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Subscriber Exclusive Content. Why are people so dang obsessed with Mars? How viruses shape our world. The era of greyhound racing in the U. See how people have imagined life on Mars through history. As with sandhill cranes, cross-season effects probably are important for whooping cranes. Chavez-Ramirez argued that variations in winter habitat conditions are related to reproductive effort in the following spring and that winter body condition could affect winter survivorship.
If winter habitat conditions influence mortality or reproduction, it may be that migration-habitat conditions affect whooping cranes in a similar way. Stehn has suggested that habitat quality at ANWR may be declining. The amount of fresh water entering ANWR is important ecologically because it influences overall productivity in the estuary, especially for.
Declining fresh-water flows have been linked to the declining abundance of blue crabs Stehn Fresh water for the estuarine refuge comes from the Guadalupe River. Whooping cranes that leave ANWR with insufficient stored fat will either migrate to WBNP, facing the potential for added mortality and reduced productivity Chavez-Ramirez , or increase stopover times on migration to acquire fat reserves. Responses by individual birds are likely to vary.
For example, nonbreeding subadults may be able to stop longer on migration than can breeding adults because they do not need to initiate nests. The potential for cross-seasonal effects means that if deteriorating habitat conditions in ANWR are severe and long-lasting, whooping cranes may not be able to acquire sufficient fat reserves and will have to acquire them in other habitats, such as the central Platte River.
Few data are available for testing the hypothesis that spring migration habitats influence energy reserves, reproduction, or mortality in whooping cranes. Some birds stay longer on spring stopover areas than do others Kuyt ; Howe , and more whooping cranes stop at the Platte River for long periods than did 25 years ago Figure b. Other species of waterfowl acquire energy and nutrient reserves on spring staging areas before arrival on breeding grounds in the manner suggested for whooping cranes Barzen and Serie Although relevant data are sparse, the hypothesis warrants further investigation.
Documented migration patterns may not predict future patterns of movement in that habitat conditions change over time at the numerous stopover and staging areas. The changes might be related to the crane population, to climatic adjustments, or to changes in altered agricultural practices. It is possible that spring migration areas could be used in new ways by whooping cranes.
This possibility cautions against underestimating the ecological value of stopover habitats to whooping cranes, especially stopover habitats on the central Platte River. Satellite telemetry studies over multiple years would help greatly in testing these ideas as they have done with sandhill cranes Krapu Accurate yearly counts of the birds arriving on the.
Although the total mortality is reasonably well known, causes of death are more problematic. Of adults and subadults that disappeared away from winter areas between April and November mortality on breeding areas is assumed to be low from , the cause of death is known in 13 cases, five of which were due to collisions with power lines Lewis et al. Because most deaths of adult whooping cranes occur during migration, mortality may be linked to the quality or quantity of stopover habitats.
A significant portion of the whooping crane population stops at the Platte River during migration Figure a,b. If the Platte River were no longer available, whooping cranes would probably shift their use to other habitats in Nebraska.
Would these shifts alter mortality? Migrating whooping cranes use wetlands near the central Platte River in the Rainwater Basin south of the river or in the central Table Playa to the north Richert Those off-stream wetlands apparently serve as good migration habitats for whooping cranes, except in droughts or during waterfowl disease outbreaks to which these wetlands are prone Friend The Platte River ecosystem is not prone to disease outbreaks, because, in contrast with off-stream wetlands, water is flowing rather than stagnant.
The Platte River also does not dry out as frequently as do surrounding wetlands; therefore, the Platte River provides safer conditions than do surrounding wetlands at least in some years Johnson Crowding of waterfowl and cranes and short-term use of unusual habitats may also affect crane mortality.
An experimentally released pair of whooping cranes unexpectedly migrated from their release area in Florida where they were part of a nonmigratory flock and spent the summer in Michigan M.
The pair began fall migration normally, but the male disappeared and presumably died during a snowstorm on the first day of migration. The female migrated successfully to Florida in 11 days, during which she used many stopover habitats similar to those described by Howe Some stopover habitats this whooping crane used, however, were unusual.
For example, she used an abandoned coal mine pond in Ohio and a forested area probably including a stream in a mountainous area of Virginia. Even though this bird survived the migration, did the probability of mortality increase when poor quality habitats were used? An incremental increase in mortality due to poor conditions on stopover habitats would be difficult to document with a small population.
Higher mortality due to nocturnal predators has resulted from use of inappropriate habitat with an. Once crane behavior was modified, and better roost habitat was used, mortality decreased Nesbitt et al. The sensitivity of a target population to changes in mortality can be assessed with simulations that use measured population characteristics. The biology of whooping cranes, however, makes the species a challenging subject for PVA. In the wild, only one functional population of whooping cranes exists, and its members use the central Platte River only to stop during migration Lewis Individual birds typically stay over for just a few days, but on occasion a bird stays for as long as several weeks.
Furthermore, specific habitat use by birds during migration and selective use of habitats by particular age groups subadult or adult , reproductive status breeding or nonbreeding , and sex are poorly known. In this context, relating the fitness of individual birds or the likely persistence of the population to central Platte River habitat conditions is tenuous. Nonetheless, three PVAs for whooping cranes are available and warrant consideration in conservation planning for the species. All use the same database for the Platte River population but use different years of data.
Mirande et al. All are age-based stochastic simulations. According to Brook et al. The Mirande et al. The model included density-dependent effects. Some simulations included catastrophes that affected reproduction and survival. The Brook et al. However, model predictions differed in details, and differences were caused by a variety of features, such as inclu-. Because there is no full-time resident or breeding population of whooping cranes in the Platte River Basin, conclusions about the role of the central Platte River in the persistence of the population must be based on some stringent assumptions, including the assumption that the loss of Platte River habitat will result in some increase in mortality or other contribution to decreased fitness of the population.
Accepting that assumption, the PVA of Brook et al. First, does lengthening the goal for population persistence from 50 years used by Brook et al.
The modified Brook et al. No other modifications were made except lengthening the time frame for viability to years. The population parameter values used in the model were gathered over decades from a population that was growing. Second, how much would adult mortality have to increase for the likelihood of population persistence to decrease significantly?
The increments were added to the existing 9. At its current population size the whooping crane is fairly well buffered against environmental and demographic variation that could cause it to go extinct. Third, given that the whooping crane lifespan is not known, what is the effect on population persistence of shortened lifespans that could result from losses of key habitats?
Loss of habitat or decreases in its availability on the central Platte River could result in a decrease in the vigor of individual birds, shortening lifespans. However, model runs with lifespans reduced from 50 years to 40 and to 30 years showed that reduction in lifespan had no statistically significant effect on population persistence Table The PVAs suggest relatively stable populations well into the future under current conditions, but the high sensitivity of population persistence.
Viable population numbers are those above 0. Source: Reed Reductions in foraging or resting habitat that manifest in decreased vigor of individual cranes could have a substantial effect on the fate of the entire population. Without central Platte River stopover habitats, alternative habitats elsewhere in the migratory pathway will be necessary to provide resources for dispersing whooping cranes.
If mortality increased only enough to slow growth, rather than to cause a population decline, adverse effects on the AWP could still occur. A net loss of alleles will continue to occur in the AWP through genetic drift a loss of genetic material from a population due to small population size until the population becomes large enough for the rate of genetic mutations which produce new alleles to roughly equal the rate of drift which loses alleles.
The longer it takes for the AWP to reach a size at which drift and mutation rates are balanced, the more genetic material will be lost from the population. Further loss of genetic diversity because of a slowed recovery could be problematic. This chapter began with three questions related to whooping cranes: Do current Platte River habitat conditions affect the likelihood of survival of the species?
Do they affect recovery of the species? Is the current designation of central Platte River habitat as critical habitat for whooping cranes supported by science? The chapter has reviewed information collected by the committee from the literature and from unpublished DOI documents concerning the species, from testimony given by agency and other specialists, from a visit to DOI facilities in Denver and Grand Island, and from field examinations.
The committee concluded that current habitat conditions along the central Platte River adversely affect the likelihood of survival and recovery of the whooping crane population. Geographically, the central Platte River occupies a critical position along the migration route of the species, between the wintering grounds in coastal Texas and the summer breeding grounds in north central Canada. The river and its closely associated lands provide useful roosting areas for birds in the midst of migrations of thousands of miles.
The portions of the river that are not heavily wooded provide open areas separated from the banks by channels—an arrangement that provides security for the roosting birds. Nearby wetlands and agricultural areas provide important forage for the birds and allow them to obtain needed nutrition to support their continued migration.
The committee concluded that there are no apparently suitable alternatives to replace the central Platte River in its function as habitat for migrating whooping cranes.
The Rainwater Basin, south of the river, includes numerous small wetland basins and patches, but these areas periodically dry completely, whereas the Platte River flows relatively continuously.
Because the Platte draws its water from distant mountain watersheds, its flows are less susceptible to periodic drought on the plains than are the. Nearby rivers also lack the consistency of the Platte, and the Niobrara and Loup Rivers and smaller streams do not offer alternative habitat with the same qualities as the Platte.
The loss of the Platte River habitat would have potentially serious consequences for the species. The general total population of migrating whooping cranes is slowly increasing from its low of only 15 in , and the proportion of the population that uses the central Platte River as a stopover each year is also gradually increasing. The river therefore directly affects species recovery. The committee also concluded that the current designation of central Platte River habitat as critical habitat for whooping cranes was supported by the science of the time of the designation and that it is supported by present scientific understanding.
When DOI agencies designated the critical habitat in , they relied on information that was available then. Agency personnel used information that was available in the refereed scientific literature, agency reports, and additional observations made by agency personnel.
Agency personnel made the designation by using procedures that the biological community commonly recognized, and internal peer review strengthened confidence in the designation. There have been no developments in scientific knowledge that invalidate the decisions. Given the small numbers of migrating whooping cranes, some parts of the designated habitat inevitably will not be used in some years.
Because both the population and the percentage that stops on the Platte River are slowly increasing, it is likely that the occasionally nonused portions of the critical habitat will be increasingly important. The general utility of the central Platte River for roosting whooping cranes also changes from one year to the next, depending on the hydrological conditions of the river, which are subject to some change.
The committee also acknowledges that conservation actions at locations outside the central Platte River, particularly in overwintering and breeding habitats, will have important effects on continued use of Platte River habitats, and that a wide variety of management responses—including captive rearing, reintroductions, and translocations—will continue to play critical roles in the conservation of the species as long as populations continue to persist at low levels. Finally, in addition to addressing the three questions related to whooping cranes, the committee identified gaps in knowledge and data that should be addressed.
The committee strongly urges managers of the central Platte River to adopt a multispecies approach to their research and decisions. Solving problems related to whooping cranes without reference to other species will probably lead to additional problems. Natural Resources Conservation Service Montana. Stay Connected. Error: Javascript is disabled in this browser. This page requires Javascript. Modify your browser's settings to allow Javascript to execute.
See your browser's documentation for specific instructions. Loading Tree Fish and Wildlife Service. Complementary Content. In , there were a total of 51 nesting pairs of cranes, with nine pairs that successfully arrived on the wintering grounds with a single young each.
That winter there were whoopers in the wild and birds in captivity for a total world population of Whooping Cranes. The Whooping Crane is determined to recover, but the only way it can is if we protect its habitat. The breeding area in Wood Buffalo National Park is protected, and part of the wintering land in Texas has been a wildlife refuge since Several migration stopover areas have since been protected in the US.
Before , there were several captive breeding programs in the United States that used wild whooper eggs from Wood Buffalo National Park. In , there were 95 whoopers in captivity. Since then, enough eggs are produced at the captive breeding sites that collecting wild eggs is no longer necessary. The Calgary Zoo remains the only captive breeding site for whoopers in Canada. There have been several cross-fostering experiments, where whooper eggs are placed with other crane flocks.
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