Feeding functional responses in a sexually size-dimorphic bird

Dietary DNA metabarcoding reveals a trophic niche partitioning among sympatric Iberian sandgrouses and bustards

The study of trophic niche partitioning is of great importance for understanding community structure and species coexistence, particularly if these are threatened. Here DNA metabarcoding was used to assess the diet of four threatened steppe bird species (two bustards and two sandgrouses), with the aim of better understanding their dietary requirements, trophic interactions, and potential threats. The results showed seasonal and interspecific differences in their plant diet, with greater importance of cultivated plants during autumn and winter (around 50 % of their diet) than spring. Plants of the genus Convolvulus and of the family Brassicaceae were frequently consumed by all species. In spring, poppies (Papaver spp.) were a considerable part of their diet, and could be used as a source of carotenoids or for their anti-parasitic properties. Furthermore, results evidenced a trophic niche partitioning among species, with a marked segregation between bustard species and, to a lesser extent, between sandgrouse species. Diet similarity was generally higher between species from different orders that occur in mixed-species flocks (bustard - sandgrouse) than between species of the same order. This partitioning was probably related to a stratification in habitat use rather than to specialisation and might prevent competition to some extent. However, the homogenization of trophic resources resulting from agricultural intensification could pose an important threat, particularly during autumn, when weeds are scarcer and the most abundant trophic resource are sown seeds, which are often treated with pesticides.

Supplementing a grain diet with insects instead of fruits sustains the body condition of an omnivorous bird

Omnivores utilize dietary sources which differ in nutrients, hence dietary limitations due to environmental change or habitat alteration could cause nutrient limitations, and thus deterioration of body condition if omnivory is obligate. We investigated how the body condition of the omnivorous Village weaver Ploceus cucullatus (weavers), which forages predominantly on grains, responds to the supplementation of its grain diet with insects instead of fruits. Forty wild-caught weavers held in aviaries were fed a combination of grains and fruits, or grains and insects ad libitum for 8 weeks. We determined diet preference by recording the number of birds on each diet option per minute for 1 h and the amount of food left-over after 3 h of foraging. Fortnightly, we assessed indices of body condition including body mass, pectoral muscle, and fat scores, packed cell volume (PCV), and hemoglobin concentration (HBC). We modeled the number of foragers, food left-over, and body condition indices as functions of diet, while accounting for time (weeks) and sex effects. Grains were the preferred diet, but males ate more fruits and insects than females. Weavers fed on grains and fruits lost body and pectoral muscle mass and accumulated less fat than those fed on grains and insects. This effect was sex-dependent: females supplemented with fruits lost more pectoral muscle mass than males of the same group and males but not females, supplemented with insects accumulated more fat reserve than those supplemented with fruits. PCV and HBC did not differ between diets but increased over the 8 weeks. Weavers are likely obligate rather than facultative omnivores, with insects as being a more nutritive supplement than fruits. Nutrient limitation arising from environmental change or habitat alteration could impair body condition and affect physiological function to environmental seasonality in obligate omnivores like the weavers.

Social organization in ungulates: Revisiting Jarman's hypotheses

Ungulates (antelopes, deer and relatives) have some of the most diverse social systems among mammals. To understand the evolution of ungulate social organization, Jarman (1974) proposed an ecological scenario of how distribution of resources, habitat and feeding style may have influenced social organization. Although Jarman's scenario makes intuitive sense and remains a textbook example of social evolution, it has not been scrutinized using modern phylogenetic comparative methods. Here we use 230 ungulate species from ten families to test Jarman's hypotheses using phylogenetic analyses. Consistent with Jarman's proposition, both habitat and feeding style predict group size, since grazing ungulates typically live in open habitats and form large herds. Group size, in turn, has a knock-on effect on mating systems and sexual size dimorphism, since ungulates that live in large herds exhibit polygamy and extensive sexual size dimorphism. Phylogenetic confirmatory path analyses suggest that evolutionary changes in habitat type, feeding style and body size directly (or indirectly) induce shifts in social organization. Taken together, these phylogenetic comparative analyses confirm Jarman's conjectures, although they also uncover novel relationships between ecology and social organization. Further studies are needed to explore the relevance of Jarman (1974) scenario for mammals beyond ungulates.

Effects of Sex and Diet on Gut Microbiota of Farmland-Dependent Wintering Birds

Gut microbiota plays an important role for bird biological and ecological properties, and sex and diet may be important intrinsic and extrinsic factors influencing gut microbial communities. However, sex difference of gut microbiota has been rarely investigated in free-living birds, and it remains unclear how sex and diet interactively affect avian gut microbiota composition and diversity, particularly under natural conditions. Here we used non-invasive molecular sexing technique to sex the fecal samples collected from two wintering sites of Great Bustard, which is the most sexually dimorphic among birds, as well as a typical farmland-dependent wintering bird. High-throughput sequencing of 16S was applied to identify the gut microbiota communities for both sexes under two diets (wheat_corn and rice_peanut). The results showed that 9.74% of common microbiota taxa was shared among four groups (sex vs. diet), revealing the conservatism of gut microbiota. Microbiota diversity, composition and abundance varied on different diets for male and female Great Bustards, suggesting that the gut microbiota was interactively influenced by both sex and diet. Under the wheat_corn diet, females had higher abundances of the phylum Verrucomicrobia than males, but lower Bacteroidetes and Firmicutes compared to males; meanwhile, the microbiota diversity and evenness were higher for males than females. In contrast, under the rice_peanut diet, females were more colonized by the phylum Firmicutes than males, but less by the phylum Bacteroidetes; while males had lower microbiota diversity and evenness than females. This study investigated the impacts of sex and diet on microbiota of Great Bustards, and highlights the need of new studies, perhaps with the same methodology, taking into account bird ages, flock size, breeding or health status, which will contribute to the understanding of ecology and conservation of this vulnerable species.