Northern Prairie Wildlife Research Center
|This flock of cranes has gathered in a harvested corn field to feed on waste corn. Most of the fat reserves cranes acquire while in the Platte Valley are derived from corn. Fat reserves are utilized by the cranes during the long migration to northern breeding areas and during reproduction.|
Major gaps remain in knowledge needed to effectively manage the midcontinent sandhill crane population. This lack of knowledge is hampering efforts by crane managers to prioritize where to focus habitat conservation and restoration efforts, develop appropriate guidelines for hunting seasons, and address other management issues. Growing information needs are resulting, in part, from questions surrounding impacts of habitat loss, particularly in the Central Platte Valley in Nebraska where the population gathers each spring and acquires fat reserves used during migration and reproduction. Encroachment of woody vegetation on the Platte River channels has severely restricted the area suitable for the cranes to roost. As a result, competition for food has increased markedly. Also, numbers of geese stopping in the Valley in late winter and early spring have increased dramatically, adding to the problem. Concerns that cranes may be having difficulty locating adequate food under changing conditions in the Valley have heightened because of information gathered in 1996 which indicated the daily rate of fat storage by sandhill cranes during spring in the Platte Valley may have declined by nearly 50% from the late 1970s. Detailed studies currently are underway to assess magnitude of change in fat and protein storage by sandhill cranes in the Platte Valley since the 1970's. This information along with other insights gained on crane needs will be used to help guide long-term habitat restoration efforts in the Platte Valley.
|Sandhill cranes prefer to roost in the shallow waters and on the sandbars in those sections of the Platte River continuing to have wide channels. Over time, encroachment of woody vegetation has eliminated large tracts of this roosting habitat causing cranes to crowd at high densities into the remaining suitable habitat.|
|Wet meadow habitats like these supply important food resources for cranes. Invertebrates such as earthworms and snails provide essential nutrients for maintenance and reproduction. (Photos by Jan Eldridge)|
Until recently, tools were lacking which would allow scientists to follow individual sandhill cranes throughout their annual cycle as needed to address unanswered questions concerning the midcontinent population. However, the recent development of small and lightweight Platform Transmitting Terminals (PTT's) which, when attached to birds, can be monitored from orbiting satellites, has made possible the tracking of migratory birds throughout their annual cycles. The 21 sandhill cranes that have been monitored to date and displayed here, were captured and radio-marked in the Platte Valley during March-April 1998-99 in the first two years of a planned 4-year study to gain a better understanding of several parameters important to management of the midcontinent population. The results of this study are expected to benefit all agencies, organizations, and individuals having a stake in management of the midcontinent sandhill crane population in the United States, Canada, Mexico, and Russia.
Specific goals of our satellite telemetry research are to: (1) identify the breeding grounds, migration routes, and wintering areas of the 3 subspecies of sandhill cranes that form the midcontinent population, (2) determine distribution and duration of stay of the subspecies and subpopulations within the Central Platte and North Platte river valleys and factors controlling their distribution and length of stay, (3) estimate the proportion of the midcontinent population present in the survey area when the annual population survey is conducted in March, which will allow a better assessment of reliability of current population estimates, and (4) determine temporal and spatial distribution and exposure of the 3 subspecies to hunting during fall migration and winter.
Funding currently is being sought to increase the sample size of PTT-marked cranes to levels considered adequate to address identified objectives. Start-up funding for the satellite telemetry work on sandhill cranes came through the Platte River Ecosystem Initiative, a multi-division study of the U.S. Geological Survey being undertaken in response to information needs on sandhill cranes and other species of migratory birds using the Platte River ecosystem. This project is addressing research needs of key species of migratory birds using the Platte Valley and adjacent areas, their habitats, and the role of hydrology and geology in influencing habitat conditions, particularly within the Platte River channels and adjoining wet meadows. The research team consists of biologists from the Northern Prairie Wildlife Research Center representing the Biological Resources Division of USGS, along with researchers from the Water Resources Division, the Geologic Division, and the Mapping Division.