Reintroduction is a critical component of endangered species restoration, and involves attempts to re-establish an organism in parts of its historical range where the species was previously extirpated. Effective reintroduction, however, involves more than just releasing animals into a suitable habitat. It involves strategic planning, a well-defined methodology, post-release monitoring of the newly-established population, and public education efforts to reduce anthropogenic factors on survival and reproduction (e.g., hunting pressure for game species). Some of these critical components are often cut from project budgets unless explicitly planned for in advance, resulting in wasted conservation funds and poor results (Armstrong and Seddon 2007, Bernardo et al. 2012).
The Red-billed Curassow (Crax blumenbachii) is an endangered species of the ancient bird Family Cracidae, a resident of the Atlantic Rain Forest region of eastern Brazil. In the 1990s, the species was classified as “Critically Endangered” by the IUCN, but following successful reintroduction of captive-bred birds (e.g., Scheres 1993), the Red-billed Curassow met the criteria for “Endangered” status (at least 2 populations of more than 50 individuals), and was re-listed (Birdlife International 2012). The historical distribution of this species spanned 1100 km, from Rio de Janeiro and adjacent areas of Minas Gerais, north to Ituberá, Bahia, but decades of hunting pressure and habitat loss led to its extirpation from Rio de Janeiro and Minas Gerais by the 1960s. Today, natural populations of this species only persist at three sites: (1) in southern Bahia, Descobrimento National Park, Ituberá, (2) in northern Espírito Santo, Vale Nature Reserve and (3) Sooretama Biological Reserve (IBAMA and Ministerio Do Meio Ambiente 2004, Srbek-Araujo et al. 2012). These sites are protected under Brazilian law, but the forest fragments used by the curassows are small and isolated, and most populations are estimated to have fewer than 50 individuals (Birdlife International 2012).
A captive breeding and reintroduction program has restored some populations in the southern part of the species’ range (Scheres 1993, Brooks and Strahl 2000, Bernardo 2007), but most of these reintroductions were poorly-planned, conducted with no soft-release strategy or post-release monitoring (see Bernardo et al. 2011a). Including the reintroduced populations, there are approximately five extant populations of Red-Billed Curassow left (Birdlife International 2012). The future of this species depends upon (1) protection of surviving populations, and (2) establishment of new populations via reintroduction of captive-bred stock (IBAMA and Ministerio Do Meio Ambiente 2004). I will discuss the reintroduction efforts of Bernardo et al. (2011a) at the Guapiaçu Ecological Reserve (REGUA), Rio de Janeiro state, where the species has been extirpated since the 1960s.
Bernardo et al. (2011a) reintroduced captive-bred Red-billed Curassows (N = 48) into a 7,200 ha private reserve at REGUA, Rio de Janeiro state, Brazil (22º 25′ S, 42º 44′ W; elevation 20–2300 m). This forest likely supported a population of Red-billed Curassows until the mid-20th century, and is found adjacent to Três Picos State Park, the largest fragment of Brazilian Atlantic Rainforest that remains today. This site was deemed optimal for the reintroduction program because (1) it contained a large amount of suitable habitat for the species, (2) the land was protected by law, and (3) the park guard system would likely act as a deterrent against hunting.
Red-billed Curassows (N=53) were transported from the breeding facility (CRAX Brazil, Contagem, Minas Gerais) to REGUA and kept in a “soft-release” enclosure for 7–71 days (mean = 41). During this acclimatization period, each bird was fed a mixed diet of commercial chicken feed (used at the breeding center) and local fruit and leaves gathered from the release site. Prior to release, each bird was marked with a radio transmitter that broadcast a unique frequency. Curassows (N=48, 26 female, 20 male) were released in seven cohorts (2–10 individuals) in secondary lowland rainforest habitat. From August 2006–October 2008, Bernardo et al. (2011a) monitored the reintroduced curassows via radio telemetry, locating all the released birds at least three times per week, and at different times during the day. If a radio signal was stationary for a week, the researchers homed in on the transmitter, determined whether the bird was alive or dead, and if the latter was true, examined the carcass to determine the cause.
Bernardo et al. (2011a) used the program MARK v.5.1 (White and Burnham 1997) to examine the influence of a variety of factors, including parameters of their soft-release strategy, on Red-billed Curassow post-release survival probabilities at REGUA. They calculated bimonthly survival probabilities to see if survival varied with time over the first 29 months following release. Capture histories were pooled over 3 month periods for each bird, and survival probabilities were analyzed against a variety of independent variables including sex, cohort size, and season.
Mean annual survival for reintroduced Red-billed Curassows at REGUA was 75% (Bernardo et al. 2011a). Estimates for some wild populations of Galliformes have been similarly high (e.g., 72% in male Hazel Grouse, Montadert and Leonard 2003), but generally survival probabilities are much lower in this taxonomic group, especially in reintroduced populations (e.g., 12–37% in Northern Bobwhite, Terhune et al. 2007). Five birds were killed during pre-release aggressive interactions in the soft-release enclosure. These violent episodes were presumably the result of dominance conflicts, but were not explained by demographic data (e.g., age, sex, cohort size). If birds that died pre-release in the enclosure are included in the analysis, the mean annual survival estimate for the sample drops to 60%.
Of the fifteen curassows that died during the post-release study period, eight were female and seven were male. Primary causes of mortality were (1) natural predators (e.g., raptors, carnivores) – 50%, (2) domestic dogs – 27%, and (3) hunting– 20%. Analysis of bimonthly survival probabilities revealed a period of vulnerability lasting one year post-release (i.e., survival probability was less than 100% during this time), after which every remaining bird survived until the end of the study (Bernardo et al. 2011a). Survival was positively correlated with cohort size and time spent in the soft-release enclosure. Females had slightly higher mean annual survival probabilities (78%) than males (70%), and survival was also higher during the wet season (80%) than the dry season (71%), but these relationships varied depending upon the statistical model used (Bernardo et al. 2011).
After the fieldwork of Bernardo et al. (2011a) was concluded in 2008, observations of the reintroduced curassows became few and informal. In 2009, a male was observed with nesting material, but sightings became rare in the following years. The surviving birds were believed to have moved deeper into the forest, but nothing was known of their status.
On June 14, 2012, an immature male Red-billed Curassow was photographed near the village of Estreito on the the far side of REGUA (Dingain 2012), and is believed to be the first evidence of post-release reproductive success at this site (all the released birds were adults).
The precipitous decline of this forest-dependent species can be generally attributed to two factors: (1) habitat loss, as a result of a change in the landscape matrix from mostly forest to mostly agriculture, (2) high mortality due to hunting, which would presumably increase as forest fragment size decreases. Reintroductions into protected forest fragments such as REGUA mitigate the influence of the latter, because park guards and rangers deter poaching activities (Bernardo et al. 2011a). Although extant populations are few, there are other suitable forest fragments in Rio de Janeiro and Minas Gerais states that could support populations if reintroductions were attempted. Because extirpation at these sites was generally caused by high hunting pressure, sustainable populations may be attainable if that limiting factor is removed (e.g., via park guards, public education, etc.). The small influence of hunting on post-release survival at REGUA supports this notion (Bernardo et al. 2011a).
High post-release survival probabilities found by Bernardo et al. (2011a) also confirm the importance of a soft-release strategy in Cracid reintroduction; by combining the results of multiple statistical models, Bernardo et al. (2011a) proposed an optimal release strategy for this species that includes 47 days of acclimatization in a soft-release enclosure followed by the release of 10 individuals per cohort. The model-predicted annual survival probability is 80% when the optimal strategy is used. Increasing cohort size to 15 in the model results in an even higher predicted survival probability (85%), but the benefit is generally outweighed by logistical costs (e.g., difficulties of maintaining large soft-release enclosures). Additionally, physical adjustments to the soft-release enclosure might be made to reduce pre-release mortality (i.e., mortality due to quarrels over social dominance); future reintroduction efforts should separate highly dominant individuals from other group members by placing physical dividers in the enclosure.
Red-billed Curassows are generally thought to form monogamous pair bonds (Sick 1997), but a recent camera trap study from a natural population in Espírito Santo detected males associating with multiple females and small mixed-sex flocks traveling together (Srbek-Araujo et al. 2012). The highly fragmented landscape that the Red-billed Curassow now inhabits prevents it from dispersing as it would in a homogenous forest environment. Because (1) populations are too few, (2) too small, and (3) we know very little about the species’ life history requirements, translocating individuals from extant populations to be used as founders of new populations is much too risky. Translocation of individuals from a small population may disrupt its biotic functioning (e.g., by disturbing social hierarchies, sex ratio, age structure, etc.), and these small populations represent all that is left of the species’ natural gene pool. Therefore, researchers attempting to found new populations in suitable forest fragments must rely on captive-bred stock (Scheres 1993, Bernardo 2011a).
Since 1991, a total of 72 adult Red-billed Curassows were released into the CENIBRA private reserve in Rio de Janeiro, but birds were not monitored post-release (Scheres 1993). Although juvenile birds have been sighted for several years by park guards (see Bernardo et al. 2011a), nothing is known about how many birds survived the 12-month vulnerability period or the size of the current population at CENIBRA. Other non-quantitative releases were conducted by the Minas Gerais government in the late 1990s, but the status of these populations is also unknown. In addition to providing primary data on post-release survival, Bernardo et al. (2011a) have also championed a more quantitative approach to curassow conservation, emphasizing project feasibility, forest fragment size and protected status, soft-release methodology, and post-release monitoring. The reintroduction at REGUA has also led to improved methodology for the attachment of radio transmitters, reducing anthropogenic influences on survival, behavior and reproduction (Bernardo et al. 2011b).
Gene flow between Red-billed Curassow populations is completely thwarted by the fragmentation of the landscape. For this reason, conservationists may eventually need to attempt translocations (depsite the risks) in order to reduce inbreeding depression. Left alone, the small size of the extant Red-billed Curassow populations (60% with fewer than 50 individuals) leaves them especially vulnerable to genetic erosion, inbreeding depression, and loss of rare alleles to genetic drift. Scientific assessment of genetic deterioration in these populations will be needed to properly craft future management strategies, especially those involving potential translocations.
In conclusion, these results provide a strong data-based foundation upon which to design future reintroduction programs for this species and other threatened Cracids (Bernardo et al. 2012). The lowland forest habitat preferred by the Red-billed Curassow has now been largely cleared for farmland, so besides protecting the extant populations in Bahia and Espírito Santo (i.e., the highest priority), reintroduction is an absolutely essential component for the restoration of this species. Thanks to Bernardo et al. (2011), future reintroduction efforts in this region have an empirically-derived protocol that serves to maximize post-release survival, the crucial first step to re-establishing a reproducing population of captive-bred individuals.
Unfortunately, the Red-billed Curassow is not likely to remain extant without continued conservation effort, including everything from concerted reintroduction programs to the daily policing of forest preserves to reduce poaching. Future management projects would do well to continue the quantitative approach promoted by Bernardo et al. (2011a); carefully-planned reintroduction strategies that include a soft-release stage and post-release monitoring are more likely to result in successful establishment of founder populations, and will contribute to a stronger understanding of both Red-billed Curassow conservation ecology and the efficacy of reintroduction as a method of restoration in the Neotropics and elsewhere.
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