Conservation

The Adelaide’s Warbler is listed as a species of Least Concern by the ICUN (Birdlife International 2009).

Historically, Puerto Rico was almost entirely covered in forests. Between 1770 and 1903, forest clearing for agriculture reduced the forest cover on the island from 94% to 0.4% (Brash 1987). The remaining forest was limited to the highest elevations, where Adelaide’s Warblers do not occur. An additional 9% of the island was used for shade coffee plantations, again typically in mountainous regions (Brash 1987). However, Adelaide’s Warblers use some shade coffee plantations (Wetmore 1916a). Other species are able to successfully reproduce in shade coffee plantations (Gleffe et al. 2006), so these may have acted as refugia for Adelaide’s Warblers and other native species. After the sugar cane industry collapsed, second-growth forests dramatically increased in the lowlands (Brash 1987). Adelaide’s Warblers may have been less affected by this forest loss that other species because they are generalists in terms of habitat use. They also occur in urbanized habitats (Suarez-Rubio and Thomlinson 2009), although no study has determined whether urban populations are self-sustaining or dependent on immigration from surrounding habitats. Forest loss, resulting from military activities, may have led to population declines on Vieques (Sorrié 1975).

Global climate change could affect populations, particularly in the dry forest habitat where they are currently most abundant. Global climate change is predicted to cause reduced rainfall during the June-August period (Neelin et al. 2006). A long-term study in Guánica Dry Forest has shown that Adelaide’s Warbler survival is positively correlated with rainfall (J. Faaborg and J. Toms, unpub. data). This is also the time of year when Adelaide’s Warblers have nestlings or fledglings, and so summer droughts could dramatically affect reproductive success. These effects of global climate change are most likely to affect populations in the dry forest habitat, and could therefore have strong negative effects on the total population size.