Clutch Size Research Articles

Life history and host preferences of Tetrastichus julis (Walker) (Hymenoptera: Eulophidae), the principal parasitoid of the cereal leaf beetle, Oulema melanopus (L.) (Coleoptera: Chrysomelidae)

Tetrastichus julis is the key larval endoparasitoid of the cereal leaf beetle, Oulema melanopus. The beetle has recently invaded cereal growing regions of western Canada, and classical biological control with T. julis is a viable management option. Although the general biology of T. julis is known, several knowledge gaps on life history traits still remain particularly in relation to host preferences and their consequences for parasitoid-beetle interactions. We investigated life history parameters and host preferences of T. julis with reference to a number of developmental parameters including survivorship, clutch size, ovipositional preferences for larval stages and their influences on realized clutch size of the parasitoid. Salient features of T. julis biology observed in this study were a short developmental time, a female-biased sex ratio, which is slightly more pronounced in larger instars, extended longevity of females, sibling mating, and more importantly, the capacity of females to live longer in the absence of hosts. The seasonal trend in parasitism rate of T. julis indicated a peak in activity in mid-June. This investigation revealed that T. julis females can discriminate among host instars and can adjust clutch size accordingly and to some extent increase production of females more than males in larger instars. In laboratory and field trials, given a choice, females laid more eggs in fourth instars than in first instars. The sex ratio was female biased and was positively correlated with clutch size. At least one male emerged from most clutches (>2) and sibling mating was common. Parasitism rates were higher after an exposure period of 48 h than 24 h. Mass rearing of T. julis can be enhanced by exposing mated T. julis females for at least 48 h to fourth-instar larvae of O. melanopus. Understanding T. julis biology can enhance mass rearing to relocate parasitoids and improve sustainable management of the cereal leaf beetle as it expands its geographic range.

A 21‐year recovery trend in green turtle nesting activity: 2002–2022

Abstract Long‐term monitoring and conservation are crucial for effective protection, since sea turtles migrate cyclically every 2–3 years and lay multiple nests during a breeding season. Therefore, this study aimed to investigate the long‐term trend of nesting activities of green turtles over a 21‐year period (2002–2022) on Samandağ beach. An early morning survey was conducted every year during both nesting and hatching seasons. The trend analyses in nesting activities were performed using Mann–Kendall and Sen's slope tests together with the augmented Dickey–Fuller stationarity test. The nest count and female abundance increased significantly, whereas clutch size, fecundity, and hatching success tended to decrease insignificantly. The percentage change between the most recent and oldest 3‐year mean nest count and mean female abundance, which is performed to comply with the Red List assessment method used by the International Union for Conservation of Nature Marine Turtle Specialist Group, was 769% and 764% respectively. Samandağ nesting population accounts for one‐third of the Mediterranean's total nest count and one‐fourth of its total female abundance. The decrease in clutch size and fecundity may be due to the recruitment of individuals with smaller body sizes or malnutrition as a result of population growth. There was an increase in the number of dead embryos and a decline in hatching success. This may be explained by density‐dependent population regulation as a result of an increase in the number of nests. It may be argued that adherence to a uniform strategy and the maintenance of continuous protection through collaboration with governmental and non‐governmental organizations with scientifically rigorous methodology are significant factors contributing to the high recovery. This study emphasizes the necessity of adopting a comprehensive conservation approach encompassing both foraging habitats and the significant role played by the population in Samandağ in the proliferation of Mediterranean green turtles.

NestWatch: An open-access, long-term data set on avian reproductive success.

Long-term avian nesting data are valuable to researchers studying various aspects of avian ecology, conservation, and management. Administered by the Cornell Lab of Ornithology, NestWatch accepts nesting data from volunteers and professionals who agree to follow its protocol and submit data in a standardized form using either the website NestWatch.org, the mobile app, or a bulk upload template. These data (N = 574,288 nest records currently spanning 1874-2023) have been used to examine geographical and temporal variation in breeding success, clutch size, nesting phenology, and other metrics of interest to researchers. When combined with other data sets (e.g., climate, land cover, maps of environmental stressors), NestWatch data have been used to explore the large-scale effects of anthropogenic change on nesting biology. These data can also be incorporated into investigations of status and trends for declining species and can potentially be aggregated with other large-scale nest-monitoring data sets to explore hemispheric or even global change. By committing these data to the public domain, we aimed to increase their use among researchers and stimulate novel studies. The NestWatch Open Data Set by the Cornell Lab of Ornithology is licensed under CC BY-NC 3.0 (creativecommons.org); users are free to copy, redistribute, remix, transform, and build upon the material in any medium or format, but must give appropriate credit, provide a link to the license, and indicate if changes were made. Users may do so reasonably, but not in any way that suggests the licensor endorses such use, and may not use the material for commercial purposes.

Reproductive ecology and natural history of Kinosternon herrerai (Testudines: Kinosternidae) at the center of its distribution


 
 
 
 Mexico harbors 10 endemic species of mud turtles of genus Kinosternon, but natural history information is lacking for most of them. Herein we describe some generalities of the reproductive ecology and natural history of one population of the Mexican endemic, Herrera’s mud turtle, K. herrerai from Hidalgo, Mexico. Females and males were similar in body mass and carapace length. Additionally, larger and heavier turtles moved more than smaller and lighter ones. Clutch size varied from one to six eggs, with an average of 3.4 ± 1.7, and egg laying occurred at environmental temperatures between 15 and 21°C (x̅ = 18.6°C). Total nesting time (from selection of nesting site to oviposition) lasted ca. 37 min, and the incubation period was 75 days in situ. These results enhance our understanding of natural history aspects of Kinosternon mud turtles, which are necessary to carry out conservation actions to preserve all of its populations.
 
 
 

Geographic variations in eco-evolutionary factors governing urban birds: The case of university campuses in China.

Urbanization alters natural habitats, restructures biotic communities and serves as a filter for selecting species from regional species pools. However, empirical evidence of the specific traits that allow species to persist in urban areas yields mixed results. More importantly, it remains unclear which traits are widespread for species utilizing urban spaces (urban utilizers) and which are environment-dependent traits. Using 745 bird species from 287 university/institute campuses in 74 cities and their species pools across China, we tested whether species that occur in urban areas are correlated with regards to their biological (body mass, beak shape, flight capacity and clutch size), ecological (diet diversity, niche width and habitat breadth), behavioural (foraging innovation) and evolutionary (diversification rate) attributes. We used Bayesian phylogenetic generalized linear mixed models to disentangle the relative roles of these predictors further, and to determine the extent to which the effects of these predictors varied among different cities. We found that urban birds were more phylogenetically clustered than expected by chance, and were generally characterized by a larger habitat breadth, faster diversification rate, more behavioural innovation and smaller body size. Notably, the relative effects of the attributes in explaining urban bird communities varied with city temperature and elevation, indicating that the filters used to determine urban species were environment dependent. We conclude that, while urban birds are typically small-sized, generalists, innovative and rapidly diversifying, the key traits that allow them to thrive vary spatially, depending on the climatic and topographic conditions of the city. These findings emphasize the importance of studying species communities within specific cities to better understand the contextual dependencies of key traits that are filtered by urban environments.

Clutch size and hatchling morphology of Parrot snake Leptophis liocercus in the north-east Atlantic Forest of Brazil

Clutch size and hatchling morphology of Parrot snake Leptophis liocercus in the north-east Atlantic Forest of Brazil

Predation Risk, and Not Shelter or Food Availability, as the Main Determinant of Reproduction Investment in Island Lizards

Reproductive investment, including the number of offspring produced, is one of the fundamental characteristics of a species. It is particularly important for island vertebrates, which face a disproportionate number of threats to their survival, because it predicts, among other things, a species’ resilience to environmental disruption. Taxa producing more offspring recover more quickly from environmental perturbations and survive environmental change better. However, ecologists do not understand which primary drivers shape a species’ reproductive investment well. Here, we compare the reproductive efforts of 14 island populations of the Aegean Wall Lizard (Podarcis erhardii), which lives across widely diverging environmental conditions. We test three hypotheses, namely that reproductive investment (measured as clutch size, clutch volume) is (1) positively associated with predation risk [‘Predation Risk Hypothesis’]; (2) positively associated with the presence of reliable vegetation cover that provides shelter [‘Gravid Female Protection Hypothesis’]; and (3) limited by (and hence positively correlated with) food availability [‘Food Limitation Hypothesis’]. Although field data are somewhat consistent with all three hypotheses, statistical analyses provide strong support for the Predation Risk Hypothesis. The results not only shed light on which fundamental forces shape reproductive investment in island vertebrates, but can also help shape conservation priorities.

Successful reproduction of female loggerhead sea turtles with severe limb amputations

AbstractWe evaluate the frequency of flipper amputation and its impact on reproduction in the threatened loggerhead turtle (Caretta caretta) population of the Eastern Atlantic, through a long‐term study on several high‐density nesting beaches of Cabo Verde. 5982 adult females were individually identified, tagged and measured, and the presence of limb amputations was recorded. 918 of them had one or multiple amputations of the rear or front flippers. Most of these turtles (n = 778) had partial rather than complete flipper amputations. However, we found no difference in body condition indices (1.2 vs. 1.1), clutch size (82 vs. 83 eggs), or hatching success (79 vs. 80%) between amputated and non‐amputated females. While amputations may cause individual mortality or reduced fitness, our results indicate that some amputated turtles successfully nest and survive across multiple nesting seasons. Moreover, the amputations do not appear to be impacting the strong recovery of this population. This study provides evidence of the successful reproductive capacity of amputated loggerhead sea turtles and, by extension, the potential reproductive success of amputees released from recovery centers.

Agricultural intensification affects birds' trait diversity across Europe

Agricultural intensification reduces the taxonomic diversity of bird communities, but its influence on functional diversity has been less studied. Here, we analyze the response of functional diversity of different cereal farmland bird communities across Europe to a gradient of agricultural intensification. We collected bibliographical information on life history traits (i.e. body mass, brain size, age of sexual maturity, clutch size, number of clutches, lifespan) of 30 species of birds recorded during field surveys in eight European countries. The index "brood value" was calculated to know each species’ level of reproductive investment per clutch. Intensification gradients at two spatial scales were obtained from field data through PCA, related to management practices at the field scale and the variation in structure and composition of farmland at the landscape scale respectively. We calculated the functional diversity index (FD) and the community-weighted mean (CWM) for each trait and sampling area, and linear mixed models in relation to the two intensification gradients were performed. Results showed that stronger intensification at the field level favors the assembly of shorter-lived communities and bird species with smaller relative brain sizes, also decreasing overall trait diversity. It also restricts the range of strategies for parental investment, reducing the functional diversity of the brood value index. More intensive field management would favor bird communities dominated by generalist and even introduced and/or managed hunting species, while putting at risk those farmland- and grassland-adapted species, typically more associated with the provision of ecosystem services. This highlights the relevance of field management (agrochemicals use, ploughing frequency) for the functional composition of bird communities and the conservation of farmland biodiversity. These findings add to existing knowledge on how species’ pace of life and cognitive capacity interact with drivers of global change, such as agricultural intensification.

Predation of sea turtle eggs by rats and crabs

Egg predation by invasive and native species may have severe impacts on endangered species and negatively affect species recovery. We assessed the levels of egg predation within green turtle (Chelonia mydas) clutches on the island of Diego Garcia (7.42°S, 72.45°E), Chagos Archipelago (Indian Ocean). Native coconut crabs (Birgus latro) and ghost crabs (Ocypode spp.), as well as introduced black rats (Rattus rattus), were predators of eggs, with these species entering nests via tunnels dug obliquely in the sand. Often whole eggs were removed from clutches. For example, the mean clutch size at oviposition (mean 127.8 eggs, n = 23, range = 74–176) was significantly larger than at the end of incubation (mean 110.9 hatched and unhatched eggs, n = 16, range = 9–147). In other cases, egg predation was recorded where the egg had been opened and contents were eaten in the nest. Overall, hatching success (the percentage of eggs laid leading to a hatchling emerging from the egg) was 64.9%, while 3.1% of eggs were predated within nests, 18.1% died during incubation without predation and 13.9% were removed. We reviewed evidence from 34 sites around the world identifying 36 predators that were either native (e.g., crabs, and goannas, n = 30) or invasive (e.g., rats, and pigs, n = 8). Depending on location, a predator could be identified as both native and invasive (e.g., dogs). We discuss how either nest protection and/or invasive predator eradication may be used to increase egg survival and when these approaches might be used.

Notes on clutch size, incubation period, and hatchling size of the Elegant-eyed Lizard, Cercosaura argulus Peters 1862

Notes on clutch size, incubation period, and hatchling size of the Elegant-eyed Lizard, Cercosaura argulus Peters 1862

The breeding ecology of the Agulhas Long-billed Lark: an endemic bird dependent on the remnant Renosterveld of the Western Cape Province, South Africa

The Agulhas Long-billed Lark Certhilauda brevirostris is restricted to the Agulhas Plain, South Africa, a region extensively transformed for crop production and sheep grazing. We present data on nest and egg characteristics, clutch and brood size, parental care and breeding success previously undescribed for this species. During field surveys in 2020 and 2021, 29 nests were located. Of these, 16 were monitored by camera traps. Laying started in late winter (July) and continued until early summer (late November). Most nests (66%) were in Renosterveld, a unique vegetation component of the Fynbos Biome, with the remainder in human-modified landscapes. Female larks were responsible for nest construction and incubation. Both sexes provisioned nestlings, with provisioning rate related to nestling age and time of day but not brood size. Breeding success was low, with only 14% of nests fledging any young. Only one repeat nesting attempt following a predation event was observed, but the attempt was abandoned. Nest predation was the main cause of nest failure, with eight species of nest predators identified. An apparent preference for nesting in Renosterveld highlights the need for protection of this endangered habitat type. As a ground-nesting species in an agriculturally transformed landscape, this lark faces numerous threats associated with habitat loss, altered predation pressure, exposure to pesticides and disturbance at nest sites.

Research activity induces change in nest position but does not affect nest success in a vulnerable babbler

AbstractStudies show that birds cognize human disturbance as a potential predation risk. However, the responses of breeding birds to long‐term continuous disturbance by research activities and whether researcher disturbance affects the fitness of target species remain poorly understood. In this study, we used field observation data collected over 6 years to assess the potential impacts of research activities on nest‐site selection and nest success of the Emei Shan Liocichla (Liocichla omeiensis), a vulnerable babbler species endemic to Southwest China. Our results showed that Emei Shan Liocichlas tended to nest in taller nesting plants or the higher parts of nesting plants to increase nest‐site height following researcher disturbance. The average height of Emei Shan Liocichla nests increased by 52.2% over the 6‐year study period, from 129.8 ± 9.2 cm in 2009 (n = 11) to 197.5 ± 12.1 cm in 2015 (n = 18). While some pairs adopted a different strategy, placing their nests in Rosaceae plants with thorns instead of the bamboo Chimonobambusa szechuanensis (the favored nesting plant of the Emei Shan Liocichla) under high interference pressure, which made it more difficult for researchers to approach their nests. There were no significant differences both in clutch size and nest success between the low‐ and high‐disturbance groups. The study revealed the behavioral response pattern of breeding Emei Shan Liocichlas to researcher disturbance, which will contribute to conservation of this threatened songbird and the knowledge of reproductive strategies of birds. Developing specific guidelines for fieldwork and strengthening visitor management within its core habitat of Emei Shan Liocichla during breeding period should be considered.

Variation in reproductive success in a fragmented Meadow Pipit population: a role for vegetation succession?

Most farmland birds experience strong declines across Europe. These declines are typically associated with agricultural intensification but research on alternative local causes remains scarce. We investigated variation in reproductive success as a potential driver for the observed population declines in a fragmented population of the Meadow Pipit Anthus pratensis, a representative inhabitant of extensively managed mountain grasslands across Europe. Intense nest surveys in the entire Meadow Pipit metapopulation of the Northern Black Forest (SW Germany) between 2020 and 2022 provided information on reproductive success for 53 females distributed across nine habitat patches along an 18 km ridge of the Northern Black Forest. Hatching dates delayed by approx. 5.0 days per 100 m altitude and were almost 10 days later in a year with cold and rainy spring weather. Mean reproductive success per female and year (3.45 fledglings) was low compared to literature values (approx. 4.5) and may thus drive ongoing population declines. Mayfield nest survival estimates (approx. 51% across the nesting period) were comparably high, with most nest failures linked with predation or adverse weather. Low reproductive success further associated with comparably small clutch sizes and low fractions of second broods in habitat patches characterized by homogeneously dense swards. We suggest that restoration through extensive permanent cattle grazing coupled with succession control may be a key factor to increase population productivity.

Whoever their partner, female blue tits breed the same

Abstract Do females modify their reproductive investment if they do not succeed in pairing with a male that matches their preference? In a two-year experiment, we asked female blue tits (Cyanistes caeruleus) to select among six males, and then successively paired them with their preferred and their most avoided male. We monitored female reproductive investment through nest building activity, timing of breeding, size and number of eggs, number of fertilized eggs, and brood sex ratio. We found that females preferred males with a chromatic coloration (blue UV chroma of the head crown) that matched their own, but also that they preferred males with a lower achromatic coloration (less bright color of the cheeks and head crown). Although females paired with their preferred males tended to build heavier nests during the breeding season, we found no evidence of an effect of the pairing treatment on timing of breeding, or any other aspects of female reproductive investment. We however found that laying dates, clutch sizes, egg sizes, and brood sex ratio were significantly repeatable within females between the two years, despite the opposite pairing treatments. These findings show that in female blue tits, the males with which they are paired do not substantially alter their reproductive decisions.

Is there an effect of electromagnetic waves from base stations on the breeding success of Ciconia ciconia ciconia in Algeria?

New nest supports used by the white stork Ciconia ciconia ciconia (Linnaeus, 1775) are mobile phone network relay antennas, which are not without danger because they emit electromagnetic waves that can have a major, although insidious, impact on the species. The aim of this study is to assess the effects of electromagnetic waves from mobile phone network base stations on white stork reproduction. We monitored the breeding phenology of the storks as a function of the distance of their nests from the base stations over 2 consecutive seasons, 2020 and 2021. The work took place in the North-East of Algeria, in Annaba and El-Tarf provinces. The nests were counted and divided into 3 distinct groups. The first is located on the relay antennae, the second less than 200 m and the third more than 300 m from the antennae. We calculated nest occupancy, number of young in the nest and number of nests without young. The results show that nests located directly on base stations have a reduced clutch size, not exceeding two storks and a low reproductive success since the majority of nests (51.9%) remained without young. The number of young storks tends to increase in nests far from base stations. Broods with 3 and 4 young are generally those located more than 300 m from relay antennas.

Impacts of a warming climate on concentrations of organochlorines in a fasting high arctic marine bird: Direct vs. indirect effects?

The present study examined how climate changes may impact the concentrations of lipophilic organochlorines (OCs) in the blood of fasting High Arctic common eiders (Somateria mollissima) during incubation. Polychlorinated biphenyls (PCBs), 1-dichloro-2,2-bis (p-chlorophenyl) ethylene (p,p′-DDE), hexachlorobenzene (HCB) and four chlordane compounds (oxychlordane, trans-chlordane and trans- and cis-nonachlor) were measured in females at chick hatching (n = 223) over 11 years (2007–2017). Firstly, median HCB and p,p′-DDE concentrations increased ~75 % over the study period, whereas median chlordane concentrations doubled (except for oxychlordane). PCB concentrations, in contrast, remained stable over the study period. Secondly, both body mass and clutch size were negatively associated with OC levels, suggesting that females with high lipid metabolism redistributed more OCs from adipose tissue, and that egg production is an important elimination route for OCs. Thirdly, the direct climate effects were assessed using the mean effective temperature (ET: air temperature and wind speed) during incubation, and we hypothesized that a low ET would increase redistribution of OCs. Contrary to expectation, the ET was positively correlated to most OCs, suggesting that a warmer climate may lead to higher OCs levels, and that the impact of ET may not be direct. Finally, potential indirect impacts were examined using the Arctic Oscillation (AO) in the three preceding winters (AOwinter 1–3) as a proxy for potential long-range transport of OCs, and for local spring climate conditions. In addition, we used chlorophyll a (Chla) as a measure of spring primary production. There were negative associations between AOwinter 1 and HCB, trans-chlordane and trans-nonachlor, whereas oxychlordane and cis-chlordane were negatively associated with Chla. This suggests that potential indirect climate effects on eiders were manifested through the food chain and not through increased long-range transport, although these relationships were relatively weak.

Diversity, plasticity and asynchrony of actuarial and reproductive senescence in the Collembola Folsomia candida (Willem, 1902)

Flourishing recent comparative studies on senescence have revealed an uncovered diversity across the tree of life of the shapes of the age trajectories of mortality (actuarial senescence) and to a lesser extent of reproduction (reproductive senescence). Evolutionary theories have been called up to explain why some species suffer from positive senescence while others benefit from negligible or even negative senescence. We still know little about how, within a species, the shapes of the age trajectories of different traits are linked to each other and how they vary or covary depending on the genetic background and environmental conditions. We report here the results of an experimental study whose aim was to describe the actuarial and reproductive senescence in various genetically distinct lineages of a Collembola, a hexapod with indeterminate growth. We compared the age trajectories of individuals raised under two food regimes to study if and how the shapes of these age trajectories are plastically modified by environmental conditions. We found clear evidence of actuarial and reproductive senescence, especially when the springtails were fully fed. Clutch size increased as female become older and then declined progressively after reproduction reached a maximum. This age decline in fertility went along with a progressive slowing down of the pace of the egg-laying, a reduction of egg quality (more sterile eggs), while egg size undergoes little change with age. We found that the onset of reproductive decline occurred before the beginning of actuarial senescence, and show that escaping senescence is physiologically possible for certain lineages under dietary restricted conditions.

Breeding biology of the Xinjiang ground-jay Podoces biddulphi in the Taklimakan Desert, NW China

The Xinjiang ground-jay (Podoces biddulphi), which is endemic to China, has a limited distribution and a small population in the Taklimakan Desert. In this study, we described the breeding biology and nestling growth patterns of this understudied species. Eleven nests were monitored over three consecutive breeding seasons (2017–2019). The Xinjiang ground-jay breeding season extends from March to May with a clutch size of two or three. The incubation period was 18 d, and females spent most of their time incubating their eggs (63 %), followed by collecting leaves (25 %), resting (10 %), turning the eggs (1 %), grooming (0.6 %), and being vigilant (0.4 %). Both parents fed the nestlings with similar feeding frequencies and durations. The growth curve of the nestlings was S-shaped, and the parameters related to nestling mortality, such as tarsus length, showed faster growth than others. Over the three breeding seasons, 32 eggs were laid across 11 nests. Fifteen (47 %) eggs hatched, and 12 hatchlings across six nests fledged (37.5 %). Our study provides detailed information on the breeding biology and nestling growth of the Xinjiang ground-jay. Given its low reproductive success rate, small population size, and limited distribution, this bird species, which is endemic to China, requires further research, and its conservation should be prioritized.

The interplay among breeding timing, brood size, food quantity, and nestling growth rate in the Eurasian eagle owl (Bubo bubo)

Abstract Optimal clutch size theory predicts a trade-off between egg number and fledgling body mass, potentially affecting their survival rate. Yet, only a few studies have directly linked clutch or brood size to energy (food), nestling growth rate, and timing of breeding. We studied the relationship among all these variables in the Eurasian eagle owl. Of 150 eggs laid in 48 nests, 119 hatched and 117 nestlings fledged, indicating low nestling mortality. The number of eggs, hatchlings and fledglings (possibly indicating territory quality) decreased with ordinal date. The total amount of food brought to the nest increased with brood size, but the average amount per nestling decreased. Nestling growth rate (and thus probably fledgling body mass) was negatively correlated with brood size. A trade-off between brood size and fledgling survival may lessen the benefit of occupying food-rich territories. However, we suggest that fledglings from large broods, despite their relatively low body mass, may have higher survival rates owing to their relatively early fledging. This may be due to: (1) higher prey abundance in late spring compared with late summer and (2) a longer period before entering the cold season. Variation in brood size may therefore represent a set of strategies linked to prey abundance.