females. It has been found that eggs laid during a time of drought tend to be larger providing the incubating chick with more nourishment and so a greater chance at survival. Mountain plovers perform uniparental incubation by both sexes. Females leave their first clutch to be incubated and tended to by the male and then lay a second clutch, which she tends to herself. This type of incubation suits the mountain plover well and allows for a greater yield of chicks compared to similar species of birds in which both the male and female tend a single clutch together. Females can mate with several males and have several male tended nests in one breeding season. This would result in a greater reproductive success for the female but there is a high energy cost on the female laying so many eggs and so it is more common for a female to lay only two clutches. If the eggs survive various dangers, especially such predators as coyotes, snakes, and swift foxes, they hatch in 28 to 31 days, and the hatchlings leave the nest within a few hours. In the next two or three days, the family usually moves one to two kilometers from the nest site to a good feeding area, often near a water tank for livestock. The population has been estimated at between 5,000 and 10,000 adult birds, although those numbers have recently been revised to the range of 11,000 to 14,000, with a total population estimate of about 15,000 to 20,000. In March 2009, a multi-agency report, the first of its kind, issued by the Cornell University Lab of Ornithology in conjunction with federal agencies and other organizations, indicated that the mountain plover is one of the birds showing serious declines in population. The population of mountain plovers is in decline because of cultivation, urbanization, and over-grazing of their living space. Fritz Knopf has closely studied the mountain plover, and has tracked population declines. These downhill trends led to a 1999 proposal to list them as a threatened species. On June 29, 2009 the U.S. Fish and Wildlife Service published a proposed rule to list the mountain plover as threatened under the Endangered Species Act. Preservation A 2005 report details that in a study conducted by Stephen J Dinsmore, Gary C White, and Fritz L Knopf, the populations of mountain plovers and prairie dogs in southern Phillips County