Breeding abundance of colonial waterbirds on the lOlllslana-VllS' ' ' '" sis' slppl-x!aDama' ' " -- coast

A documentation of "the extraordinary frequency and abundance of colonial waterbirds breeding in this rich deltaic area."

John W. Portnoy

XTENSIVESWAMPS, andes- available habitat. Results have neces- chops niger) colonies, we could count tuaries of the sarily omitted large segments of the total adults present at each colony from alluvial fan provide a diverse and ex- overall coastal colonial bird population photographs. tremely productive array of feeding and and are of limited value for discerning Total nest counts were applied to the nestingsituations for the colonial waders coast-widepopulation trends. rare nesters, Reddish Egret (Dichroma- and seabirds of the north coast of the Therefore, as part of a U.S. Fish and nassa rufescens), Sooty Tern (Sterna . Cypress-Tupelo(Taxo- Wildlife Service project to establish a fuscata), Gull-billed Tern (Gelochelidon d:um-Nyssa) , fresh, brackish complete data base of colonial bird nilotica); and to small and diffuse sea- and saline marshes, and coastal spoil abundance for all of the bird colonies on bare ground: Least and barrier islands all harbor large coast, the Cooperative Wild- Tern (Sterna albifrons), Forster's Tern breeding colonies. life ResearchUnit (LCWRU) was con- (Sterna forsterO, and some Black Skim- Before the late 1950s, numerical abun- tracted to locate and census all colonies mer colonies. We walked transects dance was assessedinfrequently on but a within the coastal and islands through shrub heronries, wherever the few well-known and accessible colonies. from SabineLake to Mobile Bay. substratewould supportour weight, and Although many early naturalistsmeticu- collected10% samplesof activenests on lously described the nesting of rarely METHODS the huge, island colonies in breeders, more common species were coastal bays. Confidence limits mentioned incidentally, and were rarely ELOCATED MOST COLONIES during calculated from transect samples on censused. approximately 100 flight hours of island heronries indicated a More recently biologists and others fixed wing aerial survey, conducted at high reliability for this method. We also have realized that it is the more abun- 4-to 6-week intervals March 13-August used belt transectsto sample Laughing dant speciesthat have the greatesteffect 4, 1976. Although we concentrated ef- Gull (Larus atricilla) nests concealedin on nutrient and energy cycling in forts on the coastal marshes and islands vegetation. swampsand .Thus, changesin southof theIntracoastal Water.way, we Small herons, egrets, and ibises nest- status at geographiccenters of breeding also searched swamps around Lake ing in swampsor freshmarshes were vis- abundance may be more important than Maurepas and in the Atchafalaya basin. ually estimated from fixed or rotary geographic limits of breeding distribu- To estimate abundance at such diverse wing aircraft. This method was of limi- tions for indicating overall population nesting aggregationsas treetop ted reliability simply because dark- trends and for evaluating the health of heronriesand barrier beach terneries, we colored species, Black-crowned Night coastal ecosystems. drew from a battery of censusand samp- Heron (Nycticorax nycticorax), Louisi- From 1958 to 1975, Alexander Sprunt ling techniquesfor eachparticular situa- ana Heron (Hydranassa tricolor), and IV and John Ogden of the National Au- tion. Aerial photographywas applied to White-faced Ibis (Plegadis chihO, and dubon Society conducted aerial surveys conspicuousnesters in the open or atop individuals nesting under vegetation, of many Louisiana heronrieswest of the shrubs or trees. Because individual incu- were difficult to seefrom aircraft. Also, Mississippi River; these researchers bating Great Egrets (Casmerodius as with any bird count, numbers were tallied over 200,000 breeding waders in albus), Sandwich Terns (Sterna sand- immediately affected by time of day, the colonies surveyed in 1975. Jacob vicensis), Royal Terns (Sterna weather, and feeding conditions. Valentine, of the U.S. Fish and Wildlife maximus), and Caspian Terns (Sterna To document seasonal changes in Service, has studied seabird besting on caspia) were easily distinguished and abundanceand to determine the peak of the Shell Keys, Isles Dernieres, and counted on developedprints, photogra- nestingfor eachcolonial species,we sur- Chandeleur Islands of Louisiana from phy yielded highly accuratenest counts. veyed most colonies at least three times the early 1960sto the present. These ef- Although we could not separate incu- during the nestingseason. Between Feb- forts have been limited to single annual bating adults from loafing birds on aeri- ruary and August 1976 we made a total surveys of only a small portion of the al photographsof Black Skimmer(Ryn- of 476 colony visits. Most colonies were

868 American B•rds, September1981 found when adults were engagedin incu- largely herbaceous . again active in 1976. We found smaller bation, and surveillance continued until Nevertheless,the importanceof the rela- groups nesting within fresh and salt fledglingsdeparted. tively small , and as yet un- marsh heronties. measured but limited area of coastal RESULTS AND DISCUSSION beaches,was clearly indicated. Little Blue Heron (Florida caerulea). Notes on the nesting habits of each This mainly freshwater species nested ELOCATED 168SEABIRD and wader speciesare arrangedin order of breeding most abundantly among Snowy Egrets colonies within the coastal wet- abundance below. Waders and seabirds on shrubsin pondsin the cypress-tupelo lands of the North Gulf Coast; 88 of are treated separately. swamps. A few small nesting groups these were principally occupied by wad- were found in black mangrove heron- ers and 80 by seabirds. Especially im- Louisiaua Heron. Although principal- ries. portant nesting areas were mapped by ly estuarine, this abundant waterbird habitat type (see Fig. 1). also nested in large numbers in fresh Great Egret. Always atop the canopy, Table I is a summaryof nestingabun- water situations. Some black mangrove this egret nested with about equal fre- dance by speciesand by habitat type. All (Avicennia germinans) heronries con- quency in all salinity and habitat types. nest counts were converted to bird tained over 5000 active nestsin May. One swamp colony contained 5000+ counts by multiplying by two. Although nestsin March. Many mixed-speciesher- multiple counts were collected for most Snowy Egret (Egretta thula). More a onries began in March as Great Egret specieson most colonies, a single num- fresh marsh wader than the Louisiana colonies(see Fig. 2). ber, representingthe highest adult bird Heron, this egret nested in shrubs and count obtained using the most reliable appeared to favor nest sites toward the Black-crowned Night Heron. Black- census technique was totalled for each center of mixed-speciesaggregations. crowneds nested most commonly in the specieson each colony. Table I givesthe salt marsh and largest colonies occurred summation of these maximum counts Cattle Egret (Bubulcusibis). This "in- in black mangrove thickets on insular for each colonial species. vader" species, which only began marsh fragments or behind barrier Thirty-one percent of all swamp and nestingin Louisiana in 1956, was present beaches. Several colonies comprised marsh nestingoccurred in cypress-tupelo in most swamp, fresh marsh, and brack- 1800+ active nests in May. swamps, 23% was in fresh marshes,9% ish marsh heronties. Somewhat sur- in brackish marshes, and 37ø7oin salt prisingwas the discoveryof 200+ pairs White-faced Ibis. Although Glossy marshes. These habitat types comprised nesting among other waders in a black Ibises (Plegadis falcinellus) were ob- roughly 29, 22, 23, and 16 percent, re- mangrove heronry of Black Bay, Loui- served on several White-faced Ibis colo- spectively, of total coastal wetlands, in- siana. nies from Timbalier Bay, Louisiana to dicating a decidedpreference by coloni- Cat Island, Alabama, we could not dis- ally nestingbirds for salineover brackish White Ibis (Eudocimus albus). A tra- tinguish nestsof the two speciesduring marshes. This preference probably re- ditional and very large colonyof approx- transect sampling and numbers were flected the scarcity of suitable wader imately 30,000 nests, in the cypress combined.(Only a few individual Glossy nest sites, i.e., woody vegetation, in the swamp north of Lake Maurepas was Ibises were definitely identified at each

/ [

• Areaso,Concentrated N•tlng • Swamp i_[•'•Fresh Marsh • BrackishMarsh Gulf Of Mexico • SaltMarsh

Fig. 1. Gulf Coast study area showing wetland habitat types and areas of concentratednesting.

Volume 35, No. 5 869 Table 1. Colonial waterbird nesting abundance by habitat type, Louisiana-Mississippi-Alabama included in Table 1). In the last decade, Coasts, 1976. Numbers indicate breeding adults. the breeding range of spoonbfilshas ex- panded from west to east across the Fresh Brackish Salta Coastalb southern Louisiana marshes. Spectes Swamp marsh marsh marsh beach Total

Brown Pelican 0 0 0 48 0 48 Anhinga (Anhinga anhinga). Because

Ohvaceous Anhingasnested in small scatteredcolo- Cormorant 1,092 5,780 788 0 0 7,660 nies in swamps,we were unable to ade- quately search out and censusthis spe- Anhlngac 2,402 180 0 0 0 2,582 cies in the time available. I therefore Great Blue Heron 9,258 860 0 0 0 10,118 suspectthat we grossly underestimated Great Egret 22,956 18,286 15,138 20,564 0 76,944 its overall abundance. Nests were placed Snowy Egret 8,074 39,463 15,932 53,018 0 116,487 high in shrubsor trees, and often among ReddishEgret 0 0 0 299 0 299 nesting Great Egrets. Cattle Egret 56,300 30,474 2,400 2,212 0 91,386 ReddishEgret. At the northern limit Lomsiana Heron 5,296 9,315 13,294 112,000 0 139,905 of this egret's breedingrange, the Loui- Little Blue Heron 45,288 33,594 250 2,206 0 81,338 siana salt marsh has historically received Black-crowned limited nesting activity. However, we N•ght Heron 51 1,030 4,604 14,729 0 20,414 found severalsmall groups on insular Yellow-crowned mangroveheronties at the edgeof Chan- Night Heron e 153 100 0 0 0 253 deleur Sound, and in coastal bays as far Plegadis spp. (mostly west as the Isles Dernieres. Earlier ob- Wh•te-facedIbis) 0 5,586 0 6,909 0 12,495 servers found greatest abundance on White Ibis 63,870 12,653 134 11,095 0 87,752 North Island of the Chandeleurs; how- RoseateSpoonbill 0 1,275 1,346 0 0 2,621 ever, we found a group of 100+ pairs in a mangroveheronry in Black Bay. Laughing Gull 0 0 0 14,318 41,768 56,086 Gull-billed Tern 0 0 0 20 159 179 Yellow-crowned Night Heron (Nyc- Forster's Tern 0 100 6,718 12,196 202 19,216 tanassaviolacea). Like the Anhinga, th•s Common Tern 0 0 0 0 12 12 specieswas grosslyunderestimated ow- ing to its habit of nesting in small, in- Sooty Tern 0 0 0 0 20 20 conspicuouscolonies in the swamps.It Least Tern 0 0 0 14 14,290 14,304 also nested sparingly among other Sandwich Tern 0 0 0 0 55,682 55,682 waders in the fresh marsh. Caspian Tern 0 0 0 194 224 418 Royal Tern 0 0 0 584 20,742 21,326 Brown Pelican (Pelecanus occidental- is). The only extant Louisiana colony Black Skimmer 0 0 50 4,303 25,627 29,980 consists of introduced Florida birds Total 214,740 158,696 60,654 254,709 158,726 847,525 nesting on a shell berm at the edge of a mangrove heronry in Barataria Bay.

alncludesSpartina alterniflora-A vicennia germinans marsh plus adjacent shell berms Laughing Gull. Most abundant blncludesunvegetated coastal beaches and spoil areas amongthe seabirds,we found the largest Cgrosslyundersampled in their principalswamp nesting habitat colony which comprised 17,000 + nests, among the beach dunes of the Isles Der- location.) Plegadis spp. ibises nested in Oiivaceous Cormorant (Phalacro- hieres. Smaller but more numerous colo- fresh and salt marshes from Texas to corax olivaceus). This was the only niesoccurred at the seawardedge of the Alabama; the White-faced always pre- speciesof cormorantfound nestingin St. Bernard Parish, Louisiana, salt dominated, even as far east as Cat Is- the study area, with most nesting in marsh. Two distinct colony types were land, Alabama, indicating a significant fresh marsh heronries in extreme apparent: those containing nests con- eastward range expansion for the southwestern Louisiana. Colonies had cealed under beachgrasson the barrier species.In mangroveheronries Plegadis up to 2000 nestsin April, and nest sites beaches, and those composed of nests spp. nestedmore often upon oystergrass were in the tallest woody vegetation built on top of oystergrassor shellon the (Spartina alterniflora) than in shrubs. available in heronties. salt marsh.

Great Blue Heron (Ardea herodias). Roseate Spoonbill (Ajaia ajaja). This Sandwich Tern. By aerial photo- Almost exclusivelya swamp nester, this is another speciesthat was restricted to graphic count, we censused20,367 incu- heron was first to begin nestingof any southwestern Louisiana. On the four bating adults (=nests) on Curlew colonial waterbird and built nests atop colonieswhere actual nesting was veri- Island, Chandeleurs May 19; this very mature cypress or tupelo in company fied, breedingadult countsranged from likely represented the largest single with Great Egrets. One swamp colony 375 to 1346. Loafing adults were seenon Sandwich Tern colony in North south of New Orleanscomprised 2000 + heronties as far east as Vermilion Bay America. We censused smaller colonies active nests in March. (only adults associatedwith nests were on spoil west of Petit Bols Island, on

870 American Birds, September1981 near Pascagoula, Mississippi. Besides the Chandeleur and Isle au Pitre groups, we noted colonies on spoil west of Petit Bois Island,and as far west as Atchafa- laya Bay, Louisiana. One of the Atcha- falaya Bay coloniescontained 66 nestsin June. Gull-billeds always nested among Black Skimmers and commonly dug a nest scrape against chunks of driftwood.

Sooty Tern. A few pairs of this species have traditionally nested on the Chan- deleur Islands; we found 20 adults nesting in this area in 1976. Interesting- ly, a singleadult Sooty Tern was observ- ed at a tern and skimmer colony near Petit Bols Island June 10. Fig. 2. Typicalblack mangrove-oystergrassheronry in Louisiana'ssalt marsh.Great Egrets are visible as white spots on the darker vegetation (mangrove) in the background. Louisiana Common Tern (Sterna hirundo). Our Herons, Snowy Egrets and Black-crowned Night Herons also nested in mangrove on this most uncommon breeding tern nested island;Forster's Ternsnested in oystergrass(lighter-colored vegetation) in the foreground. only on Dauphin Island Beach. There we North Island, East Timbalier Island, and smaller colonies, containing fewer than found two clutchesof eggsand several Shell Keys National Wildlife Refuge. 500 nests, were quite common on Loui- adults in breedingplumage June 15. This species always nested in dense siana's barrier beachesand on unvege- groups in company with Royal Terns tated spoil areas. Approximately 14% of CONCLUSIONS (see Figs. 3 and 4). nesting Least Terns utilized spoil as a nest substrate. XTENSIVEAND INTENSIVE coastwide Black Skimmer. We found largest col- aerial search, and intensive aerial onies, containing up to 4800 adults, on Caspian Tern. Small colonies were ac- photographic censusing and ground the barrier beaches of the Isles Der- tive throughout the summer either at the sampling, enabled us to document the nieres, Timbalier, and Chandeleur periphery of Sandwich-Royal Tern colo- extraordinary frequencyand abundance chains, and on spoil areas in Atcha- nies on barrier beaches, or on shell of colonial waterbirds breeding in this falaya Bay and near Southwest Pass of berms in the St. Bernard Parish salt rich deltaic area. Speciesabundance was the Mississippi River. Of the 37 colonies marsh. estimatedon most coloniesin 1976 using located, nearly one third occurred on methods that representativelysampled shell berms on salt marshes at the edge Gull-billed Tern. Small colonies were both conspicuous and cryptic species. of Chandeleur Sound. previouslyreported on the Chandeleurs, Repeatability was emphasized by Isles au Pitre in St. Bernard Parish, and avoiding highly subjective and biased Royal Tern. This speciesnested either in huge colonies with its congener, the Sandwich Tern, on barrier beaches, or alone in smaller groups on salt marsh shell berms. The Curlew Island Thaias- seus spp. colony included 7210 Royal i Tern nests May 19.

Forster's Tern. A marsh dweller, this speciescharacteristically nested on drif- ted material on the salt marsh, and often near mangrove heronties. Most colonies contained fewer than 300 nests, but Grassy Island, in MississippiSound, in- cluded 2750 incubating adults (= nests) in May. Although this was the first sea- bird to begin breeding (in April), tidal inundation and consequentnest failure prolonged nesting into July 1976.

Least Tern. Largest colonies, with up to 2000 nestsin each, occurred on public bathing beachesin Pass Christian, Long Beach, and Gulfport, Mississippi, and Fig. 3. Closeup of SandwichTern colonyon CurlewIsland, Chandeleurs,showing uniform on Dauphin Island, Alabama. Much nest spacing. Eggs are approximately 30 cm apart.

Volume 35, No. 5 871 .%

Fig. 4oIncubating Royal, $andwicl• and Caspian terns, and Black Skimmers on East Timbailer Island, Louisiana June 26, 1976.Royal and Sand- wicl•terns are uniformly and densely spaced at tilecenter of tilepl•otOo Black Skimmers are apparent around tile peripl•ery, and Caspian Terns are located at ".4 "o visual estimateswhenever possible. parableinventories can be repeatedin feredmany helpful comments. Ground Thus,a morecomplete and reliable data the near futureto improvecensus tech- censuseson many offshore islands base was establishedfor comparison niquesand to determineimportant pop- would have been abandonedif not for with futureinventories. ulation trendson this ecologicallyuni- the skill, interest,and patienceof our We believethis researchtakes an im- queand immensely productive coast. floatplane pilot, MarvinMusgrove, who portantfirst steptoward monitoring the landedus in remoteareas. Especially ap- effectsof increasedhuman technology ACKNOWLEDGEMENTS preciatedwere the comments and timely on colonialbirds in this coastalregion. suggestionsof Robert B. Hamilton, of The colonialwaterbirds in general,and I am indebtedto severalindividuals LouisianaState University, who advised the easilycensused Great Egrets, Royal for contributionsthat enhancedthe ef- me on manyaspects of logisticplanning, Terns, and SandwichTerns in par- ficiencyand completenessof the field data collection,and analysis. ticular, representsensitive and useful work. Project leader John D. Newsom bioticindicators of habitatdegradation; providedadvise and logisticsupport. J. their importance as indicator species Brent Ortego and Robert M. Ruhe, of shouldincrease along with ever-expand- LouisianaState University,assisted with --Cape Cod National Seashore, ing coastaltechnology. Hopefully corn- all phasesof the field inventoryand of- South Wellfleet,MA 02663

872 American Birds, September1981