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Below is the 2004 Least Tern Survey
Population Survey of the Interior Least Tern On the Mississippi River from Cape Girardeau, Missouri, to Baton Rouge, Louisiana 2004 by Kenneth H. Jones Associate Professor of Biology Dyersburg State Community College 1510 Lake Road Dyersburg, Tennessee 38024 Under Contract with URS Corporation On and between July 22 and July 28, 2004, Kenneth H. Jones, Associate Professor of Biology at Dyersburg State Community College, under contract with URS Corporation, conducted a survey of interior Least Tern (Sterna antillarum athalassos) nesting colonies along the Mississippi River. This annual survey is performed for the Memphis District Army Corps of Engineers and assists the U.S. Fish and Wildlife Service with its census in determining population size and distribution of the interior Least Tern. This survey was the 20th consecutive annual count since the surveys were initiated in 1985 by the Army Corps of Engineers. The survey area extended 777 miles from Cape Girardeau, Missouri (Upper River Mile 53) to Baton Rouge, Louisiana (River Mile 230) (Figure 1). In prior years three types of surveys were performed: towboat, aerial and small boat (Figure 2). The towboat surveys were discontinued in 1995 as were the aerial surveys in 1997 when it became obvious that of the three, the small boat survey yielded the highest and most accurate counts. Past years’ surveys terminated about 7 miles downstream of Vicksburg, Mississippi because early aerial surveys in 1986 indicated a scarcity of sandbars and relatively few terns downstream of Vicksburg. The extra survey time and expense, plus the belief that the coastal least tern population might overlap the interior population further south, warranted stopping the survey at Vicksburg. Recent cooperative initiatives between the Corps of Engineers with state resource agencies and the U.S. Fish and Wildlife Service from each state along the lower Mississippi River developed into habitat restoration meetings. These meetings, chaired by the Lower Mississippi River Conservation Committee, thoroughly reviewed various ways that the Corps could assist the states in constructing diverse habitat structures in the river plus assist in restoring river habitat by opening old, silted-in river channels. Many navigation safety, hydraulic, and biology aspects were discussed as each proposed habitat restoration project site was reviewed at a state meeting. It was evident there were no least tern data below Vicksburg. As a result, all agreed that we needed to know where the tern colonies are downstream of Vicksburg so this data can be incorporated into the overall restoration plans for each state and the river. The Corps was asked to extend the survey reach to thoroughly document Least Tern use. The Corps agreed with this and said the survey range would extend an additional 200 miles to Baton Rouge, Louisiana, as this is the southern limit of the sandbars. The Corps suggested the extended reach be surveyed for at least 3 years to ensure maximum survey coverage. Thus, the 2004 interior least tern survey extends 777 miles from Cape Girardeau, Missouri to Baton Rouge, Louisiana. Since 1997 the surveys have all been conducted by Dyersburg State Community College and Kenneth Jones, Associate Professor of Biology. Other observers and crew members of this year’s survey included Wanda Jones, Mike Thron, John Rumancik, Guy Haglund, Woody Clifton and Marilyn Clifton. This year’s survey yielded a total count of 11,239 Least Terns and 69 nesting colonies. Fifty-eight colonies were identified based on the presence of eggs and/or chicks (Tables 1 and 2). Eleven colonies were identified based on the presence of a large number of nest scrapes, adult behavior and other indicators of likely reproductive effort such as wetting breast feathers, setting inland, carrying fish or intense mobbing of intruders. The largest colonies were located at Nebraska Point Dikes (RM 807), Kangaroo Point Dikes (RM 647), Island #84 Dikes (RM 533) and Opposite Warnicott Landing Dikes (RM 350) with close to 600 or more terns at each site. The smallest colonies were at Terrene Dikes (RM 589) and Baleshed Landing Dikes (RM 491), with just 7 and 12 birds. Numbers of adult and juvenile Least Terns were recorded on data sheets developed by the Corps and based on the Cornell University Bird Registry Form. One data sheet was used for each observation with the following noted: date, time, river mile, latitude/longitude (decimal degrees determined from GPS), number of adult terns, presence of juveniles, chicks and eggs, locations of sandbars, substrate, distance from vegetation and type, weather conditions, nearest river gage readings, and other notes on bird behavior, signs of predation or other disturbance. Foraged fingerling fish dropped within the colony were identified and/or collected. Colony locations were marked on 1998 Flood Control and Navigation Maps of the Mississippi River, 61st edition, USACE. Data sheets and colony locations are found in Appendix A. (Microsoft Access file: password "bird"). The average number of adult terns per colony was 148, with colony sizes ranging from as little as 7 adults to as many as 658. The numbers of eggs per nest ranged from 1 to 3 and many nests were associated with debris wrack lines or in close proximity to small, random pieces of drift. Many adults were observed utilizing other habitats often miles away from the nearest colony locations. These habitats included both still and running water of all depths in the channel, behind dikes, in back chutes, tributary mouths, and fast current against revetted banks on the outside of river bends. The small boat survey was initiated July 22, 2004, 12 days after the river stage at Memphis, Tennessee fell below 12.0 feet (Table 3). The reason being that at higher river stages, many of the more optimal sand and gravel bars for tern nesting habitat are under water. During this 2004 survey the river was exhibiting a slow, continuous fall for every location on the dates surveyed. The survey proceeded downstream during daylight hours without interruption from Cape Girardeau, Mo., to Baton Rouge, La., at an average pace of 130 miles per day. Upon spotting a likely colony site, the boat would head for the greatest concentration of terns, then approach the bar as close as shallow water levels would allow, cut power, and slowly drift with the current. Two or more observers would count birds using 7x35 or 8x40 binoculars. One observer counted terns resting along the waterline, another observer counted birds in the air. After this preliminary count, the boat would beach and one or more observers would walk toward the perceived center of the colony to find evidence of nesting activity, while others would fan out in different directions to traverse the entire colony area. The presence of eggs or chicks was considered confirmation of nesting activity. Intense mobbing, wetting of breast feathers, and the presence of fresh scrapes were also considered to indicate an active nest colony at the 11 sites where eggs or chicks could not be confirmed. Once a colony was located, several counts were made, both by observers stationed at the boat and those penetrating the colony. The highest number of birds sighted by any one observer was recorded as the total number for the site, but only when at least two observers were within 5% of the same figure. Only in colonies dispersed over ½ mile in length or with back chutes not visible to all observers, were numbers counted by individual observers added together to obtain a total count. Fledged juveniles were noted at 7 colony sites. Since it is usually impossible to discriminate between flying juveniles and adults when determining total colony counts at long ranges, those 7 colony adult counts most likely include some juveniles. As with previous surveys, observations within the colony were performed as quickly as possible (< 15 minutes) to minimize the disturbance time and limit the exposure of any chicks and eggs to the intense summer heat. Though mobbing behavior was often intense upon the observers first entering the colony, it ceased almost immediately as soon as the observers retreated. The highest counts usually occurred during the initial waterline count or upon the first few minutes of mobbing when most, if not all, of the adults in the colony would join in to dissuade the intrusion. Nesting adults, nest scrapes, nests with eggs and chicks were recorded as well as other features of the habitat. Eleven thousand two hundred thirty-nine (11,239) Least Terns were recorded at 114 locations (Table 1) (Figure 1). Of these, 69 sites were identified as nesting colonies, 31 as resting bars only and 14 observations were of birds flying over feeding areas or in transit along the river. Of the identified nest colonies, 58 had eggs and/or chicks present, 11 had neither chicks nor eggs, 7 had chicks but no eggs, 51 had eggs but no chicks, and 9 had both chicks and eggs present within the colony. As with previous years, the typical tern nest colony was located on an unattached sand and/or gravel bar usually associated with a dike field. Isolation and remoteness appeared to be the main selection criteria. The larger colonies were hundreds of acres in size, while some of the smallest were just a few acres. Most of the sand and gravel bars containing colonies were associated with dike fields, however 11 were located on bars away from dikes, either on the outside of bends, below large islands or more often point bars on the inside of bends without dikes. As before, the least likely sandbars to be utilized by nesting terns were those that were directly attached to the riverbank. Only 5 colonies met this criteria. The locations of the colonies as indicated on the 1998 Navigation Maps (Appendix A-I) should be viewed as only approximations based on river mile markers visible from or nearby the sites. Since many sand and gravel bars do move or change shape often, such features on the maps do not necessarily correspond to the actual conditions at the time of the survey (hence the occasional colony indicated in open water). For exact colony locations the GPS latitude/longitude coordinates (decimal degrees) are the most accurate and should be referenced as occurring at the water’s edge on the channel side of the colony (except when specified otherwise on the data sheets). Most colonies were located on the high centers or distributed evenly across the bars showing no preference for river vs. chute sides. The colonies’ proximities to the nearest water (least distance from any nest with eggs to the waterline) varied from 0 to 1,000 feet and averaged ~292 feet. Though some colonies were densely populated, with scrapes occurring within a few feet of each other, many more colonies were extremely dispersed with nests occurring hundreds of feet apart and the colony extending as far as a mile or more across the larger sandbars. Major vegetation was absent or far removed (>300 feet) from 50 colony sites, but 19 did have sparse stands of sapling Cottonwoods (Populus deltoids) and/or Black Willows (Salix nigra) within 300 feet of active nests. The other colonies with vegetation had only very sparse, recently emerged grasses and herbs in small patches within the colony. Most open water within 2 miles of active colonies appeared to be utilized by foraging terns. These sites included swift current on revetted outside bends, slack water between dikes, chutes, mouths of tributaries and even mid-channel currents. Predation on terns, their eggs or chicks was noted at 3 colony sites. Coyotes were responsible for at least 1 confirmed chick mortality at Kangaroo Point Dikes, RM 647 (Appendix-II-62). A Great Blue Heron was seen capturing and fleeing a colony with a tern chick in it’s beak at Mhoon Bend, RM 686 (Appendix-II-55). At RM 740, Loosahatchie Bar Dikes (Appendix-II-38), 3 dead adult terns and 1 purple martin, spent shotgun shell casings, and clay target fragments indicated recent mortality from human recreation. Interestingly enough, during last year’s survey, a domestic dog accompanied by humans apparently caused chick mortality at Wrights Point Dikes, RM 819.5, a popular recreation site just across from Ed Jones Boat Ramp. This year, with continued signs of recreational use, the site was no longer being utilized by Least Terns, other than a few birds resting at the water line (Appendix-II-25). Another possible colony abandonment occurred at Densford Bar, RM 754.5 (Appendix-II-36). Historically one of the more prolific tern-breeding colony sights, this year Densford Bar was silent, with only 3 terns resting at the upper end, instead of 700 counted in 2003. Both sites, Densford Bar and Wrights Point Dikes have well maintained, public boat ramps close by, and have long been noted for heavy recreational use in previous survey years. The presence of coyote or dog tracks was noted at 16 sites and still lends strong support to the contention that coyotes and/or feral dogs are one of the more common predation threats to nesting Least Terns along the Lower Mississippi River. Of 69 colonies, 12 had evidence of recent intrusion by humans using boats or ATVs to access the sites. Another historical colony site at Racetrack Towhead Dikes, RM 431, was abandoned in 2003 and 2004 probably due to the encroachment of willows and the absence of bare sand. However, just 2 miles downstream at Below Racetrack Dikes, RM 429, a heretofore unobserved colony site with 91 terns had been established, and may have been there in the 2003 survey had it covered a few more miles. Other potential predators, or their sign, seen within colonies during this year’s survey included Great Blue Heron (Ardea herodius), Egrets (Casmerodius, Egretta, Bubulcus), Common Crow (Corvus brachyrhynchos), Turkey Vulture (Cathartes aura), Black Vulture (Coragyps atratus), Mississippi Kite (Ictinia mississippiensis), and Bald Eagle (Haliaeetus leucocephalus). Other bird species observed in close proximity to Least Tern colonies included Canada Goose (Branta canadensis), Killdeer (Charadrius vociferus), Caspian Tern (Sterna caspia), Black Tern (Chlidonias niger), Willet (Catoptrophorus semipalmatus), Greater Yellowlegs (Tringa melanoleuca), Spotted Sandpiper (Actitis macularia), Pied-billed Grebe (Podilymbus podiceps), Anhinga (Anhinga anhinga), Double-Crested Cormorant (Phalocrorax auritus), Green-backed Heron (Buterides striatus), Little Blue Heron (Egreta caerulea), White Pelican (Pelecanus erythrorhyncos), Cliff, Bank and Rough-winged Swallows (Hirundinidae), Purple Martin (Progne subis), Lesser Golden-Plover (Pluvialis dominica), Least Sandpiper (Calidris minutilla), and other, small peep sandpipers (Calidris sp.). Rare, out of normal range, sightings of Black-necked Stilt (Himantopus mexicanus), White Ibis (Eudocimus albus), and Black Skimmer (Rynchops niger) were also noted. Fingerling size fish of Gizzard Shad (Dorosoma cepedianum), Threadfin Shad (Dorosoma petenense), Largemouth Bass (Micropterus salmoides), Bighead Carp (Hypophthalmichthys nobilis) and Silver Carp (Hypophthalmichthys molitrix), and many unidentified minnows (Cyprinidae) were found at multiple colonies and are presumed to have been dropped by foraging adults. Even though this year’s survey covered almost an additional 200 river miles, the total number of colonies only increased from 68 in 2003 to 69 in 2004. One possible explanation is there was a minor, late spring flood where the river rose above the 20 ft. mark on the Memphis gage, May 31, 2004, crested June 10 at 27.8 ft., and stayed above 20 ft. until July 2, 2004. This severely limited the number of sandbars available for nesting during the June breeding cycle and colonies capable of producing hatched chicks by the time of the survey. Indeed, only sandbars with the necessary vertical height for June egg-laying (10 or more feet above the river stages at the time of the survey) were found to have Least Tern chicks present the last week of July. The increase in numbers of Least Terns counted in the Lower Mississippi River Valley is probably the result of many things. It may be the result of a learning curve and increased skills acquired over the years by the observers doing the counts, more time spent surveying colonies, better equipment (faster boats, better binoculars, e.g.). The additional 2,178 terns counted below Vicksburg, when subtracted from the total count, still yields 9,061 birds compared to last years count of the same river reach of 8,082. It may be that some of the colony counts had many more fledged juveniles that were counted as adults, though the author does not believe this to be the case, especially due to the delayed hatch caused by the June high water. Or, it may be that the population of Interior Least Terns is really on the increase with higher numbers of total colonies (69), higher average numbers of birds per colony (148), and more colonies with very large (600+) concentrations of terns. These numbers are especially impressive in view of the fact that 3 historically productive colony sites were not occupied during the latest 2004 survey. |
