in isotopically distinct lakes were incubated and reared in a common water source. Timing of developmental events and proportional contribution from yolk to otolith 87Sr/86Sr differed significantly between the two populations. We suggest that the magnitude of difference in 87Sr/86Sr between yolk and water, the relative concentrations of Sr and Ca in these isotopic sources, and population-specific effects on otolith growth and composition contribute to this variation. Understanding how these factors affect otolith 87Sr/86Sr could extend the use of otolith geochemistry for determining provenance to species and populations in which natal site rearing is limited.