Long-term micronutrient and amino acid supplementation increases embryo recovery per flush and ovarian responsiveness in donor mares.

To clarify the characteristics of spermatogenesis in Gasterosteidae, which are known to build nests for breeding, we conducted observations of gonadal tissues throughout the year and measured blood androgen (11-ketotestosterone; 11-KT) concentrations in the genus Pungitiu sinensis and compared the results with those of other genera. The presence of post-ovulatory follicles in the ovaries indicates that the breeding season for Pungitius is from April to August in Hokkaido. Spermatogenesis began in September, immediately after the breeding season, and is completed in October. Spermatozoa were then stored in the lumen of the seminal lobules throughout the winter. During the spring breeding season, spermatozoa are observed in the sperm duct. Numerous spermatozoa were suspended within the lumen of the seminal lobules, but some spermatozoa formed "sperm clusters" consisting of several dozen sperm surrounded by somatic cells along the walls of the seminal lobule. The regular distribution of sperm clusters on the walls of the seminal lobule suggests that these clusters are structures with some physiological functions. These characteristics of spermatogenesis have also been reported in other genera of Gasterosteidae and are common features of this family. A significant increase in kidney weight was observed in males during the breeding season. Serum 11-KT concentrations were low during the spermatogenesis and remained low throughout the winter. Many individuals exhibited high concentrations between March and July when spermatogenesis did not occur. These findings suggest that in Pungitius, 11-KT may promote kidney development necessary for male reproductive activity, but may not be involved in stimulating spermatogenesis.

Avian use of agricultural cover crop fields during winter, migratory stopover, and the breeding season in Tennessee

In Mexico, the Guadalupe fur seal ( Arctocephalus townsendi , GFS) is listed as Risk of Extinction, with one breeding site on Guadalupe Island, and another potential colony proposed in the late 1990s on the San Benito Archipelago (SBA). Although there are some health and mortality studies regarding GFS on Guadalupe Island, the SBA colony remains understudied. This study aimed to characterize the causes of neonatal GFS morbidity and mortality, and to assess potential threats to species conservation associated with entanglement, alopecia syndrome, and marine pollution on the West Island of the SBA during the 2024 breeding season. Field data on total births and neonate mortalities were collected during the first 30 days of life. Entanglement and alopecia syndrome incidents were recorded and analyzed to determine age class and sex predilection using Bayesian analyses. Also, marine pollution was classified and quantified by environmental debris type. The neonatal mortality rate in GFS was 29.52%. Perinate deaths were considered natural and attributed to trauma (50%) and emaciation/infectious disease (50%). The prevalence of the alopecia syndrome in non-pup GFSs was high (21% to 26%) during the 2024 breeding season. Clinically, there were bilateral and asymmetrical presentations, with a higher probability of detection of this syndrome in yearlings and juveniles, particularly in males. Entanglements were related to marine debris (100%), affecting juvenile individuals (80%) and adults (20%). A field survey of the composition of marine debris along the SBA beaches revealed that 92% was plastic, predominantly bottles (65%) and fishing gear (16%). Local or regional sources appear to contribute to pollution in the SBA based on the composition of the debris and its proximity to human habitation. Mortality and alopecia rates in immature GFSs were much higher compared to Guadalupe Island, identifying potential challenges in health and survival during early development stages in the SBA. The establishment of the GFS population in the SBA spans almost three decades; however, key demographic factors remain undetermined. Continued efforts to characterize the factors limiting the transition of the SBA from a plausible mixed to a breeding colony are warranted.

Disruption of habitat connectivity alters host movement patterns and pathogen exposure in wildlife. Changes in exposure dynamics have led to increased research interest in host-associated microbial communities (i.e., microbiomes), particularly in how repeated encounters with pathogens may drive microbial filtering processes that favor the assembly of pathogen-inhibiting microbiomes, a concept known as the adaptive microbiome principle. Understanding how habitat connectivity and pathogen exposure shape adaptive microbiomes remains a key frontier in disease ecology. For widely distributed waterborne pathogens such as the amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd), sustained host exposure in contiguous terrestrial-aquatic habitats may promote selection of microbiomes with enhanced antifungal properties. In contrast, under conditions of high habitat split, where key habitats such as forests and water bodies are spatially disconnected, limited exposure to Bd during the pre-tbreeding and overwintering seasons may hinder the selection of Bd-inhibitory microbiomes that are critical for host protection during the subsequent breeding season, when pathogen exposure in water bodies is at its peak. Our results demonstrate that habitat split may limit recruitment of putative Bd-inhibitory skin bacteria, while Bd loads increase with habitat split for certain amphibian species. Results from Joint Species Distribution Models also indicate that habitat split is a key driver of reduced skin bacterial diversity, even after accounting for biotic and abiotic metrics. Our study provides evidence that spatial connectivity among natural habitats is essential for maintaining multiple levels of biodiversity, from host species to their associated functional microbiomes, highlighting a critical link between environmental disturbance, microbial defenses, and disease dynamics.

ABSTRACT Seasonal breeders rely on light as a key environmental cue to trigger reproductive activities. While studies have been focused on male white-rumped munia (Lonchura striata), the effects on females are largely unknown. This study examined how light compositions affect female reproductive physiology. In the first experiment, female birds were exposed to short day (SD; 8 L:16D) and long day (LD; 15 L:9D) for a single day to study various transcripts involved in seasonal reproduction. The second experiment included SD and LD along with an added photoperiod of 12 L:12D, and the treatment extended for 30 d. In the third experiment, female birds were exposed to the above three photoperiod conditions, including natural day length (NDL), to assess morphological changes across 18 months. The fourth experiment evaluated seasonal variations in reproductive parameters across four months: March, June, September, and December. The fifth focused on illuminance levels (10, 50, and 100 lux) under a photoperiod of 12 L:12D, and the sixth assessed responses to red (650 nm) and blue light (450 nm) at a constant irradiance of 0.5 W/m2. In all six experiments, an assessment of body mass and follicular diameter was done, while Experiment 3 specifically examined full-body moult and primary flight feather moult as well. Hypothalamic tissue was analysed for reproductive and epigenetic markers. The first experiment revealed enhanced expression of Tshβ and Eya3 in the long-day group, while no significant changes in other reproductive (Dio2, GnRh, Dio3 and GnIh) and epigenetic (Tet1, Hat1, Hdac2, Dnmt1 and Dnmt3b) transcripts were observed. The second experiment observed increased expression of Tshβ exclusively under 15 L:9D, while Tet1, Hat1 and Dnmt1 transcripts were increased under 12 L:12D. Experiment 3 demonstrated distinct morphological responses to different photoperiods, with significant increases in follicular diameter under 15 L:9D and NDL conditions at the 7th month, but this effect was delayed until the 10th month under 12 L:12D. In contrast, no change was observed under 8 L:16D. Seasonal variations in transcripts were noted, with the highest expression of Tshβ, Dio2, GnRh, Eya3, Hat1, Tet1 and Dnmt3b in September compared to other months. The fifth experiment showed that exposure to 100 lux increased key reproductive markers (Tshβ, Dio2, and GnRh) and epigenetic regulators (Hat1 and Tet1), while the sixth experiment found no significant differences between red and blue light treatment. Overall, the findings highlight the importance of light duration and illuminance in reproductive responses. While no robust change in epigenetic transcript was observed under laboratory conditions in female birds, the epigenetic changes observed in the seasonal experiment suggest that seasonal reproductive cycles are under regulation of epigenetic mechanisms at the molecular level.

Mercury is a pervasive pollutant that readily enters the food web, accumulates within organisms and across trophic levels, and poses a significant threat to long-lived top predators, such as many seabirds. Since mercury can be deposited in feathers and therefore excreted through moult, feather analysis offers a minimally invasive way to assess mercury contamination levels in birds. However, it remains largely unclear whether mercury levels vary among feather types within individuals, how feather mercury levels relate to those in blood, and whether all levels vary with individual characteristics, such as sex and age, in a similar way. To address these issues, we collected dorsal, ventral, primary and tail feathers from > 200 common terns (Sterna hirundo) from a breeding population in the north of Germany, of which a subset was blood sampled as well. Additionally, we collected multiple dorsal feather samples from 313 individuals across years (i.e. longitudinally), to assess whether age effects were likely to reflect within-individual processes. Mercury levels were significantly correlated across feather types within individuals, with those in dorsal and ventral feathers, both grown in the wintering area, also correlating with mercury levels in blood sampled during the breeding season. Males and females did not differ in their feather mercury levels, but older birds exhibited higher mercury levels in all feather types except for tail feathers. Unique analysis of the longitudinally collected dorsal feathers showed that although the within-individual estimate for age was not significant itself, it was very similar to the among-individual age effect, suggesting that within-individual accumulation of mercury during ageing is a likely explanation for older birds having higher mercury levels in most of their feathers. We suggest that body feathers are most suitable for characterising the mercury levels of seabirds in a little-invasive way, but that being able to account for the age of the sampled individuals is important.

The influence of breed and feeding season on the level of peptides in cow's milk

Understanding the movement patterns and foraging areas of seabirds is critical for their conservation and for mitigating potential impacts from human activities, such as offshore wind farm (OWF) development. We provide the first GPS data on foraging trips and travel altitudes of European storm-petrels (ESP) Hydrobates pelagicus in the Bay of Biscay, near planned OWF development areas. We obtained 28 complete trips from 19 individuals during the incubation periods of the 2023 and 2024 breeding seasons at three colonies along the Spanish Cantabrian shore. Distribution models for ESP were developed using the maximum entropy (MaxEnt) method for each colony, and flight heights were measured using GPS triangulation, analysing data separately for daytime and nighttime. Mean trip duration was 2.7days and mean trip distance travelled was 803km, with no relevant differences among colonies. Our results indicate that foraging areas were concentrated along the edges of both the French and Iberian continental shelves. However, at night, ESP showed a more concentrated use of the continental shelf edge and exhibited a more coastal distribution, occasionally foraging in bays and estuaries and showing inter-colonies nocturnal movements. This nocturnal scenario may pose a risk of direct impact of OWFs on the breeding population of the species in the Gulf of Biscay.

Elevational replacement distribution patterns underpin montane diversity and reflect the interaction of both biotic and abiotic pressures, but the degree to which parasites exhibit elevational zonation remains unclear. Investigating infection patterns in related host species across elevational gradients can reveal whether parasites and hosts show concordant patterns of elevational turnover, potentially due to shared historical and ecological factors. Here, we assessed patterns of elevational replacement in haemosporidian parasite assemblages that infect three congeneric songbird species: Bell's vireo (Vireo bellii), gray vireo (V. vicinior), and plumbeous vireo (V. plumbeus), each of which breeds across distinct elevations and habitats in the southwestern United States. We screened a total of 248 individuals using cytochrome b PCR and microscopy. We identified 19 haemosporidian haplotypes, including eight novel lineages. We found that each of the three vireo species exhibited high haemosporidian prevalence (55.0-86.2%), with nearly all infections from the genus Haemoproteus (subgenus Parahaemoproteus). Haemosporidian assemblages varied across elevations; each sampled range of elevations harbored abundant, yet host-specific lineages with different environmental associations. Bell's and plumbeous vireos, but not gray vireos, hosted several phylogenetically distinct, putative generalist lineages, likely reflecting spillover from more diverse local breeding bird communities. Repeated infections in individuals across breeding seasons, together with moderate parasitemia (x̄ ≈ 1%) suggest that these focal vireo species harbor chronic infections during their respective breeding seasons. These results demonstrate that elevational replacement patterns in avian hosts may be mirrored by their haemosporidian parasites, particularly among host-specialized lineages.

The economic implications of abortion among ewes in Salah Al-Din Province (Iraq) have a significant negative impact on the livestock industry. Therefore, it is important to understand the hormonal changes associated with abortion, as well as the potential causative agents to devise adequate and practical prevention strategies of abortion in ewes. The objective of this study was to investigate the hormonal changes in aborted ewes and to identify the primary causes of abortion in sheep throughout Salah Al-Din Province during the breeding season of 2024. A total of 180 ewes were examined, including 120 ewes with confirmed abortions, whereas the remaining 60 ewes with healthy pregnancies served as a control group. Blood samples were taken from each ewe for hormonal analysis (progesterone, estradiol-17β, cortisol, and prolactin) using enzyme-linked immunosorbent assay. Samples from aborted ewes were microbiologically cultured, serologically tested, and histologically examined to determine the causative agents. There was a statistically significant difference between aborted and control ewes in the concentration of progesterone (1.82±0.34 ng/mL vs 4.15±0.52 ng/mL, p < 0.001), and estradiol-17β levels (12.45±2.18 pg/mL vs 28.67±3.45 pg/mL; p < 0.001). The concentration of cortisol was significantly higher in the serum of aborted ewes (45.32±6.78 ng/mL vs 22.15±3.42 ng/mL; p < 0.001). The aborted group revealed slightly lower levels of prolactin compared to controls on average. The leading causes of abortion identified were brucellosis (33.2%), toxoplasmosis (25.8%), chlamydia (19.2%), and nutritional deficiencies (15.8%). The findings from this study indicate that abortion in ewes in Salah Al-Din Province is associated with significant hormonal changes, the most notable of which were decreased progesterone and increased cortisol levels. Infectious diseases, especially brucellosis and toxoplasmosis, represented the leading causes of abortion. These observations suggest a need for comprehensive vaccination programs, improved nutritional management, and strategies to reduce stress to lower the incidence of abortion in ewes.

Hormonal actions of relaxin-like gonad-stimulating peptide in starfish.

Spatio-temporal differentiation and potential homogenization of pheasant communities by human disturbance.

Nest survival is a key determinant of birds' breeding success, particularly in ground-breeding birds, where nest predation is a major cause of reproductive failure. Birds can maximise their nesting success by optimising aspects of the sociospatial environment of a nest, for example, by reducing the risk of predation or flooding. Previous research showed that ruff (Calidris pugnax) females nest closer to leks and to nests of conspecifics, and in some years, further from the shoreline and from meadow edges than expected by chance. However, whether and how social and environmental factors affect nest survival remains unclear. To fill this gap in knowledge, we analysed daily nest survival in a breeding population of ruffs, using nest locations from six breeding seasons. Following a Bayesian approach, we estimated daily nest survival rates to assess the impacts of social, spatial and temporal factors on ruff nest survival in three models focusing on distinct sources of mortality: (i) all sources of mortality (Overall model), (ii) all sources of mortality except for predation (No-predation model) and (iii) only predation (Predation model). We also studied the effects of an intervention to protect nests at increased risk of failure by replacing their eggs with plastic dummies and artificially incubating the collected clutches. Overall, younger nests and those at intermediate distances to other nests had the highest daily nest survival, whereas laying date and distance to paths had a negative effect on daily nest survival in the No-predation model. The use of dummy eggs reduced nest mortality of protected nests at strong risk of failure from flooding and cattle trampling, as well as the impact of predation. We highlight that identifying the sources of nest mortality is necessary to inform species and habitat management, ameliorate productivity and improve the recovery of endangered wader populations.

ABSTRACTEgg recognition and rejection constitute essential host defenses against brood parasitism, with rejection decisions reflecting evolutionary adaptations shaped by cost–benefit trade‐offs. Although long‐term studies have established correlations between egg rejection behavior and parasitism risk, it remains unclear whether hosts can dynamically adjust their defenses in response to stage‐specific parasitic threats across different breeding periods. We investigated temporal variation in egg recognition and rejection latency in the green‐backed tit (Parus monticolus), analyzing both seasonal patterns and stage‐specific responses within breeding cycles. Our findings reveal that while rejection behavior remained consistently precise throughout the breeding season without seasonal variation, we observed a striking stage‐dependent pattern: complete acceptance of parasitic eggs during laying followed by near‐total rejection during incubation. This biphasic response contrasts sharply with patterns reported in most other host species. We propose this unique recognition strategy stems from the tit's egg‐covering behavior during laying—an adaptation likely driven by nest predation pressure that temporarily suppresses anti‐parasitic defenses. These results demonstrate that green‐backed tits have evolved independent adaptive responses to distinct selective pressures: nest predation during egg‐laying and brood parasitism during incubation. This study provides new insights into the plasticity of host defenses and suggests that species with egg‐covering behaviors may develop specialized anti‐parasitic strategies. Our findings offer important implications for understanding the evolutionary dynamics of host–parasite interactions and establish a framework for investigating recognition behaviors in other cavity‐nesting hosts.

Summer underwater vocalizations of male Atlantic walruses Odobenus rosmarus rosmarus near their terrestrial haul-out site.

ABSTRACTWhile secondary contact between distant lineages or sister species is a common evolutionary outcome, the factors that promote their coexistence are often unknown, especially for marine species. Focusing on two sister fish species from the East China Sea, Bostrychus donghaiensis and B. sinensis, it was assessed whether they differ in microhabitat use and life history using otoliths. Morphological data were used to test for phenotypic differences in otolith morphology between the focal species and employed laser ablation inductively coupled plasma mass spectrometry to measure microchemical changes throughout their life history. The study revealed that otolith shapes not only differ between the two species, but also between B. sinensis individuals from within and outside the contact zone. This was further supported by the microchemical analysis, indicating that both B. donghaiensis and B. sinensis from outside the contact zone primarily inhabit high salinity environments throughout their entire life history without migration. In contrast, B. sinensis from the contact zone migrates to estuaries of lower salinity during the breeding season. Overall, these findings highlight the importance of habitat changes in limiting niche competition, contributing to the understanding of life history processes of species during secondary contact.

Empirical evidence shows that brood sex ratios can be influenced by environmental factors and reproductive success–related parental traits. The Trivers–Willard hypothesis (TWH) predicts condition-dependent adjustment of offspring sex ratios and has been extended to suggest that females mated to more attractive males will bias offspring sex ratios towards sons, as sons that resemble their fathers could yield greater fitness returns through increased grandoffspring production. Although extensive research has explored the effect of male attractiveness on sex allocation, its interplay with environmental conditions is often overlooked. This study examines how brood sex ratios respond to both male attractiveness and annual rearing conditions (ARC; proxied by annual breeding success) within the framework of the TWH. Using long-term data from 2759 molecularly sexed nestlings of pied flycatchers, Ficedula hypoleuca , ringed between 1997 and 2018 (with 643 brood sex ratios determined from eight breeding seasons between 1997 and 2011) and by tracking lifetime fledgling production through the 2023 breeding season, we found support for sex ratio adjustment as predicted by the TWH. Male attractiveness and ARC positively affected the proportion of males in the broods. These associations were partially context-dependent, with each factor becoming influential only when the other was unfavourable. Analyses of nestling mortality before genetic sexing at day 13 after hatching showed that nestling mortality was more frequent in female-biased broods, decreased with favourable rearing conditions and increased with male attractiveness. Importantly, excluding broods with early nestling mortality left the main sex ratio conclusions unchanged. In addition, we did not find statistical evidence for an association between male attractiveness or ARC and offspring’s lifetime reproductive success. Our findings suggest that sex allocation is influenced by poor rearing conditions, sexually selected traits and their interplay. Further research is needed to confirm this relationship and to clarify the fitness consequences for sons and daughters. • Both male attractiveness and rearing conditions influence offspring sex ratios. • Supports Trivers–Willard hypothesis: parity in good conditions, daughter bias in poor. • Male attractiveness and rearing conditions interact in a context-dependent way. • No effect of male attractiveness or rearing conditions on offspring fitness detected. • Long-term data highlight the importance of environmental context for sex allocation.

Host species have evolved different strategies for dealing with parasites. 'Vulnerable' hosts, which suffer reduced fitness from parasites, are under selection to evolve defences. 'Tolerant' hosts, by contrast, avoid reductions in fitness by mitigating parasite damage. When tolerant and vulnerable hosts co-occur, tolerant hosts may pose an indirect threat to vulnerable hosts by serving as a source of parasite infestation. Avian vampire flies (Philornis downsi) are introduced parasites of Galapagos mockingbirds (Mimus parvulus) and Darwin's finches. Mockingbirds are relatively tolerant, while finches are more vulnerable. We tested the indirect threat hypothesis using a population genomics approach to estimate transmission of vampire flies from mockingbirds to finches on Santa Cruz Island, Galapagos. Mockingbirds nested earlier than finches, which increased their potential threat to finches. We sequenced 136 whole genomes of avian vampire flies and did kinship analysis to compare the relatedness of flies in mockingbird and finch nests over the course of the breeding season. Our data show that flies in source mockingbird nests are more often related to flies in finch nests than to flies in mockingbird nests later in the season. This pattern may be explained by the distance between nests, as finch nests are often closer to mockingbird nests than mockingbird nests are to each other. These results are consistent with the hypothesis that tolerant mockingbirds pose an indirect threat to more vulnerable finches.

Abstract Conspecific brood parasitism (CBP) has been reported in more than 100 altricial avian species, yet its frequency and underlying behavioural processes remain poorly understood. We studied CBP in the barn swallow ( Hirundo rustica ), a species in which CBP has been reported. We conducted parentage analysis on 1943 barn swallow broods involving 7827 offspring collected over 12 breeding seasons at five populations, where we found only six cases of mixed maternity (0.3% of broods). By identifying all individuals involved, we determined that only three cases could be reliably interpreted as true CBP. Other three cases resulted most likely from nest take-overs when ‘parasitic’ females laid eggs into their own nests from which they were expelled by other females. Based on a review of the literature on CBP in barn swallow and seven other Hirundinidae, where CBP has also been reported, we conclude that the only reliable evidence for CBP comes from cliff swallows ( Petrochelidon pyrrhonata ). Data on other species do not allow exclusion of non-CBP mechanisms that could generate mixed maternity, thus, failing to present sufficient evidence supporting the occurrence of CBP as an alternative reproductive strategy. Several studies relied on the appearance of two eggs in a nest within one day, however, based on the parentage analysis, we show that CBP only occurred in one out of 11 such cases in our barn swallow data. Our findings highlight that CBP is virtually absent in our barn swallow populations, and has been likely overestimated in other studies. Overall, our results challenge existing beliefs about the frequency of CBP in barn swallow and Hirundinidae in general and provide insights into the circumstances that lead to mixed maternity broods. We emphasize that frequent nest checks and rigorous genetic validation are essential in CBP research to rule out alternative causes of mixed maternity.