Answers
Animals can adapt to changes in feeding conditions by switching between foraging methods. Hence the birds can monitor its environment while foraging. The lower intake rates are provided at deeper foraging. For example, 50g of edible things are presented for two patches which is at the depth of 7cm and another at the depth of 40cm, and most of the foraging in the shallow area. Reducing the food abundance to 15g, the shallow area led to an increase in deep foraging, although the birds prefer the shallow area which does not provide a higher intake rate.
The birds did not tirn to the deep foraging until the shallow patch was empty. Hence the patches affects the survival of the humming birds.
The statement of the darwin "It is not the strongest that survive, nor the intelligent, but the one most responsive to change" defines the change to reflect for the foraging at the higher latitudes. Due to their high metabolism and small body size, to survive cold nights they rely upon a state known as torpor which conserves energy. wintering conditions impact the timing and condition of birds as they migrate north. Hummingbirds obtain much of their energy from nectar and most of their protein from insects.
With their high metabolic rates, hummingbirds are particularly susceptible to fluctuations in the availability of these resources. For example, when the amount or concentration of sucrose in nectar available to birds is experimentally decreased, hummingbirds lose weight and exhibit negative energy balance. In low‐resource winters, broad‐tailed hummingbirds delay their annual winter molt, arrive later at spring migratory stopover sites, and have lower body mass and fat scores than in years where the wintering grounds experience average or above‐average temperatures and resources. Early arrival at breeding sites often increases the individual reproductive success, by early establishment and defense of high‐quality territories, acquisition of high‐quality mates, and increased offspring survival.
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