Birds and Food Shortage
The term“food shortage”has been used for food that is inadequate in quantity,quality,or availability.Whatever the abundance of food in the environment,if it is for some reason unavailable,bird species in either inland or coastal areas may starve. Food sources like intertidal invertebrates retreat deeper in the mud in cold weather,putting them beyond the reach of shorebirds,while many soil-dwelling invertebrates move deeper into the ground during drought.Such behaviors illustrate the general points that only a proportion of potential food items may be accessible to birds at any one time,and that this proportion may change through time in response to other conditions.Secondly,if food is plentiful but of low nutrient content or digestibility,a bird may be unable to process enough each day to maintain its weight.This is particularly true of herbivores (plant eaters)eating fibrous,or coarse,vegetation,and food shortage may arise partly from the structure of a bird’s inner parts,or gut,which limits the rate at which food can be processed.In general among birds,species differences in gut structure correspond with dietary differences,and in species whose diet changes seasonally,gut structure may change accordingly.The need for change in gut structure can make some species vulnerable at times of rapid shift in diet,as when snowfall forces birds suddenly from one food type to another.
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