Does low daily energy expenditure drive low metabolic capacity in the tropical robin, Turdus grayi?

Abstract

Temperate and tropical birds possess divergent life history strategies. Physiological parameters including energy metabolism correlate with the life history such that tropical species with a slower 'pace of life' have lower resting and maximal metabolic rates than temperate congeners. To better understand the physiological mechanisms underlying these differences, we investigated the relationship of metabolic capacity, muscle oxidative capacity and activity patterns to variation in life history patterns in American robins (Turdus migratorius), while resident in central North America and Clay-colored robins (Turdus grayi) resident in Panama. We measured summit metabolism [Formula: see text] in birds from both tropical and temperate habitats and found that the temperate robins have a 60 % higher metabolic capacity. We also measured the field metabolic rate (FMR) of free-living birds using heart rate (HR) telemetry and found that temperate robins' daily energy expenditure was also 60 % higher. Thus, [Formula: see text] and FMR both reflect life history differences between the species. Further, both species operate at a nearly identical ~50 % of their thermogenic capacity throughout a given day. As a potential mechanism to explain differences in activity and metabolic capacity, we ask whether oxidative properties of flight muscle are altered in accordance with life history variation and found minimal differences in oxidative capacity of skeletal muscle. These data demonstrate a close relationship between thermogenic capacity and daily activity in free-living birds. Further, they suggest that the slow pace of life in tropical birds may be related to the maintenance of low activity rather than functional capacity of the muscle tissue.

Summit metabolic rate exhibits phenotypic flexibility with migration, but not latitude in a neotropical migrant, Parkesia noveboracensis

“…This observation led Ricklefs and Wikelski (2002) to propose that physiological systems, including energy metabolism, also follow this slow-to-fast continuum. Supporting this hypothesis, both basal (Wiersma et al 2007a), maximal (Wiersma et al 2007b) and field (Wagner et al 2013) metabolic rates of tropical birds were found to be lower than those of paired temperate species.…”

PPAR expression, muscle size, and metabolic rates across the Gray catbird's annual cycle are greatest in preparation for fall migration

“…However, the catbirds in our study exhibited similar VȮ 2summit during spring and fall migrations. Previous studies have demonstrated higher metabolic rates in resident bird species from high latitudes compared with related tropical species (Wagner et al, 2013;Wiersma et al, 2007a, b), thought to reflect the 'pace of life' in each environment (Ricklefs and Wikelski, 2002). The first study to measure metabolic capacity of songbird migrants (northern waterthrush) at both tropical and temperate locales (Corder and Schaeffer, 2015) found that although VȮ 2summit was highest during migration, rates during tropical wintering and temperate breeding were similar.…”

Heart rate reveals torpor at high body temperatures in lowland tropical free-tailed bats

“…The heart rate from radio transmitters has been visually scored at sampling intervals of 5–10 min [ 33 , 34 , 45 , 53 ]. However, complete sampling can show novel energy-saving strategies like those in tent-making bats that depress f H several times per hour [ 26 ], a pattern that would not have been detected by sampling every five to ten minutes.…”