Christopher G. Guglielmo’s research while affiliated with University of the Western Cape and other places

Migratory birds are physiologically challenged by intense exercise while fasting during flights that may last hours to days. Exercise‐induced oxidative stress could compromise flight performance by inducing mitochondrial dysfunction in the flight muscle. Endurance flight is partially fuelled by the catabolism of lean tissues, but how this catabolism is partitioned between different organs and muscles has not been previously studied under controlled conditions. We hypothesized that simulated migratory flight would result in dysfunction of flight muscle mitochondria, and selective catabolism of lean tissues. We predicted that simulated migratory flight would cause reduced mitochondrial oxidative phosphorylation capacity while increasing emission of reactive oxygen species (ROS) and that lean tissue mass catabolism would preferentially occur in digestive organs not needed in flight. We measured mitochondrial function, muscle morphology and the wet masses of organs and muscles following 8‐hour wind tunnel flights in blackpoll warblers Setophaga striata, which use multi‐day nonstop flights as part of their migration strategy. In contrast to our predictions, we found that simulated migratory flight did not alter mitochondrial fatty acid oxidation capacity or ROS emission. However, flight and fasting increased whole‐animal lean mass catabolism and were associated with reductions in the masses of liver, gizzard and proventriculus, but masses of tissues in the flight apparatus (pectoralis, heart, lungs) were unaffected. Pectoralis muscle fiber morphology was also unchanged over the tested flight duration. Our findings indicate that mitochondrial function in blackpoll warblers is robust against damage induced by simulated migratory flight, and energy deprivation is sufficient for organ catabolism.

Chronic exposure to low oxygen (hypoxia) leads to amplification of the hypoxic chemoreflex, increasing breathing and sympathetic nervous system (SNS) activation. Prolonged SNS activation redistributes blood to hypoxia-sensitive tissues, away from muscles. Recent tracking studies have shown that migratory songbirds can fly 5,000 m or higher above sea level, leading us to hypothesize that migratory birds may have a blunted hypoxic chemoreflex to maintain blood flow to muscles during migratory flight at high altitudes. To test this hypothesis, we used a hypobaric wind tunnel and measured circulating plasma catecholamines after maximal altitude flight, flight at 75% of maximal altitude, flight at ground level (~250 m), and after rest at 75% of maximal altitude and ground level in migratory myrtle yellow-rumped warblers ( Setophaga coronata). Yellow-rumped warblers were capable of flying above 4,000 m simulated altitude above sea level (average maximum altitude of ~3,600 m), and would maintain flights at 75% of individual maximum altitudes (~2,700 m). Circulating dopamine and noradrenaline were similar between resting and flight conditions at ground level and with exposure to 75% of maximal altitude, whereas adrenaline significantly increased with flight, but did not change further with flight at 75% of maximal altitude. By contrast, both adrenaline and noradrenaline concentrations increased after maximum altitude flights compared to 75% and ground level flights. Our findings show that exercise increases plasma adrenaline in migratory songbirds, and suggest that warblers flying at high altitudes below their maximum altitude may be minimally hypoxic, allowing them to maintain oxygen transport to flight muscles.

The pectoralis muscle in birds is important for flight and thermogenesis. In migratory songbirds this muscle exhibits seasonal flexibility in size, but whether this flexibility reflects changes in muscle fiber type has not been well documented. We investigated how seasonal changes in photoperiod affected pectoralis muscle fiber type and metabolic enzymes, comparing among three closely-related sparrow species: two seasonal migrants and one year-round, temperate climate resident. We quantified fast oxidative glycolytic (FOG) and fast glycolytic (FG) fibers histologically, and measured activities of citrate synthase (CS) and lactate dehydrogenase (LDH) in the pectoralis muscle of the three species that were acclimated to long- or short-daylight length conditions. In all species FOG was the predominant fiber type, but song sparrows had FG fibers regardless of daylight length. By contrast, Lincoln's sparrows incorporated FG fibers only under short-daylight length onditions, and house sparrows did not significantly express FG fibers, regardless of conditions. Both migratory species increased LDH activity in short-daylight conditions, but did not alter CS activity. In contrast, resident house sparrows did not alter CS or LDH activity with changes in daylight length. Our findings suggest that the presence of FG fibers is important for seasonal flexibility in LDH activity. Additionally, migratory species exhibited seasonal flexibility in muscle fiber type and enzyme activity, presumably to support migratory flight, while the resident species did not exhibit such seasonal flexibility, suggesting that this consistent phenotype is important year-round, despite changing thermogenic requirements.

The pectoralis major is the muscle required for migratory flight in songbirds, and has been believed to be exclusively composed of fast oxidative glycolytic (FOG) fibers in most small songbirds (< 20 g). Here, we investigated the effect of season (migratory versus non-migratory) and migratory distance (within North America versus to South America) on muscle fiber type in three songbird families: vireos (Vireonidae), warblers (Parulidae), and thrushes (Turdidae). FOG and fast glycolytic (FG) fibers were identified using myosin-ATPase staining. Short-distance migrants within the vireo and warbler families altered their pectoralis muscle to contain FG fibers during non-migratory conditions, while long-distance migrants maintained exclusively FOG fibers, regardless of season. Thrushes, a family of larger songbirds, exhibited mixed fibers regardless of season or migratory distance. This study is one of the first to identify FG fibers in small North American songbirds and highlights the potential role of migratory distance and season on muscle phenotype.

Birds remodel their flight muscle metabolism prior to migration to meet the physiological demands of migratory flight, including increases in both oxidative capacity and defence against reactive oxygen species. The degree of plasticity mediated by changes in these mitochondrial properties is poorly understood but may be explained by two non-mutually exclusive hypotheses: variation in mitochondrial quantity or individual mitochondrial function. We tested these hypotheses using yellow-rumped warblers (Setophaga coronata), a Nearctic songbird which biannually migrates two to five thousand kilometres. We predicted higher flight muscle mitochondrial abundance and substrate oxidative capacity and decreased reactive oxygen species emission in migratory warblers captured during autumn migration compared to a short-day photoperiod-induced non-migratory phenotype. We assessed mitochondrial abundance via citrate synthase activity and assessed isolated mitochondrial function using high-resolution fluororespirometry. We found 60% higher tissue citrate synthase activity in the migratory phenotype, indicating higher mitochondrial abundance. We also found 70% higher state 3 respiration (expressed per unit citrate synthase) in mitochondria from migratory warblers when oxidizing palmitoyl-carnitine, but similar H2O2 emission rates between phenotypes. By contrast, non-phosphorylating respiration was higher and H2O2 emission rates were lower in the migratory phenotype. However, flux through electron transport system complexes I-IV, II-IV and IV were similar between phenotypes. In support of our hypotheses, these data suggest that flight muscle mitochondrial abundance and function are seasonally remodeled in migratory songbirds to increase tissue oxidative capacity without increasing reactive oxygen species formation.

Recent research has shown that songbirds that reside at low altitudes can ascend to ∼6000 m above sea level during migratory flight. Since migratory flight is aerobically demanding, whether migratory songbirds exhibit plasticity in breathing to maintain oxygen uptake in low-oxygen environments is unknown. This study investigated whether the hypoxic ventilatory response of sparrows was altered between resident house sparrows (Passer domesticus (Linneaus, 1758)) and migratory song sparrows (Melospiza melodia (A. Wilson, 1810)), and Lincoln's sparrows (Melospiza lincolnii (Audubon, 1834)) or seasonally (long daylight versus short daylight length) within a species. Breathing responses were assessed by stepwise reductions in inspired O2 tension, 21, 16, 12, 9, 7, and 5 kPa during long and short days. Ventilation increased in hypoxia in all species, although song sparrows and Lincoln's sparrows exhibited greater increases in ventilation in severe hypoxia compared to house sparrows. All species became more sensitive to hypoxia during short days compared to long days (increased breathing frequency and total ventilation), with reduced pulmonary oxygen extraction. Although all sparrows had similar ventilatory responses in moderate hypoxia, our findings suggest that migratory sparrows breathe more effectively in severe hypoxia compared to house sparrows, which would be important for maintaining oxygen uptake during migratory flights.

Dietary n-3 long chain polyunsaturated fatty acids (LCPUFA) are hypothesized to be natural doping agents in migratory shorebirds, enabling prolonged flight by increasing membrane fluidity and oxidative capacity of the flight muscles. Animals can obtain n-3 LCPUFA from the diet or by conversion of dietary α-linolenic acid, 18:3 n-3. However, capacity to meet n-3 LCPUFA requirements from 18:3 n-3 varies among species. Direct tests of muscle oxidative enhancement and fatty acid conversion capacity are lacking in marine shorebirds that evolved eating diets rich in n-3 LCPUFA. We tested whether the presence and type of dietary fatty acids influence the fatty acid composition and flight muscle oxidative capacity in western sandpipers (Calidris mauri). Sandpipers were fed diets low in n-3 PUFA, high in 18:3 n-3, or high in n-3 LCPUFA. Dietary fatty acid composition was reflected in multiple tissues, and low intake of n-3 LCPUFA decreased abundance of these fatty acids in all tissues, even with a high intake of 18:3 n-3. This suggests that 18:3 n-3 cannot replace n-3 LCPUFA, and dietary n-3 LCPUFA are required for sandpipers. Flight muscle indicators of enzymatic oxidative capacity and regulators of lipid metabolism did not change. However, the n-3 LCPUFA diet was associated with increased FAT/CD36 mRNA expression, potentially benefitting fatty acid transport during flight. Our study suggests that flight muscle lipid oxidation is not strongly influenced by n-3 PUFA intake. The type of dietary n-3 PUFA strongly influences the abundance of n-3 LCPUFA in the body and could still impact whole-animal performance.

Natália Stefanini Da Silveira Rachael W. Herman The AOS Harry R. Painton Award, given in odd-numbered years, is presented to the author of an outstanding paper published in the two preceding years in Ornithological Applications. The award was established in 1961 through a bequest from physician and eminent amateur ornithologist Harry Painton; a history of the Painton Award, including winners from 1961 to 1993, was published in The Condor in 1994. The 2023 Harry R. Painton Award recipient is Natália Stefanini Da Silveira for her paper “Future climate change will impact the size and location of breeding and wintering areas of migratory thrushes in South America” (Da Silveira et al. 2021). Natália Stefanini Da Silveira has a degree in biological sciences from the State University of São Paulo (UNESP), and a master’s degree and doctorate from the postgraduate program in zoology, Institute of Biosciences, UNESP, Rio Claro. In her postgraduate studies, she examined animal movement at different scales—focusing on birds—from regional movements to migrations and the impact of environmental changes on these systems. She is currently a postdoctoral candidate at the Spatial Ecology and Conservation Lab (LEEC; UNESP-RC), and works in partnership with Tropical Water Research Alliance (TWRA) on a project for sustainable development and biodiversity conservation in the Tocantins–Araguaia Hydrographic Basin. In their winning paper, “Future climate change will impact the size and location of breeding and wintering areas of migratory thrushes in South America,” Da Silveira and her coauthors examined the potential impact of future climate change on migratory thrushes in South America—a region rich in migrating birds whose movement patterns are not well understood. The authors explored how the distribution of breeding and wintering areas in three closely related species of thrushes with different migratory patterns (one short- and two long-distance migrants) change under future climate change scenarios. They predicted declines in the area of future breeding and wintering grounds along with elevational and longitudinal shifts in distribution. Their paper is the first of its kind to describe how climate change may affect migratory birds in South America, showing that impacts will differ depending on where species breed and overwinter.

Migratory flight requires birds to maintain intensive aerobic exercise for many hours or days. Maintaining O2 supply to flight muscles is therefore important during migration, especially since migratory songbirds have been documented flying at altitudes greater than 5,000 m above sea level, where O2 is limited. Whether songbirds exhibit seasonal plasticity of the O2 cascade to maintain O2 uptake and transport during migratory flight is not well understood. We investigated changes in the hypoxic ventilatory response, haematology, and pectoralis (flight) muscle phenotype of 6 songbird species from 3 families during migratory and non-migratory conditions. Songbirds were captured during southbound migration in southern Ontario, Canada. Half of the birds were assessed during migration, and the rest were transitioned onto a winter photoperiod to induce a non-migratory phenotype and measured. All species exhibited seasonal plasticity at various stages along the O2 cascade, but not all species exhibited the same responses. Broadly, songbirds were more hypoxia tolerant during migration, withstanding 5 kPa O2, and breathed more effectively through slower, deeper breaths. Warblers had a stronger haemoglobin-O2 affinity during fall migration (decrease of ∼4.7 Torr), while the opposite was observed in thrushes (increase of ∼2.6 Torr). In the flight muscle there was an ∼1.2-fold increase in the abundance of muscle fibers with smaller fiber transverse areas during fall migration, but no changes in capillary-fiber ratio. These adjustments would enhance O2 uptake and transport to the flight muscle. Our findings demonstrate that in the O2 cascade there is no ideal migratory phenotype for all songbirds.

In many migratory songbirds, males arrive earlier at stopover sites and at the breeding grounds (‘protandry’) and older birds precede younger ones, but less is known about age differences in protandry. In seasonal environments, differential timing by sex and age is thought to reflect selection imposed by seasonality (i.e., viability selection) and intrasexual competition for space and mates. Viability and sexual selection can also favor male-biased sexual size dimorphism (SSD), leading to a positive relationship between protandry and SSD among species. We evaluated whether the relationship between protandry during spring migration and SSD in wing length (SSDW) differed between age classes in 20 sexually dimorphic songbirds. Consistent with the hypothesis that older, higher-quality males can better afford to arrive early, we found a stronger relationship between protandry and SSDW among older birds than among first-time breeders. We also tested the relationship between protandry and sexual size dimorphism of the wingtip (SSDWT) and found that greater age differences in protandry were related to greater age differences in SSDWT. We conclude that larger body sizes, energetically efficient wing shapes, and experience together select for the earlier arrival timing of older males relative to first-time breeding males and females.