Overexploitation, habitat destruction, pollution, human disturbance, and natural disasters are just some of the factors that have contributed to the overall whooping crane population decline. Historically, drainage and clearing of wetlands, and the conversion of marshlands to hay and grain production made the birds’ breeding areas unsuitable for nesting (USFWS, 2007). These alterations also disrupted the whooping cranes’ migratory routes, since stopovers sites were no longer sufficient to replenish the birds’ energy needs. Half of the whooping cranes in Louisiana were killed by a hurricane in 1940, while severe thunder storms that hit Florida in 2006 killed 18 whooping cranes of the Eastern migratory flock due to drowning.
Hunting of the cranes for food or collection, and egg harvesting also contributed to population losses (Tufty, 1964), in addition to human-caused erosion of marsh shorelines along the Gulf Coast of Texas. Whooping cranes are also exposed to contaminations associated with runoff from industrial activities on their wintering grounds in Texas. For instance, in 1988, estuaries nearby Lavaca Bay were heavily contaminated by chronic mercury, polluting sediments and nutrients, and contaminating several species of fish and crabs (Sager, 2002). In addition, oil spills along these regions also affects the availability of food for the whooping crane, decreasing the blue crab population, which is the preferred food source of the cranes.
The increased number of dams and water diversions has also played a part in preventing water flow to their natural habitats, thus decreasing the availability of food and fresh drinking water. Collisions with utility lines, fences, and other human created structures have contributed to whooping crane mortality during migration. In fact, Morkill and Anderson (1991) noted that the principle known cause of death for wild fledged whooping cranes is due to collisions with power lines. Kuyt’s (1992) study also showed that at least 19 whooping cranes have been killed since 1956 as a result of power line collisions, and two out of nine radio-marked juvenile cranes die as a result of collisions within their first 18 months of life.