Sandhill Crane Mortality Due to Blizzard of March 1996 in Nebraska
Gary R. Lingle, Platte River Whooping Crane Maintenance Trust, 2550 N. Diers Ave. Suite H, Grand Island, Nebraska 68803, (308) 384-4633 (4634), lingle@hamilton.net
Storm-related mortality of migratory birds undoubtedly occurs regularly but is difficult to quantify particularly with respect to small passerines crossing large bodies of water. Hurricanes, tornadoes, hail storms, and blizzards are among the primary causes of such deaths. On 13 March 1990, an unusual series of tornadoes and hail storms killed an estimated 30,000 waterfowl (primarily Snow Geese Chen caerulescens) in south central Nebraska. Sandhill Cranes Grus canadensis are less susceptible to direct weather-related trauma due to their size and stature. The greatest known cause of mortality of cranes in Nebraska is collisions with utility lines which increase during adverse weather conditions. On 22 March 1966, several hundred Sandhill Cranes were estimated to have died due to a blizzard, an unprecedented event at that time. The conditions leading up to that incident were very similar to those occurring on 24 March 1996 when another blizzard struck the Big Bend reach of the Platte River during the peak of the crane migration when an estimated 519,984 Sandhill Cranes were present. Several thousand cranes died as a result of the 1996 blizzard, making this event the greatest single cause of natural mortality reported for this species. Post-mortem examination of several carcasses confirmed trauma associated with collisions with the ground and other objects as the major cause of death. Events such as this reinforces the need to protect and maintain suitable habitat throughout the staging area of the Big Bend to minimize the risk of a future catastrophic event that could decimate cranes or other migratory species. As habitat conditions continue to degrade, the birds are forced to concentrate at remaining sites exposing them to increased risks. I report the details of the 1996 blizzard.
Management Implications for Least Terns and Piping Plovers in Manmade Habitats
Jeanine L. Lackey, Nebraska Game and Parks Commission, 2200 N. 33rd Street, Lincoln, Nebraska 68503, (402) 471-5421 (5528), jlackey@ngpsun.ngpc.state.ne.us
The interior least tern (Sterna antillarum) and the northern great plains population of the piping plover (Charadrious melodus) historically used riverine sandbars for nesting. During the last 30 years or more both species began to exploit unvegetated waste spoil piles at sand and gravel mines adjacent to rivers and now rely on these sites in reaches where natural riverine habitat has been lost. These sites are subject to high levels of predation and human disturbance and may serve as sinks. The objectives of this study were to identify the specific threats to least tern and piping plover nesting success at sand and gravel pits along portions of the Loup and Platte rivers, to emphasize and increase communication between biologists and sandpit operators, to test the effectiveness of predator exclosures, and to make management recommendations. Twenty-five and 18 least tern and/or piping plover breeding sites were monitored during 1991 and 1992, respectively. Fledging rates for least terns and piping plovers (0.34 fledglings/nest attempt and 0.40 fledglings/nest attempt, respectively) were well below rates needed for population stability. Predation occurred at 58% of the sites, recreational disturbances at 43%, operational disturbances at 25%, and weather related disturbances occurred at 21% of the sites. A chi-square comparison between the protected and unprotected nests showed a significantly higher proportion of least tern and piping plover nests hatched at protected sites (P<0.05). The proportion of nests that fledged at least one young was significantly higher at protected sites than at unprotected sites (P<0.05). Without communication between wildlife agencies and mining operators, the use of predator exclosures, and the control of recreational disturbances, tern and plover reproductive success at sand pits will not reach rates required to maintain or increase population.
Reproductive Success of Least Terns and Piping Plovers on Nebraska Public Power
District's Nesting Sites
Rockford G. Plettner, Nebraska Public Power District, P.O. Box 499, Columbus, Nebraska 68601, (402) 563-5493 (562-2086), rgplett@nppd.com
Nebraska Public Power District (NPPD) has developed nesting habitat at three Platte River island sites for least terns (Sterna antillarum) and piping plovers (Charadrius melodus). These sites were developed pursuant to terms of NPPD's Federal Energy Regulatory Commission annual operating license for hydroelectric Project No. 1835. Our first nesting island near Elm Creek, Nebraska was developed prior to the 1991 nesting season. We developed Lexington island in 1992 and Overton island in 1993. NPPD on its own initiative has also developed three sand pit nesting sites. NPPD began management of the Johnson sand pit located near Elm Creek, Nebraska in 1991, Lexington sand pit in 1992 and Blue Hole sand pit in 1996. Since development, these sites have been monitored for least tern and piping plover reproductive activity and success. The ratio of least tern chicks fledged per nest at our island habitats was 1.15 (32 nests fledged 37 chicks) and for sand pit habitats is 0.97 (167 nests fledged 163 chicks). The ratio of piping plover chicks fledged per nest at our island habitats was 0.46 (15 nests fledged 7 chicks) and for sand pit habitats was 1.45 (40 nests fledged 58 chicks). Overall nest success for least terns on island habitat was 75% and sand pit habitat 70%. Overall nest success for piping plovers on island habitats was 33% and sand pit habitat 80%. Our managed sand pits are contributing good numbers of fledged birds into the population and are a valuable population source in the central Platte River.
In a three year study involving managed and unmanaged sand pit habitats, predation accounted for 23% of nest loss at managed sand pits and 30% nest loss on unmanaged sand pits. These data include both least tern and piping plover nests. The unmanaged sites experienced 18% nest loss due to unknown causes while at managed sand pits is was 2$, this difference is likely attributed to more disturbance events by predators and/or humans at unmanaged sand pits. The managed sand pits hatched 71% of nests whereas unmanaged sand pits hatched 39%. The fledge ration for least terns during these three years on managed sand pits was 1.06 and unmanaged 0.29 and for piping plovers on managed sand pits 1.46 and unmanaged sand pits 1.0. Techniques used at managed habitats are valuable in improving nest and fledgling success by reducing predation and other disturbances.
Return to 1997 Platte River Basin Ecosystem Symposium
Last updated by Darren A. Jack on 2/6/97