Hannah Madden

Terrestrial bird monnitoring

Currently volunteers in collaboration with Waardenburg Ecology and DCNA are monitoring terrestrial breeding birds for all 6 islands: Aruba, Bonaire, Curacao, Sint Maarten, Saba and Sint Eustoatius.

Observations became recently available for a few months, varying per island, see summary below

At this moment it is not yet possible to provide monitoring indicators.

 

Bonaire (November, December 2022, January, February, March 2023 ): 

American Flamingo
Bananaquit
Bare-eyed Pigeon
Barn Swallow
Black-faced Grassquit
Black-whiskered Vireo
Blue-tailed Emerald
Brown Booby
Brown Pelican
Brown-crested Flycatcher
Brown-throated Parakeet
Caribbean Elaenia
Common Ground Dove
Crested Caracara
Crested Caracara (Northern)
Eared Dove
Gray Kingbird
Greater Yellowlegs
House Sparrow
hummingbird sp.
Lesser Yellowlegs
Magnificent Frigatebird
Merlin
Northern Scrub-Flycatcher
Northern Waterthrush
Osprey
Pearly-eyed Thrasher
Peregrine Falcon
Red-eyed/Chivi Vireo
Royal Tern
Ruby-topaz Hummingbird
Saffron Finch
Scaly-naped Pigeon
Tropical Mockingbird
Venezuelan Troupial
White-tipped Dove
Yellow Oriole
Yellow Warbler
Yellow Warbler (Golden)
Yellow-shouldered Parrot

 

Aruba (Arikok, March and April 2023): 

Bananaquit
Bare-eyed Pigeon
Barn Swallow
Black-and-white Warbler
Black-faced Grassquit
Blackpoll Warbler
Blue-tailed Emerald
Brown-crested Flycatcher
Carib Grackle
Caribbean Elaenia
Common Ground Dove
Crested Caracara
Crested Caracara (Northern)
Eared Dove
Groove-billed Ani
Indigo Bunting
Northern Scrub-Flycatcher
Osprey
Peregrine Falcon
Ruby-topaz Hummingbird
Shiny Cowbird
Tropical Mockingbird
Venezuelan Troupial
White-tipped Dove
Yellow Oriole
Yellow Warbler
Yellow Warbler (Golden)

 

Curacao (March and May 2023)

American kestrel
Bananaquit
Blackfaced grassquit
Blue-tailed emerald
Brown-crested flycatcher
Brown-throated Parakeet
Caribbean elaenia
Common Ground Dove
Crested Caracara
Grey Kingbird
Magnificent Frigatebird
Northern scrub flycatcher
Northern waterthrush
Pigeon
Reiger
Rufous Collared sparrow
Scaly-naped pigeon
Tropical mockingbird
Troupial
White tipped dove
White-tailed hawk
Yellow Oriole
Yellow warbler

 

Saba (April 2023) 

American Kestrel
Antillean Crested Hummingbird
Bananaquit
Barn Swallow
Black-faced Grassquit
Black-whiskered Vireo
Bridled Quail-Dove
Brown Trembler
Brown-throated Parakeet
Caribbean Martin
Eurasian Collared-Dove
Gray Kingbird
Green-throated Carib
Lesser Antillean Bullfinch
Pearly-eyed Thrasher
Purple-throated Carib
Red-tailed Hawk
Scaly-breasted Thrasher
Scaly-naped Pigeon
White-winged Dove
Yellow Warbler
Zenaida Dove

 

Statia (March, April, May 2023) 

American Kestrel
Antillean Crested Hummingbird
Bananaquit
Black-faced Grassquit
Black-whiskered Vireo
Brown Pelican
Brown Trembler
Caribbean Elaenia
Common Ground Dove
Eurasian Collared-Dove
Gray Kingbird
Lesser Antillean Bullfinch
Magnificent Frigatebird
Pearly-eyed Thrasher
Red Junglefowl (Domestic type)
Red-billed Tropicbird
Red-tailed Hawk
Scaly-breasted Thrasher
Scaly-naped Pigeon
White-winged Dove
Yellow Warbler
Yellow-crowned Night-Heron
Zenaida Dove

 

Sint Maarten (April, May, August, September, October, November 2023)

American Kestrel
Antillean Crested Hummingbird
Bananaquit
Black-faced Grassquit
Black-whiskered Vireo
Brown Pelican
Carib Grackle
Caribbean Elaenia
Caribbean Martin
Common Ground Dove
Eurasian Collared-Dove
Gray Kingbird
Great Egret
Green-throated Carib
Laughing Gull
Lesser Antillean Bullfinch
Magnificent Frigatebird
Mangrove Cuckoo
Pearly-eyed Thrasher
Rock Pigeon (Feral Pigeon)
Royal Tern
Scaly-breasted Thrasher
Scaly-naped Pigeon
White-winged Dove
Yellow Warbler
Zenaida Dove
Date
2024
Data type
Raw data
Theme
Research and monitoring
Geographic location
Aruba
Bonaire
Curacao
Saba
Saba bank
St. Eustatius
St. Maarten
Author

PARENTAL INFANTICIDE BY EGG DESTRUCTION IN RED-BILLED TROPICBIRDS PHAETHON AETHEREUS ON THE CARIBBEAN ISLAND OF SINT EUSTATIUS

Avian reproduction is a process that requires extensive energetic input by parents, particularly in pelagic seabirds. Parental infanticide has rarely been reported in pelagic seabirds, and its frequency among taxa is therefore difficult to determine. Using data from remote cameras, two cases of probable parental infanticide in Red-billed Tropicbirds Phaethon aethereus were captured on Sint Eustatius in the 2021–2022 breeding season. Both cases are presented with images collected from remote cameras as evidence. While appearing counterproductive, parental infanticide may provide an alternative reproduction strategy that favors lifetime reproductive success over short term success.

Date
2023
Data type
Scientific article
Theme
Research and monitoring
Document
Geographic location
St. Eustatius

Foraging Ecology of Red-Billed Tropicbirds on Saba, Caribbean Netherlands, during Early Chick-Rearing

Abstract

Prey resources in oligotrophic tropical marine environments are often scattered and unpredictable. Tracking studies of tropical seabirds can provide critical information about ocean habitat affinities, prey choice and the utilisation of surrounding areas, which can be useful for conservation managers. Foraging studies of Red-billed Tropicbird populations in the Caribbean are scarce but increasing. We sought to expand on this by tracking chick-rearing adults using GPS devices and subsequently linking these tracking data to remotely-sensed environmental variables. We related our spatial data to opportunistic sampling of regurgitates in a globally significant nesting colony on Saba, Caribbean Netherlands. Diet samples were dominated by flying fish (Exocoetidae; numerical frequency: 70.73%), but prey items from the squid family (Loliginidae; 9.76%) and the families of flying gurnards (Dactylopteridae; 2.44%) and the ray-finned fish (Carangidae; 2.44%) were also identified, although we were unable to identify 14.63% of samples due to digestion. An additional goal of our study was to compare the foraging ecology of Tropicbirds on Saba with those nesting on St. Eustatius, located circa 25 km south-east. As expected, Tropicbirds nesting on Saba exhibited diurnal foraging patterns, travelling a maximum distance from the colony of 553.7 km, with an average trip length of 117.2 ± 144.6 km (±SD). Adults foraged in shallower, cooler waters with higher chlorophyll a concentrations and higher Exocoetidae species richness compared to travelling points. Despite the proximity of Saba and St. Eustatius, this is contrary to what was found for Tropicbirds nesting on St. Eustatius, where adults foraged in deeper waters with a low Exocoetidae species richness. However, Tropicbirds from Saba and St. Eustatius did exhibit some similarities in their foraging behaviour; specifically, foraging adults traversed multiple exclusive economic zones and marine protected areas, reinforcing our recommendation for nature managers in the Caribbean to create a transboundary network in order to effectively protect and conserve this species.

 

Full article available here: https://bioone.org/journals/ardea/volume-111/issue-2/arde.2022.a14/Forag...

Date
2023
Data type
Scientific article
Theme
Research and monitoring
Journal
Geographic location
Saba

Incorporation of anthropogenic materials into passerine nests on St. Eustatius, Caribbean Netherlands

AbstractUrbanization has introduced novel materials for nesting birds, including anthropogenic debris that may be dangerous to adults and nestlings (e.g., entanglement or ingestion leading to injury or mortality). We present two observations of incorporation of man-made materials into passerine nests on St. Eustatius, Caribbean Netherlands. This is the first publication of such observations for St. Eustatius, and addresses a gap in literature that acknowledges the use of anthropogenic litter by landbirds in the wider Caribbean.

Date
2023
Data type
Scientific article
Theme
Research and monitoring
Geographic location
St. Eustatius

Foraging ecology of Red-billed Tropicbirds

Abstract

Prey resources in oligotrophic tropical marine environments are often scattered and unpredictable. Tracking studies of tropical seabirds can provide critical information about ocean habitat affinities, prey choice and the utilisation of surrounding areas, which can be useful for conservation managers. Foraging studies of Red-billed Tropicbird populations in the Caribbean are scarce but increasing. We sought to expand on this by tracking chick-rearing adults using GPS devices and subsequently linking these tracking data to remotely-sensed environmental variables. We related our spatial data to opportunistic sampling of regurgitates in a globally significant nesting colony on Saba, Caribbean Netherlands. Diet samples were dominated by flying fish (Exocoetidae; numerical frequency: 70.73%), but prey items from the squid family (Loliginidae; 9.76%) and the families of flying gurnards (Dactylopteridae; 2.44%) and the rayfinned fish (Carangidae; 2.44%) were also identified, although we were unable to identify 14.63% of samples due to digestion. An additional goal of our study was to compare the foraging ecology of Tropicbirds on Saba with those nesting on St. Eustatius, located circa 25 km south-east. As expected, Tropicbirds nesting on Saba exhibited diurnal foraging patterns, travelling a maximum distance from the colony of 553.7 km, with an average trip length of 117.2 ± 144.6 km (±SD). Adults foraged in shallower, cooler waters with higher chlorophyll a concentrations and higher Exocoetidae species richness compared to travelling points. Despite the proximity of Saba and St. Eustatius, this is contrary to what was found for Tropicbirds nesting on St. Eustatius, where adults foraged in deeper waters with a low Exocoetidae species richness. However, Tropicbirds from Saba and St. Eustatius did exhibit some similarities in their foraging behaviour; specifically, foraging adults traversed multiple exclusive economic zones and marine protected areas, reinforcing our recommendation for nature managers in the Caribbean to create a transboundary network in order to effectively protect and conserve this species.

 

Date
2023
Data type
Other resources
Theme
Research and monitoring
Geographic location
Saba

Plant–frugivore interactions across the Caribbean islands: Modularity, invader complexes and the importance of generalist species

Abstract

Aim: Mutualistic interactions between plants and animals are fundamental for the maintenance of natural communities and the ecosystem services they provide. However, particularly in human-dominated island ecosystems, introduced species may alter mutualistic interactions. Based on an extensive dataset of plant–frugivore interactions, we mapped and analysed a meta-network across the Caribbean archipelago. Specifically, we searched for subcommunity structure (modularity) and identified the types of species facilitating the integration of introduced species in the Caribbean meta-network.

Location: Caribbean archipelago (Lucayan archipelago, Greater Antilles, Lesser Antilles).

Methods: We reviewed published scientific literature, unpublished theses and other nonpeer-reviewed sources to compile an extensive dataset of plant–frugivore interactions. We visualized spatial patterns and conducted a modularity analysis of the cross-island meta-network We also examined which species were most likely to interact
with introduced species: (1) endemic, nonendemic native or introduced species, and (2) generalized or specialized species.

Results: We reported 3060 records of interactions between 486 plant and 178 frugivore species. The Caribbean meta-network was organized in 13 modules, driven by a combination of functional or taxonomic (modules dominated by certain groups of frugivores) and biogeographical (island-specific modules) mechanisms. Few introduced species or interaction pairs were shared across islands, suggesting little homogenization of the plant–frugivore meta-network at the regional scale. However, we found evidence of “invader complexes,” as introduced frugivores were more likely to interact with introduced plants than expected at random. Moreover, we found generalist
species more likely to interact with introduced species than were specialized species.

Main conclusions: These results demonstrate that generalist species and “invader complexes” may facilitate the incorporation of introduced species into plant–frugivore communities. Despite the influx of introduced species, the meta-network was structured into modules related to biogeographical and functional or taxonomic affinities. These findings reveal how introduced species become an integral part of mutualistic systems on tropical islands.

 

Date
2022
Data type
Scientific article
Theme
Research and monitoring
Geographic location
Saba
St. Eustatius
St. Maarten

FORAGING ECOLOGY OF RED-BILLED TROPICBIRD PHAETHON AETHEREUS IN THE CARIBBEAN DURING EARLY CHICK REARING REVEALED BY GPS TRACKING

Investigating the foraging patterns of tropical seabirds can provide important information about their ocean habitat affinities as well as prey choice. Foraging studies of Red-billed Tropicbird Phaethon aethereus populations in the Caribbean are lacking. We sought to rectify this by opportunistically sampling regurgitates at nest sites on the island of St. Eustatius, Lesser Antilles, and by linking the GPS tracks of foraging adults to remotely sensed environmental variables. Diet samples were dominated by Exocoetidae (59.5%) and Belonidae (14.9%), although we were unable to identify 25.5% of samples due to digestion. Tropicbirds nesting on St. Eustatius exhibited diurnal foraging patterns, foraged in deeper waters with higher chlorophyll concentration, and consumed fewer Exocoetidae species compared to travelling behaviour. The maximum distance travelled from the colony was 953.7 km, with an average trip length of 176.8 (± 249.8) km. The biologged birds crossed multiple exclusive economic zones and marine protected areas, and on that basis, we suggest that efforts to protect and conserve this species may require transboundary collaboration throughout the wider Caribbean.

Date
2022
Data type
Scientific article
Theme
Research and monitoring
Geographic location
St. Eustatius

Reproductive Success of Red-Billed Tropicbirds (Phaethon aethereus) on St. Eustatius, Caribbean Netherlands

Abstract

The daily nest-survival rates of Red-billed Tropicbirds (Phaethon aethereus) were estimated over six breeding seasons on St. Eustatius in the Caribbean. We analyzed 338 nesting attempts between 2013 and 2020. The daily survival rate (DSR) of tropicbird nests was modeled as a function of nest initiation date, sea surface temperature (SST), elevation, vegetation in front of the nest, and year. Yearly nest survival rates (± SE) of the best fitting models ranged from 0.21 ± 0.06–0.74 ± 0.13 (n = 338 nests). DSR of the most parsimonious models averaged 0.39 ± 0.04 during the incubation period, 0.83 ± 0.05 during the chick-rearing period, and 0.30 ± 0.04 during the nesting period (incubation through fledging) when data were pooled across all years. Models with linear and quadratic trends of nest initiation date combined with SST and elevation received strong support in the incubation and nesting periods. Nests initiated in peak nesting season, when SSTs were lower, had higher DSR estimates than nests initiated early or late in the season. Compared to studies of the same species from Saba and the Gulf of California, survival probability on St. Eustatius was lower during the incubation stage but higher during the chick-rearing period. Similar to populations in the Gulf of California, tropicbird reproduction differed and laying date varied among years, and survival was influenced by SST. Our results are consistent with a study on White-tailed Tropicbirds (Phaethon lepturus) in Bermuda which found that survival was affected by temporal factors rather than physical site characteristics. Our study contributes to a better understanding of the factors that influence Red-billed Tropicbird survival on a small Caribbean island

 

https://www.researchgate.net/publication/365346690_Reproductive_Success_...

Date
2022
Data type
Scientific article
Theme
Research and monitoring
Journal
Geographic location
St. Eustatius

Saba Iguanas Receive Attention

The Caribbean Netherlands island of Saba is home to a unique but relatively unknown iguana population. Given the many threats faced by islands worldwide, including the Lesser Antilles and Saba, fieldwork was conducted in 2021 in order to bring attention to this unique species and the threats it faces. As on St. Eustatius, the most urgent threats appear to be low survival of hatchlings, limited nesting sites, and the presence of non-native iguanas.

Precise taxonomic status in discussion

Saba black iguana. Photo source: Thijs van den Burg

The iguana population on Saba forms part of a recently described species, Iguana melanoderma. Although there is no doubt about the unique appearance of the iguanas, experts are still deliberating over its exact taxonomic status. Despite this, it is clear that the population requires urgent protection given the number of threats it faces. The biggest concern is the presence of and possible further influx of non-native iguanas from nearby St. Maarten.

Thankfully more iguanas than originally thought

A recent study estimated the iguana population at just 200-300 individuals. This number is worrying and would be extremely concerning for the long-term survival of the population. However, because the data in the aforementioned study were preliminary, additional fieldwork was conducted on Saba in 2021. During this time, 38 transects were surveyed multiple times using distance sampling methodology, which allowed the population to be estimated more accurately. An unexpected positive result of this analysis is that the population is at least ten times larger than originally estimated, in the thousands rather than hundreds.

Saba black iguana. Photo source: Thijs van den Burg

More melanism at higher altitudes?

It is widely believed that black reptile species have evolved this color in order to be able to get warmer faster in colder climates, given that they are cold-blooded. This may also apply to the iguanas on Saba, which boasts the highest mountain in the Kingdom of the Netherlands: Mount Scenery (887m). This high volcano ensures that Saba is often cloudy, which could make it difficult for reptiles to get warm. However, we did not find any relationship between the extent of melanism and the elevation at which iguanas were found. In other words, iguanas that live higher up the volcano are not darker than iguanas at lower elevations.

Is there another explanation for why the iguanas on Saba are black? One hypothesis is that the original iguanas that established on Saba were already black. This is in line with the existence of partially black iguanas in Venezuela, which appear to be closely genetically related to the iguanas on Saba.

Few nest sites or juvenile iguanas

In order for successful reproduction and conservation of an iguana population, good quality nest sites are essential. It is well known that goats can destroy iguana nest sites through overgrazing, which leads to habitat destruction. Furthermore, goats can trample iguana nests and destroy the embryos inside eggs.

On Saba there is an enormous goat population (several thousands) which negatively impacts the island’s vegetation and causes erosion. During fieldwork we searched for iguana nest sites to evaluate their availability, distribution and quality. While this was not the main goal of the research, we were disappointed to find only four nest sites.

Juvenile iguana. Photo source: Thijs van den Burg

Another area of concern was the low number of juvenile iguanas found during fieldwork. Despite finding over 600 individuals, just 2.4% of these were juveniles or hatchlings. While the exact reason for this is unknown, one possible cause could be the feral cat population. Previous research on Saba demonstrated that feral cats exist in the lower altitudes of the island where they hunt for prey, which are exactly the same areas where iguanas prefer to nest. In fact, iguana remains were found in 9% of the cat scats examined.

Unfortunately, the situation for the melanistic iguana on Saba appears to be similar to that of the Lesser Antillean iguana on St. Eustatius, where the presence of cats and goats and an absence of suitable nest sites are well-known issues.

Remaining areas of concern

Despite the larger than expected iguana population on Saba, there are still many causes for concern. Clearly the species needs better protection as well as continued knowledge-building. Pressing concerns for the long-term existence of this species are the presence of free-roaming goats and feral cats, as well as the low number of juveniles and absence of suitable nest sites. However, by far the biggest threat is the presence of non-native iguanas which, though competitive hybridization, can mate with and thereby suppress the native population. During fieldwork, some individuals were found that looked different to the native iguana, and preliminary genetic research has confirmed that these animals were indeed invasive. This situation therefore requires the authorities to take immediate action in order to halt the invasion of non-native iguanas.

 

More info

For more info, e.g. considering student projects please contact dolfi.debrot@wur.nl and thijs.burg@gmail.com

More info in the Dutch Caribbean Biodiversity Database

 

Published in BioNews 56.

Date
2022
Data type
Media
Theme
Research and monitoring
Geographic location
Saba

Hurricane Effects on Critically Endangered Reptiles

Caribbean flora and fauna have always coped with the destructive forces of hurricanes. However, climate change leading to an increase in their frequency and strength, and because many species have declined in abundance due to anthropogenic causes, a better understanding of how hurricanes effect local populations is essential.

The Quill before and after Hurricane Irma. Photo credit: Hannah Madden

2017 Hurricane Season

The 2017 Caribbean hurricane season was the most intense recorded to date. Both Irma and Maria, category-5 hurricanes, closely passed Sint Eustatius and caused major destruction on the island; reported in this Nature Today article. Although immediately after the storms it was clear that trees were heavily affected and mostly defoliated, understanding which species were affected and to what extent requires time for data collection and comparison. Since 2017, several studies have provided pieces of information in order to understand how local populations coped, or not, with the 2017 hurricane season.

Since 2017, researchers found that >90% of all trees were defoliated by more than ¾, and that especially trees at higher elevations (such as on the Quill volcano) were affected more severely. Another study that focused on the Bridled Quail-dove (Geotrygon mystacea), demonstrated that the population declined by 77% in 2019 compared to pre-hurricane levels. A follow-up study in 2021 (not yet published) recorded a further decline to just 125 individuals, and the Bridled Quail-dove will likely be re-assessed by the IUCN.

Reptiles

Focusing on reptile species, a novel study further aids our understanding of the ecosystem-wide impact that the 2017-hurricane season had on Statian biodiversity:

The new study, focusing on the Critically Endangered Lesser Antillean iguana (Iguana delicatissima), shows that its population decreased by at least 20% during 2017. Comparing sighting and survey data from 2017–2018, the authors found a decrease in both the occupancy and population size of the iguana species. Importantly, no recovery was observed in 2019, suggesting that this already small population needs multiple consecutive years without major hurricanes to recover. Interestingly, similar to Statia’s forests, iguanas at higher elevations were found to have been affected more severely.

 

Letter Antillean Iguana. Photo credit: Philippa King

Importance

Small islands such as Sint Eustatius are home to declining populations of rare and endangered species. In many cases, these isolated populations are unable to migrate between islands and thus populations can only increase in size locally. These new studies highlight the need to improve habitat quality and lower anthropogenic threats to optimize the natural recovery of these species. Ideally, at least for population increase could be aided by a local head-starting project where baby iguanas are nourished in temporary captivity and released once they are larger and more likely to survive.

You can find the full study here entitled “Hurricane-induced population decrease in a Critically Endangered long-lived reptile” using the DCBD link below.

 

 

More info in the Dutch Caribbean Biodiversity Database
 

Downloads & links >

 

Published in BioNews 54

Date
2022
Data type
Media
Theme
Research and monitoring
Geographic location
St. Eustatius