Structural vegetation damage and food limitation are important effects of major hurricanes, particularly

for fruit/seed-eating, forest-dependent Caribbean birdswith restricted distributions and small

populations, such as the Bridled Quail-dove Geotrygon mystacea. Motivated by the lack of abundance

estimates, corrected for detection probability, we conducted distance-sampling surveys inside

and outside theQuill National Park eachMay in 2016-2019.Detection mode was the most important

covariate, with others receiving no support fromthe data. Detectability of available single individuals

and clusters of individuals within 60mof transect centrelines averaged 0.957 0.114 standard error

for audio detections, 0.434 0.052 for visual detections, and 0.693 0.064 for detection modes

combined. Availability averaged 0.475 0.138 and the product of detectability and availability

averaged 0.329 0.098. Density averaged 1.459 0.277 individuals ha-1 and population size

averaged 642 122 individuals in 440 ha. Density did not differ along and away from forest trails,

but was higher inside than outside the park and at elevations within 201-400 m than 100-200mand

401-600 m.Density declined by 76%after hurricanes IrmaandMaria in 2017.We suggest thatmajor

hurricanes together with free-ranging livestock overgrazing degraded foraging habitats, limited food

supply, and caused a population bottleneck. Our methodology can be implemented across the

distribution range to assess population status and trends and evaluate the result of management

actions at key conservation sites. Bridled Quail-dove populations probably were declining on most

islands before the 2017 hurricanes and population status warrants revision.

Keywords: Bridled Quail-Dove, distance sampling, hurricanes, population assessment, St.

Eustatius

The Bridled Quail-dove is a regionally endemic species that, on Statia, is only found in upper elevations of the Quill (above ~150m) and inside the crater.  Since 2017, annual surveys have highlighted an alarming decline in populations.  At an estimated population decrease of ~77% since 2017, this species has caught the attention of conservationists and requires immediate protection.

The Plight of the Dove

Last year we reported the results of a post-hurricane assessment of the Bridled Quail-dove (Geotrygon mystacea) population on Statia. Once thought to have been a common resident of the West Indies, declining populations are now isolated within coastal dry forest patches of the eastern Caribbean. Introduced, non-native predators such as feral cats, mongooses and rats are thought to negatively impact Bridled Quail-dove populations by preying on adults, eggs and/or chicks. Other external factors that contribute to population declines include hunting, volcanic activity, hurricanes, and habitat loss and alteration. Furthermore, this species is sensitive to openings in the forest canopy, which also affects nesting. Despite its current classification as a species of Least Concern by the IUCN (in 1992 it was classified as Near Threatened), the Bridled Quail-dove is likely of conservation concern due to data deficiency and population declines across its entire habitat. The only surveys we are aware of took place in Montserrat (2007) following a volcanic eruption, St. Croix (1992) following hurricane Hugo, and Guana Island, British Virgin Islands (2018). Populations on other islands such as Puerto Rico are thought to be so limited that the species was excluded from a Columbid study (1995). Calling and breeding activity are dependent on rainfall, therefore the dove is sensitive to hurricanes and extended periods of drought. Similar to other Columbids, the Bridled Quail-dove lays clutches of two eggs in a flimsy nest made of twigs up to six meters above the forest floor. Furthermore, Bridled Quail-doves do not fare well in areas of human activity. 

Current Study Highlights Rapid Decline in Population

Our pre-hurricane assessment in May 2017 was initially encouraging, with an estimated 1,039 (minimum 561 -maximum 1,621) quail-doves across its local habitat of 440 hectares, possibly the highest known density in the region. Post-hurricanes season, in November 2017, we repeated the surveys and recorded a decrease of 22% to 803 (minimum 451 -  maximum 1,229). Furthermore, in May 2018, we recorded a decline to 253 individuals (minimum 83 - maximum 486). 

We repeated surveys across the entire Quill (440 hectares) during May 2019, coinciding with the quail-dove’s peak breeding season. Estimations for detection probability, density and population size were calculated by measuring the perpendicular distance of the quail-dove from the transect centerline during repeated surveys. The results are very concerning since the population has continued to decline to 238 individuals (minimum 118 - maximum 390). The surveys of May 2018 and 2019 showed that little if any successful post-hurricane reproduction has occurred. Additionally, the majority of detections were recorded inside the crater and near the crater rim, with very few detections at lower elevations. This means that the population is highly clumped at low numbers, which increases the chance of local extinction.  

Possible Causes for Population Decline

Indirect effects of hurricanes, human-induced habitat degradation and increased predation continued to affect quail-dove survival and reproduction in 2019. Rat and other invasive predator species may increase in density following hurricane-induced changes in foraging resources, affecting quail-dove survival and reproduction even further. A feral cat was detected during surveys inside the crater, probably as a result of forest openness after the hurricane.  Due to the fact that members of the Columbidae family have early maturity and short lifespans, conservation efforts should focus on successful reproduction through invasive species management. The integrity of the Quill should be improved to help forest-dependent birds and other wildlife recover in order to enhance their prospects for long-term survival on Statia.

Uncertain Future for Quail-Doves on Statia

Unfortunately, the frequency and intensity of hurricanes are predicted to increase as a result of climatic change. Furthermore, Caribbean islands are expected to see more frequent and severe droughts. Between 2013 and 2016, the region experienced a widespread drought due in part to El Niño. Large scale trends are difficult to estimate since precipitation has been very inconsistent over the past century.  However, there does appears to be a regional trend towards an increase in variability of precipitation.   This increase in variability will continue to threaten the local quail-dove populations.

We are grateful to BirdsCaribbean for funding Frank’s travel expenses in 2017, to St. Eustatius National Parks for allowing us to conduct surveys in the Quill National Park, and to Caribbean Netherlands Science Institute (CNSI) for facilitating this ongoing project. This July, Hannah Madden presented the results of this research at BirdsCaribbean’s regional meeting in Guadeloupe. 

Green turtles Chelonia mydas and hawksbill turtles Eretmochelys imbricata are neg- atively impacted by natural and anthropogenic disturbances. Unknown numbers of turtles are killed annually in the coastal waters of Bonaire and Klein Bonaire, Caribbean Netherlands. We used N-mixture models, conventional distance sampling and the multiple Lincoln-Petersen method to estimate abundance from transect-count and net-capture surveys. Maximum likelihood and Bayes- ian generalised linear models were used to assess trends in annual abundance in 2003−2018, and a Bayesian state-space logistic model was developed to generate the posterior distributions of pop- ulation parameters and make abundance predictions for 2019−2030. Mean ± SE annual abun- dance was 555 ± 149 green turtles (2.5th and 97.5th percentiles = 337, 943) and 70 ± 13 hawksbill turtles (49, 101), and there were no trends in western Bonaire and Klein Bonaire in 2003−2018. Mean annual abundance was 348 ± 135 green turtles (171, 731) and there was a positive trend inside Lac Bay, southeast Bonaire, 2003−2018. Green turtles have higher population growth rate and carrying capacity, and therefore can sustain higher human-induced mortality than hawksbill turtles. However, under low mortality rates (<0.100), both species can fluctuate stably between the lower and upper limits of the carrying capacity. The methodology implemented can be adapted to estimate sea turtle abundance, monitor and model their population dynamics, and assess the neg- ative impact of human-induced mortality in other Caribbean islands.

KEY WORDS: Chelonia mydas · Eretmochelys imbricata · Abundance · N-mixture model · Distance sampling · Multiple Lincoln-Petersen method · Generalised linear model · Bayesian state-space logistic model

In the December 2017 edition of BioNews, we provided an overview of the results of two population assessments of the Bridled Quail-dove (Geotrygon mystacea) that had been conducted that year. This article provides the results of a third assessment that was conducted eight months after two major hurricanes impacted St. Eustatius.

The Bridled Quail-dove is a regionally endemic species in the family Columbidae that, on Statia, is only found in upper elevations of the Quill (above ~150m) and inside the crater. It is easily distinguished from other dove species by the torquoise patch on its neck and white stripe (bridle) under the eye. With its habit of wandering the forest floor during daylight hours in search of food (seeds, fruits and the occasional gecko or snail), observant hikers are likely to spot this bird. Activity and breeding are very much dependent on rainfall, and the dove is sensitive to hurricanes and extended periods of drought. Similar to other Columbids, the Bridled Quail-dove lays clutches of two eggs in a flimsy nest made of twigs up to six meters above the forest floor. Bridled Quail-doves do not fare well in areas of human activity and numbers have declined across the species’ range, presumably due to habitat loss, but also due to hunting and predation by invasive mammals such as the Black Rat (Rattus rattus). 

Irma and Maria were the first recorded category five hurricanes to hit the Windward Islands, and while Statia was spared extensive infrastructural damage in urban areas, its forest ecosystems did not fare so well. According to a recent publication by Eppinga and Pucko (2018), an average of 93% of tree stems on Statia and Saba were defoliated; 83% lost primary/secondary branches, 36% suffered substantial structural stem damage, and average tree mortality was 18% (with mortality being almost twice as high on Statia than Saba). 

Our pre-hurricane assessment in May 2017 was initially encouraging, with an estimated 1,030 (standard error [SE] = 275, 95% confidence interval [CI] = 561-1,621) quail-doves across its local habitat of 440 hectares, possibly the highest known density in the region. Post-hurricanes, in November, we repeated the surveys and recorded decrease of around 22% in the population to 803 (SE = 208, 95% CI = 451-1,229). Nevertheless, we feared that the population would continue to decline as a result of hurricane-induced habitat degradation and the negative impacts of severe vegetation damage, loss of vegetation cover, food limitation, and increased predation.

We repeated surveys in May 2018, hoping to coincide with the quail-dove’s peak breeding season. However instead of the usual ~70 transects, we had to walk a total of 255 transects in order to detect sufficient doves for analysis. No doves were heard calling, most likely as a result of delayed breeding, and only 32 were detected during 2018 surveys compared with ~92 in previous years. As expected, the quail-dove population continued declining in May 2018 (-76% compared with May 2017) and is currently very small at around 253 individuals (SE = 105, 95% CI = 83-486). 

Reduced survival and reproduction, and thus abundance fluctuations at low numbers, could lead to local extirpation. Because of the life-history characteristics shared by members of the family Columbidae (e.g., early maturity and short lifespan), conservation efforts are now urgently required. Although survival and reproduction rates of the Bridled Quail-dove on Statia are poorly understood, Black Rats are present in all vegetation types within the terrestrial protected areas. Management of these invasive mammalian predators within the dove’s range is needed as a first step towards increasing reproduction and survival, and therefore population recovery to pre-hurricane levels, of this highly vulnerable species.

The authors are grateful to St. Eustatius National Parks Foundation for granting permission to conduct surveys in the Quill National Park. Thanks to funding by the Dutch Ministry of Economic Affairs (now Ministry of Agriculture, Nature and Food Quality (LNV)) under their Nature Fund initiative, a rodent control project, facilitated through the Caribbean Netherlands Science Institute (CNSI), is running on St. Eustatius. The end date of this project was recently extended to October 2019. 

Abundance estimates based on adequate survey design and count methodology are needed for population monitoring and modelling, and for assessing the results of conservation actions taken to boost or maintain population size at desired target levels. We monitored Bonaire’s population of yellow-shouldered parrot Amazona barbadensis rothschildi using systematic distance sampling surveys in 2009–2017, and developed a Bayesian state-space logistic model to predict changes in abun- dance resulting from increased human-induced mortality in 2018–2066. Survey-based abundance estimates (mean ±bootstrapped SE) were 0.172 ± 0.020 parrots ha–1 and 2924 ± 340 parrots at a survey region covering 17 000 ha. Model- based posterior distribution estimates (mean ± MCMC SD) of maximum population growth rate, maximum sustainable mortality rate, maximum sustainable mortality, population carrying capacity and equilibrium population size were 0.179 ±0.129, 0.090 ± 0.064, 219 ± 135, 5623 ± 2043 and 2811 ± 1022 parrots. With low to moderate mortality rates (0.001– 0.100, 0.101–0.250), predicted population sizes (mean ± MCMC SD) were 2963 ± 668 and 2703 ± 1660 parrots in 2018, and 2754 ± 690 and 2297 ± 1301 parrots in 2066. With high mortality rates (0.251–0.500), predicted population sizes were 1780 ± 1160 parrots in 2018 and 26 ± 139 parrots in 2066. Because the relative importance and magnitude of human–parrot conflicts are unknown but may be unsustainable, we consider the parrot population vulnerable to the risk of extinction during the modelled time horizon. Therefore, we recommend long-term monitoring and modelling for assessing changes in abundance and the results of conservation actions taken to keep the population above 2800 parrots in the survey region (i.e. population size N > 2.5% percentile of the posterior distribution of population carrying capacity K).

Sea Turtle Conservation Bonaire (STCB) has been protecting sea turtles on Bonaire since 1991, so this year represents the 26th Anniversary of our organization. In 2002, we standardized our research and monitoring efforts, following the appointment of a Scientific Officer. Annually we monitor our nesting beaches around Bonaire, conduct intensive in-water netting and snorkel surveys, and we regularly track sub-adult and post-breeding migrations using satellite telemetry. These techniques provide us with a better understanding of Bonaire sea turtles’ breeding success, abundance, health, growth rates, migratory paths and distant feeding grounds, residency duration, habitat quality, and threats. In 2017, Scientific Advisor Dr. Frank Rivera-Milán analyzed in-water transect counts, net captures, and nesting data that STCB has collected over the years. In cooperation with STCB, Rivera-Milán will produce scientific publications in the coming years, as well as review STCB’s methodology for netting (net captures), in-water surveys (transect counts) and nesting. 

During the 2017 season, we recorded 78 nests at our index beach on Klein Bonaire. A total of 61 hawksbill and 17 loggerhead nests and suspected nests were documented on “No Name Beach”. On the beaches on Bonaire and Klein Bonaire combined, we observed three sea turtle species (hawksbills, loggerheads and green turtles) crawling 228 times, which included a total of 128 confirmed or suspected nests. 21 green turtle nests were recorded in northeastern Bonaire. Hawksbills and loggerheads mainly nested on Klein Bonaire and the beaches of southern Bonaire. That said, three loggerhead and three hawksbill nests were recorded in northeastern Bonaire. The nesting period on Bonaire in 2017 ran from April to December with the highest number of nests laid between mid-June and mid-September. 

Estimates of clutch size and hatch success suggest that around 12,155 turtles hatched from nests on Klein Bonaire and Bonaire in 2017, including approximately 7,988 hawksbills, 2,033 loggerheads, and 2,134 green turtles. Sea turtle nesting activities across Klein Bonaire and Bonaire have been increasing since monitoring began in 2002. 

During in-water snorkel surveys, we counted and, when possible, captured green turtles and hawksbills in all regions sampled, including Klein Bonaire, along the west coast of Bonaire, and near the reef bordering Lac. Netting in Lac was conducted in three weekly sessions across the year. The aggregation of green turtles near Lac remains much larger than sites along the west coast, and greens captured there were bigger than conspecifics elsewhere, perhaps a result of the composition and high densities of sea grasses in Lac. 

The total occurrence of fibropapillomatosis (FP) among green turtles captured in nets at Lac declined considerably in 2017, continuing the downwards trend observed in 2015. This year only 5.5% of green turtles captured in and around Lac had visible FP tumors. 

STCB co-authored an important research paper in 2017: “Ecological regime shift drives declining growth rates of sea turtles throughout the West Atlantic” together with researchers led by Karen A. Bjorndal.

During 2017, there were 35 sea turtle hotline incidents reported, 32 of which were directly related to turtles in trouble; one involved the general public harassing sea turtles; and one call was related to poaching. The fishing industry and associated by-catch, one of the biggest threats Caribbean-wide, was implicated in approximately 23% of the turtles in trouble. A total of nine incidents were related to a large mass of seaweed sargassum that drifted inside the Lagoen and Sorobon area at the end of December. In the open ocean, these floating mats are extremely diverse, providing important habitat for over 250 species of fish and invertebrates, many of which are not found anywhere else. Young sea turtles often spend their tender years finding refuge and a plentiful food supply in these floating seaweed mats. However, when it enters coastal areas and starts rotting, it can cause mortality. Unfortunately, climate change has brought warmer temperatures, which increases algal growth rates, and possibly stronger currents/shifting currents, which combined with more and more land-based nutrients flowing into our oceans, are thought to be the reason why we are seeing more and more massive ‘strandings’ of these floating seaweed mats.

Sea Turtle Conservation Bonaire (STCB) has been protecting sea turtles on Bonaire since 1991, so this year represents the 25th Anniversary of our organization. In 2002 we standardized our research and monitoring efforts, following the appointment of a Scientific Officer. Annually we monitor our nesting beaches around Bonaire, conduct intensive in-water netting and snorkel surveys (capture-mark-recapture), and we regularly track sub-adult and post-breeding migrations using satellite telemetry. These techniques provide us with a better understanding of Bonaire sea turtles’ breeding success, abundance, health, growth rates, migratory paths and distant feeding grounds, residency duration, habitat quality, and threats. 

In December 2009, we sampled 62 6-minute random-systematic counting points (k) to estimate the density and population size of yellow-shouldered parrots and brown-throated parakeets in a survey region (A) of 7,873 hectares, which covered the WashingtonSlaagbai National Park and forest, suburban, and agricultural areas between Brasil, Karpata, Dos Pos, Rincón, and Fontein. In March 2010, we sampled 104 points, covering a survey region of 17,000 hectares that included forest, urban, suburban, and agricultural areas in northern, central, and southern Bonaire....

About 210 resident and migratory bird species are found on the island of Bonaire. More than half of these species are landbirds. Some of the landbirds are endemic subspecies. Despite its small area, Birdlife International designated five Important Bird Areas (IBAs) on Bonaire. This manual is a working tool for STINAPA employees and volunteers doing landbird surveys on Bonaire.

1) The monitoring program covers the areas considered potential habitat for feeding, nesting, and roosting of the selected species of landbirds on Bonaire. 2) Surveys are conducted at least twice per year (February-March and September-October). About 10 days are needed per sampling period. 3) Morning counts start after sunrise and stop at 10:00 hours. Afternoon counts start at 16:00 hours and stop before sunset. 4) At least two observers are needed for the collection of count and supplementary data related to habitat, food, disturbance, and other factors that may affect species detection and abundance at sampling units (fixed on-road and off-road points). 5) Additional information are collected about uncommon observations, such as large flocks in roosting areas, nesting activity, the presence of predators, and any other observation that may be of interest for research, monitoring, and management purposes. The location of these observations is recorded using GPS units. Date, time, and additional comments are also recorded. When possible photos are taken to provide complete documentation for future reference and consultation as needed. 6) Weather conditions are recorded as part of standard data collection. 7) Just like any other activity conducted by STINAPA Bonaire, human safety is always considered a priority over the completion of survey activities.