David J. Cerasale

A Field Validation of Plasma Metabolite Profiling to Assess Refueling Performance of Migratory Birds

Plasma metabolite profiling offers a potential means to assess stopover refueling performance of migratory birds from a single capture. However, this method has not previously been validated where site quality has been determined independently using analysis of capture data. We captured and blood sampled six passerine bird species refueling at known high‐quality (BASE) and low‐quality (TIP) sites at Long Point, Ontario, Canada. Plasma triglyceride, an indicator of fat deposition, was higher at the BASE in three early‐season species: the hermit thrush, the American robin, and the white‐throated sparrow. Plasma B‐OH‐butyrate, an indicator of fasting and lipid utilization, was lower at the BASE in the same three species. Plasma glycerol was lower at the BASE in American robins, and plasma phospholipid did not differ between sites. No metabolite suggested better conditions at the TIP in any species. Regression of size‐corrected mass on time of day also indicated better refueling performance at the BASE in some species, but metabolite profiling was generally more sensitive to site differences. The relationship between plasma glycerol and triglyceride was U‐shaped, indicating high glycerol production during both lipolysis (as was previously known) and rapid fat deposition. Our results confirm the validity of metabolite profiling to assess stopover habitat quality and individual performance in refueling migrants.

An Integrative Assessment of the Effects of Tamarisk on Stopover Ecology of a Long-Distance Migrant Along the San Pedro River, Arizona

ABSTRACT. The riparian habitats of the arid southwestern United States provide critical stopover habitat for avian migrants, but they have been severely altered by invasive tamarisk (Tamarix spp.). The responses of birds to such habitat alterations are not well understood. We combined ecological and physiological measurements to provide an integrative assessment of how tamarisk invasion affects the stopover ecology of vernally migrating Wilsons Warblers (Wilsonia pusilla) along the San Pedro River in Arizona. Despite higher arthropod biomass in native cottonwood—willow habitat, the refueling rate of Wilsons Warblers, as measured by plasma metabolite profiling, was higher in tamarisk. Density and detections of Wilsons Warblers did not differ between habitats, but both measurements were significantly higher in cottonwood—willow habitat for the other members of the Wilsons Warbler foraging guild. Our measurements of food resources and migrant densities suggest that cottonwood—willow may provide high-quality stopover habitat. But when plasma metabolites are included, our results indicate that tamarisk offers superior habitat for refueling Wilsons Warblers, possibly because of release from high interspecific competition in cottonwood—willow. Our results demonstrate the importance of measuring refueling performance in the assessment of stopover habitat quality and the value of including plasma metabolite profiling in studies of avian stopover ecology.

Phylogeny of the Tachycineta genus of New World swallows: insights from complete mitochondrial genomes.

The Tachycineta genus of swallows is comprised of nine species that range from Alaska to southern Chile. We sequenced the entire mitochondrial genome of each member of Tachycineta and generated a completely resolved phylogenetic hypothesis for the corresponding mitochondrial gene tree. Our analyses confirm the presence of two sub-clades within Tachycineta that are associated with geography: a North American/Caribbean clade and a South/Central American clade. We found considerable variation among regions of the mitochondrial genome in both substitution rates and the level of information that each region supplied for phylogenetic reconstruction. We found no evidence of positive directional selection within mitochondrial coding regions, but we identified numerous sites under purifying selection. This finding suggests that, despite differences in life history traits and distributions, mitochondrial genes in Tachycineta are predominantly under purifying selection for conserved function.

Behavioral and physiological effects of photoperiod-induced migratory state and leptin on Zonotrichia albicollis: II. Effects on fatty acid metabolism

The migratory flights of birds are fuelled largely by fatty acids. Fatty acid transporters, including FAT/CD36, FABPpm and H-FABP, and enzymes involved in fatty acid oxidation (CPT, CS, HOAD) are seasonally up-regulated in flight muscle to meet the demands of this intense aerobic exercise. The mechanisms that control these biochemical changes in response to migration are mostly unknown. We studied the effects of a photoperiod-induced migratory state and a 7 day treatment with murine leptin (1 μg/g body mass, twice per day) on fatty acid metabolism in captive white-throated sparrows. Sparrows that were exposed to a long-day migratory photoperiod increased flight muscle FAT/CD36 and H-FABP mRNA by 154% and 589%, respectively, and had 32% higher H-FABP protein than birds kept on a short-day photoperiod that mimicked wintering conditions. Migrants increased activities of flight muscle CPT, CS and HOAD by 57%, 23% and 74%, respectively, and decreased LDH activity by 31%, reflecting an increase in aerobic relative to anaerobic capacity. The expression of fatty acid transporters and the activities of metabolic enzymes in cardiac muscle were unaffected by migratory state. Leptin had no effect on transport proteins or enzymes in either skeletal or cardiac muscle suggesting that other signaling pathways control fatty acid metabolism during migration. These data indicate that photoperiod alone is sufficient to prime flight muscles for migratory flights by promoting enhanced protein-mediated fatty acid transport and oxidation. However, the endocrine controls and other factors underlying these changes remain to be thoroughly investigated.

Plasma Metabolite Profiles: Effects of Dietary Phospholipids in a Migratory Passerine (Zonotrichia leucophrys gambelii)

Plasma metabolites, including triglycerides, β‐hydroxybutyrate, and glycerol, can be used to estimate mass change in birds. Although dietary fatty acids can be ingested and absorbed as phospholipids, they have been largely overlooked as a potential indicator of mass change. The plasma ratio of triglyceride to phospholipid could also provide insight into diet quality because a high ratio in food items indicates high relative energy content. Variability in dietary phospholipid content and triglyceride:phospholipid may also affect the relationships between metabolites and mass change. We fed Gambel’s white‐crowned sparrows (Zonotrichia leucophrys gambelii) diets differing in phospholipid content and triglyceride:phospholipid and measured metabolites during mass loss and mass gain. Plasma phospholipids were higher and triglyceride:phospholipid was lower in birds fed a diet higher in phospholipid content and lower in triglyceride:phospholipid. Contrary to our expectations, plasma phospholipids were negatively related to mass change. Plasma triglyceride levels were positively related to mass change and unaffected by diet. The relationships between mass change and both plasma β‐hydroxybutyrate and glycerol were affected by diet. Plasma triglyceride appears to be the most reliable metabolite predicting body mass changes, but inclusion of plasma phospholipids and triglyceride:phospholipid into metabolite profiles may provide additional information on diet quality.

Laterality and Flight: Concurrent Tests of Side-Bias and Optimality in Flying Tree Swallows

Behavioural side-bias occurs in many vertebrates, including birds as a result of hemispheric specialization and can be advantageous by improving response times to sudden stimuli and efficiency in multi-tasking. However, behavioural side-bias can lead to morphological asymmetries resulting in reduced performance for specific activities. For flying animals, wing asymmetry is particularly costly and it is unclear if behavioural side-biases will be expressed in flight; the benefits of quick response time afforded by side-biases must be balanced against the costs of less efficient flight due to the morphological asymmetry side-biases may incur. Thus, competing constraints could lead to context-dependent expression or suppression of side-bias in flight. In repeated flight trials through an outdoor tunnel with obstacles, tree swallows (Tachycineta bicolor) preferred larger openings, but we did not detect either individual or population-level side-biases. Thus, while observed behavioural side-biases during substrate-foraging and copulation are common in birds, we did not see such side-bias expressed in obstacle avoidance behaviour in flight. This finding highlights the importance of behavioural context for investigations of side-bias and hemispheric laterality and suggests both proximate and ultimate trade-offs between species-specific cognitive ecology and flight biomechanics.