Sea birds

New Red-billed Tropicbird data suggested declining nest survival rates may be more related to parental behavior than previously thought. A researcher from Utrecht University, along with STENAPA and CNSI staff analyzed nest characteristics, trap camera photos and historical data to better understand the driving factors to declining nest survival rates.

Seabird populations are facing unprecedented levels of threats which has resulted in nearly 70% loss of monitored seabird populations over the past fifty years.  This is faster than any other group of birds worldwide and can be linked to overfishing, habitat destruction, invasive species, increased storm events and changes in food availability.

Red-billed Tropicbird and chick. Photo credit: Michiel Boeken

Pilot Hill

The Red-billed Tropicbird are an iconic species for the northern Dutch Caribbean islands.  In fact, a small but globally significant colony of breeding pairs nests within the Boven Important Bird Areas of Sint Eustatius.  Unfortunately, this area has been experiencing high rates of nest failure over the past decade. New research, conducted by Utrecht University student Hailley Danielson-Owczynsky, analyzed a combination of previously collected information with new monitoring data from the Pilot Hill nesting area in an attempt to better understand what is causing these low success rates.

Nest Monitoring

Previously, high predation by cats, rats and crabs were blamed for declining egg survival rates.  This was partially linked to the success of predator control projects on Saba, where nest survival of one site was improved from 0 to 40% after two-seasons of cat removal. Additionally, when reviewing the 1.6 million photos taken by nest cameras between 2017 and 2022, 80.5% of monitored nests showed predator presence, leading managers to blame predators for declining numbers. Further analysis conducted by Danielson-Owczynsky found that before being consumed by predators, many of the eggs had already been left unattended by parents for a prolonged period of time.  This same study found that predators were much less likely to visit a nest when a parent was nearby. Therefore, egg failure is more likely attributed to parent behavior prior to its predation.  It is important to note that invasive predators are still a concern, these results merely give an additional factor for conservation managers to consider.

Difficult foraging conditions for Tropicbird parents could lead to decreased nest attendance.  Red-billed Tropicbird’s diet is comprised primarily of flying-fish; however, overfishing has led to a decrease in overall fish populations requiring parents to forge over greater distances for longer periods of time.

Red-billed tropicbird. Photo source: Christian König

Implications

Pelagic seabirds, such as the Red-billed Tropicbird possess many unique traits, such as long lifespans, slow development and low reproductive rates, often attributed to their limited and sporadic food supply.  Given their long-life spans and the fact that they forage across wide ranges, these birds have been used as indicators for overall marine ecosystem health.  Therefore, the rapid decline in local populations gives key insight and rising concern for overall marine environmental conditions.  Understanding the magnitude of threats facing these and other related species will be key in safeguarding a strong and resilient marine environment moving forward.

Report your sightings

Species reports by local communities and tourists are invaluable for nature conservation efforts to help increase public awareness and overall species protection.

You can report your Red-billed Tropicbird sightings and photos on the website www.Observation.org or download the free apps (iPhone (iObs) & Android (ObsMapp)). You can also send your information to research@DCNAnature.org for support. An automatic species recognition tool is in development, so stay tuned for updates.

To learn more, you can find the full report by using the link below.

More info in the Dutch Caribbean Biodiversity Database

Published in BioNews 56.

The Jan Thiel lagoon can be considered the most important wetland of Curaçao based on its combined value as a feeding habitat for terns. As is likely the case in general with the other saliñas of Curaçao, Jan Thiel lagoon appears to be of the greatest significance to flamingos during the dry season when the larger wetlands in Venezuela run dry. The lagoon is also an area that has historically provided conditions suitable for massive nesting by rare species of terns. Nesting by terns still occurs but on a much lesser scale and with fewer species. During the rainy season, and because of the presence of many dams which retain fresh water on the eastern half of the lagoon, the area is of persistent value to several waterbirds which showed a preference for feeding in less saline water. These include species such as ducks, sandpipers, and black-winged stilts.

The lagoon is approximately 80 ha and is surrounded by approximately 228 ha of additional scenic conservation area which contain rare tracts of native vegetation and which provide valuable habitat to many other native species such as konènchi, sloke, tapa kaminda, and warawara. The best vegetations are found on the eastern side of the lagoon, particularly the southern quadrant of the eastern half of the lagoon. This quadrant has quite rare vegetation, best described as a Haematoxylon-Coccoloba vegetation in which the dreifi shimaron is found to be abundant on volcanic soil. Such vegetation is also known from areas of Oostpunt, Malpais, and Seru Cocori. Other species remarkably abundant in the Haematoxylon-Coccoloba unit include the mata piska and the palu di pushi while the presence of scattered kibrahacha and mangel di sabana likely indicate species which were once much more abundant but which have somehow survived the intensive use of this area in the past. Rare plant species found in the area include the trees lumbra blanku (Croton niveus), kurahout (Peltophorum acutifolum), mata kombles (Schoepfia schreberi), "fuma machu" (Vitex cymosa). For the latter species, less than 20 trees are known to exist in the Dutch Antilles. 

A major limitation to the avifaunal use of the lagoon, particularly the flamingos and tern nesting is the current high level of uncontrolled recreational disturbance. Unintentional recreational disturbance can likely be greatly reduced by a combination of properly informing visitors, by planting vegetation barriers to shelter visitors from the constant sight of the birds and by partially redirecting trails.

The planned Jan Thiel-Amandelweg road is a major threat to the ecological integrity of the conservation area. The road is protected to lie directly in the two most important freshwater areas bordering the lagoon and on top of one of the four locations which support tern breeding. The mere physical presence of the road is in itself a scourge to the vegetation as is cuts through a part of the Haematoxylon-Coccoloba vegetation and lies directly on top of three (fortunately resprouting) very rare Vitex cymosa trees. If this road is ever built it will add a large source of constant disturbance (incl. traffic noise) for much of the eastern half of the lagoon (which is the principal area used by the avifauna), and a major source of littering and contaminants from vehicles. 

The abandoned landfill of Koraal Specht has not been sealed to prevent rainwater percolation and several seeps were seen to emanate from the landfill and flow into the lagoon. The landfill likely forms a serious long-term threat to the lagoon and a study is needed with regards to the potential leaching of contaminants.

During the HNLMS 'TYDEMAN' bathymetric expedition on the Saba Bank, April - May 1996, two observers spent 7 weeks on board and to collect data on the distribution of
seabirds, marine mammals, and human activities (fishing, shipping). The results show that the Saba Bank has a bird fauna that is relatively rich as compared with the surrounding seas, whilst the birds seem to be concentrated along the edges of the Bank. Observed cetaceans included three dolphin and one whale species. The bird and cetacean observations were made during a transitional season in which groups of animals are migrating into the area whilst others are migrating out.
Human activities included fishing (the distribution of fish pots was determined, and the activities of a few fishermen observed) and shipping. Especially the observation of large
tankers anchoring close to the edge of the Bank in areas where coral reefs occur, was identified as a threat.

The report presents the primary results of an opportunistic project which has yielded many rough but valuable data about the Saba Bank in April-May. These data are available
for future management of the Saba Bank. The preliminary elaboration of the data in this report confirm the importance of especially the edges of the the Saba Bank for birds and
suggest the Bank being a feeding area for populations that breed on the neighbouring islands. Together with the observations of different species of cetaceans, the results
confirm the idea that the Saba Bank has considerable importance or the marine biodiversity in the region of the leeward Antilles. The position of the Saba Bank, partly
within the territorial waters of the Netherlands Antilles but completely within the limits of a hypothetical Exclusive Economic Zone, offers a great promise that protection (and sustainable use) of these natural values can be legally effected.

Abstract:

The Saba Bank is a large submerged carbonate platform of approximately 2,200 km2 in the Caribbean Sea which lies partially within the Exclusive Economic Zone of the Netherlands and partially within the territorial waters of Saba and St. Eustatius. It was declared a protected area by the Dutch Government on 15 December 2010 and has been registered as such in the Specially Protected Areas and Wildlife (SPAW) protocol of the Cartagena Convention for the Protection and Development of the Marine Environment of the Wider Caribbean. Applications for a Particularly Sensitive Sea Area (PSSA) at IMO and Ecological or Biological Significant Area (EBSA) at CBD are pending.

As part of the Saba Bank research program 2011-2016, commissioned by the Dutch Ministry of Economic Affairs (EZ), an expedition to the Saba Bank was conducted from 22 to 29 October 2011. The Saba Bank research program aims to obtain information on the biodiversity, key ecological processes and carrying capacity for commercial fisheries to facilitate sustainable management of the area. The primary objectives of the 2011 research expedition were to collect data on benthic and reef fish communities; sponges and nutritional sources of the sponge community; seabirds and marine mammals; water quality, water velocity and other physical parameters. A multidisciplinary team conducted video and visual surveys on benthos, fish and sponges during 10 SCUBA dives at 20-30m depth, while sea birds and marine mammals were surveyed by means of on-board visual surveys and acoustic data loggers. Water velocity and water quality were also measured on-board using an Acoustic Doppler Current Profiler (ADCP) and Conductivity, Temperature and Depth (CTD) device.

During the expedition 8 sponge species were collected and 37 scleractinian coral species and 85 fish species were identified.Fish biomass varied per site between 1.3 kg to 4.4 kg.
Part of the measurements on water velocity, water quality and benthic cover are still in the process of being analysed. Data collected will also be used as baseline for future monitoring and analyses of biodiversity and key ecological processes within the framework of the 2011-2016 research program. 

Management Recommendations:

• To keep collecting data for long term monitoring programs. It is fundamental for the proper management of our natural resources.
• Try to recruit regular local volunteers and provide them with training until financial resources to hire professional staff are available.
• Increase the number of bird surveys as resources and trained personnel become available.
• If a third year of surveys brings again positive results consider lowering the frequency of the surveys in order to cover other species that need attention. 

Lac Bay, Bonaire is the most important mangrove and seagrass area of Bonaire and has been undergoing steady ecological decline in the last decades. Based on an initial assessment of conservation management issue and potential solutions, as, conducted by IMARES in June 2010, the Dutch Ministry of Agriculture, Nature and Food Quality (LNV) asked IMARES to return to Bonaire to work with Stinapa Bonaire to choose narrower priorities and jointly make a short-list of topics as a working document for cooperation and action. In the beginning of September, site visits and discussions were held in Bonaire with the manager of Lac Bay and various stakeholders to identify and agree on priority issues for action. This working report gives the results of that visit.

Four action spear point projects were identified, based on urgency and feasibility based on local Bonaire and Dutch IMARES expertise. The projects are as follows:

1. Mangrove restoration demonstration pilot study
The basic objective is to reestablish water depth and tidal connection in high marsh salt areas that have resulted from infilling with sediment, and restore them as effective mangrove and low marsh fish nursery habitats. By collecting baseline data before the restoration activities take place, it will be possible to monitor and compare and assess changes in fauna and flora at the restoration sites and hence evaluate the effectiveness of the measures implemented.

2. Baseline ecological study of the zonation of aquatic communities
The goal is to complete a scientific description of Lac’s aquatic community zonation as it exists at landscape level today. This will provide the framework against which large-scale community change and effectiveness of mitigation measures can be monitored and evaluated.

3. Recreational and land use survey for Lac Bay and its catchment area
The goal is to identify user problems and potential solutions by mapping and assessing user density and pressures in Lac

4. Study of avifaunal habitat use of Lac Bay
The goal is to identify bird habitat use problems and potential solutions by assessing habitat use of Lac by birds during the migratory season.

(A fifth project for implementation by Stinapa and Dienst LVV was identified)
5. Lac mangrove channel clearing project
Re-establish water flow from the Bakuna dam to Lac using a pipe system.

The Lac mangrove channel clearing project of Stinapa was reviewed and judged to be valuable and important. The baseline study of zonation of aquatic communities (project 2) is urgently needed in this respect to allow short and long-term evaluation of this project which need to become a structural part of Lac Bay management. Routine mangrove channel maintenance was identified as ideal work for involvement of Bonaire youths and volunteers, to rekindle public involvement in caring for Lac and its rich natural and cultural-historical heritage. 

Management Recommendations:

A project plan is presented by which all four projects can be delivered by December 2012. These projects can count on government and broad community support. In this all, Stinapa indicated to be willing to provide basic free lodging to interns and scientists at their science accommodations at the entrance of Washington-Slagbaai National Park. The ability and willingness of IMARES to recruit and guide students and interns for these projects was an important selection criterion to help restrain total project costs. The action spear points will, nevertheless, require funding as well as permits from the Island Government of Bonaire. With LNV various funding options were reviewed and discussed, and the need for permits was discussed with DROB (Dienst Ruimtelijke Ontwikkeling en Beheer) Bonaire. DROB envisioned few problems with the required permits. The visit was concluded by the joint resolve to work out ways to maintain momentum and proceed towards the implementation phase.

Management Recommendations:

• To keep collecting data for long term monitoring programs. It is fundamental for the proper management of our natural resources.
• Try to find permanent local volunteers to do these surveys until an adequate amount of professional staff is available.
• Provide more training for the volunteers. 

Management Recommendations:

• To keep collecting data for long term monitoring programs. It is fundamental for the proper management of our natural resources.
• Given the lack of staff and the achievement of the objectives, lower the frequency of the surveys and use the new methodology that requires only one surveyor.
• Increase the number of staff in the Natural and Historic Resources Unit.
• Discuss possible management actions to mitigate or eliminate the threats discovered at the roost. 

Abstract:

In October 2011 an expedition took place to the Saba Bank, on board of the ship the Caribbean Explorer II. Main aim of the expedition was collecting data on underwater fauna and coral reefs. Apart from that data were collected on nutrients, water flow, sponges and seabirds and marine mammals. Data on the last group were collected by deploying acoustic data loggers, and by means of visual surveys. These visual surveys were conducted whenever the other activities permitted it. This cruise report presents an brief overview of the results obtained during the October 2011 survey. It contains a short day to day report, a full list of all birds, mammals and particular pieces of floating matter seen, and a brief presentation of the results. Furthermore the report contains a brief account of observed birds on Sint Maarten, since published accounts on the birdlife of the island are scarce.

Findings

Seabirds

• The seabirds most often spotted were the Brown Booby and the Magnificent Frigatebird.
• No marine mammals were observed.
• Red-Billed Tropicbirds were primarily spotted near the shore of Saba.

Birds on Sint Maarten

The first ever records of the following birds were made during this expedition:

• Cinnamon Teal (possibility of a hybrid cannot be excluded).
• Marbled Godwit (flying over the Great Salt Pond).
• A Merlin was seen hunting amongst Cliff Swallows and Barn Swallows.
• Three Ospreys were recorded.
• Breeding Caribbean Coots or adults with chicks were seen at several small ponds and in the salines.

Most Common (sighted>10)

• Cattle Egret (Bubulcus ibis)
• Snowy Egret (Egretta thula)
• Magnificent Frigatebird (Fregata magnificens)
• Brown Pelican (Pelecanus occidentalis)
• Black-necked Stilt (Himantopus mexicanus)
• Spotted Sandpiper (Actitis macularius)
• Carib Grackle (Quiscalus lugubris)
• Bananaquit (Coereba flaveola)

Least Common (sighted<2)

• Merlin (Falco columbarius)
• American Oystercatcher (Haematopus palliatus)
• Wilson's Plover (Charadrius wilsonia)
• Short-billed (Dowitcher Limnodromus griseus)
• Wilson's Snipe (Gallinago delicata)
• Marbled Godwit (Limosa fedoa)
• Whimbrel (Numenius phaeopus)
• Solitary Sandpiper (Tringa solitaria)
• Lesser Black-backed Gull (Larus fuscus)
• Cabot's Tern (Thalasseus acuflavidus)
• Eurasian Collared Dove (Streptopelia decaocto)
• Rose-ringed Parakeet (Psittacula krameri)
• Yellow-billed Cuckoo (Coccyzus americanus)
• Green-throated Carib (Eulampis holosericeus)
• Antillean Crested Hummingbird (Orthorhyncus cristatus)
• Northern Parula (Parula americana)
• Caribbean Elaenia (Elaenia martinica)
• Pearly-eyed Thrasher (Margarops fuscatus)
• House Sparrow (Passer domesticus)
• Northern Parula (Parula americana)
• Blackpoll Warbler (Dendroica striata)
• Prothonotary Warbler (Protonotaria citrea)

Notes:

The vessel that was used during this survey was not well suited for dedicated seabird and cetacean surveys. However, the gathered data fits in well with the seasonal pattern in observed seabird species and densities described for Guadeloupe for the same time period (distinct dip from August to October). According to Debrot et al, there are few records of cetaceans in October.