The Energy Savings-Oxidative Cost Trade- Off for Migratory Birds During Endurance Flight

Elite human and animal athletes must acquire the fuels necessary for extreme feats, but also contend with the oxidative damage associated with peak metabolic performance. Here, we show that a migratory bird with fuel stores composed of more omega-6 polyunsaturated fats (PUFA) expended 11% less energy during long-duration (6 hr) flights with no change in oxidative costs; however, this short-term energy savings came at the long-term cost of higher oxidative damage in the omega-6 PUFA-fed birds. Given that fatty acids are primary fuels, key signaling molecules, the building blocks of cell membranes, and that oxidative damage has long-term consequences for health and ageing, the energy savings-oxidative cost trade-off demonstrated here may be fundamentally important for a wide diversity of organisms on earth

Progesterone modulates aggression in sex-role reversed female African black coucals

Testosterone is assumed to be the key hormone related to resource-defence aggression. While this role has been confirmed mostly in the context of reproduction in male vertebrates, the effect of testosterone on the expression of resource-defence aggression in female vertebrates is not so well established. Furthermore, laboratory work suggests that progesterone inhibits aggressive behaviour in females. In this study, we investigated the hormonal changes underlying territorial aggression in free-living female African black coucals, Centropus grillii (Aves; Cuculidae). Females of this sex-role reversed polyandrous bird species should be particularly prone to be affected by testosterone because they aggressively defend territories similar to males of other species. We show, however, that territorial aggression in female black coucals is modulated by progesterone. After aggressive territorial challenges female black coucals expressed lower levels of progesterone than unchallenged territorial females and females without territories, suggesting that progesterone may suppress territorial aggression and is downregulated during aggressive encounters. Indeed, females treated with physiological concentrations of progesterone were less aggressive than females with placebo implants. This is one of the first demonstrations of a corresponding hormone–behaviour interaction under challenged and experimental conditions in free-living females. We anticipate that our observation in a sex-role reversed species may provide a more general mechanism, by which progesterone—in interaction with testosterone—may regulate resource-defence aggression in female vertebrates

Trade-off between migration and reproduction: Does a high workload affect body condition and reproductive state?

Migratory birds have to invest much energy into flight to reach their summer and winter quarters. Many studies have shown how migration affects body physiology, including the accumulation of energy stores and the reduction of nonessential organs. In spring, the costs of migration may trade-off with preparations for breeding, such as the timing and extent of development of primary and secondary sexual traits. Birds arriving earlier on the breeding grounds often have a higher reproductive success than late-arriving birds, but no study to date has addressed whether and how the flight workload during migration itself influences reproduction. Using a wind tunnel, we investigated the effect of a high workload during long flights on measures of body condition and reproductive state in male rose-colored starlings (Sturnus roseus). We compared an experimental group that flew in the wind tunnel every day and covered a total flight distance of > 4700 km in 49 days with a control group of males that did not fly. All birds had ad lib access to food. After the "migration" period, individuals from both groups were kept in a common breeding aviary, where they directly competed for nest-boxes and females. Contrary to expectation, birds from the experimental and control group did not differ significantly in the spontaneous seasonal changes in fat score, in breast muscle thickness, in plasma testosterone levels, and in bill and mantle color. Body mass increased more slowly in experimental than in control birds, but it reached the same level soon after the migration period. We did not observe any effect of the experimentally increased heavy workload on behavior during the early breeding phase or on any parameter of reproductive success. We thus failed to find a trade-off between long flight and the development of traits in preparation for breeding or reproductive success. A possible treatment effect might have been obscured by the unrestricted food supply. However, we cannot exclude effects on other life-history stages such as future survival, migration, or reproduction. Our results attest to the strong endogenous control of seasonal physiological changes in preparation for breeding that occur independently of the extreme effort invested in long-distance migration