Migratory direction established in inexperienced bird migrants in the absence of magnetic field references in their pre-migratory period and during testing

Several studies have investigated the importance of different orientational cues that pre-migratory, naïve bird migrants might use to develop their appropriate migratory orientation. We tested the hypothesis that, without any interplay with the magnetic compass in the pre-migratory period, celestial rotation alone cannot lead to any migratory orientation that differs significantly from due south, i.e. celestial rotation is used as a reference only and it is set by the geomagnetic compass to the species-specific migration direction. In the present study, juvenile whitethroats, Sylvia communis, trapped in the field soon after fledging, developed appropriate migratory orientation when held in outdoor cages in full view of celestial cues, but in a strong, heterogeneous magnetic field without any meaningful, magnetic directional information and tested in a strong and approximately vertical magnetic field. The migratory orientation of these birds did not differ from that of birds held in an undisturbed magnetic field, and both differed significantly from south. Thus, the birds established a deviation from south (away from celestial rotation) in the absence of meaningful magnetic information in the pre-migratory phase. This indicates that magnetic information is not necessary for establishing the appropriate migratory direction when natural celestial cues are available in the pre-migratory period. key worDs: migration direction, orientation, animal behaviour, whitethroat, Sylvia communis

Juvenile Songbirds Compensate for Displacement to Oceanic Islands during Autumn Migration

To what degree juvenile migrant birds are able to correct for orientation errors or wind drift is still largely unknown. We studied the orientation of passerines on the Faroe Islands far off the normal migration routes of European migrants. The ability to compensate for displacement was tested in naturally occurring vagrants presumably displaced by wind and in birds experimentally displaced 1100 km from Denmark to the Faroes. The orientation was studied in orientation cages as well as in the free-flying birds after release by tracking departures using small radio transmitters. Both the naturally displaced and the experimentally displaced birds oriented in more easterly directions on the Faroes than was observed in Denmark prior to displacement. This pattern was even more pronounced in departure directions, perhaps because of wind influence. The clear directional compensation found even in experimentally displaced birds indicates that first-year birds can also possess the ability to correct for displacement in some circumstances, possibly involving either some primitive form of true navigation, or ‘sign posts’, but the cues used for this are highly speculative. We also found some indications of differences between species in the reaction to displacement. Such differences might be involved in the diversity of results reported in displacement studies so far

Collective animal navigation and migratory culture: From theoretical models to empirical evidence

Animals often travel in groups, and their navigational decisions can be influenced by social interactions. Both theory and empirical observations suggest that such collective navigation can result in individuals improving their ability to find their way and could be one of the key benefits of sociality for these species. Here, we provide an overview of the potential mechanisms underlying collective navigation, review the known, and supposed, empirical evidence for such behaviour and highlight interesting directions for future research. We further explore how both social and collective learning during group navigation could lead to the accumulation of knowledge at the population level, resulting in the emergence of migratory culture

Effects of sprint interval training on ectopic lipids and tissue-specific insulin sensitivity in men with non-alcoholic fatty liver disease

Purpose: This study examined the feasibility of sprint interval exercise training (SIT) for men with non-alcoholic fatty liver disease (NAFLD) and its effects on intrahepatic triglyceride (IHTG), insulin sensitivity (hepatic and peripheral), visceral (VAT) and subcutaneous adipose tissue (ScAT). Methods: Nine men with NAFLD (age 41 ± 8 years; BMI 31.7 ± 3.1 kg m−2; IHTG 15.6 ± 8.3%) were assessed at: (1) baseline (2) after a control phase of no intervention (pre-training) and (3) after 6 weeks of SIT (4–6 maximal 30 s cycling intervals, three times per week). IHTG, VAT and ScAT were measured using magnetic resonance spectroscopy or imaging and insulin sensitivity was assessed via dual-step hyperinsulinaemic-euglycaemic clamp with [6,6-D2] glucose tracer. Results: Participants adhered to SIT, completing ≥ 96.7% of prescribed intervals. SIT increased peak oxygen uptake [ V O2peak: + 13.6% (95% CI 8.8–18.2%)] and elicited a relative reduction in IHTG [− 12.4% (− 31.6 to 6.7%)] and VAT [− 16.9% (− 24.4 to − 9.4%); n = 8], with no change in body weight or ScAT. Peripheral insulin sensitivity increased throughout the study (n = 8; significant main effect of phase) but changes from pre- to post-training were highly variable (range − 18.5 to + 58.7%) and not significant (P = 0.09), despite a moderate effect size (g* = 0.63). Hepatic insulin sensitivity was not influenced by SIT. Conclusions: SIT is feasible for men with NAFLD in a controlled laboratory setting and is able to reduce IHTG and VAT in the absence of weight loss

β-Aminoisobutyric Acid Induces Browning of White Fat and Hepatic β-Oxidation and Is Inversely Correlated with Cardiometabolic Risk Factors

The transcriptional coactivator peroxisome proliferator-activated receptor-gamma coactivator-1α (PGC-1α) regulates metabolic genes in skeletal muscle and contributes to the response of muscle to exercise. Muscle PGC-1α transgenic expression and exercise both increase the expression of thermogenic genes within white adipose. How the PGC-1α-mediated response to exercise in muscle conveys signals to other tissues remains incompletely defined. We employed a metabolomic approach to examine metabolites secreted from myocytes with forced expression of PGC-1α, and identified β-aminoisobutyric acid (BAIBA) as a small molecule myokine. BAIBA increases the expression of brown adipocyte-specific genes in white adipocytes and β-oxidation in hepatocytes both in vitro and in vivo through a PPARα-mediated mechanism, induces a brown adipose-like phenotype in human pluripotent stem cells, and improves glucose homeostasis in mice. In humans, plasma BAIBA concentrations are increased with exercise and inversely associated with metabolic risk factors. BAIBA may thus contribute to exercise-induced protection from metabolic diseases