Delnevo, A.

Aruba’s four IBAs cover just 610 ha, but between them they support over 30,000 seabirds and a number of other significant bird populations. Tierra del Sol Salina IBA (AW002) is set

within a privately-owned golf course and is unprotected. The other three IBAs are state owned with differing levels of protection afforded them. Bubali Wetlands IBA (AW001) enjoys de facto protection as a nature reserve, although it is unclear what formal protection status exists for the area. Oranjestad Reef Islands IBA (AW003) is benefiting from nonregulatory

protection provided by the coastguard, harbour authorities and the police, but again, its formal protected status is uncertain. San Nicolas Bay Reef Islands IBA (AW004) is not formally protected, although informal protection is provided by staff of the adjacent oil refinery, and the coastguard. Building these sites into a formalised legislative framework for national conservation and protected area establishment would help facilitate much needed conservation action and management.

The IBAs have been identified on the basis of 12 key bird species that variously trigger the IBA criteria. While four of these species occur within two IBAs, the majority of these birds

(the breeding seabirds) are confined to the San Nicolas Bay Reef Islands IBA (AW004), highlighting the critical importance of these islands for maintaining Aruba’s biodiversity. However, there is a proven between-year movement of breeding Cayenne Terns S. sandvicensis eurygnatha between the colonies at the San Nicolas Bay IBA and Oranjestad Reef Islands IBA (AW003) showing that these two IBAs should really have shared conservation management plans.

Aruba’s ornithological importance is largely focused on its 10 species of nesting terns, and this is reflected in the identification of two IBAs specifically for these seabirds. During the 1950s, the population of terns breeding on Aruba was very low (and for some species non-existent), but they have demonstrated a dramatic increase as a result of the protection (albeit informal) afforded the Oranjestad Reef Islands IBA (AW003) and San Nicolas Bay Reef Islands IBA (AW004). The increasing populations have been monitored on an annual basis since 1999 through the Aruba Tern Project. This monitoring could be used to inform the assessment of state, pressure and response variables at each of Aruba’s IBAs in order to provide an objective status assessment and highlight management interventions that might be required to maintain these internationally important biodiversity sites.

Retrieved from Birdlife International

Executive Summary:

The eleventh field season of the Aruba Tern Project was completed in 2009. The study continued its stated aim of producing a quantitative description of the status and distribution of nesting terns and laughing gulls within San Nicolas Bay and around the island of Aruba.

The 2009 field season began during the third week of June, which was later than in most previous years. Consequently, we were unable to gain accurate egg counts, egg measures and population counts for those species nesting early in the season, primarily Cayenne terns and sooty terns. We were also unable to confirm the nesting status of regionally threatened roseate terns and some common terns. Despite these challenges we were able to generate population estimates for each species, although the margin of statistical error and reliability of the estimates, for the earlier nesting species, was more variable.

We observed a continuation of the gradual increase in the number of nesting bridled terns. We also recorded average or greater than average numbers of sooty tern, common tern, brown noddy and laughing gull. The numbers of Cayenne terns were within the range of numbers experienced in previous years. The nesting island for Cayenne terns shifted from island 3 to island 2 and there were no Cayenne terns observed nesting on the islets opposite Oranjestad. The absence of Cayenne terns near Oranjestad was unusual but may be an observer bias as we were not on the island to see whether birds nested in that area and failed before we arrived.

The egg size, clutch size, chick growth and juvenile and adult survivorship was within the range recorded for all species in previous years. In general, and despite the challenges associated with relatively late data collection, we believe that 2009 represents a slightly better than average year for all tern species nesting on Aruba. The increase of nesting laughing gulls must be the result of immigration as the local population could not account for the scale of increase observed in this species. Laughing gulls continue to remain a serious threat to ground- nesting terns, most notably Cayenne terns. 

Aruba, and particularly the San Nicolas Bay islands are unique within the Caribbean and most probably the world. In 2009 San Nicolas Bay contained approximately 25% of the world’s population of Cayenne terns, over 90% of the Caribbean population of common terns, 25% of the Caribbean’s black noddy, 3% of the Caribbean’s brown noddy, >1% of the Caribbean’s bridled terns and 4% of the Caribbean’s laughing gull. We are unaware of any other location in the world that contains the diversity and abundance of terns observed in San Nicolas Bay. For this reason BirdLife International (2008) has declared the Bay islands to be a globally important bird area (IBA).

The project was conducted in collaboration with the Aruba Veterinary Service, the Department of Agriculture, Husbandry and Fisheries, and the Government of Aruba, whose support is gratefully appreciated. We thank Valero Aruba Refinery for funding the study and also providing logistical and lodging support. We thank Caribe Alaska for their continued support and encouragement with this project. 

This manual is intended as an introduction to bird monitoring and census techniques. Counting birds, or indeed any animals or plants, is probably one of the most underestimated aspects of biology and field ecology. People often assume that all one has to do is go out there and count. Regrettably it is not quite that easy.

The take-home message of this document is to instill upon the reader that in order to conduct appropriate and meaningful monitoring they must first start by asking questions. What exactly do they want to know? Do they want a total count of all bird species or a general idea of what may be present at certain times of the year?

If the questioner wants to know how to manage habitat to the benefit of birds and other wildlife then clearly they will also need to ask additional questions about the habitat, vegetation and the broader ecological environment. Having established the appropriate questions, the observer should then decide how this can be done in such a way that is practical, meaningful and achievable. It would be unfortunate to have designed a great study if the resources of time, personnel, finance and equipment were limited and/or not available. Consequently, it is important to realistic as to what you can do.

Many individuals may start a study with sincere and good intentions. They have organised their thoughts and have devised a good program but have not paid enough attention to what they will do with the data, and how it will be stored and subsequently analysed. It is not uncommon for these data to languish in a file and never see the light of day. In truth, we are just as guilty of this as anyone but we should all strive to communicate our findings and our hard work in the field. Thus the writing of a report that details what questions were asked, how the work was done, and the findings and conclusions of that work is essential. We submit that one of the important aims of the bird monitoring workshop is to form the basis for long-term monitoring of the birds and their habitat. It is only with these data that informed species and habitat management may be achieved. 

This manual emphasises on practical methods, and some methods which (though highly accurate) are too labour-intensive or time-consuming for general monitoring use have been omitted. The methods presented in this manual deal only with assessment of population sizes, population changes, and the numbers of chicks produced by breeding pairs. It is also important to monitor other population parameters such as adult survival rates, diet, rate of food-delivery to chicks, or growth- rates of chicks. However, the methods required for monitoring survival rates, in particular, are labour-intensive for widespread use and are thus beyond the scope of this document. Some other measures and suggestions worth considering have been provided, but these largely go beyond monitoring and into the realm of research.

Please use this document as a guide, but remember there has been little published work on tropicbird species. Consequently, the opportunity to find new and important things about their biology, population ecology and conservation awaits you.