Martin J. Folk

Evaluating release alternatives for a long-lived bird species under uncertainty about long-term demographic rates

The release of animals to reestablish an extirpated population is a decision problem that is often attended by considerable uncertainty about the probability of success. Annual releases of captive-reared juvenile Whooping Cranes (Grus americana) were begun in 1993 in central Florida, USA, to establish a breeding, non-migratory population. Over a 12-year period, 286 birds were released, but by 2004, the introduced flock had produced only four wild-fledged birds. Consequently, releases were halted over managers’ concerns about the performance of the released flock and uncertainty about the efficacy of further releases. We used data on marked, released birds to develop predictive models for addressing whether releases should be resumed, and if so, under what schedule. To examine the outcome of different release scenarios, we simulated the survival and productivity of individual female birds under a baseline model that recognized age and breeding-class structure and which incorporated empirically estimated stochastic elements. As data on wild-fledged birds from captive-reared parents were sparse, a key uncertainty that confronts release decision-making is whether captive-reared birds and their offspring share the same vital rates. Therefore, we used data on the only population of wild Whooping Cranes in existence to construct two alternatives to the baseline model. The probability of population persistence was highly sensitive to the choice of these three models. Under the baseline model, extirpation of the population was nearly certain under any scenario of resumed releases. In contrast, the model based on estimates from wild birds projected a high probability of persistence under any release scenario, including cessation of releases. Therefore, belief in either of these models suggests that further releases are an ineffective use of resources. In the third model, which simulated a population Allee effect, population persistence was sensitive to the release decision: high persistence probability was achieved only through the release of more birds, whereas extirpation was highly probable with cessation of releases. Despite substantial investment of time and effort in the release program, evidence collected to date does not favor one model over another; therefore, any decision about further releases must be made under considerable biological uncertainty. However, given an assignment of credibility weight to each model, a best, informed decision about releases can be made under uncertainty. Furthermore, if managers can periodically revisit the release decision and collect monitoring data to further inform the models, then managers have a basis for confronting uncertainty and adaptively managing releases through time.

Sandhill Crane Roost Site Characteristics in the North Platte River Valley

We documented sandhill crane (Grus canadensis) roost site characteristics in the North Platte River Valley (NPRV) of Nebraska in riverine and semipermanent palustrine wetlands from late February through mid-April in 1988 and 1989. Crane roost sites in the river were located closer to visual obstructions, in narrower channels, and in a wider range of water depths than determined previously in the Platte River. Cranes roosted in semipermanent wetlands where widths were _12 m, water depths were 5.0-24.4 cm, and distance to shore was _1 m. Based on the estimated peak number of sandhill cranes and roosting capacity estimates, availability of roosting habitat was not limiting use of the NPRV by cranes. North Platte river flows should be maintained to provide channel widths _48 m and water depths 521 cm for roosting cranes. Temporary (wet meadow) and semipermanent palustrine wetlands adjacent to the river should be preserved to provide important diurnal and nocturnal crane habitat. J. WILDL. MANAGE. 54(3):480-486 The North Platte and Platte River valleys of Nebraska are the primary spring staging areas for the midcontinental population of sandhill cranes (Benning and Johnson 1987). Cranes are dependent upon these valleys to provide high energy foods (especially corn) necessary to accumulate lipid reserves for use in nesting areas (Krapu et al. 1985, Tacha et al. 1987). Loss of grasslands and wetlands to agricultural and commercial development has altered staging habitat of sandhill cranes (Lewis et al. 1977, Currier and Ziewitz 1987). Flow reductions in the rivers allowed encroachment of woody vegetation on sandbars used by cranes for roosting. Current management of crane roosting habitat includes maintenance of water flows and costly mechanical removal of woody vegetation (Lingle 1982). Iverson et al. (1987) found up to 67,500 (45% of total) cranes using off-river temporary and semipermanent wetland roost sites in the North Platte River Valley (NPRV) and recommended the preservation of existing sites and development of additional off-river roost sites. However, no studies of roost site selection have been conducted in the NPRV. Our objectives were to determine factors associated with crane use and selection of river and adjacent wetland roosts and to estimate the roosting capacity of the NPRV. We thank G. A. Wingfield of the Nebraska Game and Parks Commission and P. McDonald of the U.S. Fish and Wildlife Service (USFWS) for providing valuable assistance in Nebraska. Landowners in the NPRV granted access to their property. P. A. Vohs and A. Woolf reviewed the manuscript. This study was funded by USFWS Purchase Orders 64412-00302-88 and 64412-8900026 and the Cooperative Wildlife Research Laboratory, Southern Illinois University at Carbondale (SIUC). Additional support was obtained from the Department of Zoology and the Graduate School at SIUC.

HELMINTH AND ARTHROPOD PARASITES OF EXPERIMENTALLY INTRODUCED WHOOPING CRANES IN FLORIDA

Nine species of nematodes, unidentified larval nematodes, three species of trematodes, two species of acanthocephalans and a single species of chewing louse were collected from 1993 to 1995 from 25 introduced whooping cranes (Grus americana) in Florida (USA). In spite of a quarantine procedure involving anthelmintic therapy, three helminth parasites may have been introduced from captive populations. Other parasites acquired were similar to those found in a local congener, the Florida sandhill crane (Grus canadensis pratensis), or only occurred infrequently.

Reproductive Performance of Female Key Deer

The reproductive performance of the endangered Key deer (Odocoileus virginianus clavium) is a potential limiting factor in its conservation. We analyzed data collected by necropsy of 142 female Key deer from 1968 through 1989 to provide a better understanding of their reproduction. A breeding season of about 6 months was longer than for more northerly herds of white-tailed deer. Productivity of Key deer was low (0.76 fetuses/F -1 yr of age at breeding) and fetal sex ratio (74% M) was high for the species. Rates of reproductive activity (% pregnant or lactating) for females at age of breeding were 4% for fawns, 58% for yearlings, 61% for ages 2-4 years, and 90% for females -5 years of age. Eight (17%) of 48 pregnant females carried twins, and the remainder carried single fetuses. We hypothesize that poor reproductive performance of female Key deer is due to a nutrient deficiency or that it evolved as an adaptation to an insular habitat. J. WILDL. MANAGE. 55(3):386-390 The endangered Key deer of the lower Florida Keys are smallest in mass of the subspecies of North American white-tailed deer (Hardin et al. 1984) and are isolated from mainland Florida by 60 km of water. Prior to protection from hunting, the population of Key deer declined to a low of 25-80 in 1951-52 (Dickson 1955). Klimstra et al. (1978), using spotlight surveys, estimated that the population increased to 300-400 in the early 1970s. The U.S. Fish and Wildlife Service (1985) reported a decline in population to 250-300 by 1984. Low reproductive output apparently contributed to the slow recovery of the Key deer population from the low of the early 1950s (Hardin 1974). Currently, development encroaching on habitat (U.S. Fish Wildl. Serv. 1985) and mortality due to collisions with automobiles result in a precarious status for the Key deer population. Nutrition, one of the most important factors affecting productivity of white-tailed deer (Verme 1967, McCullough 1979), affects both ovulation rate and the proportion of females that become pregnant (Sadleir 1987). An imbalanced ratio of calcium (Ca) : phosphorus (P) or deficiencies of cobalt (Co), iron (Fe), or copper (Cu) probably contribute to low productivity of whitetailed deer from the southeastern United States (Smith et al. 1956, Harlow 1972, Smith and Hunter 1978). The diet of Key deer may be deficient in P (Widowski 1977) or other nutrients, forcing females <4 years old (that have not reached peak mass) to concentrate energy and nutrients on body growth rather than reproduction. We analyzed long-term data collected from mortalities of female Key deer to indirectly test this hypothesis. Numerous individuals of the National Key Deer Refuge and the Cooperative Wildlife Research Laboratory at Southern Illinois University, Carbondale contributed to the collection and examination of carcasses. We thank M. L. Folk, J. W. Hardin, J. L. Roseberry, T. G. Scott, T. J. Wilmers, and A. Woolf for reviewing a draft f the manuscript. The Key Deer Refuge pr vided use of computer facilities. This project was funded by a grant from the Richard King Mellon Foundation.

Environmental Correlates of Reproductive Success for Introduced Resident Whooping Cranes in Florida

Abstract. Reproduction within a recently re-introduced resident flock of Whooping Cranes ( Grus americana) in Florida during 1992–2007 was poor compared to an established wild flock. Pairing and nesting increased with average age of the flock, but fertility, hatching and fledging were variable among years, suggestive of an environmental influence. For climatic variables measured during the incubation period, only maximum soil temperature was associated with the failure of late nests in dry years. However, pre-nesting winter precipitation and water elevation were positively correlated with an index of nesting effort. Winter precipitation was associated with fertility and hatchability, whereas winter marsh water levels were associated with earlier nesting dates and increased egg volume. Both winter precipitation (>8 cm mean monthly) and water elevation (>20.3 m above mean sea level or 68% of full marsh surface area or perimeter) greater than a threshold level appeared to be good predictors for successful reproduction in central Florida, but occurred together in only four of ten study period years. Pairs delayed nesting, had smaller eggs, and hatched and fledged fewer chicks in years with low winter water elevation. Low winter precipitation associated with decreased fertility of eggs may explain the failure of fully incubated nests to hatch in some years. Insufficient stimulation of the neuroendocrine system due to limited rainfall and poor physiological condition due to poor food resources in low water marshes are proposed mechanisms for low fertility and delayed nesting and egg size, respectively. Drought appears to encourage birds to use lake edges for nesting which have increased hazards. Thus, conservation of wetlands for cranes should include deep marshes and lake edges with controlled boat usage during the nesting season. Further investigation is recommended for pre-nesting and incubation behaviors, diseases of eggs, and egg volumes.

Natal dispersal in florida sandhill cranes

Knowledge of natal dispersal is essential for understanding how nonmigratory crane populations expand and how this process can be augmented by relocation or reintroduction. We conducted a study from 1988 to 1999 and found that natal dispersal in Florida sandhill cranes (Grus canadensis pratensis) was female-biased. Females (n = 16) dispersed an average of 11.6 km from their natal territory. Male (n = 12) dispersal averaged 3.9 km. This difference was significant (P 0.05) or affected by gender (P > 0.05). Male philopatry and female-biased natal dispersal are consistent with theories of a resource-based mating system. Timing of the start of dispersal (family breakup) was found to be more closely tied to the females laying the subsequent clutch than to the age of the juvenile crane.

Predation and Scavenging by American Alligators on Whooping Cranes and Sandhill Cranes in Florida

Abstract We documented 15 cases of Grus americana (Whooping Crane) mortality in 6 Florida counties during 1997–2010 that may have been associated with Alligator mississippiensis (American Alligator; hereafter Alligator) predation or scavenging. In four cases, Whooping Crane remains were identified within Alligator mouths or stomachs. The latter is a first in the literature. Other cases were less conclusive but suggestive that Alligators were involved with predation or scavenging of Whooping Cranes. An Alligator was videotaped eating the eggs of G. canadensis pratensis (Florida Sandhill Crane), plus Alligators were implicated in the depredation of eggs from another Sandhill Crane nest and a Whooping Crane nest; the latter was the first record of Alligators depredating Whooping Crane eggs. All 4 populations of Whooping Cranes and 4 populations of Sandhill Cranes in the southeastern United States spend at least part of the year within the range of Alligators. To improve survival of cranes in areas where water management is practiced, water depths should be maintained at optimal levels (10–20 cm) for crane nesting and roosting to discourage intrusion by larger Alligators and to allow the cranes to detect approaching Alligators.

Is Male-biased Collision Mortality of Whooping Cranes (Grus americana) in Florida Associated with Flock Behavior?

Abstract. Male-biased collision mortality of Whooping Cranes (Grus americana) in Florida may be associated with the tendency of males to lead flocks. The sex of Whooping Cranes was recorded for individuals leading flocks while flying and walking (n = 255). Males were more likely to lead than females both while walking and especially when flying. These observations support anecdotal reports that males tend to lead flocks. This flock behavior may partly explain male-biased mortality from collisions observed in Florida. Collision with power lines is the greatest known source of mortality for fledged Whooping Cranes. Our findings have implications for reintroductions and for the single existing self-sustaining population, which numbers > 250 individuals.

COPULATORY BEHAVIOR OF NON-MIGRATORY WHOOPING CRANES IN FLORIDA

Abstract Whooping Cranes (Grus americana) are a long-lived, monogamous avian species, yet little documentation of copulatory behavior and timing in relation to egg-laying has occurred in wild populations. We monitored 10 crane pairs in Florida before and during the 2010 breeding season to document copulation timing and pre- and post-copulatory behavior. Monitoring began 111 days before incubation initiation for the first nest of the season. Pairs were observed for 124.62 hrs (  =  76.30 min, range  =  14–375 min) during 98 observation periods; 17 observation periods occurred on days with precipitation. Three copulations were observed, two by one established pair and another by unpaired individuals. The copulations by the established pair occurred 9 and 18 days before incubation began. The third was an extra-pair copulation, which occurred between a paired female and a lone male, the first documented for the species. No copulations were observed on days with precipitation. We examined flock monitoring accounts from 1999 through 2009 in this non-migratory population; 21 observations of copulations revealed Whooping Cranes copulated up to 62 days before incubation began and between 0510–1345 hrs EST. Our data suggest copulation occurs between early morning and early afternoon and does not appear to be associated with precipitation.