WSP05055 - Laserfiche WebLink

Home Browse Search

"'- 14 Parents separate from their young of the previous year upon departure from Aransas N\IIIR in northward migration, whila en route to the breeding grounds or soon after arrival on the breeding grounds (Allen 1952. Archibald et al. 1976, Stehn unpubl, 1992. Kuyt unpubl.). Information on marked individuals suggests that most juveniles and subadults spend the summer near their natal area (Kuyt 1979b. 1981 a). E, Reasons for Listing The impact of human settlement upon the wildlife 6f interior North America is dramatically evident in the changing status of the whooping crane. Cranes disappeared as agriculture claimed the northern Great Plains of the U.S. and Canada (Allen 1952), Only one small population survived. Ironically, the traditions which appear to have saved the whooping crane as a small relict breeding population in WBNP, prevent its voluntary return to what was once its principal nesting range, Re-colonization of these former breeding areas remains unlikely unless man assists with purposeful reintroduction, ; c. ~ Bioloaical Characteristics: Delayed sexual maturity, small clutch size, and low recruitment rate preclude rapid population recovery, The current northern breeding grounds may be another handicap to productivity because the ice-free season is only 4 months. During that time, pairs must incubate their eggs for 29-31 days, and rear their chicks to flight age in 3 months. Consequently, unless nest loss occurs early in incubation. there is rarely time to lay a second clutch and fledge young if the first clutch fails. During 1939-1964when there was no human interference in the form of egg removal, 180 breeding pairs produced 15 sets of siblings or one of each 12 families arriving on the Texas coast in fall contained 2 juveniles (pers. comm, E. Kuyt 1993). During years when whooping cranes were surveyed on the breeding grounds (when no eggs have been removed). about one out of every four hatched chicks survived to reach the Texas coast. Factors which limit chick survival remain open to conjecture, Most mortality occurs soon after hatching. and chicks that fledge have a high probability of successfully completing their first migration (Kuyt 1976a). Most immediate post-hatching mortality may be related to sibling aggression and short-term food shortage because eggs hatch asynchronously and the precocial young are extremely aggressive toward each other. The dominant chick apparently obtains principal access .to food made available by the parents. consequently brood-size is rapidly reduced during periods of food shortage (Miller 1973. Drewien 1973), Prolonged food shortage. possibly related to drought, and drought-increased predation (Kuyt 1981.\)) may account for additional mortality, Suitable nesting habitat conditions are the chief reasons for population increases 1984 through 1990, Little is known about the importance of diseases or' parasites as mortality factors. At the time of his capture (mid-September) in WBNP. due to a wing injury (Novakowski 1965). "CAN-US" was found to be infected with coccidia, . Coccidia have been found in whooping crane droppings collected on the wintering grounds (Forrester et ai, 1978), and have caused deaths of several whooping crane chicks at Patuxent Wildlife Research Center (Carpenter et al. 1980). Fecal accumulations and concentrations. of coccidia oocysts at brooding sites on the breeding grounds may infect preflight birds. Chicks may be especially vulnerable to attack by coccidia due to the absence of acquired immunity. However. droppings normally