Red-billed Tropicbird

Summary

Red-billed Tropicbird publication in Dutch.

Hoeveel mensen hebben ooit de majestueuze roodsnavelkeerkringvogel gezien? Een exotische vogel van de ‘bijzondere gemeenten’ Saba en Sint Eustatius, in het Caribisch deel van ons koninkrijk. Reden waarom Vogelbescherming natuurbeschermers op de eilanden bijstaat in hun pogingen om deze bijzondere zeevogel te helpen. Zijn bestaan op de eilanden wordt bedreigd door ratten en katten. 

Samen voor vogels en natuur | Vogelbescherming en/of Caribisch Nederland | Vogelbescherming

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...

Abstract

Robert L. Norton encountered a Red-billed Tropicbird (Phaethon aethereus) approximately 60 km NNW of Aruba, providing Aruba’s first record of this species. Given the pelagic distribution of this species during the non-breeding season, and nine antecedent records from Bonaire and Curaçao, additional records seem likely for Aruba, especially given an increase in reports of seabirds from cruise ships off Aruba

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_...

Abstract

Red-billed Tropicbirds have historically been considered rare visitors to the waters around the islands of Aruba, Curaçao, and Bonaire in the southern Caribbean. However, in recent years there has been an increase in documented records. We summarize all known Red-billed Tropicbird records for the region and review broader regional population and movement data to place this increase in records in context. We recommend continued careful documentation of Red-billed Tropicbird records on and around the islands of Aruba, Curaçao, and Bonaire and the implementation of a standardized monitoring pro-gram across the Caribbean range for the species to better understand the species' population status, trends, and breeding and at-sea distribution

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.

One of the most deleterious invasive introduced predators worldwide is the domestic cat which has been found responsible for many island extinctions worldwide. Cats can live off both natural prey and garbage and can be a particularly serious threat to ground-nesting bird populations. Saba is an important location for the Red-billed Tropicbird, Phaethon aethereus and feral cats are thought to be the main reason for the low breeding success in the southern coastal colonies of this bird.

To make proper decisions in invasive predator management, information is needed on the effects of cat removal on the tropicbird breeding success and the possible resulting increase in egg predation by rats in the case of any “mesopredator release effects”. In this study we collected the first season of data needed to assess the effect of cat removal on the breeding success of the tropicbird on Saba. Two tropicbird nesting colonies (Great Level and Tent) were monitored in terms of egg and chick predation, under different net cat-removal intensities and the resulting survival was compared to survival prior to cat removal (as documented elsewhere).

In total, Saba Conservation Foundation removed 19 cats from the entire study area, of which eleven adult cats were removed from the Great Level colony and only six adult cats and two kittens were removed from the Tent colony. The gut contents of the 17 of these 19 feral cats consisted of natural prey (grasshoppers, rats, chickens, anoles and crickets), bait placed in the trap or even plant material. In the previous season 18 cats had already been removed (12 trapped, 6 shot) from the Great Level area.

During the period of September 2013 to May 2014, 46 occupied tropicbird nests were monitored, 27 at Tent, 15 at Great Level and 4 at Fort Bay. Fort Bay was not used in the data analysis. Egg-laying was documented in 34 of these nests. Observed egg failures were due to a variety of causes such as failure to hatch , broken eggs, including the breaking of an egg by an adult, and the disappearance of the whole nest due to heavy rainfall. Egg survival did not show a significant difference between the two colonies. In total 23 chicks were born, of which at least 15 died. Chick survival did show a significant difference between the two colonies, whereas prior to cat removal both had had zero chick survival. The breeding success of the tropicbirds and percentage of chicks fledged did appear to increase encouragingly in the breeding colony where cats had been more intensely culled (Great Level; 28 of initial 35 adult cats removed during two trapping seasons). The success on Great Level is notable, because in the breeding season of 2011/2012 the breeding success had been zero percent for several years.

Around the Tent colony only six adult cats were removed this season (total of 7 removed during two trapping seasons), which was insufficient to effectively increase breeding success in the tropicbird. A comparison of camera-trap densities showed that effective cat density at Tent by the end of trapping remained 4-5 times higher than at Great Level where 28 of the initial 35 adult cats had been removed. In total four black rats were observed on the camera traps but only appeared to be scavenging and no active egg predation was observed. These preliminary results suggest that cat removal seems to improve fledgling survival at no appreciable expense in terms of egg predation and that risks of any hypothetical “mesopredator release effects” are limited. Due to the low sample sizes in this first season, and natural fluctuations in breeding success which are normal in seabirds, clearly happenstance or other causative factors could equally explain the results obtained. Therefore, more definitive conclusions will depend on a more extensive and multi-year effort. 

Key recommendations:

• Continue with and expand feral cat removal from the main tropicbird nesting colonies.
• Simultaneously monitor nesting success and fledgling survival to develop a more robust data set over a longer time-frame. With an expanded sample size, the benefits in terms of net fledgling survival and any risks of potential “mesopredator release effects” can be more firmly assessed.
• Many cats were documented to be wary of traps. Trapping was also very labour-intensive and entailed both trapping and handling stress. For these reasons additional, more effective yet humane methods (such as predator baiting or shooting) should be used. These methods have proven to be key to effective control of invasive predators worldwide.
• As long as legislation and control of cat importation, keeping and sterilization remain less than strictly implemented and failsafe solutions remain wanting, we recommend to focus removal efforts towards key tropicbird nesting colonies shortly before or during the main nesting season each year.

  This research was funded as part of the Wageningen University BO research program (BO-11-011. 05- 029) under project number 4308701028 (A Debrot, PI). 

Red-billed tropicbird peak attendance and nesting success on St.Eustatius. 

Please contact Hannah Madden for more information.

We assessed the breeding success of Red-billed Tropicbirds Phaethon aethereus on St. Eustatius, particularly in relation to predation at the nest. We conducted weekly surveys at five sites during 2012-2013 and measured chick and adult morphometrics. Apparent nest success ranged from 55-100% across five breeding areas, while apparent fledge success ranged from 63-100% at those same locations. We used cameras and baited rat traps to document the presence of predators at nest sites. Predation rates captured on cameras were low (ca. 20 images of predators from ca. 263,000 images over 11 weeks). Cameras documented cats and rats at accessible nests. Although we could not confirm the cause of egg loss or the death of some chicks, the presence of cats and rats suggests that additional effort be expended to accurately measure their impact.
 
Retrieved from http://www.statiapark.org on April 13, 2015

Assessment of the breeding success of Red-billed Tropicbirds (Phaethon aethereus) at the Pilot Hill site on St. Eustatius, particularly in relation to predation at the nest. We conducted weekly surveys during 2013-2014 and measured chick and adult morphometrics. Overall apparent hatching success was 64.6%, while apparent fledging success was 75.6%. We used cameras to document the presence of predators at nest sites and wax bait blocks to estimate rat density. Camera traps documented rats opportunistically scavenging eggs that were left unattended for even short periods of time. In total we documented nine predation events of eggs by rats at eight individual nesting cavities.