Abstract
The Attwater’s prairie-chicken (APC) (Tympanuchus cupido attwateri), a grouse species historically found in large numbers on the coastal prairies of Texas and Louisiana, was listed as endangered in 1967 under the Endangered Species Act of 1966. Habitat loss is primarily responsible for APC decline, and already by 1937, 93% of the six million acres of coastal prairie habitat was lost.1 For the last 20 years, the species has been intensively managed with a wild population of fewer than 110 individuals dependent on the release of captive-reared birds. Several factors limit recovery of this species including poor brood survivability in the wild and insufficient numbers of birds for release.10 However, recent advances for the wild and captive populations promise some long-awaited optimism for the full recovery of this species.
Decreased insect abundance was hypothesized to limit APC brood survivability in the wild. Insects are the main source of food for young prairie-chickens8 and compared to an increasing population of greater prairie-chickens (GPC) (Tympanuchus cupido pinnatus), APC brood habitat contained 70% fewer insects than GPC brood habitat (Pratt, unpublished data). Red imported fire ants (RIFA) (Solenopsis invicta) have a deleterious effect on insect abundance,6 and APC populations declined during the 25-year period following invasion of habitat by RIFA starting around 1970.4 A 2009–2012 investigation found that successful brood sites had over twice the number of insects compared to unsuccessful sites, and RIFA-suppressed areas had significantly more insects compared to untreated areas.4 These data clearly show that insect availability is a limiting factor for brood survival, and large scale RIFA treatment is planned for the 2014 season with improved brood survivability expected.
Ensuring a successful wild population is a matter of numbers. With an average survival of 17%, the release of 200 birds a year only results in 17 hens producing on average four total broods. Captive-rearing facilities are at maximum capacity (65 breeding pairs) and are not able to produce enough chicks for release annually to achieve a self-sustaining wild population. The construction of a new facility in Oklahoma, with the eventual capacity to double the existing number of breeding pairs, could potentially tip the balance to a self-sustaining wild population by providing more birds for release.
The APC Recovery Program has achieved important successes. Post-release survival of 17% is better than other pen-reared and released galliform species, including GPC,9 and grey partridge.7 The use of acclimation pens for two weeks prior to release improves survivability over a three-day and one-week acclimation period by 425%3 and 51%, respectively (Morrow unpublished data). Nest success has been increased with the use of predator deterrent fences; average nest success from 2000–2013 was 72% with fences, whereas nest success averaged 32% historically.5 Captive-reared birds seem to exhibit normal behavior, despite potential genetic bottlenecks and the selective effects of captivity over time. Released birds utilize habitat normally,2,3 although brood survival remains problematic. For hens that successfully reared broods from 2009–2012, there was no significant effect of any hen characteristics hypothesized to affect brood success including age, whether captive-reared or wild-bred, number of years since release, previous nest experience, or success with fledging chicks.4 Availability of invertebrate resources is currently considered the best predictor of brood survival.
Significant improvements have also been made in the captive breeding of APC, resulting in increased production and thus greater numbers available for release. On average across the six breeding facilities, from 1996–2005 the number of chicks surviving to about eight weeks was 186 (48%) and from 2006–2013 was 294 (59.5%). At the largest captive breeding facility (Fossil Rim Wildlife Center [FRWC]) the same statistics show an even greater improvement, with average chick survival going from 52% to 74%. Several factors are likely responsible for this increase. A 2005 dietary study conducted in collaboration with the Fort Worth Zoo, FRWC, and Houston Zoo resulted in dietary adjustments with likely the most significant change to the diet being the standardization of pelleted diet offered and decrease in amount of greens and insects offered to chicks. At FRWC the body weight of four-week-old chicks doubled after 2005 (McClements, unpublished data). Additionally, fine tuning and standardization of husbandry techniques, with annual meetings to share successful changes, have contributed to improved captive success. The development of a web-based database has improved record keeping and provided access to collected data for more prompt analysis. While challenges persist for the captive flocks, including inanition deaths during the first week, leg malformations, and population threats associated with reticuloendotheliosis virus, APC Recovery Program partners are encouraged by the overall trend of success.
Literature Cited
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