Breeding Aggregations Research Articles

Migration dynamics simulation of migratory fish in rivers

The decline of migratory fish stocks is a major problem facing the global aquatic ecosystem. Understanding the dynamics of fish migration and their entire life history is crucial for quantitatively assessing the impact of natural and anthropogenic barriers on migratory fish and to understand the mechanisms of their decline. However, this understanding is largely ambiguous due to limited field survey data in the absence of models. Although Huang and Wang (Curr. Biol. 28, 2018, 3640–3647) and Huang (iScience 19(9), 2019, 772–785) proposed a Migration Dynamics Model (MDM) to describe the upriver and downriver migration processes of the Chinese sturgeon, but a crucial intermediate link—the breeding aggregation process—is still missing, while the standard Crank-Nicolson scheme, a common computational method, of finite difference methods cannot adapt to the model parameters changing with time and space. Here we propose a six-point implicit scheme to address the complexity of model parameters. The parameters of migration speed and diffusion coefficient are decomposed into fish-related and current-related components for analyzing their effects on model parameters and estimating them. Additionally, we propose a parameterization method for the aggregation process of spawners during the breeding season by introducing a set of clustering functions. Next, we examine the complete migration processes of adult and juvenile Chinese sturgeons in the Yangtze River and elucidate the underlying mechanisms behind the fish migration dynamics, including their spatiotemporal distributions, aggregation behavior, and migration schedule. We discover that the Gezhouba Dam (GD) significantly impacted the breeding aggregation behavior of Chinese sturgeon during the breeding season. The GD altered the distribution of fish along their migration path and schedule. Prior to the construction of the dam, 99.9 % of the total Chinese sturgeon were able to reach the 240 km-long spawning ground. However, after the dam was built, only 36.7 % were able to reach the 30 km-long spawning ground below the GD on the day of mating. Finally, we discuss the aggregation phenomenon and its driving factors during Chinese sturgeon migration, and categorize it into three types, namely biotic-driven, abiotic-driven and dual-driven aggregation behaviors. We reveal the existence of aggregations for non-biological reasons, such as the slowdown of fish migration speed induced by natural and anthropogenic barriers and estuarine tidal effects.

Monitoring population-level foraging distribution of a marine migratory species from land: strengths and weaknesses of the isotopic approach on the Northwest Atlantic loggerhead turtle aggregation

Assessing the linkage between breeding and non-breeding areas has important implications for understanding the fundamental biology of and conserving animal species. This is a challenging task for marine species, and in sea turtles a combination of stable isotope analysis (SIA) and satellite telemetry has been increasingly used. The Northwest Atlantic (NWA) loggerhead (Caretta caretta) Regional Management Unit, one of the largest sea turtle populations in the world, provides an excellent opportunity to investigate key biological patterns as well as methodological aspects related to the use of stable isotopes to infer spatial distribution of turtles in foraging areas. We provide the first comprehensive assessment of the annual distribution of NWA adult female loggerheads among foraging areas and investigate the efficacy of various analytical approaches as well as the effect of sample size in these types of studies. A total of 5168 individual females were sampled from seven Management Units (MUs) between 2013-2018. We provide the first estimate of the proportion of females originating from each MU that uses each foraging area and show how this proportion varies over time. We also estimate the relative importance (in terms of number of turtles) of each foraging area to the overall loggerhead breeding aggregation nesting in Florida and in the NWA for each year of the study. The foraging area used by reproductively active females differs considerably across MUs. One of these, the Subtropical NWA, is by far the most important foraging area in terms of both number of individuals and genetic diversity, and therefore this region may be considered as a conservation priority. Through simulations, we show that limited sizes of sample groups (unknowns; training; priors) may result in false geographic differentiation and consequently mislead interpretations. We provide thresholds and methodological recommendations for future studies. This study establishes a fundamental baseline for monitoring the annual contribution of foraging area to a terrestrial-based breeding aggregation of a marine animal in a cost-effective way. This type of monitoring allows for early detection of changes in foraging distributions—a possible effect of climate change on marine ecosystems or of area-specific anthropogenic threats.

Male Cope’s gray treefrogs (Hyla chrysoscelis) in amplexus have elevated and correlated steroid hormones compared to solitary males

Gonadal steroid hormones are typically elevated during the breeding season—a finding known as an associated reproductive pattern. Though less studied, there is also evidence, in both sexes, for elevated adrenal/interrenal steroids, including acute elevations on the day of mating. I investigated gonadal and interrenal steroids in wild male Cope’s gray treefrogs at breeding aggregations. I collected blood from males found in amplexus with female mates (amplexed males) and males sampled at the same time and location that were actively advertising vocally and without a mate (solo males). Concentrations of plasma corticosterone, testosterone, and 17β-estradiol (CORT, T and E2, respectively) were validated and measured. These two categories of males differed in four ways: (1) amplexed males exhibited significantly elevated concentrations of all three steroids compared to solo males (CORT: +347 %; T: +60 %; and E2: +43 %); (2) these hormone profiles alone accurately predicted male mating category with ca. 83 % accuracy using a discriminant function analysis; (3) amplexed males exhibited significant between-hormone correlations (T and E2 were positively correlated and CORT and E2 were negatively correlated) whereas no correlations were found in solo males; (4) amplexed males showed a negative correlation with CORT concentration and the time of night, whereas no such pattern was present in solo males. These findings suggest an acute and strong coactivation of the interrenal and gonadal axes that could drive phenotypic integration during this fitness-determining moment. I discuss these findings and suggest experiments to determine causation, including the role of motor behavior driving endocrine states and the role of female selection on endocrine profiles.

Анализ структурной организации сообщества крупных хищных птиц Ремдовского заказника

Анализ структурной организации сообщества крупных хищных птиц Ремдовского заказника

Multimale breeding aggregations by “many-friends” snakes: courtship behaviours by Malagasy Pseudoxyrhophiine snakes, Dromicodryas bernieri and D. quadrilineatus, and their sexual size dimorphism

When several male snakes dispute over one female in the breeding season, two major male-male rivalries are known to occur: male-male combat and multimale breeding aggregation. The roles of male body size and the degree of sexual size dimorphism are different between these rivalries. We report field observations of mating behaviour including a multimale breeding aggregation of pseudoxyrhophiins, Dromicodryas bernieri and D. quadrilineatus, in northwestern Madagascar, which have a local name, “Maro longo”, meaning “many friends”. To examine the relationships between sexual size dimorphism and mating strategies of males, we also analysed the body size of the two species of Dromicodryas and two other pseudoxyrhophiins, Leioheterodon madagascariensis and L. modestus, which are known to exhibit the male-male combat. Our data obtained during a long-term field study showed that D. bernieri and D. quadrilineatus have female-biased sexual size dimorphism, whereas L. madagascariensis and L. modestus have male-biased sexual size dimorphism. This result conforms to the general tendency of the relationship between body size and male-male rivalry in snakes.

Ecology and evolution of bird sounds

Birds are among nature's most social animals. They are renowned for their group migrations, their cooperative foraging, their communal roosting, their synchronous breeding aggregations, their precise parent-offspring interactions, their coordinated group defenses and their intricate territorial and courtship rituals. In these and other contexts, and indeed in most moments of their lives, birds' capacities to navigate complex social demands and relationships can tip the balance between health or sickness, between reproductive success or failure, between life or death. It is thus no surprise that birds have evolved sophisticated systems for mediating social interactions. Foremost among these are communication signals, most evident in birds as songs, calls, color patterns and postural displays. These and other communication signals can transmit information about a signalers' status, motivations and possible future actions, for sensory and cognitive processing by signal receivers. In general, signals provide benefits for both signal senders and receivers. Consider the bright spring plumage of a male wood warbler who has established a breeding territory. The male's plumage pattern benefits him by signaling his 'ownership' of his territory, which can help him attract potential mates and preempt conflict with potential rivals. His plumage pattern also benefits his intended audiences: it informs females about the signaler's potential as a mate, and it informs other males about the degree of threat they might face were they to attempt a territory take-over. Communication signals are, in essence, a glue that maintains the cohesion of bird societies, and a currency that mediates sophisticated relationships within.

Multi‐night territorial behavior, chorus attendance, and mating success in red‐eyed treefrogs

AbstractFor many frog species that aggregate around ponds or streams, chorus attendance, the percentage of time or nights a given male is present and actively calling at an aggregation, is the strongest documented predictor of inter‐male variation in reproductive success in the wild. Males are, thus, thought to compete via endurance rivalry, where available energetic reserves and individual physiology interact to determine chorus tenure. Frogs often exhibit territorial behavior within these aggregations, and territorial status is likely to influence a male's rate of energy expenditure. While males of several anuran species have been shown to hold territories across nights, it is not well understood whether such calling site fidelity is correlated with chorus attendance or mating success. Using subdermal RFID (PIT) tags to minimize disturbance to chorus structure, we quantified site fidelity, chorus attendance, and mating success for all male red‐eyed treefrogs (Agalychnis callidryas) within a breeding aggregation in Panama across 50 consecutive nights. We found that nearly half of these males held territories across nights, that this cross‐night territorial behavior was highly correlated with chorus attendance, and that chorus attendance was, in turn, the strongest predictor of male mating success. Males were most faithful to calling sites containing vegetation contiguous with adjacent sites and were more likely to remain at a site if they were successful in acquiring a mate there on the previous night. To our knowledge, this is the first study linking male site fidelity to chorus attendance and mating success in anurans. While female mate choice is an established driver of lineage diversification and the evolution of sexual signals, agonistic interactions between males at breeding aggregations are well‐documented from a wide range of anuran taxa. The relationship between male–male interactions and mating success deserves broader research attention among anuran species.

Aerial Drones Reveal the Dynamic Structuring of Sea Turtle Breeding Aggregations and Minimum Survey Effort Required to Capture Climatic and Sex-Specific Effects

Quantifying how animals use key habitats and resources for their survival allows managers to optimise conservation planning; however, obtaining representative sample sizes of wildlife distributions in both time and space is challenging, particularly in the marine environment. Here, we used unoccupied aircraft systems (UASs) to evaluate temporal and spatial variation in the distribution of loggerhead sea turtles (Caretta caretta) at two high-density breeding aggregations in the Mediterranean, and the effect of varying sample size and survey frequency. In May–June of 2017 to 2019, we conducted 69 surveys, assimilating 10,075 inwater turtle records at the two sites. Optimal time interval between surveys to capture the dynamics of aggregations over the breeding period was <2-week intervals and >500 turtles (from the combined surveys). This minimum threshold was attributed to the core-area use of female turtles shifting across surveys in relation to wind direction to access warmer nearshore waters and male presence. Males were more widely distributed within aggregations than females, particularly in May when mating encounters were high. Most males were recorded swimming and oriented parallel to shore, likely to enhance encounter rates with females. In contrast, most females were generally stationary (resting on the seabed or basking), likely to conserve energy for reproduction, with orientation appearing to shift in relation to male numbers at the breeding area. Thus, by identifying the main factors regulating the movement and distribution of animals, appropriate survey intervals can be selected for appropriate home range analyses. Our study demonstrates the versatility of UASs to capture the fine-scale dynamics of wildlife aggregations and associated factors, which is important for implementing effective conservation.

Novel passive detection approach reveals low breeding season survival and apparent lactation cost in a critically endangered cave bat.

Capture-mark-recapture/resight (CMR) methods are used for survival-rate studies, yet are often limited by small sample sizes. Advances in passive integrated transponder (PIT) technology have enabled passive detection or ‘resight’ of marked individuals using large antennas with greater read-ranges than previously possible. We used passively-detected resight data and CMR models to study survival rates of the southern bent-winged bat Miniopterus orianae bassanii, a critically endangered, cave-dwelling bat. Over three years, we used PIT-tagging to monitor 2966 individuals at the species’ largest breeding aggregation, using daily detection data (> 1.6 million detections) to estimate seasonal survival probabilities, structured by age, sex and reproductive status, and parameterise population projection matrices. This has hitherto been impossible using traditional CMR methods due to disturbance risk and low recapture rates. Bats exhibited lowest apparent seasonal survival over summer and autumn, particularly for reproductive females in summer (when lactating) and juveniles in autumn (after weaning), and high survival in winter. Lowest survival rates coincided with severe drought in summer–autumn 2016, suggesting that dry conditions affect population viability. Under all likely demographic assumptions, population projection matrices suggested the population is in deterministic decline, requiring urgent action to reduce extinction risk. Passively-collected resight data can now be used in combination with CMR models to provide extensive, robust information for targeted wildlife population management.

Residency and movement patterns of adult Port Jackson sharks (Heterodontus portusjacksoni) at a breeding aggregation site.

Examining the movement ecology of mesopredators is fundamental to developing an understanding of their biology, ecology and behaviour, as well as the communities and ecosystems they influence. The limited research on the residency and movements of benthic marine mesopredators has primarily used visual tags, which do not allow for the efficient and accurate monitoring of individual space use. In this study, the authors investigated the residency and movement patterns of Port Jackson sharks Heterodontus portusjacksoni (Meyer 1793) at a breeding aggregation site in Jervis Bay, south-eastern Australia, using passive acoustic telemetry to further our understanding of the movement ecology of these important mesopredators. Between 2012 and 2014, individuals were tagged with acoustic transmitters, and their residency and movements within the bay were monitored for up to 4 years. H. portusjacksoni showed strong preferences for particular reefs within and between breeding seasons. Males had significantly higher residency indices at their favoured sites relative to females, suggesting that males may be engaging in territorial behaviour. Conversely, female H. portusjacksoni exhibited higher roaming indices relative to males indicating that females may move between sites to assess males. Finally, H. portusjacksoni showed temporal variation in movements between reefs with individuals typically visiting more reefs at night relative to the day, dusk and dawn corresponding with their nocturnal habits.

Confirmation Bias Perpetuates Century-Old Ecological Misconception: Evidence Against ‘Secretive’ Behavior of Eastern Spadefoots

Despite a 1944 publication questioning the misconception that Eastern Spadefoots (Scaphiopus holbrookii) and other Scaphiopodidae are ‘secretive’ outside of rain-induced migration and breeding aggregations, confirmation bias has perpetuated this fallacy. As a result, S. holbrookii is one of the least studied frogs in the United States. Amassing a large postmetamorphic dataset, we examined the misconception that S. holbrookii are secretive outside of breeding aggregates or optimal environmental conditions. Using eyeshine spotlighting, we conducted transect, mark–recapture, and haphazard spotlighting surveys in Virginia and Rhode Island forests. Although no breeding events or migration occurred during this study, we detected thousands of postmetamorphic S. holbrookii in Virginia and dozens in Rhode Island, the majority of which were subadults—a demographic category severely overlooked in the literature. These results are in direct contradiction with historical surveys of our sites. Spotlighting was an efficient method of detecting S. holbrookii eyeshine in forests, which were easily differentiated from arthropod eyeshine. Minimal effort was needed to detect the presence of S. holbrookii in Virginia and Rhode Island, even though both states have different climates and S. holbrookii densities. We also discovered a previously undetected population in Rhode Island. Scaphiopus holbrookii of all postmetamorphic size classes emerged regularly from burrows, even with no precipitation. We discuss how confirmation bias and lack of appropriate field methods for nonbreeding life history stages has fueled the misconception that S. holbrookii are difficult to find outside of optimal weather conditions, which has hindered progress studying the ecology and conservation of this species.

Development of methodology and reference intervals for the analysis of the free-ranging Atlantic horseshoe crab Limulus polyphemus hemolymph.

The Atlantic horseshoe crab, Limulus polyphemus, is valuable to fishing and biomedical industries, for education in public aquaria, and of ecological importance because the eggs provide a critical food source for migratory shorebirds. While hematologic and biochemical analyses are fundamental tools for health assessment, reports are limited for the four extant species of horseshoe crabs; Lpolyphemus (East Coast North America), Carcinoscorpius rotundicauda (mangrove horseshoe crab Southeast Asia), Tachypleus gigas, and Tachypleus tridentatus (Southeast and East Asia). This prospective study measured hemolymph values to determine RIs from free-ranging horseshoe crabs during the annual breeding aggregation in Delaware Bay, USA. Near-shore animals were briefly manually restrained for hemolymph collection from the cardiac sinus. Hematologic samples (25 males, 25 females) were collected for hemocytometer counts using the Natt and Herrick method. A second set of 50 animals (25 males, 25 females) was sampled for biochemistry measurands, including copper concentration by spectrophotometer, osmolality by vapor pressure osmometer, and protein electrophoresis. Total hemocyte counts varied widely (RI 6600-44300/µL). Electrolytes were consistent with osmoconformers living in seawater. There was a marked difference in sexes, with females showing much lower protein, glucose, and copper levels. Eleven females had multiple outliers, and all data were excluded from RI calculations. Further studies of this species outside of spawning season are needed. Expanding our knowledge of horseshoe crab health is important to decreasing morbidity and mortality in research applications and maximizing longevity and overall health in display settings.

Impact of Nest Predators on Migratory Woodpigeons Columba palumbus in Central Europe — Breeding Densities and Nesting Success in Urban Versus Natural Habitats

The Woodpigeon Columba palumbus is a species generally increasing in numbers in most of its populations, including the urban population, which, two centuries after its emergence, is still expanding across the European Lowland. New for the species is a tendency to form dense breeding aggregations in suitable urban parks, with a corresponding slower increase in some other towns. This trend was driven by the presence of important nest predators, mostly Hooded Crows Corvus corone. Another factor involved was access to open farmland within the economic range of feeding flights. Nesting success (1st brood) in urban habitats free of important predators was up to 50–77% but it fell to only 3–7% when predators appeared. Consequently, some urban populations of the Woodpigeon went into a phase of decline. In the farmland and secondary woods, the nesting success was also variable, ranging between 12 and 42% for unknown reasons. Safe urban populations produced 4–5 times more offspring per pair per season, yet their expansion was rather slow. Therefore, the urban overproduction may contribute to an increase in the total species abundance, owing to (deduced) overspill of recruits to the poorly reproducing subpopulation in the countryside. Alongside other factors such as amelioration of winter conditions and changes in agriculture, this would contribute to the documented growth of the whole population of the species. The shortage of firm data on the pristine breeding success (from extensive natural forests) remains the main obstacle to better understand the population dynamics of this migratory species.

Breeding biology of Malabar Tree Toad Pedostibes tuberculosus (Anura: Bufonidae) from Castle Rock, Karnataka, India

The Malabar Tree Toad Pedostibes tuberculosus Günther, 1876 is an endemic and endangered species from the Western Ghats biodiversity hotspot, however, its reproductive biology is barely understood. In 2018, we opportunistically encountered a breeding aggregation of P. tuberculosus at Castlerock, Karnataka, and recorded its breeding behavior. We found P. tuberculosus in the northern Western Ghats to aggregate in choruses and breed for a short duration (a couple of nights). Males physically competed in short duels to gain access to females. The males clasped the females around the armpits in a tight axillary amplexus lasting an entire night. The female in an overnight amplexus laid approximately 150 eggs. We observed the tadpoles to rapidly develop and complete metamorphosis within a month. We highlight the variation in reproductive traits in populations of P. tuberculosus distributed along the Western Ghats biodiversity hotspot which will aid in conservation and systematics of this species group.

Coastal breeding aggregations of threatened stingrays and guitarfish in the Levant

Abstract Stingrays and guitarfish are globally threatened by overexploitation, particularly so in the Mediterranean Sea. Nevertheless, very little information is known about their ecology, behaviour, and taxonomy in the Mediterranean, and especially in the Levant, where water temperature, salinity, and the impact of invasive species are relatively high. Although it has been suggested that some species may aggregate in the Levant, this has not been formally documented and the scale of this phenomenon, the taxonomic composition, and the temporal dynamics are unknown. Visual surveys were conducted, which allowed the documentation of stingrays and guitarfish behaviour, and which was not available from data based on fishery catches. The census took place within a marine protected area over a period of 3 years. Altogether, we documented 675 batoid observations. One of the observed species is Endangered (Glaucostegus cemiculus) and one is Vulnerable (Dasyatis pastinaca), whereas the others are classed as Least Concern (Torpedo torpedo and Torpedo marmorata), Data Deficient (Taeniurops grabatus), non‐assessed within the Mediterranean (Dasyatis chrysonota), and Not Evaluated (Himantura uarnak). Results show clear seasonal patterns, with dense aggregations recorded during spring and early summer, when densities reached 85 observations per kilometre. In addition, there were clear indications of breeding behaviour in D. pastinaca and D. chrysonota, including the first recorded documentation of D. pastinaca courtship in the Mediterranean. Large seasonal stingrays and guitarfish aggregations in shallow waters have not, to our knowledge, been documented in the Mediterranean Sea previously. This highlights the importance of conserving shallow habitats as potential breeding grounds. As these sites are easily reached while both snorkelling and diving, the aggregation of these charismatic species can serve as potential ecotourism sites. Finally, this study shows the benefits of using simple visual census, as opposed to catch‐based methods, to record both the diversity and the behaviour of batoids.

Individual variation in migratory movements of chinstrap penguins leads to widespread occupancy of ice-free winter habitats over the continental shelf and deep ocean basins of the Southern Ocean.

A goal of tracking migratory animals is to characterize the habitats they use and to interpret population processes with respect to conditions experienced en route to, and within, overwintering areas. For migratory seabirds with broad breeding ranges, inferring population-level effects of environmental conditions that are experienced during migratory periods would benefit by directly comparing how birds from different breeding aggregations disperse, characterizing the physical conditions of areas they use, and determining whether they occupy shared foraging areas. We therefore tracked 41 adult and juvenile chinstrap penguins (Pygoscelis antarctica) from three breeding locations in the northern Antarctic Peninsula region during the austral winter of 2017. The satellite tracking data revealed overlap of individuals over continental shelf areas during autumn months (Mar-May), shared outbound corridors that track the southern Antarctic circumpolar current front, followed by occupancy of progressively colder, deeper, and ice-free waters that spanned the entire western hemisphere south of the Polar Front. Despite broadly similar physical environments used by individuals from different colonies, the proportion of birds from each colony that remained within 500km of their colony was positively correlated with their local population trends. This suggests that local migration strategies near the Antarctic Peninsula may benefit breeding populations. However, the magnitude of inter-colony and intra-colony overlap was generally low given the broad scale of habitats occupied. High individual variation in winter movements suggests that habitat selection among chinstrap penguins is more opportunistic, without clear colony-specific preference for fine-scale foraging hotspots. Mixing of individuals from multiple colonies across broad regions of the Southern Ocean would expose chinstrap penguins from the Antarctic Peninsula to a shared environmental experience that helps explain the regional decline in their abundance.

Nestling carcasses from colonially breeding wading birds: patterns of access and energetic relevance for a vertebrate scavenger community

Energy transfer is fundamental to ecosystem processes, affecting productivity and community structure. Large aggregations of colonially breeding birds are known as nutrient sources through deposition of feces, but also may deposit large quantities of energy in the form of dead nestlings. The magnitude and ecological relevance of this process to the scavenger community is poorly understood. We used trail cameras to monitor the fates of size-appropriate chicken carcasses in heron colonies in order to quantify the proportion of available fallen nestlings that were consumed by scavengers in the Everglades of Florida, USA. Overall, 85% of 160 carcasses were consumed, with Turkey Vultures (Cathartes aura, 47%) and American Alligators (Alligator mississippiensis, 29%) being the primary consumers. Probability of consumption by alligators or vultures was related to distance from nest to water, local nesting density, and colony type. Consumption probabilities of both scavengers in relation to habitat covariates suggested clear resource partitioning promoting coexistence. We estimate fallen nestlings throughout this ecosystem could support 16% of the alligator population and 147 adult Turkey Vultures during a nesting season. This work indicates that fallen nestlings can serve as an important source of energy for scavengers at colonial breeding aggregations, particularly in oligotrophic systems.

Environmental DNA sampling reveals high occupancy rates of invasive Burmese pythons at wading bird breeding aggregations in the central Everglades.

The Burmese python (Python bivittatus) is now established as a breeding population throughout south Florida, USA. However, the extent of the invasion, and the ecological impacts of this novel apex predator on animal communities are incompletely known, in large part because Burmese pythons (hereafter “pythons”) are extremely cryptic and there has been no efficient way to detect them. Pythons are recently confirmed nest predators of long-legged wading bird breeding colonies (orders Ciconiiformes and Pelecaniformes). Pythons can consume large quantities of prey and may not be recognized as predators by wading birds, therefore they could be a particular threat to colonies. To quantify python occupancy rates at tree islands where wading birds breed, we utilized environmental DNA (eDNA) analysis—a genetic tool which detects shed DNA in water samples and provides high detection probabilities. We fitted multi-scale Bayesian occupancy models to test the prediction that pythons occupy islands with wading bird colonies at higher rates compared to representative control islands containing no breeding birds. Our results suggest that pythons are widely distributed across the central Everglades in proximity to active wading bird colonies. In support of our prediction that pythons are attracted to colonies, site-level python eDNA occupancy rates were higher at wading bird colonies (ψ = 0.88, 95% credible interval [0.59–1.00]) than at the control islands (ψ = 0.42 [0.16–0.80]) in April through June (n = 15 colony-control pairs). We found our water temperature proxy (time of day) to be informative of detection probability, in accordance with other studies demonstrating an effect of temperature on eDNA degradation in occupied samples. Individual sample concentrations ranged from 0.26 to 38.29 copies/μL and we generally detected higher concentrations of python eDNA in colony sites. Continued monitoring of wading bird colonies is warranted to determine the effect pythons are having on populations and investigate putative management activities.

Satellite surveys: a novel approach for assessing sea turtle nesting activity and distribution

Range of occurrence and abundance is a fundamental information that describes an animal population and is particularly important for species of conservation concern such as sea turtles. Although sea turtles lay clutches on land, which helps identifying breeding aggregations, the current knowledge on the distribution of these animals is far from being complete. Traditional ground surveys and more recent aerial surveys bear limitations due to logistic constraints, cost and safety concerns. We tested a novel approach based on high-resolution satellite imagery on a 12-km tract along the Atlantic coast of Florida (USA) by comparing counts from a satellite image with counts from traditional ground surveys. Daily track counts were underestimated in zones with higher human presence, probably due to tracks deleted or confounded by human activity, and overestimated in zones with lower human presence, probably due to persistence of old tracks. Results show that satellite surveys can provide the order of magnitude of nesting level in relatively undeveloped or low-frequented coastal tracts, which represent the main objective of any preliminary survey on sea turtle occurrence. Satellite imagery represents a new complementary tool available to conservationists for filling gaps about sea turtle occurrence, especially in remote or unsafe areas.

Population genetic analyses reveal female reproductive philopatry in the oviparous Port Jackson shark

Restricted gene flow and reproductive philopatry are increasingly being described in marine predators such as sharks. However, observing shark reproductive behaviour in situ is problematic because of issues associated with sampling in the marine environment. As such, molecular tools have become fundamental to unravelling complex mating behaviours. In this study, we examined patterns of genetic structure in the oviparous Port Jackson shark (Heterodontus portusjacksoni) using 10 microsatellite loci and the mitochondrial (mt)DNA control region. Patterns of genetic structure were investigated between breeding aggregations in Sydney and Jervis Bay, as well as between two sites within Jervis Bay. Significant genetic differentiation was detected between Sydney and Jervis Bay using mtDNA, but no structure was observed within Jervis Bay. No significant genetic differentiation was found with microsatellites within or between aggregations. Mean assignment index values were significantly higher for females than males in Jervis Bay, but not in Sydney. Both females and males migrate inshore during the Austral winter for breeding, but it appears females may exhibit higher levels of reproductive philopatry than males. This is the first study to document reproductive philopatry in an oviparous shark, highlighting the importance of conserving and appropriately managing breeding sites for H. portusjacksoni and potentially other oviparous shark species.