Fernando Simal

ABSTRACT: Abundance estimates corrected for changes in detection are needed to assess population trends. We used transect-count surveys and N-mixture models to estimate green turtle Chelonia mydas and hawksbill turtle Eretmochelys imbricata detection and total abundance at foraging grounds in Bonaire during 2003−2018, and we used these total abundance estimates to fit a Bayesian state–space logistic model and make abundance predictions for 2019−2030. During 2019−2022, we also recorded distance categories to estimate detection and total abundance using distance sampling and N-mixture models. In the present study, we focus on distance sampling to estimate observer detectability and total abundance, and to determine if total abundance increased, declined, or did not change during 2019−2022 and when compared with 2003−2018 estimates and 2019−2030 predictions. Detectability averaged 0.53 (SE = 0.02) for green turtles and 0.51 (SE = 0.06) for hawksbill turtles. Density (ind. km−2) and population size (individuals in the 4 km2 survey region) averaged 72.1 (SE = 17.3) and 288 (SE = 69) for green turtles and 21.8 (SE = 4.6) and 87 (SE = 18) for hawksbill turtles. Green turtle total abundance did not change during 2019−2022 (p > 0.05) but remained low when compared with 2003−2018 estimates and 2019−2030 predictions. Hawksbill turtle total abundance declined between 2020 and 2021 (z = 2.15, p = 0.03) and increased between 2021 and 2022 (z = −3.04, p = 0.002), but 2019−2022 estimates were similar to 2003−2018 estimates and 2019−2030 predictions. Our methodology can be used to monitor sea turtle populations at coastal foraging grounds in the Caribbean. 

Abstract

The island of Bonaire is a nesting location for at least four tern species: a subspecies of the Least Tern (Sternula antillarum
antillarum), the Common Tern (Sterna hirundo), the Royal Tern (Thalasseus maximus), and a subspecies of the Sandwich
Tern (Thalasseus sandvicensis eurygnathus). The island is also a significant nesting site for the Caribbean Least Tern (Sternula
antillarum) population. Our main objectives were to: a) measure and compare breeding success at five known nesting sites on
northern Bonaire, b) document and compare the impact of natural and introduced predators on each site, and c) give management
recommendations for increasing breeding success based on our results. Our nest counts from 2014 indicate a significant
decline in nest abundance compared to historical observations from the 1950s, matching previous studies and observations
from the last two decades. Among the five nesting sites in our study, terns at the two island sites had the largest number of
breeding pairs and achieved the greatest success, fledging a maximum of ~0.8 chicks per nest, compared to all other sites which
were connected to the shoreline. We recorded rats and cats as predators at the peninsula site and field observations suggested
that predation by Laughing Gulls (Leucophaeus atricilla) might also be occurring at two sites. Both natural and artificial islands
on hypersaline lagoons provide good nesting sites for terns on Bonaire as they are protected from mammalian predators. However,
recreational disturbance remains the single most serious and pervasive threat to the future of seabird nesting on Bonaire
and requires concerted action. We propose a list of management actions to increase the numbers of nesting terns throughout
the sites studied. Increasing protection from predators and human disturbance by making artificial nesting islands will provide
the potential for Bonaire, and its sister islands, to become major refuges for southern Caribbean metapopulations of these four
tern species.

Abstract

Bats play key ecological roles on the islands of Aruba, Bonaire and Curaçao (ABC islands), Caribbean Netherlands; however, most bat species on these islands are either threatened or their conservation status is unknown. We investigated the use of roosts by cave-dwelling bats in this insular system to propose conservation measures aimed at their protection. We conducted bi-monthly species inventories of cave-dwelling bats in 13 of the best-known caves and mines used as day and maternity roosts on the ABC islands. Bats were captured with mist nets and a harp trap (only one cave) placed either inside or at the entrance of the roosts during the first hours (3 to 5 hrs) after sunset. For Aruba and Curaçao, bat monitoring comprised two years of sampling. In the case of Bonaire, depending on the cave, bat monitoring involved one, two or four years of sampling. We identified six species of cave-dwelling bats associated with these roosts, Mormoops megalophylla, Pteronotus davyi, Natalus tumidirostris, Myotis nesopolus, Glossophaga longirostris and Leptonycteris curasoae. All the examined caves and mines were occupied year-round. The two abandoned mines were inhabited exclusively by the nectar-feeding G. longirostris and L. curasoae, whereas caves containing hot chambers were occupied by up to five species of bats, including insect-feeding M. megalophylla, P. davyi, M. nesopolus and N. tumidirostris, and migratory L. curasoae. Nursery roosts occupied by insect-feeding bats were Quadirikiri on Aruba; Orizjan, Pos di watapana and Pos di Antoin on Bonaire; and Raton and Noordkant on Curaçao. Nectar-feeding bats used all the caves and mines examined as day roosts, nursery roosts or both. All the cave-dwelling bats studied had a single annual reproductive period. In the case of insectivorous bats, pregnancy and lactation occurred mainly between July and December, overlapping with the rainy season. For nectar-feeding bats, pregnancy and lactation took place between March and September, overlapping with the flowering and fruiting seasons of chiropterophilous cacti. Most of the examined bat roosts require protection due to one or more of the following conditions: (1) the presence of multiple species dependent on hot chambers, (2) their use as nursery roosts, and (3) the presence of large colonies of L. curasoae.

Full text available here: Bat Inventories at Caves and Mines on the Islands of Aruba, Bonaire and Curaçao, and Proposed Conservation Actions (bioone.org)