Treat Sula brewsteri as a separate species from Brown Booby S. leucogaster (Part A), and if Part A passes, establish English name for Sula brewsteri (Part B)

Proposal (995) to South American Classification Committee

(Note from Remsen: This proposal was submitted to the North American Classification Committee and passed, and it is submitted here with permission from Eric VanderWerf. Note that brewsteri, as represented by the subspecies etesiaca, breeds in the SACC area on Isla Gorgona, Colombia.)

Treat Sula brewsteri as a separate species from Brown Booby S. leucogaster (Part A), and if Part A passes, establish English name for Sula brewsteri (Part B)

Part A.

Background:

Note: much of the background information below is from VanderWerf et al. (2023)

The Brown Booby (Sula leucogaster) is a pantropical seabird found in the Pacific, Atlantic, and Indian Oceans that exhibits geographic morphological variation. Five subspecies have been described based on differences in color of the plumage, bill, and facial skin (Table 1; Nelson 1978, VanderWerf 2018a, Schreiber & Norton 2020). Sula l. plotus has the largest geographic range, from the Red Sea and Indian Ocean east to the central Pacific. In both sexes of S. l. plotus, the head is dark brown, and the bill is yellow (females) or bluish-yellow (males). The nominate subspecies, S. l. leucogaster, occurs in the Atlantic and Caribbean and is similar to plotus but has a more pinkish bill. The form of Brown Booby occurring in the eastern Pacific, S. l. brewsteri, is the most distinctive morphologically and originally was described as a separate species called Brewster’s Booby (S. brewsteri; Goss 1888). Male S. l. brewsteri have a geographically variable white head, a more grayish-blue bill, and a more greenish-blue gular pouch. In the Gulf of California and the western coast of Mexico south to the Revillagigedo Islands, male S. l. brewsteri have a white head and a pale brown upper neck. On some islands off Central America and South America, the white on the head of males is restricted to the forehead, and this form sometimes is considered a separate subspecies, S. l. etesiaca, but also has been grouped with S. l. brewsteri (Harrison 1983, Schreiber & Norton 2020). The form breeding on Clipperton Island is the palest, with the entire head and neck white in males, and is sometimes referred to as S. l. nesiotes (Heller and Snodgrass 1901, Pitman & Balance 2002, Schreiber & Norton 2020).

As noted above, Brewster’s Booby originally was described as a species, S. brewsteri, by Goss (1888) based on type specimens from San Pedro Mártir Island, Mexico. In the description, Goss noted that characteristics of the species included the pale color of the head and neck, especially in the male, a dark brown iris with a narrow outer ring of grayish-white, and “unfeathered parts also differently colored.” In 1944, S. l. brewsteri was lumped with other forms of the Brown Booby (Wetmore et al. 1944), who cited “Peters, checklist, 1, 1931” and Wetmore (1939) as justification for the lump. Wetmore (1939) stated that “while apparently uniform over large areas of the tropical oceans of the world there are three (barely possibly four) races of Sula leucogaster to be recognized…on the Pacific coast of the Americas… These differ from all other subspecies of the species.” Wetmore (1939) discusses at length the variation among the forms in the eastern Pacific, which seems to support their distinction, and did not offer any explanation for why S. l. brewsteri should be lumped with other forms of the Brown Booby, yet he did so, and this, paradoxically, served as the basis for the lumping by Wetmore et al (1944).

Genetic population structure of Brown Boobies largely matches patterns of morphological variation (Steeves et al. 2003, Morris-Pocock et al. 2010, 2011). Mitochondrial haplotypes were not shared between the eastern and central Pacific or between the eastern Pacific and Caribbean (Steeves et al. 2003), and colonies grouped into four major, genetically differentiated populations; Caribbean, central Atlantic, Indo-central Pacific, and eastern Pacific (Morris-Pocock et al. 2011). The eastern Pacific population was found to be the most different genetically and was estimated to have diverged from all other populations approximately one million years ago (Morris-Pocock et al. 2011). These populations have diverged because of a combination of physical barriers (the Isthmus of Panama and the Eastern Pacific Basin) and a behavioral tendency in the Brown Booby to forage closer to shore than other booby species (Steeves et al. 2003).

Table 1. Distinguishing characteristics of Brown Booby subspecies. Copied from VanderWerf et al. (2023).

Character	plotus	leucogaster	brewsteri	nesiotes	etesiaca
Male head color	brown	brown	white head and upper neck	white head and entire neck	white forehead
Female head color	brown	brown	whitish forehead	whitish forehead	whitish forehead
Male bill color	bluish-yellow	bluish-yellow	grayish-blue	grayish-blue	grayish-blue
Female bill color	yellow	pinkish yellow	pinkish yellow	pinkish yellow	pinkish yellow
Ventral lesser wing coverts	white	white	white with brown bar	white with brown bar	?

New Information:

Three types of new information support recognizing Brewster’s Booby as a separate species: 1) morphological data demonstrating that males and females of the subspecies differ in additional ways not previously recognized; 2) behavioral data on pairing patterns showing that interbreeding between plotus and brewsteri is rare despite increasing sympatry; 3) information on behavioral ecology demonstrating that the morphological differences between plotus and brewsteri act as a reproductive isolating mechanism that inhibits interbreeding. The information on behavioral ecology is not that new, but its relevance to taxonomy does not seem to have been considered previously.

1. Morphology. Descriptions of Brown Booby subspecies relied primarily on the appearance of males and did not consider the appearance of females. VanderWerf (2018) described differences between females of the subspecies that can be used to identify them in the field: female S. l. brewsteri have a pinker bill and paler forehead than female S. l. plotus. Females can be distinguished as reliably as males of these subspecies, although the characters used to identify females are less obvious. VanderWerf (2018) also showed that the underwing coverts in both sexes of S. l. brewsteri are less extensively white than those of S. l. plotus.

I have unpublished data showing that iris color and bill curvature also differ among Brown Booby subspecies, but I am still in the process of collecting and analyzing these data. I do not think this information about additional distinguishing characters is needed to assess the taxonomy of Brown Boobies, but it will be useful in their identification.

2. Pairing Patterns. The Eastern Pacific Basin is an enormous, island-free ocean area that for millennia has formed a physical barrier to dispersal and promoted geographic differentiation of many seabirds, including the Brown Booby (Avise et al. 2000, Steeves et al. 2003, Morris-Pocock et al. 2011). Recently, Brown Boobies have been overcoming the barrier posed by the Eastern Pacific Basin and have dispersed eastward and westward across the Pacific. VanderWerf et al. (2008) documented an increasing number of S. l. brewsteri present and breeding in the central Pacific, and Kohno and Mizutani (2011) documented the occurrence and breeding of S. l. brewsteri males on islands near Japan. Isla San Benedicto, in the Revillagigedo Islands off the west coast of Mexico, was recolonized by Brown Boobies following a volcanic eruption in 1952, and both plotus and brewsteri males are present and breeding on the island (Pitman and Ballance 2002, Morris-Pocock et al. 2011). VanderWerf et al. (2023) showed that the westward expansion of brewsteri has continued, resulting in even greater sympatry between the subspecies. The increasing sympatry of S. l. brewsteri and S. l. plotus could result in gene flow and erosion of differentiation between these forms if they interbreed.

VanderWerf et al. (2023) also collected data on pairing patterns in locations where both forms were known to breed together. Quantitative data showed pairing by S. l. brewsteri and S. l. plotus was primarily assortative and interbreeding was rare (Table 2). At Moku Mana, Maui, in 2021, there were fewer mixed pairs (zero), than expected by chance (X² = 18.00, df = 1, p < 0.001). On Palmyra, there also were fewer mixed pairs than expected by chance (X² = 181.1, df = 1, p < 0.001), although the sample size was small.

Anecdotal evidence also indicates that pairing was primarily assortative, and that interbreeding was rare. On Wake Island in 2021, J. Gilardi observed 301 S. l. plotus pairs, six S. l. brewsteri males, and one S. l. brewsteri female, which was paired with one of the male S. l. brewsteri. The other five male S. l. brewsteri on Wake that year did not attract a mate despite the presence of many unpaired S. l. plotus females. On Wake in 2022, J. Gilardi observed that the brewsteri-brewsteri pair remained together and raised another chick, but the other five brewsteri males were unpaired. On Wake in 2023, J. Gilardi observed seven male and four female brewsteri; all 4 brewsteri females were paired with brewsteri males, and the three single brewsteri males built nests but had no mate. On Moku Manu, Oahu, in May 2021, E. VanderWerf observed 93 S. l. plotus pairs and only one male and one female S. l. brewsteri, which were paired with each other and had a large chick. In September 2022, E. VanderWerf observed five S. l. brewsteri females on Moku Manu, all of which were unpaired. On Laysan, a nest with a male brewsteri and female plotus was reported in 1998 (VanderWerf et al. 2008), but re-examination of photos using identification criteria from VanderWerf (2018) revealed that the female was S. l. brewsteri, representing another instance in which a male and female brewsteri paired with each other amid large numbers of male and female plotus. The only instances of interbreeding occurred in locations where no female brewsteri were present. On Midway, J. Plissner observed a male brewsteri x female plotus pair that raised a chick in 2020, when no female brewsteri were present. At Nakanokamishima Island, Japan, one brewsteri male paired and raised offspring with a plotus female from 2012-2014, but a second brewsteri male was not able to attract a mate despite frequent courtship attempts with plotus females (Kohno and Mizutani 2015).

Moku Mana Islet off the north coast of Maui is a particularly interesting case. It was colonized by Brown Boobies recently, with the first nest documented in 2004 by J. Penniman. In 2021, the island held twice as many S. l. brewsteri pairs as S. l. plotus pairs, with no mixed pairs. This is the easternmost location in the Hawaiian Islands where Brown Boobies breed, and the colonies were formed by individuals dispersing from the east (S. l. brewsteri) and west (S. l. plotus), much like the situation on Isla San Benedicto (Pitman and Ballance 2002).

Table 2. Pairing patterns of Brown Boobies by subspecies, including only cases in which the identity of both parents was known. Copied from VanderWerf et al. (2023).

Location	Year	Male plotus + female plotus	Male plotus + female brewsteri	Male brewsteri + female plotus	Male brewsteri + female brewsteri
Palmyra Atoll^†	2014	~200	1	0	8
Moku Mana	2021	6	0	0	12
Moku Manu	2021	93	0	0	1
Laysan	1998	~70	0	0	1
Midway^‡	2020	15	NA	1	NA
Wake Island	2023	301	0	0	4
Nakanokamishima^‡	2009	~900	NA	1	NA

^† At Palmyra 30 nests were observed with at least one brewsteri parent, but some nests were attended by a single parent and the identity of the mate was unknown.

^‡ At Midway and Nakanokamishimano female brewsteri were present so there was no chance of a mixed pair.

3. Reproductive Isolating Mechanisms. Mate choice and breeding biology of Brewster’s Booby have been studied extensively in Mexico, and this literature is important for understanding the pairing patterns observed in the central Pacific. Most importantly, López-Rull et al. (2016) showed that male S. l. brewsteri with their head painted brown to look like male S. l. plotus were treated aggressively by their mate and that the level of aggression was higher at a colony closer to the zone of overlap between the forms. They concluded that female dislike of foreign males may function as a reproductive barrier in populations close to contact zones, where the risk of possibly maladaptive hybridization is highest. Montoya et al. (2018) showed that the carotenoid-based greenish-blue color of the gular pouch of males was energetically expensive to maintain, that its chroma peaked during courtship, and that it may serve as a reliable signal of individual quality. Michael et al. (2018) showed that color of the gular pouch in Brown Boobies in México was related to foraging range and location, with individuals in poor body condition constrained to low-cost, short-distance foraging trips closer to shore, where they were unable to obtain the pelagic diet necessary for production of the carotenoid-rich gular pouch ornament important in mate attraction. Cumulatively, this research indicates that the morphological differences between S. l. brewsteri and S. l. plotus act as an isolating mechanism that inhibits interbreeding.

The morphological and genetic differences between S. l. brewsteri and other forms of the Brown Booby meet the standards for species recognition under the typological (or morphological) and phylogenetic species concepts, respectively (Mayr 2000, Wheeler 2000). The behavioral evidence described in this study, increasing sympatry with primarily assortative mating and rare interbreeding, meets the standards of the biological species concept (Mayr 2000). Cumulatively, all three forms of evidence suggest that it would be appropriate to consider Brewster’s Booby as a separate species again.

Occasional hybridization between S. l. brewsteri and S. l. plotus and the presence of some individuals of intermediate appearance do not constitute evidence that they are conspecific. Similar situations exist in two other pairs of booby species, specifically Blue-footed Booby (S. nebouxii) and Peruvian Booby (S. variegata), and Masked Booby (S. dactylatra) and Nazca Booby (S. granti). Blue-footed and Peruvian boobies are largely allopatric, but breeding colonies occur together on two islands off Peru, where mating is primarily assortative, with few instances of hybridization, resulting in genetic differentiation and only limited introgression (Figueroa 2004, Figueroa and Stucchi 2008, Taylor et al. 2012). Nazca Booby was considered a subspecies of Masked Booby but was split into a separate species based on morphological differences and assortative mating (Pitman and Jehl 1998, AOU 2000), which subsequently was supported by evidence of genetic differentiation (Friesen et al. 2002).

Part B. English name:

For the English common name, according to NACC guidelines for English names, when a split restores species status and a previously existing English name exists, that name would be resurrected. In this case the name would have been Brewster’s Booby. However, given the recent decision by AOS to change all eponymous common bird names, the name Brewster’s Booby is no longer an option. Below I have listed several possible alternative English common names, grouped by whether they are geographical or descriptive of the bird. I have offered some discussion of each name, including the pluses and minuses. My personal favorite is Cocos Booby and I recommend that as the new English common name for. S. brewsteri.

GEOGRAPHIC NAMES

Cocos Booby. The rationale for this name is similar to that of the Nazca Booby, which is named for a tectonic plate in the earth’s crust that contains part of the range of that species. The Cocos Plate is located in the eastern Pacific and is adjacent to and north of the Nazca Plate. The Cocos Plate extends off the west coast of the Americas from Panama north to the Mexican state of Jalisco (Figure 1). The volcanoes and earthquakes in western Mexico and Central America are fueled by plate convergence and subduction of the Cocos Plate under the North American and Caribbean plates. The Cocos Plate is named for Cocos Island, which rides upon the plate and is the only part of the plate above sea level. Cocos Island is an important nesting site for S. brewsteri, although the colonies there are not among the largest of the species. One downside to this name is that the Cocos Plate encompasses only a small portion of the geographic range of S. brewsteri, although it contains a larger proportion of the range than the Nazca Plate contains of the Nazca Booby range. The parallel naming of Nazca Booby and Cocos Booby would provide a logical, geographical rationale for these two species that overlap considerably in range.

Mexican Booby. The name Mexican Booby would recognize that much of the range of S. brewsteri occurs in Mexico and Mexican Waters and that the type specimens were collected in Mexico. Two drawbacks to this name are that 1) two subspecies that would be included with S. brewsteri (S. b. nesiotes and S. b. etesiaca) are not found in Mexico, and 2) increasingly less of the range of S. brewsteri will be in Mexico if the current range expansion continues across the Pacific. These same drawbacks also pertain to the name Cocos Booby. The name Mexican Booby would provide historical context for the likely origin for many of these dispersing birds.

Evidence of Plate Motions - Geology (U.S. National Park Service)

Figure 1. Map of the earth’s tectonic plates, showing the location of the Cocos Plate. From National Park Service: https://www.nps.gov/subjects/geology/plate-tectonics-evidence-of-plate-motions.htm

Tropical Eastern Pacific Booby. The Tropical Eastern Pacific is a name applied to one of twelve marine realms that cover the coastal waters and continental shelves of the world's oceans as part of a global classification system called Marine Ecoregions of the World (MEOW), which was devised by an international team, including conservation organizations, academic institutions and intergovernmental organizations (Spalding et al. 2007). It extends along the Pacific Coast of the Americas, from the southern tip of the Baja California Peninsula in the north to northern Peru in the south. The range of S. brewsteri largely coincides with this geographic unit, though the species range does extend farther to the north and south. Among geographic names this would be the most geographically appropriate because it coincides most the with range of the species. The main downside to this name is that it is long and cumbersome, consisting of four words.

DESCRIPTIVE NAMES

White-headed Booby. The name White-headed Booby is based on the most distinctive character of the species, the white head of males, which was the character that seems to have contributed most to its description as a separate species. However, this name has two significant drawbacks that in my opinion disqualify it: 1) it would pertain only to males of the brewsteri and nesiotes forms, and not to males of etesiaca; and 2) it would not pertain to females of any form, and thus would perpetuate the neglect of female appearance that has occurred already.

Pale-headed Booby. Pale-headed Booby would be preferable to White-headed Booby because it would apply to females and males of all forms that would be included in S. brewsteri. The main downside is that it seems a little bland.

Recommendation:

I recommend that S. l. brewsteri be split from other forms of the Brown Booby into a separate species. This split has been mentioned previously (Schreiber and Norton 2020), and the additional evidence described in this proposal strengthens the rationale for the split. The scientific name for the re-split species would revert to S. brewsteri, as it was originally described by Goss (1888). Sula brewsteri should include all pale-headed subspecies that breed in the eastern Pacific, including nesiotes and etesiaca recognized by some authors (Schreiber and Norton 2020). If subspecific status continues to be recognized for these forms, they would become S. brewsteri nesiotes and S. brewsteri etesiaca, respectively. Although etesiaca males have a pale, not white, head, etesiaca females are similar to females in other forms of brewsteri, and genetically etesiaca clearly grouped with other populations in the eastern Pacific (Steeves et al. 2003, Morris-Pocock et al. 2010). No changes are needed in taxonomic status or nomenclature of the other Brown Booby subspecies, which are more similar to each other morphologically and genetically (Morris-Pocock et al. 2011). Thus, S. l. plotus and S. l. leucogaster would remain subspecies of the Brown Booby.

For the English name, I recommend Cocos Booby, for the reasons discussed above.

Note from Remsen on voting on Part B. A YES vote is for Cocos Booby, the recommendation of the proposal and the unanimous choice of NACC, and a NO is for some other name; please indicate if that is Brewster’s Booby, the traditional name of the taxon, or some novel name.

Literature Cited:

Avise, J. C., W. S. Nelson, B. W. Bowen, and D. Walker. 2000. Phylogeography of colonially nesting seabirds, with special reference to global matrilineal patterns in the sooty tern (Sterna fuscata). Molecular Ecology 9:1783-1792.

Del Hoyo, J., A. Elliott, and J. Sargatal. 1992. Handbook of birds of the world. Volume 1. Barcelona: Lynx Editions.

Figueroa, J. 2004. First record of breeding by the Nazca Booby Sula granti on Lobos de Afuera Islands, Peru. Marine Ornithology 32:117-118.

Figueroa, J., and M. Stucchi. 2008. Possible hybridization between the Peruvian Booby Sula variegata and the Blue-footed Booby S. nebouxii in Lobos de Afuera Islands, Peru. Marine Ornithology 36:75-76.

Friesen, V. L., D. J. Anderson, T. E. Steeves, H. Jones, and E. A. Schreiber. 2002. Molecular support for species status of the Nazca Booby (Sula granti). Auk 119:820–826.

Goss, N. S. 1888. New and rare birds found breeding on the San Pedro Martir Isle. Auk 5:240-244.

Heller, E. and Snodgrass, R.E. 1901. Descriptions of two new species and three new subspecies of birds from the Eastern Pacific, collected by the Hopkins-Stanford expedition to the Galapagos Islands. Condor:74-77.

Kohno, H., and A. Mizutani. 2011. The first record of Brewster’s Brown Booby Sula leucogaster brewsteri for Japan. J. Yamashina Institute for Ornithology 42:147‒153.

Kohno, H., and A. Mizutani. 2015. First record of breeding behaviour of Brewster’s Brown Booby Sula leucogaster brewsteri in Japan. J. Yamashina Institute for Ornithology 46:108-118.

López-Rull, I., N. Lifshitz, C. M. Garcia, J. A. Graves, and R. Torres. 2016. Females of a polymorphic seabird dislike foreign-looking males. Animal Behaviour 113:31-38.

Michael, N.P., R. Torres, A. J. Welch, J. Adams, M. E. Bonillas-Monge, J. Felis, L. Lopez-Marquez, A. Martínez-Flores, and A. E. Wiley. 2018. Carotenoid-based skin ornaments reflect foraging propensity in a seabird, Sula leucogaster. Biology letters 14:20180398.

Montoya, B., C. Flores, and R. Torres. 2018. Repeatability of a dynamic sexual trait: Skin color variation in the Brown Booby (Sula leucogaster). The Auk: Ornithological Advances 135:622-636.

Morris-Pocock, J. A., D. J. Anderson, and V. L. Friesen. 2011. Mechanisms of global diversification in the Brown Booby (Sula leucogaster) revealed by uniting statistical phylogeographic and multilocus phylogenetic methods. Molecular Ecology 20:2835‒2850.

Morris-Pocock, J. A., T. E. Steeves, F. A. Estela, D. J. Anderson, and V. L. Friesen. 2010. Comparative phylogeography of Brown (Sula leucogaster) and Red-footed Boobies (S. sula): the influence of physical barriers and habitat preference on gene flow in pelagic seabirds. Molecular Phylogenetic and Evolution 54:883‒896.

Nelson, J. B. 1978. The Sulidae. Oxford University Press, London.

Pitman, R. L., and L. T. Ballance. 2002. The changing status of marine birds breeding at San Benedicto Island, Mexico. Wilson Bulletin 114: 11-19.

Pitman, R., and J. Jehl. 1998. Geographic variation and reassessment of species limits in the “Masked” boobies of the eastern Pacific Ocean. Wilson Bulletin 110:155–170.

Rauzon, M. J., D. Boyle, W. T. Everett, and J. Gilardi. 2008. The status of birds of Wake Atoll. Atoll Research Bulletin 561:1-41.

Schreiber, E. A., and R. L. Norton. 2020. Brown Booby (Sula leucogaster), version 1.0 In Birds of the World (S.M. Billerman, Ed.). Cornell Lab of Ornithology, Ithaca, NY, USA: https://doi.org/10.2173/bow.brnboo.01

Spalding, M.D., H. E. Fox, G.R. Allen, N. Davidson, et al. 2007. Marine Ecoregions of the World: A Bioregionalization of Coastal and Shelf Areas. Bioscience 57(7):573–583.

Steeves, T. E, D. J. Anderson, H. Mcnally, M. H. Kim, and V. L. Friesen. 2003. Phylogeography of Sula: the role of physical barriers to gene flow in the diversification of tropical seabirds. J. Avian Biology 34:217-223.

Steeves, T. E, D. J. Anderson, and V. L. Friesen. 2005. A role for nonphysical barriers to gene flow in the diversification of a highly vagile seabird, the Masked Booby (Sula dactylatra). Molecular Ecology 14:3877-3887.

Taylor, S. A., D. J. Anderson, C. B. Zavalaga, and V. L. Friesen. 2012. Evidence for strong assortative mating, limited gene flow, and strong differentiation across the Blue‐footed/Peruvian booby hybrid zone in northern Peru. Journal of Avian Biology 43:311-324.

VanderWerf, E. A. 2018a. Geographic variation in the Brown Booby. Field identification of males and females by subspecies. Birding 50:48-54.

VanderWerf, E. A., B. L. Becker, J. Eijzenga, and H. Eijzenga. 2008. Nazca Booby Sula granti and Brewster’s Brown Booby Sula leucogaster brewsteri in the Hawaiian Islands and Johnston and Palmyra Atolls. Marine Ornithology 36:67–71.

VanderWerf, E. A., M. Frye, J. Gilardi, J. Penniman, M. Rauzon, H. D. Pratt, R. S. Steffy, and J. Plissner. 2023. Range expansion, pairing patterns, and taxonomic status of Brewster’s Booby Sula leucogaster brewsteri. Pacific Science 77:1-12.

Wetmore, A. 1939. Birds from Clipperton Island collected on the presidential cruise of 1938. Smithsonian Miscellaneous Collections 98(22):1-6.

Wetmore, A., Friedmann, H., Lincoln, F.C., Miller, A.H., Peters, J.L., van Rossem, A.J., Van Tyne, J., and Zimmer, J.T. 1944. Nineteenth supplement to the American Ornithologists’ Union Check-list of North American birds. Auk 61:441-464.

Wheeler, Q. D. 2000. The phylogenetic species concept (sensu Wheeler and Platnick). Pp. 55-60 in Species Concepts and Phylogenetic Theory: a Debate (Q.D. Wheeler and R. Meier, eds.). Columbia University Press, New York.

Eric A. VanderWerf, April 2024

Additional notes on Part B – English name. When Remsen told VanderWerf that SACC was not bound by the edict of the AOS Council on removing all eponyms, VanderWerf responded by noting that he was not opposed to eponyms but still preferred Cocos Booby for the following reasons: “I prefer Cocos Booby for 3 reasons: 1) I like geographic names, and this offers a nice parallel with Nazca Booby; 2) if the NACC also adopts the split, then there would be a chance that the same English name, Cocos Booby, would be recognized by both groups. Having different common names would be confusing; and 3) the Spanish name, which has not been discussed and I don’t know where/how/when that would happen, presumably would be Bobo Cocos, which has a nice ring to it.”

Comments from Remsen:

“Part A: YES. The lack of non-assortative mating is striking especially because reproductive isolating mechanisms in birds tend to be weakest when range expansions bring taxa together that have had little previous contact. Also, note that the phenotypic differences between Sula dactylatra and Sula granti roughly comparable to those between brewsteri and leucogaster. Note also that there was no evidence for the Peters-Wetmore lump of the two species. The 4^th edition of the AOU Check-list (1931) treated it as a separate species, Brewster’s Booby (S. brewsteri) from Sula l. leucogaster (White-bellied Booby), and the broadly defined species treatment then appeared in the 5^th edition (1957) based solely on Peters’ and Wetmore’s treatment.

“Part B: NO. I think Cocos is a much better name than any of the others in the proposal for the biogeographic rationale outlined therein. Nevertheless, the title of VanderWerf et al.’s paper makes it clear why Brewster’s is the better name in that that is the name that seabird people use for the distinctive taxa of the eastern Pacific. What better evidence do we need than this that the name has about 130+ years of formal and informal association with the eastern Pacific taxa? See also the title of VanderWerf et al. (2008) above. See also any of the 20+ papers, most of them published in The Auk, that used “Brewster’s Booby”, as revealed by Google Scholar. Google search on “Brewster’s Booby” produces 934 hits. Brewster’s Booby was the name used by the AOU (1931), where treated as a separate species. Hellmayr and Conover (1948) also used Brewster’s Booby for S. l. brewsteri. More recently, Howell and Zufelt (Oceanic Birds of the World, 2019, Princeton Univ. Press) used “Brewster’s Brown Booby” for S. l. brewsteri.

“Although Goss, who also described brewsteri, made no attempt to justify that name and in fact did not make it clear that brewsteri presumably honored “the” Brewster of ornithology, i.e. William Brewster. That was because it was so obvious that William Brewster’s contributions to the avifauna of Baja California (e.g., “Birds of the Cape region of Lower California”, 1902, Bull. Museum Comp. Zoology, 241 pp., and many additional papers, based on existing collections and collections that he commissioned, but not on his own fieldwork) were so important that no explanation was needed.

“William Brewster’s contributions to ornithology go far beyond Baja California. He was one of three founding members of the American Ornithological Society itself (1873), and served as its president for three years. The AOS’s Brewster Medal is one of the three highest awards it gives for research. Brewster was a Fellow of the American Academy for Advancement of Science (AAAS). He was the founder and a president of the Nuttall Ornithological Club, the oldest ornithological society in the Western Hemisphere. He was the first president of Mass Audubon from 1896 to 1913, and the major goal of that society was to restrict the killing of wild birds and was a force behind passage of the Lacey Act of 1900 (which prohibits interstate commerce in wild birds killed illegally). Brewster was curator of birds at Harvard’s Museum of Comparative Zoology from 1885 until his death in 1919. Henshaw’s 23 page memorial to Brewster in the Auk in 1920 outlines his many additional contributions and personal attributes; Henshaw made it clear that Brewster was what we would call a “good guy” nowadays:

‘He was charitably disposed to all, and inclined to judge the delinquent leniently and with forbearance. He never spoke ill of any man. He was generously inclined, and, within his means, gave freely to those less fortunate than himself, though of his beneficence he said nothing, preferring that it should remain unknown.

‘He was absolutely truthful, habitually refrained from all exaggeration, and falsehood and evasion were foreign to his nature. As he was sincere and truthful, so was he honorable and pure minded, and his conversation reflected the thoughts and imaginings of a pure soul.’

“Some tidbits gleaned from these and other sources: All three of his siblings died in childhood; their early deaths evidently inspired the poem The Open Window, by Henry Wadsworth Longfellow, one of the Brewster family’s neighbors. Brewster had some sort of vision problem as a child, but that seems to have passed as he became an adult. His extensive field notes have been digitized and are online, and browsing through these, it is clear that Brewster was not only a keen observer of birds but really loved them. Actually watching birds and describing their behavior was his passion, and in this way seemed ahead of his time despite what must have been primitive optics. Perhaps in compensation, he had a reputation for extremely sharp hearing and ability to identify birds at a distance by voice to the extent that Henshaw considered him supremely talented:

‘His hearing was extraordinarily acute, and his ability to recognize the notes of birds at a distance and amid other and confusing sounds was little less than marvelous, and far exceeded that of any one I ever knew.’

“His 38 years of fieldwork at Lake Umbagog, on the Maine-New Hampshire border, produced some legendary observations, often from his canoe, to the point that Robert Stymiest published excerpts as a paper in the Bird Observer in 2004. At Lake Umbagog, he made the first detailed observations of the nesting behavior of the Philadelphia Vireo, as just one of his many contributions. He was also one of many famous naturalists who made extensive observations in the Concord, Massachusetts, and kept copious field notes on his experiences there; in fact, in 1937, a 300 page book of selections from his Concord journals was published. Brewster was also interested in bird migration, and actually spent 6 weeks in Fall 1885 at a lighthouse in the Bay of Fundy do study the behavior of migrating birds. The paper he published on these observations was a classic of the era.

“I herein take the opportunity to make some positive remarks on eponymous English names. Brewster’s case, in my opinion, provides a strong example of the value of eponyms. Yes, many of these founders of American ornithology are memorialized in other ways, including scientific names. However, most birders and even many professional ornithologists have a weak knowledge of scientific names, and even fewer are inclined to delve into the general history of ornithology in North America on their own. An English name, however, gets the attention of every bird person who uses it. Most will never take the time to read about these people, but those who do will hopefully be inspired and will be reminded that we got where we are today in our understanding of birds through the work of those who preceded us. Knowing that we humans are instinctively interested in stories about other humans, I doubt that I am the only one inspired by the stories of people like Brewster. Some of you may know why I have a special admiration for Brewster, but I hope all of you will appreciate this accomplishments and the reverence in which he was held by his peers. Contrast the window into ornithology opened by “Brewster’s Booby” compared to the value of a name like “Brown Booby,” its sister species. Yes, Brown Booby is an excellent descriptive name. It is indeed a brown booby, brownest of the genus. But that’s where the value ends. There is no depth, no cachet, no inspiration. In my opinion, I think that having a tiny percentage of English names that honor contributors to ornithology acknowledges that we did not get here on our own and provides potential inspiration for others to contribute to ornithology and especially in a case like Brewster to appreciate birds more deeply.

“Additional points: one problem with Cocos is that the name is clearly associated with three endemics of Cocos Island (Cocos Cuckoo, Cocos Flycatcher, Cocos Finch) and thus the natural implication of the name “Cocos Booby” is that it is another island endemic. Few people are aware of the name Cocos Plate, and so confusion will be inevitable. By the way, there is no need to discuss adding group names in this case, e.g. “Cocos Brown-Booby” etc., because our guidelines indicate that there is no need for that if two species previously split, then lumped, and then re-split --- the original species treatment used Brewster’s Booby for S. brewsteri (and White-bellied Booby for S. leucogaster). Using White-bellied Booby for narrowly defined S. leucogaster also should be discussed, as recommended in our guidelines on English names because it calls attention to the species split and restores a historical name used in much literature prior to 1957.”

Comments from Don Roberson (voting for Claramunt on Part B): YES on Cocos Booby. Although "Brewster's Booby" would have been okay with me, some people disfavor eponymous common names, so a different English name is fine at this point in time. The genus Sula currently has a nice set of English names: Red-footed, Blue-footed, Brown, Peruvian, Masked, and Nazca. [in the Sulidae, only the monotypic genus Papasula has an eponymous name, but it resides far from the New World.]

“Traditionally, the long-standing set of the five basic Sula boobies were Red-footed, Blue-footed, Brown, Peruvian, and Masked. All are short, distinctive, and memorable -- 4 are based on plumage and/or soft-parts color, and one is named for the Peruvian Current where it occurs. Red-footed and Blue-footed are surely among the "really good English names" for those species. Brown and Masked are accurate and serviceable. Then came the first split in Sula, and I was delighted when the authors of the taxonomic paper (Pitman & Jehl 1998) concluded with this line: "As a common name for Sula granti we propose Nazca Booby, which recognizes that the current breeding range and probably evolutionary history of this species is closely associated with the Nazca Crustal Plate."

“This was a great English name -- short, very memorable, reasonable accurate, and innovative. In 1989, when I spent 4 months in the eastern tropical Pacific on a NOAA ship, with Bob Pitman on a sister ship on that cruise, Bob asked me to take notes on the juvenal "Masked" Boobies when we went through the Galapagos, which he used in writing his 1998 paper [later, I wrote a paper on ID issues in Masked & Nazca Boobies.] On that same cruise, we had the good fortune to visit Isla del Coco [Cocos Island, off Costa Rica] and even land on the island. My notes also mention a "breeding colony on Nuez I., where Gary Fredrichsen saw fledglings" of brewsteri Brown Booby while I was on Cocos itself (Nuez is a tiny islet in Chatham Bay; we also scoped it with the ship's Big Eyes).

“Now, we have an opportunity to give S. brewsteri another excellent English name: Cocos Booby. It parallels the name Nazca Booby nicely. Neither name includes all the breeding range of the Sula involved, let alone its at-sea distribution, but Cocos is a core breeding location, well represents core at-sea range, and does so better than the Nazca Plate did for Nazca Booby. It is really a fine choice: short, very memorable, reasonable accurate, and innovative in parallel with Nazca. While it is useful to name local resident landbird endemics for the island on which they occur (e.g., Cocos Finch), it is also appropriate to name a seabird after the tectonic plate which covers a good portion of both its breeding and its pelagic range, postulating, as did Pitman & Jehl, that it is likely that the "evolutionary history of this species is closely associated with the Cocos Crustal Plate."

“None of the other options are as attractive. "White-headed" and "Pale-headed" are rather boring, do not accurately describe all subspecies, and focus only on adult male plumages but would not be accurate for well over half of the birds encountered (females, sub-adults, and juvs). "Tropical Eastern Pacific Booby" is a jaw-breaker, not significantly more accurate, and would break the string of having the names of all Sula boobies be short, distinctive, and punchy. Finally, "Mexican Booby" is misleading is multiple ways -- Mexico (including the western coast of Mexico) has multiple species of boobies, but more importantly, the eastern coast of Mexico will have a Brown Booby from the Gulf that is not brewsteri, so a "Mexican Booby" would not even include the Caribbean coast, with its entirely different type of "Brown Booby", adding to confusion.

“VanderWerf et al. (2023) did point out that there are four major lineages in Brown Booby: Caribbean, central Atlantic, Indo-central Pacific, and eastern Pacific. Some have suggested that all might be elevated to species level, and that in doing so, a hyphenated English name -- Brown-Booby -- should be preceded by a modifier to create, say, Caribbean Brown-Booby, Atlantic Brown-Booby etc. SACC has adopted this sort of scheme multiple times, but generally in complex situations (e.g., the Trogonidae, Thamnophilidae). The Sula boobies are currently just 7 species (with brewsteri) and only 10 species if the other 3 Brown Booby lineages were to be split, and even the entire Sulidae would be just 14 species. I don't think we need hyphenated English names is this relatively small group of Sulids, and to do so would create long names which are neither short, memorable, or punchy. But even if later taxonomic changes might be made, Cocos Booby or "Cocos Brown-Booby" would still be the best choice, in my opinion, for the eastern Pacific taxa.

“Citation: Pitman & Jehl (1998) Geographic variation and reassessment of species limits in the "Masked " boobies of the eastern Pacific Ocean. Wilson Bull 110: 155-170.”

Comments from Claramunt (Part A): “A. YES. The combination of morphological, genetic and behavioral information provides compelling evidence for the species status of E Pacific taxa.”

Comments from: “A. YES to Split Sula brewsteri from S. leucogaster. B. NO. I definitely prefer Brewster’s as the E-name, given my strong objection to AOS’s decision to abolish all eponyms, thus ignoring nomenclatural history and Brewster’s significant contributions to the development of American ornithology.”

Comments from Robbins: “A. YES for recognizing Sula brewsteri as a species given that this taxon appears to be consistent with species-level treatment of other taxa in Sula.”

Comments from Areta: “A. YES, the evidence is more fitting with species status for brewsteri, although I would not be averse to having more genetic information on the distinction and effect of gene flow between the syntopic birds.”

Comments from David Ainley (voting for Del-Rio): B. NO on Cocos Booby and YES on something else. Cocos too geographically restrictive for the species. Brewster's Brown Booby would be fine with me, and kind of how I have always considered it. For what it's worth, though, if given the choice, I'd go with Eastern Pacific BB (for S. brewsteri) should the other BBs become known as Indo-Pacific BB and Atlantic BB. That's more in line with how Gannets are named.”

Comments from Bonaccorso: “A. YES. All the evidence supports the idea that Sula brewsteri is a good species, morphologically diagnosable and reproductively isolated.”

Comments from Jaramillo:

“A – YES to the split of Brown Booby. Apart from the biology of sympatry and avoidance of hybridization with is key here. I will also point out, and this is in the proposal that for years it has been stated that the females are unidentifiable. But VanderWerf et al. have shown that they are actually identifiable -- it is just more difficult. We have started using these criteria in the field, and they seems to work.

“B – YES to Cocos Booby. Memorable, easy to spell, and a name that is similar in etymology to Nazca. Cocos means a lot of things, including coconuts in most Spanish places, but it is slang for testicles in Chile. Most words are slang for testicles in Chile, so I would not be concerned, and this is the English Name, not the Spanish Name. But I wanted to mention that. It also can mean your brain/mind in slang.”

Comments from Debra Shearwater (voting for Bonaccorso): “YES to Cocos would be my vote. Memorable, easy to spell, short. It bookends with Nazca Booby.”

Comments from Lane: “YES on both. It seems NACC has already accepted this split and the English name “Cocos Booby.” The assortative nesting certainly suggests that the S. brewsteri is acting as a good species where it overlaps with other populations of S. leucogaster in the central and eastern Pacific. The English name “Cocos,” whereas calling to mind a single island to me, follows the logic of “Nazca Booby” and thus makes sense after some thought.”

Comments from Scott Terrill: B:”NO to Cocos Booby. In voting no on B, I agree with all of the rationale provided, in detail, by Remsen, including but not limited to: (1) The extensive historical precedence for the name "Brewster's" Booby with eastern Pacific taxa; (2) Brewster's immense early contributions to ornithology and, as Remsen put it; (3) "Henshaw made it clear that Brewster was what we would call a 'good guy' nowadays."

Additional comments from Stiles: “Here, I have a very strong opinion that “Cocos Booby” is a singularly inappropriate name for Sula brewsteri, and that the reasons for NACC’s adoption of it are most ill-founded. To begin with, geography. The majority and best-known part of the Cocos plate constitutes the floor of the Caribbean, which immediately causes confusion by implying that brewsteri is a Caribbean bird. By contrast, Cocos I. is near the western extreme of this plate, effectively an outlier as well as constituting only a minute fraction of the distribution of brewsteri. Regarding the presence of this species on Cocos I., my experience suggests that it is also an insignificant part of this distribution. I spent a week in 1975 on and around Cocos and, mindful of a previous unconfirmed record of its breeding there on an outlying islet at about the same time of year, I made a special effort during two slow circuits of the island to observe this species on these islets as well as the many cliffs of the island itself – and never saw it there, or in the surrounding waters. My conclusion was that if brewsteri breeds (or even occurs) there, it must be in small numbers and probably not regularly. All of this puts Cocos Booby in the same league for aptness in distributional terms as Tennessee Warbler or Philadelphia Vireo. The analogy between Cocos Booby and Nazca Booby (for S. granti), while sounding cute, is also flawed (simply compare the data for the distribution and status of brewsteri above with that of S. granti with respect to the Nazca plate, the distribution of which lies entirely offshore in the Pacific, the rest being subducted under the South American continent. The major and best-studied breeding colony of granti is centered on this plate and its seaward distribution is also centered on and around it, making Nazca Booby a most appropriate name. In fact, the seaward distribution of brewsteri also includes the Nazca plate (to a greater extent than its occurrence on the Cocos plate: it could even be called the “Lesser Nazca Booby” more appropriately). Finally, regarding English names, Brewster’s Booby has a considerable track record among the seabird fraternity, which after all has a better appreciation of its global distribution (than at least, the NACC, which due to its recently-acquired obligatory eschewing of eponyms, must ignore “Brewster´s Booby”. I see no reason why SACC should follow suit and condone, much less honor this practice and strongly suggest that members of the SACC approving “Cocos Booby” should reconsider their votes and give more serious consideration to “Brewster´s Booby” as a better name. Following the leader out of “loyalty” to the NACC seems unwise if the “leader” itself, makes what from any knowledgeable viewpoint is an unwise decision.”

Additional comments from Remsen: The proposal maps the Cocos Plate, and I decided to elaborate by mapping brewsteri breeding distribution on the plate in a crude way.

Here’s a more detailed map of the Cocos Plate from Wikipedia:

And here’s my first attempt at crudely mapping by eye the breeding distribution of brewsteri from some of its most prominent breeding locations as given in Birds of World and elsewhere (yellow circles). I will likely refine this to make it more accurate, and additions/corrections are welcome. But the bottom line, barring gross inaccuracy, is that for geographic name, Cocos Booby is pretty good in that it looks like the tectonic activity of the plate produced many of the islands on which the species breeds, and even some of the islands not on the plate were formed by interactions between the plate and other ridges. Much of the distribution in Mexico lies north of the plate and of course the range expansion to Hawaii has added territory far from the plate, but nonetheless for a geographic name that doesn’t refer to a single island or isolated mountain range, it’s not bad at all in my opinion. The species occurs mainly along the margins of the plate, not the deep ocean within the plate.