Blue-footed Booby Population Analysis
Dr. David Anderson, Wake Forest University
Blue-footed booby pair © Shelale Savash.
- In 2012, a coastal survey of blue-footed boobies in Galapagos indicated a reduction in number from an estimated 20,000 adult birds in the 1960s to less than 6,500. There has been a general lack of successful reproduction in the Galapagos blue-footed booby population since El Niño 1997. This reduction is likely related to a decline in the sardine population throughout the Archipelago.
- In 2017, a second comprehensive count of blue-footed boobies was completed, using the same methods as in 2012. Several hundred juvenile blue-foots (1-2 years old) were observed, indicating the first significant successful reproduction since 1997. Diet samples show weak indications of higher sardine availability.
Blue-footed boobies (Sula nebouxii) are iconic birds that contribute to the biodiversity of the Galapagos Islands. Toward the end of the 1990s, concerns that the booby population was declining on an archipelago-wide scale prompted a call for periodic, comprehensive studies to assess the population size, understand the cause of the decline, and inform necessary conservation actions.
In 2011, seabird biologists Dave Anderson of Wake Forest University, Kate Huyvaert of Colorado State University, and David Anchundia of the Charles Darwin Foundation, completed the first comprehensive survey of blue-footed booby distribution and population dynamics in Galapagos, with support from Galapagos Conservancy, Galapagos Conservation Trust, and Swiss Friends of Galapagos.
Adult blue-footed booby © Jenny Howard
The team completed four intensive searches of major breeding colonies in Galapagos at four-month intervals. This was followed by a coastal survey around the entire Archipelago (except several northern islands) in 2012. In both years, few juvenile birds were observed (<100), indicating that little breeding was occurring. The estimate of the adult population was less than 6,500 birds, in comparison to 20,000-30,000 breeding birds estimated in the 1960s and 1970s.
Anecdotal sightings of more juvenile blue-footed boobies early in 2017 — the first evidence of substantial reproductive success since the 1997 El Niño — prompted a follow-up survey. In June 2017, researchers Anderson, Huyvaert, and Anchundia completed a second survey, using the same methods as in 2011-12, again with support from Galapagos Conservancy. They also collected information on the booby diet.
During the second blue-footed booby survey, the researchers observed several hundred blue-foots in the juvenile plumage of one- to two-year-olds. In comparison, in 2012, they’d seen only two. New diet analyses show weak indications of higher sardine availability, so the work continued into 2018. Even with a potential return of sardines, this population has a long way to achieve recovery to pre-1997 numbers.
This work is in part funded by The Blue Feet Foundation, an ambitious endeavor started by two young brothers in Massachusetts, who have donated more than $40,000 (as of October 2018) to Galapagos Conservancy since 2016 from the sale of their colorful blue-footed booby socks.
Galapagos Report 2013-14: Chronic lack of breeding by Galapagos blue-footed boobies and associated population decline – Anderson et al.
Blog Article: February 2018, Twenty years of a declining blue-footed booby population by Dave Anderson of Wake Forest University