Estimation of density and population size and recommendations for monitoring trends of Bahama parrots on Great Abaco and Great Inagua

Abstract

Once abundant and widely distributed, the Bahama parrot (Amazona leucocephala bahamensis) currently inhabits only the Great Abaco and Great Inagua Islands of the Bahamas. In January 2003 and May 2002–2004, we conducted point‐transect surveys (a type of distance sampling) to estimate density and population size and make recommendations for monitoring trends. Density ranged from 0.061 (SE = 0.013) to 0.085 (SE = 0.018) parrots/ha and population size ranged from 1,600 (SE = 354) to 2,386 (SE = 508) parrots when extrapolated to the 26,154 ha and 28,162 ha covered by surveys on Abaco in May 2002 and 2003, respectively. Density was 0.183 (SE = 0.049) and 0.153 (SE = 0.042) parrots/ha and population size was 5,344 (SE = 1,431) and 4,450 (SE = 1,435) parrots when extrapolated to the 29,174 ha covered by surveys on Inagua in May 2003 and 2004, respectively. Because parrot distribution was clumped, we would need to survey 213–882 points on Abaco and 258‐1,659 points on Inagua to obtain a CV of 10–20% for estimated density. Cluster size and its variability and clumping increased in wintertime, making surveys imprecise and cost‐ineffective. Surveys were reasonably precise and cost‐effective in springtime, and we recommend conducting them when parrots are pairing and selecting nesting sites. Survey data should be collected yearly as part of an integrated monitoring strategy to estimate density and other key demographic parameters and improve our understanding of the ecological dynamics of these geographically isolated parrot populations at risk of extinction.

Estimation of Abundance and Recommendations for Monitoring White‐Cheeked Pintails in Wetlands of Puerto Rico and Territorial Islands

“…75-100; Buckland et al 2001). However, food scarcity and patchiness may increase cluster size variation and clumping level and decrease the precision of density estimates (Rivera-Milán et al 2005). Therefore, we recommend surveying 186 points 3 times (i.e.…”

Cryptic diversity and conservation units in the Bahama parrot

“…Currently considered as stable but vulnerable , the splitting of Bahama parrots into three distinct phylogenetic species transforms the conservation status of this group. First, the conservation status of the Abaco phylogenetic species should immediately be elevated, given the small census and effective parrot population sizes [mean N c = 2386 (Rivera-Milan et al 2005); mean N e = 70 (current study)], and the increasing human population on the island (30% growth from 10,000 to 13,000 from 1990 to 2000; reviewed in Wiley et al 2004). The increased development and road construction associated with human population growth on Abaco promises to exacerbate threats that have emerged since the mid-20th century, including:…”

“…A mean effective population size (N e ) of 70 (95% interval: 32-312) and 270 (95% interval: 65-infinity) individuals were inferred for Abaco and Inagua, respectively, as calculated according to the method of Waples and Do (2008). The overall effective population size to census size ratios (N e /N) using the mean estimate of census (Abaco: n = 2386; Inagua: n = 4450; Rivera-Milan et al 2005) were 0.03 (Abaco), and 0.06 (Inagua). These estimates were lower than the median estimate of 0.11 obtained for 102 species of wild unmanaged populations of various taxonomic groups (Frankham 1995) and 0.14 from a similar review by Palstra and Ruzzante (2008) based on indirect genetic methods.…”

“…Describing a visit to what some believe was Acklins or Crooked Island in 1492, Christopher Columbus noted ''flocks of parrots which darken the sun…'' (Hale 1891;Attrill 1980;Keegan 1992). More recently, populations of Bahama parrots have been estimated at approximately 4,000-10,000 individuals (reviewed in Wiley et al 2004), restricted to the northernmost and southernmost extremities of the archipelago on Abaco (n = 1576-3612; Rivera-Milan et al 2005) and Great Inagua (n = 3486-7490; Rivera-Milan et al 2005), respectively. In addition to the variation in morphological and plumage characteristics described by Reynolds and Hayes (2009), differences in nesting behavior and flight calls between Abaco and Inagua have also been reported (Gnam and Burchsted 1991;Reynolds 2006).…”

Survey duration and season influence the detection of introduced eastern rosella (Platycercus eximius) in New Zealand

“…Superficially, it may seem that rosella have a high probability of detection, being both visually and vocally conspicuous to the human observer (Berg and Bennett 2010). When silent and stationary in foliage, however, these birds can be extremely difficult to detect ; other studies have also noted the difficulty of detecting seemingly conspicuous parrots in dense vegetation (Heinsohn et al 2005;Rivera-Milan et al 2005). Furthermore, rosella are particularly wary in the presence of humans (Higgins 1999;Blumstein 2003), and could potentially avoid observers during surveys.…”