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Archaeological Evidence for a Double-Crested Cormorant(Phalacrocorax auritus) Colony in the Pacific Northwest, USAAuthor(s): Kristine M. BovySource: Waterbirds, 34(1):89-95. 2011.Published By: The Waterbird SocietyDOI: http://dx.doi.org/10.1675/063.034.0111URL: http://www.bioone.org/doi/full/10.1675/063.034.0111

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89

Archaeological Evidence for a Double-crested Cormorant (Phalacrocorax auritus ) Colony in the Pacific Northwest, USA

KRISTINE M. BOVY

Department of Sociology and Anthropology, University of Rhode Island, 507 Chafee Building,Kingston, RI, 02881, USA

E-mail: kbovy@uri.edu

Abstract.—Double-crested Cormorants (Phalacrocorax auritus) were not observed breeding in the inner coast ofWashington and British Columbia until the 1920s and 1930s, whether the breeding was either a re-colonizing eventor a new expansion was unknown. Archaeological evidence from Watmough Bay, a shell midden site on Lopez Is-land, San Juan Islands (Washington State), was analyzed to place the recent changes in breeding distribution indeeper historical context. The Watmough Bay faunal assemblage contains large numbers (n = 2,397) of cormorantbones. Of those specimens that could be identified to species (n = 358), 99.7% were identified as Double-crestedCormorants. The majority (97%, n = 2,336) of the cormorant remains are from juveniles or chicks, which were col-lected while still at the colony. Radiocarbon dating indicates the majority of the site accumulated between AD 300-600. Evidence for a ca. 1,500-year-old Double-crested Cormorant colony near Lopez Island confirms that the speciesdid breed in the region prior to the early 20th century. The study further documents the value of archaeologicaldata for current wildlife management. Received 15 January 2010, accepted 30 August 2010.

Key words.—archaeology, breeding distribution, Double-crested Cormorant, human hunting, Pacific North-west, Phalacrocorax auritus, colony, zooarchaeology.

Waterbirds 34(1): 89-95, 2011

Historically, population sizes and breedingranges of Double-crested Cormorants (Phalac-rocorax auritus) (DCCO) have fluctuatedthroughout much of North America (Drentand Guiguet 1961; Vermeer and Rankin 1984;Carter et al. 1995; Hatch 1995; Wires and Cuth-bert 2006), creating speculation on both thetiming and cause of these changes. In general,DCCOs are more abundant today than 100years ago, which has resulted in conflicts withthe fishing industry and management effortsto reduce their numbers and impact on fishpopulations (e.g. Sullivan et al. 2006; Wiresand Cuthbert 2006; Duerr et al. 2007; Russell etal. 2008). Recently, Wires and Cuthbert(2006) reviewed early ornithological and ar-chaeological records and concluded that DC-CO numbers were larger prior to 1900 and thecommon notion of the species being “over-abundant” today is likely erroneous whenplaced in a historical context. However, due tolimitations with the historical and archaeolog-ical data, questions remain about the specificpre-1900 breeding populations on the PacificNorthwest Coast (Hobson and Driver 1989;Wires and Cuthbert 2006).

In the Pacific Northwest, DCCOs werefirst recorded breeding in the interior waters

of the Strait of Georgia in 1927 (Mandarte Is-land, British Columbia); by 1937 they hadexpanded into the San Juan Islands of Wash-ington (Carter et al. 1995; Fig. 1). BreedingDCCOs became common in the region dur-ing the mid-1900s, with population fluctua-tions in the latter half of the century, per-haps due to human disturbance, predationby Bald Eagles, and El Niño events (Vermeerand Rankin 1984; Speich and Wahl 1989;Carter et al. 1995; Hatch 1995; Wires et al.2001). Researchers have questioned whethercolonization in the 1900s represented an en-tirely new range expansion or a re-coloniza-tion event (e.g. Drent and Guiguet 1961;Hobson and Driver 1989; Hatch 1995; Wiresand Cuthbert 2006). Drent and Guiguet(1961) speculated that the observed rangechanges could be due to the decline of “egg-ing” by both North Americans and Euro-Americans and/or climatic shifts that creat-ed a more abundant food supply or extend-ed breeding seasons.

A synthesis of archaeological evidencefor marine birds in the Strait of Georgiafound DCCOs had been identified from fivearchaeological sites (out of twelve in the sam-ple) spanning the past 5,000 years (Hobson

90 WATERBIRDS

and Driver 1989), suggesting the species wasrelatively abundant in the past. However,none of the assemblages contained nestlingbones, so it was unclear whether breedingpopulations had formerly been present. Ju-venile DCCO bones have been identifiedfrom other sites along the Pacific Coast, suchas the Emeryville Shellmound in San Fran-cisco Bay (Broughton 2004), so the potential

exists to recover and identify such remainsfrom the Gulf of Georgia. Bird bones wereanalyzed from a late Holocene archaeologi-cal site in the San Juan Islands (WatmoughBay) as part of a larger study to investigatehistorical waterbird populations along thePacific Northwest Coast and the effects of cli-mate change and human hunting on thosebirds (Bovy 2005). The bird bones from Wat-mough Bay were identified to taxon and as-signed to age categories, thereby providingthe data needed to clarify the long-termbreeding status of the DCCO in the PacificNorthwest.

METHODS

Faunal Recovery and Sampling

The Watmough Bay site (Site # 45-SJ-280) is a largeshell midden located near both a saltwater bay andfreshwater marsh on Lopez Island in the San Juan archi-pelago, Washington State (Fig. 1). A University of Wash-ington field school excavated the site in 1968, and theartifacts and notes were curated at the Burke Museumof Natural History and Culture (BMNHC) in Seattle.The site was excavated in 2

× 1 m units and 20 cm arbi-trary levels. All vertebrate faunal material was screenedthrough

¼” mesh (6.35 mm); while small bird boneswere undoubtedly lost through the mesh, the screen-size bias is comparable throughout the assemblage.

Bird bones from ten 1

× 2 m excavation units andtwo 1 x 1 m units (“baulks”), with depths varying from160 cm to 210 cm below the surface, were analyzed. Twounits were eliminated from the results because eitherfaunal material is missing (0N/24W), or the stratigra-phy and chronology is incommensurate with the rest ofthe site (9N/3W). There were 19 cormorant bonesidentified from these two excluded units.

Taxonomic Identification

Since the Double-crested, Brandt’s (Phalacrocoraxpenicillatus) and Pelagic Cormorants (P. pelagicus) are allfound on the Pacific Northwest Coast, it was necessaryto differentiate between the bones of these three close-ly-related species. The three species overlap in bodysize, with the DCCO typically largest and the Pelagicsmallest. Most adult elements can be readily identifiedto species using morphological criteria and comparativespecimens (Howard 1929; Ono 1980; Siegel-Causey1988; Broughton 2004). The Watmough Bay bones wereidentified using the extensive comparative collectionsof the Zoology Division of the BMNHC. In addition tothe criteria described in the above sources, additionalosteological and metric criteria were used to distinguishnumerous elements of the three cormorant species (seeBovy 2005:336-337).

While many specimens could be identified to spe-cies, others were identified only as “Phalacrocorax sp.” or“cf. Phalacrocorax sp.” When possible, these unidentifi-able cormorants were assigned to size classes. These

Figure 1. The Gulf of Georgia region and the San JuanIslands (black shaded area). Inset shows southeast Lo-pez Island (Washington State), including the location ofthe Watmough Bay site (�) and place names mentionedin the text.

1,500-YEAR-OLD CORMORANT COLONY 91

specimens were typically small fragments lacking diag-nostic attributes, elements that were not identified tospecies (e.g. distal wing digits, carpals, fibulae, phalan-ges), or sub-adult specimens. Bird bones were quanti-fied using the Number of Identified Specimens(Grayson 1984), and specimens recovered within thesame excavation levels were refit, if possible. No attemptwas made to identify vertebrae or ribs below the classlevel.

Aging of Cormorants

In order to assess whether the Watmough Bay assem-blage contained cormorants hunted while at the colony,an attempt was made to determine the approximateages of the archaeological specimens. The cormorantbones were initially sorted into the three age categoriesdefined by Broughton (2004:8): chicks, whose bonesare small, porous and lack adult cortical bones and mus-cle attachments; juveniles, whose bones are similar tothose of adults in size but lack completely developedcortical bone; and adults, whose bones are full grownwith completely developed cortical bone. A fourth cate-gory “juvenile/chick” was added for those specimensthat had some attributes of both Broughton’s “juvenile”and “chick” categories (e.g. approached adult size, butlacked muscle attachments).

An example of the three sub-adult age categories isshown for the tibiotarsus in Fig. 2a. The juvenile tibio-tarsus (left) has both proximal and distal epiphyses ossi-fied, and is similar in size to adults. The juvenile/chick(center) has the distal epiphysis ossified, but the proxi-mal lacks the epiphysis and is much thicker and less de-fined than an adult. Finally, the chick (right) is muchsmaller than an adult and lacks both epiphyses. ThreeDCCO comparative specimens, two young chicks andone fledgling, were obtained in order to help deter-mine rough estimates for the age categories used in thisanalysis (Table 1).

RESULTS

Taxonomic Identification

Cormorants comprised 33% of the birdbones identified from Watmough Bay; the ma-jority (97%, n = 2,336) of these cormorant re-mains were from sub-adults (Table 2). All bodyparts (skulls, pectoral girdle, wings, legs) fromthe sub-adult cormorants were recovered(Bovy 2005). The most abundant element inthe sub-adult assemblage was the ulna; 94 prox-imal right ulnae were identified, indicatingthat the remains of at least 94 immature indi-viduals were present at the site. Nearly 15% ofthe cormorant specimens were identified tospecies (n = 358) using morphological andmetric criteria; all of these were DCCO exceptfor one, a complete carpometacarpus of anadult Pelagic Cormorant. In addition, there

were four adult distal wing elements (three car-pometacarpi, one first phalanx of the seconddigit) identified as “Phalacrocorax sp. - small,”which were likely either Pelagic or Brandt’sCormorants. Two adult Brandt’s Cormorantproximal radii were identified, but both wererecovered from Unit 9N/3W (which was ex-cluded in this analysis). Thirty-three percent (n= 298) of the juvenile and 3.6% (n = 24) of thejuvenile/ chick bones were developed enoughto identify to species; all of these were DCCOs,and the rest were consistent in size with thislarge species.

Age Determination

The Watmough Bay cormorant assem-blage was sorted into the four general age

Figure 2. (a) Tibiotarsus bones from three age classes ofsub-adult cormorants from Watmough Bay: Juvenile(left), Juvenile/Chick (center), and Chick (right). (b)-(d) Comparison of bones from a two- to three-week-oldDCCO comparative specimen (left of each photo) withthose of comparable age from the Watmough Bay site(right of each photo). (b) Humerus (c) Quadrate (d)Tarsometatarsus. Photos courtesy of the BMNHC (cata-log # 45SJ280) and the Peabody Museum Zooarchaeol-ogy Lab (#ZM-471-PEL).

92 WATERBIRDS

categories, adults (2.5%, n = 61), juveniles(37.6%, n = 901), juveniles/chicks (27.7%,n = 663), and chicks (32.2%, n = 772).These numbers exclude the five adult wingbones that were too small to be DCCO. Fewof the specimens from Watmough Bay ap-peared to be as young as the four-day-oldcomparative specimen (ZM-0469-PEL; Ta-ble 1), although the bones of this chickwere so small that they would not havebeen recovered in the

¼” mesh. Many ofthe chick and juvenile/chick bones fromthe Watmough Bay site were similar in de-velopment to the two- to three-week-oldcomparative specimen (ZM-0471-PEL; Fig.2b-d). All of the sub-adult bones were lessdeveloped than the three- to four-month-old specimen (MVZ-179932), whose boneswere adult-like in appearance.

Temporal Change and Site Chronology

In order to assess change through time,the data were aggregated into nine excava-tion levels (Table 2); aside from level 1 (plow-zone), which was 30-40 cm thick, all otherswere 20 cm arbitrary levels. Although levels 7-9 had small sample sizes (n

≤ 30), each levelcontained four cormorant bones. Cormo-rants were abundant in levels 6 and 5, com-prising 87% and 55% of the total bird assem-blage, respectively. Cormorants then gradual-ly decreased in the top levels, from 24% in lev-el 4, to less than 2% in levels 1 and 2.

Twenty-eight radiocarbon dates havebeen obtained from the Watmough Bay site(Stein et al. 2003; Deo et al. 2004; Bovy 2005),13 of which were from units and levels thatcontained the densest bird bone deposits.

Table 1. DCCO comparative osteological specimens consulted for age determination.

Specimen #Collection

DateCollectionLocation

EstimatedAge1 Appearance Classification

ZM-0469-PEL2 24 July 1989 Massachusetts 4 days very small & under-developed;porous; wing bones difficult toidentify to element

chick

ZM-0471-PEL2 24 July 1989 Massachusetts 2-3 weeks small; porous; unfused epiphyses;lacks muscle attachments &cortical bone

chick

MVZ-1799323 21 Sept. 1999 California 3-4 months completely developed corticalbone; ossified epiphyses

adult

1See Bovy 2005 for more information on the age estimation of these specimens.2Zooarchaeological Laboratory of the Peabody Museum of Archaeology and Ethnology (Harvard).3Museum of Vertebrate Zoology at the University of California-Berkeley.

Table 2. Cormorant specimens identified at Watmough Bay by age class and excavation level.1

Age Class

Excavation Level

Total1 2 3 4 5 6 7 8 9

Adults 3 1 9 15 10 23 0 0 0 61

Sub-adults

Juveniles 3 3 12 153 453 273 0 3 1 901Juvenile/Chick 0 3 12 105 309 230 0 1 3 663Chick 2 3 8 124 299 332 4 0 0 772

Sub-adult Total 5 9 32 382 1061 835 4 4 4 2336Cormorant Grand Total 8 10 41 397 1071 858 4 4 4 2397

Total Identified Birds 551 710 1361 1683 1936 981 30 19 8 7279

1Includes data for units 0N/0E, 0N/3W, 0N/6W, 0N/9W, 0N/15W, 0N/18W, 1N/9W, 1.5N/0E, “Baulk A,” and“Baulk C.” Excludes five adult cormorant specimens that were too small to be DCCO. Level 1 (plow zone) was 30-40 cm thick; all others were 20 cm arbitrary levels.

1,500-YEAR-OLD CORMORANT COLONY 93

The dates were corrected using the Robin-son and Thomson (1981) marine reservoircorrection value (

ΔR = 401 ± 23 years) andcalibrated using CALIB 5.0.2 (Stuiver andReimer 1993; see Bovy 2005 for more detailsabout dating strategies and results). The ra-diocarbon dates indicate that the bulk of thebird bones shown in Table 1 accumulated be-tween AD 300-600. Two shells were datedfrom level 5 (100-120 cm), which contained1,061 sub-adult cormorant specimens. Thetwo-sigma calibrated age of a chiton shellfrom “Baulk A” is AD 335-555. A single bi-valve fragment from 0N/18W was datedthree separate times; the overlapping agerange of these three dates is AD 435-495.

DISCUSSION

There is strong zooarchaeological evi-dence for a DCCO colony in the San Juan Is-lands approximately 1,500 years ago. Numer-ous (n = 2,336) sub-adult cormorant boneswere identified from the Watmough Bay ar-chaeological site. The sub-adult bones wereoften small and under-developed and lackeddiagnostic features, which made taxonomicidentification more difficult than for adults.In particular, the wing elements develop tomaturity at a slower rate and are thereforemore difficult to identify than the leg bonesof similarly aged birds. All of the sub-adultspecimens that could be identified to species(n = 322) were DCCO, and therefore the im-mature cormorant bones that could not besecurely identified to species on the basis ofmorphology are presumably also DCCO.

Determining the age of the cormorantsat the time they were harvested was difficult,given the lack of juvenile comparative speci-mens of known age or research on the skele-tal development of cormorants. The age cat-egories (juvenile, juvenile/chick, chick)used in this analysis were useful, but wereproblematic for at least two reasons. First,the three stages of sub-adults are not equal indevelopmental time (Douglas Causey, per-sonal communication) and, therefore,should only be used and interpreted at theordinal scale. Secondly, observations of com-plete juvenile cormorant comparative speci-

mens make it apparent that these age catego-ries are not necessarily consistent across ele-ments due to differences in timing of fusionand development. For example, a four-day-old DCCO chick specimen collected fromBoston Harbor (Table 1) already had recog-nizable leg and axial elements, while the ra-dii, ulnae and carpometacarpi were barelyrecognizable to element. Therefore, the legelements from one individual may be classi-fied in this system as “juvenile/chick”, whilethe wing elements would be labeled “chick.”

While additional immature comparativespecimens are needed to fully understandthe timing of osteological development incormorants, the three individuals listed inTable 1 helped shed light on the age of thearchaeological specimens; those bones clas-sified as chick were likely less than onemonth old at the time of death, while the ju-venile/chicks and juveniles were approxi-mately one to three months old, and theadults were older than three or four months.In ground colonies, DCCO young may leavetheir nests and roam through the colonywhen they are three to four weeks old, andare able to fly and begin fishing on their ownby six to seven weeks (Drent and Guiguet1961; Hatch and Weseloh 1999). Therefore,it is clear that at least some of the immaturecormorants from the Watmough Bay sitewere collected on or near the colonies. To-day, DCCOs breed on Colville Island, just tothe south of Lopez Island, in the Strait ofJuan de Fuca (Fig. 1).

Sub-adult cormorant bones are infre-quent (n = 46) in the upper levels of the Wat-mough Bay site (levels 1-3; above 80 cm).Possible explanations for the decline in im-mature cormorants, including climatechange, tectonic events and human huntingpressure, are discussed elsewhere (Bovy2007). The few sub-adult bones present inlevels 1-3 may indicate the people living atWatmough Bay still encountered immaturecormorants on occasion, or these bonescould be intrusive from earlier deposits.

The Watmough Bay archaeological re-mains provide a much deeper time-depththan historical accounts for DCCOs and maytherefore help inform management of DC-

94 WATERBIRDS

COs in Washington State. In particular, theWatmough Bay assemblage clarifies the his-torical breeding distribution of DCCOs inthe region. The 1,500-year-old DCCO nest-ling bones recovered from the site providethe first reliable evidence for DCCOs breed-ing in the Gulf of Georgia prior to the 1920s,confirming that the 20th century breedingrange expansion of the species in the regionwas a re-colonization event, rather than anew expansion (Drent and Guiguet 1961;Hobson and Driver 1989; Hatch 1995; Wiresand Cuthbert 2006). The colonizers mostlikely expanded from colonies on the outercoast of Washington State (Drent andGuiguet 1961). Possible explanations for thedecline in DCCO breeding populations dur-ing the 19th and early 20th centuries includeincreased habitat disturbance, direct humanpersecution and/or the practice of collect-ing eggs (Drent and Guiguet 1961; Wires etal. 2001; Wires and Cuthbert 2006).

In addition, archaeological evidencefrom the Watmough Bay site and others (e.g.Hobson and Driver 1989) make it clear thatDCCOs were common in the Strait of Geor-gia prior to European colonization. TodayDCCOs are considered to be “overabun-dant” (Wires and Cuthbert 2006) and effortshave been made elsewhere to curb popula-tions of the fish-eating cormorants in orderto protect fisheries (e.g. Sullivan et al. 2006;Duerr et al. 2007). Should similar conflictsbetween DCCOs and the fishing industryarise in the Pacific Northwest, the findingsdiscussed here would help wildlife managersto determine the “natural” DCCO popula-tion levels and inform decisions aboutwhether or not to reduce cormorant popula-tions.

ACKNOWLEDGMENTS

The research was supported by a grant from the U.S.Environmental Protection Agency’s Science to AchieveResults (STAR) program (grant #U-91576301) and aNational Science Foundation Dissertation Improve-ment Grant (#BCS-0242632). Thanks to BMNHC Ar-chaeology staff (P. Lape, L. Phillips, M. Noble) forfacilitating the loan of the Watmough Bay assemblageand photographing the bones. R. Faucett, S. Rohwerand C. Wood provided access to bird skeletons at theBMNHC. R. Meadows, T. Largy and P. Burns (Peabody

Museum, Harvard) and C. Cicero (Museum of Verte-brate Zoology, UC-Berkeley) facilitated long-distanceloans of juvenile cormorant specimens. Advice was pro-vided by J. Baumel, J. Broughton, D. Causey, D. Graysonand S. Wolverton. The manuscript was improved by L.Wires and G. Mayr.

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