The gastrointestinal tract microbiota is known to play very important roles in the well being of animals. It is a complex community composed by hundreds of microbial species interacting closely among them and with their host, that is, a microbial ecosystem. The development of high throughput sequencing techniques allows studying the diversity of such communities in a realistic way and considerable work has been carried out in mammals and some birds such as chickens. Wild birds have received less attention and in particular, in the case of penguins, only a few individuals of five species have been examined with molecular techniques. We collected cloacal samples from Chinstrap penguins in the Vapour Col rookery in Deception Island, Antarctica, and carried out pyrosequencing of the V1-V3 region of the 16S rDNA in samples from 53 individuals, 27 adults and 26 chicks. This provided the first description of the Chinstrap penguin gastrointestinal tract microbiota and the most extensive in any penguin species. Firmicutes, Bacteoridetes, Proteobacteria, Fusobacteria, Actinobacteria, and Tenericutes were the main components. There were large differences between chicks and adults. The former had more Firmicutes and the latter more Bacteroidetes and Proteobacteria. In addition, adults had richer and more diverse bacterial communities than chicks. These differences were also observed between parents and their offspring. On the other hand, nests explained differences in bacterial communities only among chicks. We suggest that environmental factors have a higher importance than genetic factors in the microbiota composition of chicks. The results also showed surprisingly large differences in community composition with other Antarctic penguins including the congeneric Adélie and Gentoo penguins.

The costs to females of participating in extrapair copulations is an interesting but hitherto neglected topic in behavioral ecology. An obvious potential cost to females is male physical sanctions. However, although retaliation and punishment by male partners has been proposed as a basic cost for female extrapair behavior in theory, it has not been experimentally demonstrated. We studied the breeding biology of the lesser gray shrike (Lanius minor) and combined field observations and a field experiment to show that (1) there is a high intrusion rate during the female's fertile period, and extrapair copulations occur in this population; (2) by detaining females during the fertile phase, males were induced to retaliate physically against their partners, thereby increasing costs related to female extrapair behavior; and (3) there were no obvious costs to males of punishing their mates. DNA fingerprinting reveals that extrapair paternity is rare or absent in this population. Although we cannot conclude that monogamy at the genetic level is the result of male retaliation, we do show that male physical sanction is a cost that deceptive females have to assume. Males' strategies based on coercion should be considered when explaining variation in extrapair paternity across species.

Recent behavioural and molecular studies have shown that in most monogamous bird species extra–pair copulations and fertilizations outside the pair bond occur routinely. The consequences of female extra–pair behaviour might comprise effects on important life–history traits, such as the extent of male parental care. In this study we test the assumption that, within a species, females' options for extra–pair mating depend on female quality and the environments that females occupy. This‘constrained female hypothesis’ predicts that females in good environments or high–quality females are able to resist males' control efforts better than females in poor environments or low–quality females. We test the idea in the socially monogamous serin. We found that the likelihood of extra–pair paternity is significantly higher in territories with high availability of food. There was a negative relationship between environmental quality (food availability) and paternity both in natural and in experimentally manipulated habitats. Male feeding rates were negatively related to food availability and positively related to paternity. These data and the additional result that in better environments all of a females' offspring were sired by one extra–pair male provide support for Gowaty's ‘constrained female hypothesis’.

1. The response of frugivorous birds to an enlargement of fruit size, and the consequences for both birds and plants, are analysed for the interaction between avian seed dispersers and olives (Olea europaea). 2. The enlargement of fruit size promotes a shift in frugivorous birds’ feeding behaviour, from swallowing fruits whole to pecking pieces of pulp. The relative frequency of olive consumption using each feeding behaviour was assessed by combining field data on frequency of appearance of olive pulp and seeds with data from laboratory trials. 3. Sardinian Warblers (Sylvia melanocephala) and European Robins (Erithacus rubecula) were mainly peckers both on cultivated and wild olives. Blackcaps (Sylvia atricapilla) consumed wild olives mainly by swallowing but consumed cultivated olives (larger than the wild ones) primarily by pecking. Song Thrushes (Turdus philomelos) were primarily swallowers of both types of fruits. 4. Laboratory trials with Song Thrushes, Blackcaps and European Robins showed that: (a) all were able to peck fruits; (b) fruit size determined a shift from swallowing to pecking, as pecking frequency increased with the enlargement of the fruit size; (c) all the species had an increased fruit handling failure rate when trying to swallow increasingly large fruits; and (d) from the birds’ perspective, small shifts in fruit size may have important consequences on fruit profitability. 5. Pecking on olives turns the mutualistic fruit–frugivore interaction into a fruit‐pulp predator interaction, thus arising a conflict between the plant and frugivorous birds. 6. This study shows that heavy dependence on fruit is not always simply related to seed dispersal. The same frugivorous bird species can act as a seed disperser or a pulp predator for the same plant species. The threshold between these roles is highly influenced by the ratio gape size/fruit size.