Avian Predators Research Articles

Do ditch‐side electric fences improve the breeding productivity of ground‐nesting waders?

Abstract Insufficient reproduction as a consequence of predation on eggs and chicks is a major determinant of population decline in ground‐nesting birds, including waders. For many populations, there is an urgent need to maintain breeding populations at key sites, and conservation practitioners need to find viable management solutions to reduce predation. One tool available to the practitioner is fences that exclude key predators from areas containing breeding birds. Temporary electric fencing is an increasingly popular predator exclusion intervention, but such fences have costs associated with purchase and the time needed to erect and maintain them. Their effectiveness and optimal application are also frequently questioned. We evaluate the use of temporary ditch‐side four‐strand electric fences in lowland grasslands in two countries, The Netherlands and England, in areas containing high densities of breeding waders. In both countries and in all years, godwit and lapwing nest survival was significantly higher within areas enclosed by ditch‐side electric fences. Brood survival, assessed for godwits in The Netherlands, was also higher within fenced areas in all years. This demonstrates that using temporary electric fences to enclose ground‐nesting birds can be an effective tool for improving breeding productivity. In our study, closely managed electric fences were effective at excluding red foxes Vulpes vulpes, but not avian and other mammalian predators. The positive effect that electric fencing had on nest and brood survival therefore likely results from a reduction in the total number of visits by mammalian predators, and especially visits by foxes. Although it requires a substantial time investment throughout the period of use, our temporary electric fence design provides flexibility compared to other fence designs when it comes to enclosing different areas within a season and between years, as the targets for protection change or as land and flood management dictate. This conservation intervention can help buy the time required to develop and implement longer term solutions for application at larger scales.

Linking agri‐environment scheme habitat area, predation and the abundance of chick invertebrate prey to the nesting success of a declining farmland bird

Abstract1. Across Europe, farmland bird populations have continued to decline since the 1970s owing to the intensification of farming practices. Studies of such declines have tended to focus specifically on either the impacts of habitats (nesting and foraging), nest predators or prey availability on bird demographics. The study presented here provides new insights into the relative effects of each of these factors on yellowhammer nest survival. The yellowhammer was selected for this study as it is a UK Red‐Listed bird species whose population is in decline across much of Europe.2. We use a long‐term dataset of 147 nests, monitored between 1995 and 2007, to provide an insight into how yellowhammer nest survival is influenced by nesting habitat (nest concealment and nest height), foraging habitats (habitat coverage within 100 m of nests), the removal of nest predators (magpiePicaabundance as an inverse measure of avian predator removal through gamekeeping) and food availability (measured with a D‐vac invertebrate suction sampler).3. Our results indicated that yellowhammer hatching success was negatively related to the coverage of spring agri‐environment scheme habitats, a group which represents invertebrate‐rich agri‐environment habitats, but hatching success increased with nest height. Fledging success was positively related to the coverage of the seed‐rich habitat wild bird seed mixture. The farm‐level abundance of yellowhammer chick‐food invertebrates declined over the study period.4. Our results highlight the importance of simultaneously considering multiple agents that shape avian breeding success, that is their ability to produce offspring, to inform conservation management. Our key finding for land managers relates to the positive relationship between the proportion of seed rich foraging habitat within the yellowhammer's average foraging range and yellowhammer fledging success, which shows that a habitat intended primarily to provide winter food resources is also important to breeding birds. Chick food abundance in this habitat was, however, similar to broadleaf and cereal crops. We recommend that this habitat should be provided near to potential yellowhammer nesting sites and adjacent to invertebrate‐rich agri‐environment scheme habitats such as beetle banks and conservation headlands to further boost invertebrate resources for a declining farmland bird.

Bioaccumulation of Per and Polyfluoroalkyl Substances in Antarctic Breeding South Polar Skuas (Catharacta maccormicki) and Their Prey

Per and polyfluoroalkyl substances (PFASs) are found in Antarctic wildlife, with high levels in the avian top predator south polar skua (Catharacta maccormicki). As increasing PFAS concentrations were found in the south polar skua during the breeding season in Antarctica, we hypothesised that available prey during the breeding period contributes significantly to the PFAS contamination in skuas. To test this, we compared PFAS in south polar skuas and their main prey from two breeding sites on opposite sides of the Antarctic continent: Antarctic petrel (Thalassoica antarctica) stomach content, eggs, chicks, and adults from Svarthamaren in Dronning Maud Land and Adélie penguin chicks (Pygoscelis adeliae) from Dumont d’Urville in Adélie Land. Of the 22 PFAS analysed, seven were present in the majority of samples, except petrel stomach content [only perfluoroundecanoate (PFUnA) present] and Adélie penguins (only four compounds present), with increasing concentrations from the prey to the skuas. The biomagnification factors (BMFs) were higher at Dumont d’Urville than Svarthamaren. When adjusted to reflect one trophic level difference, the BMFs at Svarthamaren remained the same, whereas the ones at Dumont d’Urville doubled. At both the colonies, the skua PFAS pattern was dominated by perfluorooctanesulfonic acid (PFOS), followed by PFUnA, but differed with the presence of branched PFOS and perfluorotetradecanoate (PFTeA) and lack of perfluorononanoate (PFNA) and perfluorodecanoate (PFDA) at Dumont d’Urville. At Svarthamaren, the pattern in the prey was comparable to the skuas, but with a higher relative contribution of PFTeA in prey. At Dumont d’Urville, the pattern in the prey differed from the skuas, with the domination of PFUnA and the general lack of PFOS in prey. Even though the PFAS levels are low in Antarctic year-round resident prey, the three lines of evidence (pattern, BMF difference, and BMF adjusted to one trophic level) suggest that the Antarctic petrel are the significant source of PFAS in the Svarthamaren skuas, whereas the skuas in Dumont d’Urville have other important sources to PFAS than Adélie penguin, either in the continent or external on the inter-breeding foraging grounds far from Antarctica.

Nest colonies of Baya Weaver Ploceus philippinus (Linnaeus, 1766) on overhead power transmission cables in the agricultural landscape of Cuddalore and Villupuram districts (Tamil Nadu) and Puducherry, India

Nesting habits of Baya Weaver Ploceus philippinus with specific reference to overhead power transmission cables was studied between April and November 2021 in the agrarian landscape of 10 villages covering Cuddalore and Villupuram districts (Tamil Nadu), and Puducherry. A total of 408 nests of various stages (wad stage-35, ring stage-21, helmet stage-227, egg-chamber closed stage-49, complete nests-22, and abnormal nests-54) and 411 birds were enumerated on 25 nest colonies. The number of nests in each colony ranged from 1 to 82. Baya Weavers had selected power cables as nesting sites despite the availability of three nest-supporting trees (n= 2,255), such as Cocos nucifera, Borassus flabellifer, and Phoenix sylvestris within 500 m of nesting cables. Birds used leaves of sugarcane Saccharum officinarum, Indian Date Palm Phoenix sylvestris, and Narrow-leaf Cattail Typha angustifolia as a source of fibres for the construction of nests. Twenty-three out of 25 nest colonies were found on power cables running over sugarcane crops. Abnormal nests constituted 13.23% (n= 54) of the total nests and 92.91% (n= 223) helmet stage nests had clay deposits on the inner walls. A total of 285 fallen nests in various stages of development were scattered on the ground. There were opportunistic sightings of avian predators, such as House Crow Corvus splendens, Large-billed Crow Corvus macrorhynchos, Rufous Treepie Dendrocitta vagabunda, and Shikra Accipiter badius found perched on power cables bearing nests and caused damages to eight nests.

Predation of Greylag Goose (Anser anser) gosling by Carrion Crow (Corvus corone corone)

Evidence of avian predation on Greylag Goose (Anser anser) goslings is generally inferential. Here, we report an observation of a Carrion Crow (Corvus corone corone) preying on a gosling in Port Meadow, Oxford, United Kingdom. Our observation demonstrates that, in addition to being an egg predator, Carrion Crows are opportunistic predators of Greylag Goose goslings. To our knowledge, this is the first time that this interaction has been documented in the literature.

Population and Nesting Site Evidence for Diamondback Terrapins, Malaclemys terrapin, in Northeast Florida

Diamondback terrapins (Malaclemys terrapin)are listed as Vulnerable by the IUCN Red List Index of Threatened Species. Among the challenges terrapins encounter are habitat loss due to coastal development and sea level rise, mortality at all life stages by mammalian and avian predators, road mortality, boat strikes, harvest for the pet trade, and drowning in crab traps. The primary objective of this study was to locate populations and nesting areas of diamondback terrapins in the four northeastern-most counties of Florida (Nassau, Duval, St. Johns, and Flagler). We conducted head counts and performed land surveys of shorelines and high spots for evidence of terrapin presence. During the land surveys we searched for crawls, intact and depredated nests, dead terrapins, and terrapin bones. To evaluate whether woody plant presence affected nest site choices, we recorded the occurrence of 10 common woody plant species during each land survey and compared areas where nesting did and did not occur. We collected 404 records of terrapin activity in 2013 and 2014. Most were from Nassau County (277) and only one was from Flagler County. Most data were in the form of depredated nests (205) and terrapin remains (147). The woody plant data suggest that terrapins were significantly more likely to nest when Christmas berry (Lycium carolinianum) was present, and nesting was less likely when either wax myrtle (Myrica cerifera) or oak (Quercusspp.) were present.

A rodent herbivore reduces its predation risk through ecosystem engineering

Predator-prey interactions are ubiquitous and powerful forces that structure ecological communities.1-3 Habitat complexity has been shown to be particularly important in regulating the strength of predator-prey interactions.4-6 While it is well established that changes in habitat structure can alter the efficacy of predatory and anti-predatory behaviors,7-9 little is known about the consequences of engineering activity by prey species who modify the external environment to reduce their own predation risk. Using field surveys and manipulative experiments, we evaluated how habitat modification by Brandt's voles (Lasiopodomys brandtii) influences predation risk from a principal avian predator (shrike; Lanius spp.) in a steppe grassland, located in Inner Mongolia, China. We found that voles actively modify habitat structure by cutting down a large, unpalatable bunchgrass species (Achnatherum splendens) in the presence of shrikes, a behavior that disappeared when these avian predators were excluded experimentally. The damage activities of these voless dramatically decreased the volume of unpalatable grasses, which in turn reduced visitations by shrikes and thus mortality rates. Our study shows that herbivorous prey that act as ecosystem engineers can directly reduce their own predation risk by modifying habitat structure. Given the ubiquity of predation risks faced by consumers, and the likely ability of many consumers to alter the habitat structure in which they live, the interplay between predation risk and ecosystem engineering may be an important but unappreciated mechanism at play in natural communities.

THE COMPOSITION AND INTERACTIONS OF SCAVENGERS ON A HUMPBACK WHALE CARCASS IN ALASKA

Many avian and mammalian predators are facultative scavengers and will opportunistically forage from carcasses. A food source as large as a whale carcass could be valuable to wildlife because of its size and high lipid content. Large carcasses can elicit unique behaviors and interactions in wildlife, but because whale beachings are relatively uncommon, little research has examined the scavenging dynamics at whale carcasses. Here, we used a remote camera to investigate the composition and interactions of scavengers at a Humpback Whale (Megaptera novaeangliae) carcass that washed ashore in Glacier Bay National Park, Alaska, in 2016. We split the consumption process into 3 stages based on how much soft tissue remained. Bald Eagles (Haliaeetus leucocephalus) were the first to feed on the carcass and appeared to dominate the food source, preventing many smaller birds from feeding. Gray Wolves (Canis lupus), corvids (Corvus spp.), and gulls (Larus spp.) were also regularly detected. Scavenger numbers remained high during the first 2 stages of carcass consumption and declined by the 3rd stage. Most interactions observed were between individual Bald Eagles and occurred during the 1st stage. Following the eagles' departure after the 1st stage, interactions between individuals were far less common. These results suggest that a carcass of this size in the intertidal zone is utilized primarily by avian scavengers and that interactions between individuals decrease as the food resource declines. These findings help advance our understanding of scavenger dynamics and the general ecology of coastal Pacific Northwest ecosystems.

PREDATION ON ADULT LONG-TOED SALAMANDERS AND A NORTHERN RED-LEGGED FROG BY A BELTED KINGFISHER ON VANCOUVER ISLAND, BRITISH COLUMBIA: A REVIEW OF DEFENSIVE STRATEGY ADAPTATIONS

A case of predation by a Belted Kingfisher (Megaceryle alcyon) on adult Long-toed Salamanders (Ambystoma macrodactylum) and a Northern Red-legged Frog (Rana aurora) is reported. This general note provides a description of the predation events with photographs of the amphibians being devoured. Additional photographs showing scars in long-toed salamanders are presented and considered in review of types of predatory attacks and defensive strategies. A literature review was completed to identify reported cases of predation on these two amphibian species. We discuss what is known about their anti-predator defensive strategies and what species are involved in the ecological and evolutionary dynamics at play. Traits exhibited by these amphibians are discussed as anti-predator adaptations that include warning colorations, defensive postures, tail dropping, crypsis, and glandular skin secretions that can be adhesive, unpalatable, or toxic. A potentially significant role of avian predators is considered in light of the evidence presented.

Contrasting effects of eucalyptus, pine and oak plantations on nest predation risk in Mediterranean grasslands

Large scale afforestation (i.e., establishment of forests on farmland, grassland and other land not previously forested) is increasingly regarded as a cost-effective option to mitigate climate change by promoting carbon sequestration. However, this strategy can have negative biodiversity impacts, potentially causing the loss and fragmentation of open habitats of conservation value, as well as edge effects that can extend well beyond forest boundaries. Mitigating impacts of afforestation programs thus requires a detailed understanding of the mechanisms whereby they affect biodiversity, particularly where new plantations are established close to areas important for open habitat species. Here, we examined how afforestation with oak, pine or eucalyptus trees, commonly planted in Mediterranean Europe, may have distinct effects on nest predation risk of grassland birds in southern Portugal. We used artificial nests with quail eggs and camera traps to: (i) identify nest predators and estimate predation risk of ground-nesting birds in grasslands adjacent to oak, pine and eucalyptus plantations across a distance gradient (0 m to 300 m) from the plantation edge; and (ii) examine how predation risk was influenced by avian predator abundance, sward height and vegetation clearing for photo-monitoring (nest-site manipulation), and their interactions with plantation type. Carrion crow was by far the main egg predator identified, followed by Montagu’s harrier, raven and magpie. Overall, nest predation risk and predator abundance were higher around eucalyptus plantations, compared to either pine or oak plantations. Predation decreased with increasing sward height, but this effect was less noticeable when vegetation around nests was cleared. In pine and oak plantations, predation risk was slightly higher close to edges, and decreased with distance from the edge. Conversely, in eucalyptus plantations predation was lower close to edges, and increased with distance to edges. Distance effects around eucalyptus plantation were, however, absent in manipulated nests. Overall, results show that afforestation with different tree species has distinct impacts on predation risk of artificial nests in Mediterranean farmland. This is probably a consequence of an increasing structural complexity of the plantations, from oak to eucalyptus, driven by differences in tree growth rates and undergrowth cover. These findings suggest that farmland afforestation should favour agro-forest plantations with slow growing species (oak and pine) to mitigate negative effects on breeding grassland birds in adjacent open habitats.

Winter Irruption of Two Geranoaetus Hawks in the Monte Desert of Argentina

ABSTRACT Winter irruption refers to an unpredictable increase in the number of individuals usually dominated by one age class, either juvenile or adult, into a given area as a response to fluctuations in the food supply. Irruptions are well documented for avian predators breeding in the Arctic and Subarctic regions whereby individuals irrupt into irregular nonbreeding areas across the Boreal Temperate Region. However, this phenomenon is largely unknown across the Austral Temperate Region. We studied the age class composition of Variable Hawks (Geranoaetus polyosoma) and Black-chested Buzzard-Eagles (G. melanoleucus) during six austral winters (nonbreeding season) at an overlapping breeding and overwintering area in the Monte Desert (semiarid grassland and shrub steppes) of the Andean foothills at Mendoza province in central Argentina (33°S). We measured the overall abundance per winter (combining the five age classes) and calculated the relative abundance per age class for each winter of both species. We used the ratio of total number of individuals observed in a single winter/the total hours of observation per winter as an index of abundance, because sampling effort was not equal across winters. We found that (1) both species exhibited winter irruptions, (2) the irruptions were largely driven by a marked increase of Basic I individuals (the youngest age class); at the same time, Basic V individuals (the oldest age class) exhibited their (modestly) lowest abundance, and (3) winter irruptions might be species-specific, as the responses differed between the two species, with a joint irruption event in the austral winter 2016 and a second irruptive event only recorded for Black-chested Buzzard-Eagles in the austral winter of 2018. We posit that the marked increase of Basic I individuals during the irruptive winters cannot be fully explained by successful breeding of the local population, and is likely largely a result of individuals born elsewhere, presumably at southern latitudes, and overwintering at our study site in central Argentina.

Status of breeding birds at Observatorio and Goffré Islands, Argentina

Continental islands are often sites of low diversity and endemism, as well as important areas for the protection of bird populations, especially seabirds. On Isla Observatorio and the Año Nuevo Islands, in the Southwestern Atlantic, the latest assessment of avifauna dates from more than 20 years ago. In this study, we use a combination of methods to update the status of the main seabird colonies and the most abundant avian terrestrial predator at Observatorio and Goffré Islands during the breeding season. In only 4.5 km2, the islands would harbour ~ 90,000 breeding seabirds. Seabird colonies occupied different areas of the islands and varied in their population status, with Imperial Shags (Leucocarbo atriceps) showing an increase and Southern Giant Petrels (Macronectes giganteus) a decrease according to the last surveys. Magellanic Penguin (Spheniscus magellanicus) population estimations also suggest a decrease but the last survey was based on total, and not on occupied nest sites. We recorded and assessed one new breeding species: The globally near-threatened Striated Caracara (Phalcoboenus australis), which has an important breeding population of around 15 territorial pairs at Observatorio Island. These islands appear to be an important regional bird site and future studies would determine their trends and threats, especially those related with invasive species.

Avian predators taste reject mimetic prey in relation to their signal reliability

Aposematic organisms defend themselves through various means to increase their unprofitability to predators which they advertise with conspicuous warning signals. Predators learn to avoid aposematic prey through associative learning that leads to lower predation. However, when these visual signals become unreliable (e.g., through automimicry or Batesian mimicry), predators may switch from using visual signals to taste sampling prey to choose among them. In this experiment, we tested this possibility in a field experiment where we released a total of 4800 mealworm prey in two clusters consisting of either: (i) undefended prey (injected with water) and (ii) model-mimics (injected with either quinine sulphate [models] or water [mimics]). Prey were deployed at 12 sites, with the mimic frequency of the model-mimics ranging between 0 and 1 (at 0.2 intervals). We found that taste rejection peaked at moderate mimic frequencies (0.4 and 0.6), supporting the idea that taste sampling and rejection of prey is related to signal reliability and predator uncertainty. This is the first time that taste-rejection has been shown to be related to the reliability of prey signals in a mimetic prey system.

Cathemeral Behavior of Piping Plovers (Charadrius melodus) Breeding along Michigan’s Lake Superior Shoreline

Shorebirds commonly exhibit cathemeral activity and commonly forage throughout a 24 h period. Conservation of endangered shorebirds should then extend to protection at night, yet little data exists on overall time budgets of such species at night. The Great Lakes population of piping plovers (Charadrius melodus) is the smallest and most endangered, making each breeding pair an essential part of recovery. Intense monitoring of breeding individuals occurs during the daytime, yet we have little understanding of the time budgets of plovers at night. To gain better insight into the cathemeral behavior of plovers we recorded behaviors of 12 plovers from along Michigan’s Lake Superior shoreline during both day and night in 2018 with the use of a night-vision-capable camera, and compared time budgets of plovers between daytime and nighttime. Overall, piping plovers spent more time and a greater proportion of their time foraging at night and more time devoted to being alert during the day. These differences were especially evident during the chick rearing phase. Limited observations suggest that copulatory activity may also be more common at night. Likely, the threat of avian predation on this population drives the increase in nighttime foraging, despite decreased efficiency. Recognizing the importance of decreasing potential for disturbance during the night should be considered in future management strategies regarding the recovery of this endangered species.

Love thy neighbour?—Spatial variation in density dependence of nest survival in relation to predator community

AbstractAimIn many species, density‐dependent effects on reproduction are an important driver of population dynamics. However, it is rarely considered that the direction of density dependence is expected to vary over space and time depending on anti‐predator behaviour and predator community. Aggregation may allow for effective group mobbing against avian nest predators while aggregation may also attract mammalian predators, causing negative density dependence. We aim to quantify spatial variation in the effect of conspecific breeding density on nest survival in a mobbing bird species (Eurasian oystercatcher;Haematopus ostralegus) and identify whether this variation in density dependence can be explained by the predator community.LocationCountry‐wide (The Netherlands).MethodsWe integrated reproductive data with breeding territory maps of Eurasian oystercatchers and occupancy maps of avian and mammalian predator species across the Netherlands for a 10‐year period.ResultsSpatial variation in the composition of the predator community explained the effects of neighbour density, showing decreasing nest survival when both conspecific density and mammalian dominance increased. Also, heterospecific density (from breeding godwits and lapwing) has an additional effect on the oystercatcher nest survival. Strikingly, this pattern did not extend to mammal‐free island populations.Main conclusionsOur study provides evidence that both the strength and sign of density dependence can vary spatially within species, implying that it is dangerous to generalize results from a single local population to large‐scale management implications and modelling exercises. The study also suggests that conservation actions that aim to attract breeding birds should be prioritized in areas with fewer mammalian predators, but this idea requires further testing on island populations.

Bear presence attracts avian predators but does not impact lesser snow goose daily nest attendance

The presence of foraging bears in Arctic breeding bird colonies has been increasingly reported in the literature, and these may constitute disturbance events which cause incubating birds to leave their nest. Avian predators may associate with bears during such events, likely to capitalize on unattended nests in the presence of bears. Here, we estimated changes in daily nest attendance of lesser snow geeseAnser caerulescens caerulescensin the presence of foraging bears, and estimated the association between foraging bears and avian predators. We predicted decreased nest attendance by geese on days with bears, and close associations between avian predators and bears. We monitored snow goose nests with cameras from 2013 to 2018 to assess nest attendance behaviours on days when bears were in the colony compared to control days without bears. When bears were present in colonies, we estimated the probability of avian predator occurrence compared to control periods. When controlling for day of incubation and camera placement types, we found no significant effects of bears on daily nest attendance behaviours of snow geese (n = 85). We found a significantly higher probability of observing avian predators when bears were present (0.72) compared to control periods without bears (0.11). We show that snow geese do not alter daily nest attendance in the presence of foraging bears, and suggest this is due to the presence of avian predators.

Conspicuous cruciform silk decorations deflect avian predator attacks.

Although camouflage as an effective antipredator defense strategy is widespread across animals, highly conspicuous color patterning is not uncommon either. Many orb-web spiders adorn their webs with extra bright white silk. These conspicuous decorations are hypothesized to deter predators by warning the presence of sticky webs, camouflaging spiders, acting as a decoy, or intimidating predators by their apparent size. The decorations may also deflect predator attacks from spiders. However, empirical evidence for this deflection function remains limited. Here, we tested this hypothesis using the X-shaped silk cruciform decorations built by females of Argiope minuta. We employed visual modeling to quantify the conspicuousness of spiders and decorations from a perspective of avian predators. Then, we determined actual predation risk on spiders using naïve chicks as predators. Spider bodies and decorations were conspicuous against natural backgrounds to the avian visual systems. Chicks attacked the spider main bodies significantly less frequently on the decorated webs than on the undecorated webs, thus reducing predation risk. When both spiders and decorations were present, chicks also attacked the spider main bodies and their legs or decorations, and not randomly: they attacked the legs or decorations sooner and more frequently than they attacked the main bodies, independent of the ratio of the surface area between the decoration and spider size. Despite the increase in detectability, incorporating a conspicuous cruciform decoration to the web effectively defends the spider by diverting the attack toward the decoration or leg, but not by camouflaging or intimidating, thus, supporting the deflection hypothesis.

Telomere length in relation to persistent organic pollutant exposure in white-tailed eagle (Haliaeetus albicilla) nestlings from Sweden sampled in 1995–2013

Telomeres are used as biomarkers of vertebrate health because of the link between their length, lifespan, and survival. Exposure to environmental stressors appears to alter telomere dynamics, but little is known about telomere length and persistent organic pollutant (POP) exposure in wildlife. The white-tailed eagle (WTE; Haliaeetus albicilla) is an avian top predator that accumulates high levels of POPs and may subsequently suffer adverse health effects. Here we study the Baltic WTE population that is well documented to have been exposed to large contaminant burdens, thereby making it a promising candidate species for analyzing pollutant-mediated effects on telomeres. We investigated telomere lengths in WTE nestlings (n = 168) over 19 years and examined legacy POP concentrations (organochlorines and polybrominated diphenyl ethers) in whole blood and serum as potential drivers of differences in telomere length. Although we detected significant year-to-year variations in telomere lengths among the WTE nestlings, telomere lengths did not correlate with any of the investigated POP concentrations of several classes. Given that telomere lengths did not associate with POP contamination in the Baltic WTE nestlings, we propose that other environmental and biological factors, which likely fluctuate on a year-to-year basis, could be more important drivers of telomere lengths in this population.

Structure and projected decline of a Karoo dwarf tortoise population

AbstractInconspicuous, secretive, or sparsely distributed species receive relatively little research attention, potentially leading to uncertainty about their status and lack of efforts to conserve them. Karoo dwarf tortoises (Chersobius boulengeri) are endemic to South Africa, spend most of the time in retreats at remote arid locations, and are seldom seen. We conducted a 3‐year (2018–2020) mark‐recapture study to investigate the size and structure of the only Karoo dwarf tortoise population currently known to exist. The population in the 16‐ha core of our study site consisted primarily of adult males and females, at a density of 3.3 individuals/ha. Many individuals had severely worn shells and appeared old. Small individuals (straight carapace length <65 mm) represented just 8% of the population and were mostly recent hatchlings. Overall, tortoises had high estimated survival rates (0.77–0.95; lower 95% confidence limit for the smallest tortoises was 0.16), despite a 15‐month drought. The lack of small individuals may reflect low levels of recruitment and population decline. Predation by corvids was an obvious threat to all size classes. We estimated that the local population across the 250‐ha study area was 800–900 males and females, and recommend precautionary conservation measures focused on reducing human‐subsidized avian predation.

Exogenous Application of Methyl Jasmonate Increases Emissions of Volatile Organic Compounds in Pyrenean Oak Trees, Quercus pyrenaica.

Simple SummaryThe tri-trophic interactions between plants, insects, and insect predators and parasitoids are a dominant component of many terrestrial ecosystems. Within these interactions, many predators of herbivorous arthropods use chemical signals provided by the host plants when searching for prey. The exogenous application of methyl jasmonate (MeJA) often induces the release of volatile organic compounds (VOCs) similar to those induced by herbivores in plants. Therefore, it has been used as a method to estimate attraction to VOCs in arthropod and avian predators. In this study, we examined whether potential differences in the composition of VOCs produced by herbivore-induced and MeJA-treated Pyrenean oak trees (Quercus pyrenaica) were related to differential avian attraction. Results showed that the overall emission of volatiles produced by MeJA-treated and herbivore-induced trees did not differ and were higher than emissions of Control trees. However, MeJA-treated trees seem to exhibit a higher reaction and release several specific compounds, which may explain the lack of avian attraction to MeJA-treated trees observed in some previous studies.The tri-trophic interactions between plants, insects, and insect predators and parasitoids are often mediated by chemical cues. The attraction to herbivore-induced Plant Volatiles (HIPVs) has been well documented for arthropod predators and parasitoids, and more recently for insectivorous birds. The attraction to plant volatiles induced by the exogenous application of methyl jasmonate (MeJA), a phytohormone typically produced in response to an attack of chewing herbivores, has provided controversial results both in arthropod and avian predators. In this study, we examined whether potential differences in the composition of bouquets of volatiles produced by herbivore-induced and MeJA-treated Pyrenean oak trees (Quercus pyrenaica) were related to differential avian attraction, as results from a previous study suggested. Results showed that the overall emission of volatiles produced by MeJA-treated and herbivore-induced trees did not differ, and were higher than emissions of Control trees, although MeJA treatment showed a more significant reaction and released several specific compounds in contrast to herbivore-induced trees. These slight yet significant differences in the volatile composition may explain why avian predators were not so attracted to MeJA-treated trees, as observed in a previous study in this plant-herbivore system. Unfortunately, the lack of avian visits to the experimental trees in the current study did not allow us to confirm this result and points out the need to perform more robust predator studies.