Breeding Pairs Research Articles

Group mating in Cretaceous water striders.

Fossilized mating insects are irreplaceable material for comprehending the evolution of the mating behaviours and life-history traits in the deep-time record of insects as well as the potential sexual conflict. However, cases of mating pairs are particularly rare in fossil insects, especially aquatic or semi-aquatic species. Here, we report the first fossil record of a group of water striders in copulation (including three pairs and a single adult male) based on fossils from the mid-Cretaceous of northern Myanmar. The new taxon, Burmogerris gen. nov., likely represents one of the oldest cases of insects related to the marine environment, such as billabongs formed by the tides. It exhibits conspicuous dimorphism associated with sexual conflict: the male is equipped with a specialized protibial comb as a grasping apparatus, likely representing an adaptation to overcome female resistance during struggles. The paired Burmogerris show smaller males riding on the backs of the females, seemingly recording a scene of copulatory struggles between the sexes. Our discovery reveals a mating system dominated by males and sheds light on the potential sexual conflicts of Burmogerris in the Cretaceous. It indicates the mating behaviour remained stable over long-term geological time in these water-walking insects.

Survey of a snow petrel nesting site in a remote high mountain region to inform designation of an Antarctic Specially Protected Area

Despite the sensitivity of ecosystems in extreme conditions, only 0.029% of the Antarctic continent is currently granted special protection as Antarctic Specially Protected Area (ASPA). Additionally, protected areas are unevenly distributed and unrepresentative of the biodiversity of Antarctica. The Antarctic Treaty Consultative Parties are thus striving to establish a more coherent network of protected areas. In this context, the Otto-von-Gruber-Gebirge was identified as an area highly worthy of protection due to its unique ecosystem including one of the largest snow petrel breeding sites, and relative pristine nature. However, in the process of designation, an update of knowledge, particularly of the population status of snow petrel in the area, was recognized to be needed. This study was aimed at estimating a population census of snow petrel breeding pairs in the Lake Untersee catchment, an important subarea of the potentially protected area. Investigations were severely limited by the remoteness and harsh conditions of the area, enabling only a short fieldwork period with limited resources. Thus, a combination of remote sensing and traditional methods was applied. We conducted a ground survey of a smaller reference area, including locating nest sites and assessing nest site characteristics. Snow petrels usually nest in the cavities of large boulders and we thus classified habitat suitability based on boulder presence. To do so, the study area was remotely surveyed by unpiloted aerial vehicles to gain orthophotomosaics in sufficient resolution to distinguish on-ground conditions for breeding. We then calculated nest site densities for the reference area. We also studied nest site data such as nest cavity depth, orientation, and attendance to gain basic knowledge of the characteristics of the breeding site. Finally, we measured a sample of four live snow petrels to determine which morph was present at the site. We were able to obtain nest site data and to extrapolate it, which produced population numbers of 11,765 breeding pairs for the whole study area. This underpins the size of the breeding site and thereby its importance for the species.

Investigating the effect of parental pre-gestational stress on ethological parameters in male rat offspring

Investigating the effect of parental pre-gestational stress on ethological parameters in male rat offspring

The origin, connectivity, and individual specialization of island wolves after deer extirpation.

Wolves are assumed to be ungulate obligates, however, a recently described pack on Pleasant Island, Alaska USA, is persisting on sea otters and other marine resources without ungulate prey, violating this long-held assumption. We address questions about these wolves regarding their origin and fate, degree of isolation, risk of inbreeding depression, and diet specialization by individual and sex. We applied DNA metabarcoding and genotyping by amplicon sequencing using 957 scats collected from 2016 to 2022, and reduced representation sequencing of tissue samples to establish a detailed understanding of Pleasant Island wolf ecology and compare them with adjacent mainland wolves. Dietary overlap was higher among individual wolves on Pleasant Island (Pianka's index mean 0.95 ± 0.03) compared to mainland wolves (0.70 ± 0.21). The individual diets of island wolves were dominated by sea otter, ranging from 40.6% to 63.2% weighted percent of occurrence (wPOO) (mean 55.5 ± 8.7). In contrast, individual mainland wolves primarily fed on ungulates (42.2 ± 21.3) or voles during a population outbreak (31.2 ± 23.2). We traced the origin of the Pleasant Island pack to a mainland pair that colonized around 2013 and produced several litters. After this breeding pair was killed, their female offspring and an immigrant male became the new breeders in 2019. We detected 20 individuals of which 8 (40%) were trapped and killed while two died of natural causes during the 6-year study. Except for the new breeding male, the pedigree analysis and genotype results showed no additional movement to or from the island, indicating limited dispersal but no evidence of inbreeding. Our findings suggest wolves exhibit more flexible foraging behavior than previously believed, and hunting strategies can substantially differ between individuals within or between packs. Nevertheless, anthropogenic and natural mortality combined with limited connectivity to the mainland may inhibit the continued persistence of Pleasant Island wolves.

Predation event and shelter site use by a threatened monitor lizard, Varanus rosenbergi, in the Little Desert, Victoria

AbstractHeath monitors (Varanus rosenbergi) are arguably the most thoroughly studied Australian varanid, largely stemming from long‐term research on Kangaroo Island, South Australia. However, research on other populations within this species' disjunct distribution is limited. We opportunistically tracked a heath monitor in the Little Desert National Park, Victoria, after it consumed a painted dragon (Ctenophorus pictus) which we were radiotracking for another study. We report the first record of a heath monitor depredating a painted dragon, as well as the first record of heath monitors repeatedly using a hollow log for shelter. The hollow log was occupied on 10 consecutive occasions over 18 days, and then again on five occasions 9–11 months later. Our observations identify hollow logs as a habitat resource which should be considered in conservation strategies for this threatened monitor lizard. Furthermore, we observed two individuals in close proximity, possibly a breeding pair, in January. This implies that breeding may occur in summer for the Victorian mallee population, as has been reported in other populations, rather than in spring as has been speculated. Research is sorely needed across this species' disjunct distribution across southern Australia. To date, populations of heath monitors in the Victorian mallee have garnered no scientific study, despite their listing as Critically Endangered.

AI-assisted selection of mating pairs through simulation-based optimized progeny allocation strategies in plant breeding.

Emerging technologies such as genomic selection have been applied to modern plant and animal breeding to increase the speed and efficiency of variety release. However, breeding requires decisions regarding parent selection and mating pairs, which significantly impact the ultimate genetic gain of a breeding scheme. The selection of appropriate parents and mating pairs to increase genetic gain while maintaining genetic diversity is still an urgent need that breeders are facing. This study aimed to determine the best progeny allocation strategies by combining future-oriented simulations and numerical black-box optimization for an improved selection of parents and mating pairs. In this study, we focused on optimizing the allocation of progenies, and the breeding process was regarded as a black-box function whose input is a set of parameters related to the progeny allocation strategies and whose output is the ultimate genetic gain of breeding schemes. The allocation of progenies to each mating pair was parameterized according to a softmax function, whose input is a weighted sum of multiple features for the allocation, including expected genetic variance of progenies and selection criteria such as different types of breeding values, to balance genetic gains and genetic diversity optimally. The weighting parameters were then optimized by the black-box optimization algorithm called StoSOO via future-oriented breeding simulations. Simulation studies to evaluate the potential of our novel method revealed that the breeding strategy based on optimized weights attained almost 10% higher genetic gain than that with an equal allocation of progenies to all mating pairs within just four generations. Among the optimized strategies, those considering the expected genetic variance of progenies could maintain the genetic diversity throughout the breeding process, leading to a higher ultimate genetic gain than those without considering it. These results suggest that our novel method can significantly improve the speed and efficiency of variety development through optimized decisions regarding the selection of parents and mating pairs. In addition, by changing simulation settings, our future-oriented optimization framework for progeny allocation strategies can be easily implemented into general breeding schemes, contributing to accelerated plant and animal breeding with high efficiency.

Selenium Deficiency Exacerbates Hyperoxia-Induced Lung Injury in Newborn C3H/HeN Mice.

Extremely preterm infants are often treated with supraphysiological oxygen, which contributes to the development of bronchopulmonary dysplasia (BPD). These same infants exhibit compromised antioxidant capacities due in part to selenium (Se) deficiency. Se is essential for basal and inducible antioxidant responses. The present study utilized a perinatal Se deficiency (SeD) mouse model to identify the combined effects of newborn hyperoxia exposure and SeD on alveolarization and antioxidant responses, including the identification of affected developmental pathways. Se-sufficient (SeS) and SeD C3H/HeN breeding pairs were generated, and pups were exposed to room air or 85% O2 from birth to 14 d. Survival, antioxidant protein expression, and RNA seq analyses were performed. Greater than 40% mortality was observed in hyperoxia-exposed SeD pups. Surviving SeD pups had greater lung growth deficits than hyperoxia-exposed SeS pups. Gpx2 and 4 protein and Gpx activity were significantly decreased in SeD pups. Nrf2-regulated proteins, Nqo1 and Gclc were increased in SeD pups exposed to hyperoxia. RNA seq revealed significant decreases in the Wnt/β-catenin and Notch pathways. Se is a biologically relevant modulator of perinatal lung development and antioxidant responses, especially in the context of hyperoxia exposure. The RNA seq analyses suggest pathways essential for normal lung development are dysregulated by Se deficiency.

Post-Fledging Movements and Factors that Influence Permanent Departure of Juvenile Crested Caracaras in Florida

ABSTRACT We tracked 48 young Crested Caracaras (Caracara plancus) in south-central Florida from fledging through their first year and sought to define the post-fledging pre-dispersal period and the timing and drivers of permanent departure (PD) from the natal area. By examining Euclidean distances between telemetry locations and the nest for each tagged caracara, we defined the post-fledging dependency period as the first 2 mo after fledging, when fledglings remained mostly within 2.5 km of the nest and were dependent on their parents for food. Before PD, young caracaras explored areas as much as 11 km from their nest but returned to the natal area, resulting in areas used by fledglings up to 6 times the average home range size of an adult breeding pair. Some caracaras remained within their parents’ home range for several months after fledging, even after becoming independent of their parents for food. A fledgling permanently departed its natal area when telemetry indicated it made an abrupt long-distance movement away from its natal area and did not return. We used generalized linear mixed models and a hierarchical modeling approach to test environmental and biological factors that may affect the timing of PD. The most supported model indicated that PD depended on parental reproductive strategy and on the timing of fledging relative to the length of the breeding season. Birds with parents that raised only one brood remained in the natal area for 11.6–21.0 wk longer than birds with parents that raised multiple broods in the same breeding season; fledglings from the first of two broods departed at a younger age, suggesting that the PD decision is partially triggered by the level of parental investment in the first and subsequent brood. Additionally, birds that fledged early in the breeding season departed the natal area 2.8–12.2 wk earlier than those that fledged later in the breeding season, and birds that were exposed to high heat during the nestling stage departed the natal area earlier than those exposed to less heat. The period between fledging and permanent departure from the natal area is important for the conservation of species with delayed dispersal. When developing a conservation strategy for Florida’s caracara population, attention should be paid to protecting areas used by fledglings until PD rather than just focusing on a limited protection zone around the nest.

Breeding performance and nest-site selection of Woodchat Shrikes Lanius senator near the southern edge of their breeding distribution

Numerous Woodchat Shrike (Lanius senator) populations, and Laniidae in general, are globally declining. A deeper understanding of their breeding ecology, including their nest-site selection and breeding performance, from hatching success to post-fledging survival, could contribute to their conservation. We studied breeding Woodchat Shrikes near the southern edge of their breeding range in Northern Israel, monitoring breeding pairs throughout the breeding season from March to July 2023 in three study areas at the slopes of the Golan Heights in a semi-open shrubland. We collected data on birds’ nesting success, including hatching and fledging success, as well as on breeding pairs’ productivity and post-fledging survival of Woodchat Shrikes. Furthermore, we gathered information on nest-site characteristics. In this part of their range, Woodchat Shrikes breed in relatively high densities, opportunistically selecting nest-sites within the area. Most pairs had at least two brood attempts and up to four were recorded. On average breeding pairs laid 4.63 eggs per brood, with a decreasing brood size later in the season. Breeding performance was not related to the nest-site characteristics with the exception of nest height above the ground, which had a positive influence on nesting success. The breeding performance of Woodchat Shrikes was relatively low compared to other studies, particularly when considering fledging success. Nest predation was likely a predominant cause for nest failures here; however, breeding pairs were able to substantially increase their breeding success with replacement broods. Compared to the low nesting success, the post-fledging survival was relatively high, indicating much higher predation pressure on nests compared to fledglings.

Network social dynamics of an ex-situ colony of African penguins following the introduction of unknown conspecifics

Zoos often alter social groups by moving individuals between collections to control numbers, maintain optimal genetic diversity, and for husbandry and management purposes. However, the impact of introducing new individuals into an existing social group is overlooked, and the consequences of these stressful events from an animal welfare perspective are underestimated. In this study, we use Social Network Analysis (SNA) to monitor and to investigate how the social dynamics of a colony of African penguins (Spheniscus demersus, n = 19) were affected by the introduction of groups of unfamiliar individuals (n = 6 and then n = 10) at different time intervals. The proximity data collected over a period of four months suggest that penguins established a non-random association and developed a significant level of preferred associations within the colony. Breeding pairs had a high degree of interaction with the rest of the colony, and their level of association was stable even when a new group was introduced. We found that the association preferences observed in the colony after introduction were not driven by sex and reproductive age. Instead, the main driver of association was the time of introduction, with individuals introduced at the same time being more likely to interact than those introduced at different times. We also speculate that, in addition to arrival time, familiarity plays a key role in group integration. In our specific case, the introduced penguins were already familiar with each other, having shared the same colony before arriving at the new one. Although the results are based on a case study and require further validation, they support the importance of maintaining relevant social ties within colonies and of relocating a few selected individuals who share prior familiarity to facilitate integration into a new colony. Our findings highlight the usefulness of implementing SNA to evaluate the impact of stressful events on the lives of animals.

Mating behavior and responses to sublethal concentrations of imidacloprid in the predator Cyrtorhinus lividipennis.

Mating is an essential factor that governs the size of insect populations that reproduce sexually. The extensive application of insecticides has both lethal and sublethal effects on the physiology and mating behavior of insect natural enemies. The predatory bug Cyrtorhinus lividipennis is a natural enemy of planthopper and leafhopper populations in the rice ecosystem. Unfortunately, the effects of insecticides on the mating behavior of C. lividipennis are not well-understood. The mating behavior of C. livdipennis consisted of mounting, antennal touch and mating attempts, genital insertion, adjustment of posture, and separation of the mating pair. Approximately 82.5% of the C. lividipennis mating pairs displayed their first mating at 12-36 h postemergence. Mating activity occurred throughout a 24-h period, with peak activity at 12:00-14:00 h, and the mean duration of mating was 48.75 min. Sublethal exposure to imidacloprid increased mating latency. Compared with the controls, the duration of courtship, pre-mating and adjusting posture for males treated with imidacloprid were prolonged. The duration of mating for females treated with imidacloprid was prolonged relative to untreated controls. The fecundity and daily spawning capacity of females treated with imidacloprid were higher than the untreated controls. Our results provide insight into the mating process of C. lividipennis. Imidacloprid prolonged the duration of mating, which may explain the enhanced reproductive output in C. lividipennis females treated with imidacloprid. These findings will be useful in both rearing C. lividipennis and deploying this natural enemy in rice fields. © 2024 Society of Chemical Industry.

Second-breeding events of the common kestrel (Falco tinnunculus) in the Czech Republic

Abstract The laying of two clutches in a single breeding season can increase the fitness of the parent birds and stabilise a population. Our study analysed the rate of second-breeding attempts in the common kestrel (Falco tinnunculus) population in the Czech Republic. In the research, a total of 8,049 common kestrel nests were checked between 1979 and 2019. Of the 1,197 breeding events recorded during the study period in Moravia, 1,184 cases were first clutches and 13 cases (1.1%) were second breeding attempts. In Bohemia, a total of 6,852 breeding events were observed during the same study period, of which 6,811 were first clutches, 32 cases were late breeding attempts and 9 cases (0.1%) were second clutches. Second breeding events occurred only rarely, mainly during population outbreaks of prey species. During the mass outbreak of the common vole (Microtus arvalis) population in the Czech Republic in 2019, 5 (5.2%) of the 97 studied common kestrel pairs nested for the second time in Moravia; in Bohemia, second clutches were recorded in 3 (8.1%) of the 37 studied pairs. The second breeding attempts were recorded at an altitude of 272 ± 123 m (mean ± SD, range 179–560 m, n = 22) and commenced between 24 June and 25 July (29 June on average, n = 5). The range of the time gap between the first and the second clutch was 54 to 92 days (70.8 ± 16.3 days, n = 5). The second clutches consisted of an average of 4.1 ± 0.9 eggs (range 3–6, n = 12), with an average of 3.7 ± 0.9 fledglings in each successful breeding pair (range 2–5, n = 11) and 2.6 ± 1.9 fledglings for each initiated breeding attempt (range 0–5, n = 16).

Pairs show similar risk taking behaviour but only female risk taking behaviour is linked to nest microhabitat choice in the Kentish plover

Abstract Risk taking behaviour — how individuals perceive and respond to threat — varies among individuals. In birds, this behaviour influences the choice of nest microhabitat presumably because exposure to predation depends on the structural composition of the nest microhabitat (i.e., a small area where a bird builds its nest). Thus, a chosen nest microhabitat can indicate an adaptation to predation risk. However, where both parents participate in or share breeding roles, it is unknown whether the chosen nest microhabitat is influenced by risk taking behaviour of the female, the male or both parents. Moreover, risk taking may affect other behaviours during breeding, thus having a partner with similar risk taking behaviour may be important for pair complementarity. We investigated risk taking behaviour of breeding Kentish plovers (Charadrius alexandrinus) using flight initiation distance (FID) as a proxy. First, we tested whether FID is repeatable. Second, we tested whether members of breeding pairs have similar FID. Third, we investigated whether male and female’s FID is associated with the choice of nest microhabitat. We classified nest microhabitat by two indices: cover directly above the nest scrape (above nest cover) and cover around the nest (around nest coverage). We found that (i) FID was highly repeatable, (ii) FID was correlated within members of breeding pairs and (iii) female’s risk taking behaviour is linked to the use of around nest coverage. Specifically, females with longer FID, (i.e., more risk-averse ones) tended to use less concealed nest microhabitat. We concluded that nest microhabitat choice in the Kentish plovers is likely a reflection of the female’s risk taking behaviour. Breeding partners likely have similar risk taking behaviour, an indication of assortative mating. We advocate partitioning of correlation within breeding pairs to ascertain estimates of within pair correlation attributable to assortative mating.

Social associations are predicted by nest proximity but not kinship in a free-living social parrot

Abstract Social associations among conspecifics are typically non-random, often being a function of relatedness, familiarity, or spatial distributions. The aim of this study was to combine field observations with molecular genetic techniques and social network analysis to investigate the predictors of social associations in free-living monk parakeets, Myiopsitta monachus. Monk parakeets are non-territorial parrots whose nests are often aggregated, with relatives clustered in kin neighbourhoods and within cooperatively breeding groups. First, we characterized social associations when away from the nest, showing that individuals typically had a few strong social ties. Second, we investigated whether these social associations were related to nest proximity or genetic relatedness. The strength of association decreased with increasing inter-nest distance, but there was negligible influence of relatedness on the strength of associations. These patterns did not differ between same-sex and opposite-sex dyads. Finally, we investigated whether members of breeding pairs were close social associates, finding that in most cases the closest associate of an individual was their mate, although social bonds also existed outside of the pair; members of breeding groups also associated closely when foraging. Social associations are poorly known in parrots owing to methodological challenges, hence our results add to the limited knowledge of sociality in this taxon.

Design and test of novel scent enrichments to enhance breeding of zoo-housed lemurs.

Zoos use environmental enrichments, including scents, which may have applications to improve breeding success for taxa, such as lemurs, which rely heavily on olfactory communication. We aimed to develop novel, biologically-relevant scent enrichments to trigger mating behaviours of zoo-housed lemur species, which are critically endangered in the wild and show a low success rate in captive breeding programmes. We examined anogenital odour secretions, released by female gentle ( Hapalemur alaotrensis) and ruffed ( Varecia variegata) lemurs, using solid-phase microextraction and gas chromatography-mass spectrometry techniques. We identified the key compounds distinguishing the volatile chemical profile of female lemurs during the breeding season and used them to develop species-specific scent enrichments. We then tested the scent enrichments, made up of synthesized mixtures conveying information about female lemur fertility, on unsuccessful breeding pairs of lemurs hosted in European zoos. We evaluated the effects of the newly designed scent enrichments on their target species by combining behavioural observations with faecal endocrinology. We identified and reproduced fertility-specific signals associated with female scents. These scent mixtures triggered male sexual behaviours, including mating, during and after the enrichment condition. We also found effects on faecal testosterone levels, with increased levels after the enrichment condition albeit not statistically significant. Our findings suggest that biologically-relevant scent enrichments may trigger natural species-specific behaviours, with potential implications for conservation breeding of zoo-based endangered lemur species, and highlight that combining more assessment methods may assist with evaluating the impact of environmental enrichments.

Wind Farms and Power Lines Reduced the Territory Status and Probability of Fledgling Production in the Eurasian Goshawk Accipiter gentilis

Wind power is commonly used to reduce greenhouse gas emissions but often has negative effects on biodiversity. In this study, I investigated the effects of wind farm and power line construction on the territory status of the Eurasian goshawk Accipiter gentilis, whether fledglings were produced or not, and the number of fledglings. Included were 55 goshawk territories investigated before and after the construction period. I found that the territory status declined significantly in the influence area within 3 km from the disturbance compared to the control area more than 7 km away. Interestingly, the decline in territory status was similar in the distance categories 0–1 km, 1–2 km, and 2–3 km, while there was nearly no change in territory status in the control area, thus indicating that the influence area from this kind of disturbance was minimum 3 km from the nest. The number of breeding pairs declined significantly during the construction period only in the influence area. Possible reasons might be higher mortality caused by collisions with power lines, desertion, avoidance of the areas with noise and disturbance from the constructions, and possible indirect effects caused by reductions in prey species. I found no effects of the construction on the number of fledglings.

Fecundity decline is male derived following transfluthrin exposures in a field strain of Aedes albopictus (Diptera: Culicidae).

Volatile pyrethroids are effective in reducing mosquito populations and repelling vectors away from hosts. However, many gaps in knowledge exist for the sublethal impacts of volatile pyrethroids on mosquitoes. To that end, transfluthrin exposures were conducted on a field strain of Aedes albopictus (Skuse) held as a laboratory colony. Dose-response analysis was conducted on both sexes at either 1-4 days old or 5-10 days old. Resultant concentration data were used to evaluate the LC20 and LC50 values in various mate pairings of treatments and controls in which either the male or female was from a selectively treated group and mated with a counterpart that was treated independently. Blood feeding proportion, delayed mortality after a 24-h recovery period, egg collection totals, and F1 larval survival were determined following transfluthrin treatment in the F0, but outcomes were not significant. In contrast, sterility was predicated on male treatment, with treated females resulting in higher overall egg viability. Treated males in the mating pair resulted in significantly lower egg viability and accelerated larval hatch in the F1. Additionally, the presence of sperm in female spermathecae was significantly diminished in test groups containing treated male mosquitoes. Male sublethal effects may be a critical determinant of a mixed population's reproductive success.

Sex-specific effects of inbreeding in juvenile brown trout.

Inbreeding depression, that is, the reduction of health and vigour in individuals with high inbreeding coefficients, is expected to increase with environmental, social, or physiological stress. It has therefore been predicted that sexual selection and the associated stress usually lead to higher inbreeding depression in males than in females. However, sex-specific differences in life history may reverse that pattern during certain developmental stages. In some salmonids, for example, female juveniles start developing their gonads earlier than males who instead grow faster. We tested whether the sexes are differently affected by inbreeding during that time. To study the effects of inbreeding coefficients that may be typical for natural populations of brown trout (Salmo trutta), and also to control for potentially confounding maternal or paternal effects, we sampled males and females from the wild, used their gametes in a block-wise full-factorial breeding design to produce 60 full-sib families, released the offspring as yolk-sac larvae into the wild, sampled them 6 months later, identified their genetic sex, and used microsatellites to assign them to their parents. We used whole-genome resequencing to calculate the kinship coefficients for each breeding pair and hence the expected average inbreeding coefficient per family. Juvenile growth could be predicted from these expected inbreeding coefficients and the genetic sex: Females reached lower body sizes with increasing inbreeding coefficient, while no such link could be found in males. This sex-specific inbreeding depression led to the overall pattern that females were on average smaller than males by the end of their first summer.

Brood protection is essential but not sufficient for population survival of lapwings Vanellus vanellus in central Switzerland

Lapwing are among those ground nesting bird species that suffered strong population declines following agricultural intensification in many parts of Europe. The key problem appears to be a low breeding success which, depending on the situation, may be due to predation of eggs and chicks, starvation of chicks especially during dry conditions, agricultural activities leading to direct killings, and suboptimal breeding habitat. Here, we report on a population of 40–60 lapwing breeding pairs in an intensively cultivated arable landscape in central Switzerland, where protection from farming activities, implementation of special lapwing habitat and nest fencing to exclude terrestrial predators (mainly red fox) started in 2005 and is still ongoing. Chicks were ringed and families subsequently observed every 2–3 days. Hatching success for fenced nests built before May was high. Low hatching success was observed in unfenced nests due to high predation rates and in late nests due to abandonment by the female when the vegetation was growing too tall (e.g. maize). Regularly, chicks disappeared during the night shortly after hatching. Most likely many of them first left the fence and were predated outside. Our observations from a fenced field with wet soils and puddles suggest that lapwing may produce sufficient offspring if predation can be reduced and if large enough areas with suitable habitat are available.

Discrete-Time Model of an Exploited Population with Age and Sex Structures: Instability and the Hydra Effect

This study proposes a discrete-time mathematical model to investigate the impact of selective harvesting on the dynamics of a population with age and sex structures. The model assumes that the birth rate depends on the sex ratio of the population and the number of breeding pairs. The growth rate is regulated by limiting juvenile survival, where an increase in population size decreases the survival of immature individuals. We consider the following selective proportional exploitation: harvesting of juveniles and harvesting of mature males. Depending on the values of population parameters, selective harvesting can lead to the stabilization of population dynamics by dampening oscillations or the emergence and amplification of fluctuations in population size. The model reveals multistability domains in which different dynamic modes coexist, and variations in initial conditions can lead to changes in dynamic modes. Depending on the values of the population parameters, the proposed models with harvest reveal the hydra effect, indicating an increase in the equilibrium abundance of the exploited group after reproduction but before harvesting, with an increase in the harvesting rate. Selective harvesting, resulting in the hydra effect, increases the remaining population size due to reproduction and the number of harvested individuals.