Baby Hummingbirds In The Nest

The dynamic range of metabolic rates in hummingbirds requires a corresponding dynamic range in kidney function. The glomerulus is a cluster of capillaries in the nephrons of the kidney that removes certain substances from the blood, like a filtration mechanism. The rate at which blood is processed is called the glomerular filtration rate (GFR). Most often these fluids are reabsorbed by the kidneys. During torpor, to prevent dehydration, the GFR slows, preserving necessities for the body such as glucose, water and salts. GFR also slows when a bird is undergoing water deprivation. The interruption of GFR is a survival and physiological mechanism unique to hummingbirds.
Studies of hummingbirds' metabolisms are highly relevant to the question of how a migrating Ruby-throated Hummingbird can cross 800 km (500 mi) of the Gulf of Mexico on a nonstop flight. This hummingbird, like other birds preparing to migrate, stores up fat to serve as fuel, thereby augmenting its weight by as much as 100 percent and hence increasing the bird's potential flying time.
• Lifespan
Hummingbirds have long lifespans for organisms with such rapid metabolisms. Though many die during their first year of life, especially in the vulnerable period between hatching and leaving the nest (fledging), those that survive may live a decade or more. Among the better-known North American species, the average lifespan is probably 3 to 5 years. By comparison, the smaller shrews, among the smallest of all mammals, seldom live more than 2 years. The longest recorded lifespan in the wild is that of a female Broad-tailed Hummingbird that was banded (ringed) as an adult at least one year old, then recaptured 11 years later, making her at least 12 years old. Other longevity records for banded hummingbirds include an estimated minimum age of 10 years 1 month for a female Black-chinned similar in size to Broad-tailed, and at least 11 years 2 months for a much larger Buff-bellied Hummingbird.