Justification of Red List Category
This species has a very large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). The population trend appears to be stable, and hence the species does not approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is very large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.
The population is suspected to be stable in the absence of evidence for any declines or substantial threats.
This species is found on the western coast of the Americas, ranging from north-west Mexico and Panama to north Peru and the Galápagos Islands, Ecuador. When food is scarce, it can be seen as far north as California (U.S.A.) and northern Chile.
The Blue-footed Booby is strictly marine, feeding in adjacent inshore waters, tending to exploit cool, rich waters in areas of upwelling. It specialises in catching fish by plunge-diving, often in unison. It takes sardines, achovies and mackerel, but also flying-fish and squid. It has been seen fishing in the company of dolphins and Peruvian Boobies. Breeding is seasonal in places and otherwise opportunistic, nesting on cliffs and islets in areas with little or no vegetation (del Hoyo et al. 1992).
The Galápagos subspecies of Blue-footed Booby, Sula nebouxii excisa, appears to be suffering from a food shortage related to a reduction in the population of clupeid fish. This has induced chronic lack of breeding in the Galápagos Islands, with all monitored colonies containing fewer than 15% of the historical maximum number of nests (Anchundia et al. 2014). Further to this, the majority of clutches observed failed without producing a nestling (Anchundia et al. 2014). It is thought that this failure to breed began in the El Niño Southern Oscillation event in 1997/98. The periodic disappearance of clupeid fish from the waters around the Galápagos is connected with the Southern Decadal Oscillation in the Pacific Ocean, but the El Niño event of 1997/98 appeared to spark the present period of chronic low abundance, which appears to be causing adult Blue-footed Boobies to continually defer breeding (Anchundia et al. 2014). Since 2001, this appears to have been leading to an ongoing decline in this population, with fears that offspring produced have not recruited into the breeding population since this time and a crash may be imminent unless sardines return (Anchundia et al. 2014).
Text account compilers
Butchart, S., Calvert, R., Fjagesund, T., Martin, R., Miller, E., Ekstrom, J.
BirdLife International (2019) Species factsheet: Sula nebouxii. Downloaded from http://www.birdlife.org on 14/10/2019. Recommended citation for factsheets for more than one species: BirdLife International (2019) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 14/10/2019.