ing torpor, to prevent dehydration, the GFR ceases, preserving needed compounds such as glucose, water, and nutrients. Further, body mass declines throughout nocturnal torpor at a rate of 0.04 g per hour, amounting to about 10% of weight loss each night. The circulating hormone, corticosterone, is one signal that arouses a hummingbird from torpor. Use and duration of torpor vary among hummingbird species and are affected by whether a dominant bird defends territory, with nonterritorial subordinate birds having longer periods of torpor. The hummingbirds of the Andes in South America are known for entering exceptionally deep torpor and dropping their body temperature. Lifespan Hummingbirds have unusually 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 fledging, those that survive may occasionally live a decade or more. Among the bet ter-known North American species, the typical lifespan is probably 3 to 5 years. For comparison, the smaller shrews, among the smallest of all mammals, seldom live longer than 2 years. The longest recorded lifespan in the wild relates to 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 hummingbird similar in size to the broad-tailed hummingbird, and at least 11 years 2 months for a much larger buff-bellied hummingbird. Predators Praying mantises have been observed as predators of hummingbirds. Other predators include dragonflies, frogs, orb-weaver spiders, and other birds, such as the roadrunner. Reproduction As far as is known, male hummingbirds do not take part in nesting. Most species build a cup-shaped nest on the branch of a tree or shrub, alt hough a few tropical species normally attach their nests to leaves.[citation needed] The nest varies in size relative to the particular species – from sma