By guest author Dr. Dave Anderson of Wake Forest University.
How long do you have to study a bird to achieve a basic understanding of its breeding biology? In the case of blue-footed boobies in Galapagos, more than 20 years. Since 1997, visitors and scientists in Galapagos have observed little evidence of a fundamental aspect of the blue foots’ biology: reproduction. I began a long-term study of blue-footed booby breeding back in 1984. It went great until 1997, the year of a powerful El Niño warm water event. Many seabirds struggle under El Niño conditions, so when the blue-footed boobies vanished from our study site on Española Island, I was not surprised.
Habituated for 13 years to this species’ enthusiasm for making babies, I did, however, expect their return in 1998. But instead of adding their annual ~1,000 new “teenagers” to the Galapagos population, blue-footed boobies never returned in meaningful numbers. To the present day, my group makes annual visits to Española to carry out long-term studies of Nazca boobies and waved albatross. We always watch for blue-footed boobies and are always disappointed.
Had the blue-footed boobies stopped breeding on Española and relocated elsewhere in Galapagos? Nope. Other scientists studying finches on Daphne Island, in the center of Galapagos, had a view every day into the crater which was a prime blue-foot breeding site. Before 1997, they saw lots of eggs and nestlings. After 1997, they saw almost nothing. Less systematic but nearly weekly observations by tour guides, at formerly large breeding sites on North Seymour and Isabela Islands, indicated little successful breeding year after year. Although adults often aggregated at the colonies and behaved as if breeding was on their minds, few young were produced. What could account for the birds not reproducing for so long — longer even than the lifespan of most adults?
In 2012 we aimed to find out. With financial support from Galapagos Conservancy and two other NGOs, Ecuadorian graduate student David Anchundia spent 12 months making frequent visits to all known colonies, monitoring breeding and examining diet samples from adults. Few adults that attended the colonies attempted to breed, and even fewer succeeded. David saw almost no young.
And the diet…not good. Our data from Española during the boom years before 1997 showed that almost the entire blue-foot diet was oil-rich sardines taken from large schools. In 2012, a wide variety of species were represented, but few sardines. Breeding success of their close relatives, Nazca boobies, had dropped by 50% when sardines disappeared from the diet in…yes, 1997. Nazca boobies ate a lot of sardines before 1997, but were not sardine specialists like blue-footed boobies.
Our take on this was that sardines are an exceptional food and good to specialize on if they are available, but blue-footed boobies had apparently specialized to the point of a fatal attraction. After 1997, when sardines apparently disappeared, blue-foots could live — but not live and breed — eating other food items.
What happens to the population of a species that, from 1997 until 2012, fails to replace older birds that die? It should become progressively smaller, and older. We used an estimate from the late 1960s of 20,000, possibly more, adults as a benchmark for comparison. In 2012, we sent five teams throughout the Archipelago on a three-day comprehensive survey of the coastlines. We also deployed small GPS loggers on birds that confirmed our assumption that adult blue-footed boobies spend most of their time perched on coastal rocks, in coastal colony sites, or flying parallel to or near the coast. Our estimate was around 6,400 adults — a dramatic decline, but what you would expect for a population of 20,000 in 1997 (with expected annual adult mortality of 10%) that never produced young for 15 years.
Five years after the first survey, Galapagos Conservancy funded another assessment thanks to donations from the Blue Feet Foundation, a venture by two young brothers in Massachusetts to sell colorful blue-footed booby socks to help protect this species in Galapagos. The 2017 coastline survey was run in the same way, and mostly by the same people, as in 2012. With sardines still absent from the diet of Nazca boobies on Española, we expected to see continued decline of the adult blue-foot population. Our preliminary analysis is consistent with this expectation; stay tuned for the final, firm estimate.
However, during our most recent trip we did see several hundred blue-foots in the juvenile plumage of one- and two-year-olds. In 2012 we saw only two, so possibly reproduction picked up last year. New diet samples show weak indications of higher sardine availability, but it’s too early to say if that’s real. Still, we have some grounds to speculate that the long nightmare of Galapagos blue-foots is ending. But even if sardines come back and breeding improves, this population has a long way to recover its pre-1997 numbers, especially since most of the remaining adults are probably senior citizens, with the breeding capacity that you would expect of the elderly.
If our study of blue-foots had begun in 1997 instead of 1984, the 20-year pattern would describe a peculiar species indeed — one with perpetually negative population growth. We would know nothing about the importance of sardines to their population dynamics. This is testament to the value of long-term studies made possible by conservation and other funding organizations and by committed scientists.
And what happened to the sardines? We can’t say with confidence, but we propose that the Galapagos schools rise and fall in association with sardines on the continental margin, on a scale of several decades. If that is correct, we would expect an upturn in sardine availability in the next 5-10 years, based on the up-down cycle in the 1900s. What a joy to see colonies full of yammering fluffy blue-foot nestlings again; I could re-start that project on Española!
Dr. Dave Anderson began long-term studies of Galapagos seabirds in 1984. His work revealed the previously unrecognized dramatic decline in the waved albatross population, due to hook-and-line capture in fishery operations near the coast of South America, which led to uplisting its IUCN status to Critically Endangered. His Nazca booby study is the most complete for any tropical seabird and has provided a variety of insights into demography, hormonal regulation of animal behavior, breeding tactics, and even child abuse. Nineteen graduate students have been trained within the project, including two Ecuadorians, and more than 50 Ecuadorian students have participated, including 10 who completed their Licenciatura thesis within the project. Author photo © Dave Anderson.