How are the red-billed tropicbirds on St Eustatius doing?
Marine birds such as the red-billed tropicbird are among the most endangered bird species in the world. In the Caribbean region, various factors are having an adverse effect on nesting colonies of the red-billed tropicbird: coastal development, predation by non-native species (such as rats and cats), and site disturbance due to natural causes such as severe weather.
Although numerous seabirds visit St Eustatius, the red-billed tropicbird is the only species that actually nests on the island. This species lays a single egg each nesting season (between October and June). If a pair’s first attempt at breeding fails, they may lay a second egg if it is still early in the nesting season.
Hatching success is six in ten eggs on average
To find out more about the breeding success of the red-billed tropicbird, their nests have been monitored during every breeding seasons since 2013. Hatching success refers to the percentage of chicks that hatch (of the total number of eggs laid in a season) and is an indicator of the overall population trend. The survival rate of chicks into adulthood, however, is lower than the hatching success rate.
Hatching success has been relatively stable over time. The lowest recorded number was 34 chicks from 65 eggs laid (52 percent hatching success), which was in the 2022–’23 season. The average hatching success rate has been 61 percent, and the highest hatching success was achieved in 2017–’18 (79 percent). In the 2023–’24 season, hatching success was about average, at 60 percent.
| Breeding season | Hatching success |
|---|---|
| Breeding season | . |
| 2023-'24 | 60 |
| 2022-'23 | 52 |
| 2021-'22 | 61 |
| 2020-'21¹⁾ | . |
| 2019-'20 | 55 |
| 2018-'19 | 60 |
| 2017-'18 | 79 |
| 2016-'17¹⁾ | . |
| 2015-'16 | 59 |
| 2014-'15 | 56 |
| 2013-'14 | 68 |
| Source: St Eustatius National Parks Foundation (STENAPA) and Dutch Caribbean Biodiversity Database | |
| ¹⁾No data available. | |