Consequences of using Conspecific Attraction in Avian Conservation: A Case Study of Endangered Colonial Waterbirds

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1 Consequences of using Conspecific Attraction in Avian Conservation: A Case Study of Endangered Colonial Waterbirds Author(s) :Michael P. Ward, Brad Semel, Cindi Jablonski, Charlie Deutsch, Vincent Giammaria, Sarah B. Miller and Benjamin M. McGuire Source: Waterbirds, 34(4): Published By: The Waterbird Society DOI: URL: BioOne ( is a nonprofit, online aggregation of core research in the biological, ecological, and environmental sciences. BioOne provides a sustainable online platform for over 170 journals and books published by nonprofit societies, associations, museums, institutions, and presses. Your use of this PDF, the BioOne Web site, and all posted and associated content indicates your acceptance of BioOne s Terms of Use, available at page/terms_of_use. Usage of BioOne content is strictly limited to personal, educational, and noncommercial use. Commercial inquiries or rights and permissions requests should be directed to the individual publisher as copyright holder. BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, research libraries, and research funders in the common goal of maximizing access to critical research. PersonIdentityServiceImpl

2 Consequences of using Conspecific Attraction in Avian Conservation: A Case Study of Endangered Colonial Waterbirds MICHAEL P. WARD 1,*, BRAD SEMEL 2,CINDI JABLONSKI 3,CHARLIE DEUTSCH 4, VINCENT GIAMMARIA 4, SARAH B. MILLER 4 AND BENJAMIN M. MCGUIRE 4 1 Department of Natural Resources and Environmental Sciences, University of Illinois, Urbana- Champaign, 1102 S. Goodwin Ave. Urbana, IL, 61801, USA 2 Illinois Department of Natural Resources, 8916 Wilmot Road, Spring Grove, IL, 60081, USA 3 Applied Ecological Services, Smith Road, Brodhead, WI, 53520, USA 4 US Army Corps of Engineers, Rivers Project Office, 301 Riverlands Way, West Alton, MO, 63386, USA *Corresponding author; mpward@illinois.edu Abstract. Through the use of conspecific models and vocalizations, populations of conservation concern can be established in locations where limiting factors may be controlled or mitigated, assuming managers can both identify and create high-quality locations. From 2003 to 2008, conspecific attraction was used to establish populations of the state-endangered Forster s Tern (Sterna forsteri) in northeastern Illinois, USA. In 2009 and 2010, similar techniques were used with the federally-threatened Least Tern, (Sternula antillarum) near the confluence of the Missouri and Mississippi Rivers in Missouri, USA. At both locations, managers attempted to control factors that may limit tern reproductive success. While in most cases nesting populations were established, in some cases resulting in the greatest documented reproductive success in the region for decades, nest predation the year after the colonies were established was significantly higher than in the year the colony was established. The establishment of colonies attracted a variety of predators, some of which gained access to the colonies and predated tern nests. Conspecific attraction behavior may be a strategy used by birds to stay one step ahead of nest predators, and the repeated use of conspecific attraction by managers may result in individuals nesting at a site with high rates of nest predation. As a conservation tool, conspecific attraction should only be used in situations where nest predators can be effectively controlled. Received 4 May 2011, accepted 22 July Key words. conspecific attraction, Forster s Tern, Least Tern, nest predators. Waterbirds 34(4): , 2011 Over the last decade there has been a rapid increase in research towards understanding the role of conspecifics in habitat selection among birds (Alhering et al. 2010). Over this same time period, managers have increasingly used conspecific attraction to establish populations of birds in predetermined locations (e.g., Ward and Schlossberg 2004). Conspecific attraction techniques in which conspecific models and/or vocalizations are deployed have been shown to facilitate the settlement and nesting of numerous species, but have been most effective among colonial waterbirds (e.g. Atlantic Puffins, Fratercula arctica, Kress 1983; Least Terns, Sternula antillarum, Kotliar and Burger 1984; Burger 1988). By definition, colonial birds prefer to breed near conspecifics; therefore mimicking the presence of conspecifics should be an effective management tool in establishing new colonies. Many species of colonial waterbirds have experienced significant population declines (e.g., interior Least Terns, Thompson et al. 1997). These populations have been devastated by degradation of nesting habitat (Thompson et al. 1997), changes in the hydrology of rivers (Sidle et al. 1992), environmental contamination (Ward et al., 2010) and nest predation (Rimmer and DeBlinger 1992). However, suitable breeding areas for these species exist or degraded areas can be restored. Given the diversity and extent of these limiting factors, conspecific attraction techniques provide an attractive tool for use in establishing nesting populations where these impediments are either absent or can be mitigated. Many colonial species that breed in large colonies have high site fidelity (e.g., Dittmann and Becker 2003), with breeding colonies present at a location for decades (Nisbet and Cam 2002). However, some 476

3 colonial waterbirds typically have smaller, more ephemeral, colonies. For example, the average lifetime of a Forster s Tern (Sterna forsteri) colony in Louisiana was 4.1 years (Visser and Peterson 1994) and Least Tern colonies are known to be ephemeral in nature (Burger 1984). Also, species with ephemeral breeding colonies exhibit lower breeding site fidelity as compared to other colonial terns that nest in large colonies (e.g., Least Terns; Renken and Smith 1995). Colonial species with low site fidelity should exhibit a high degree of conspecific attraction; due to the low probability of locating a new colony, especially for relatively rare species with ephemeral nesting habitats. Given the ecology and behavior of colonial waterbirds, coupled with the tenuous conservation status of several species, we used conspecific models and vocalizations to investigate whether this technique could be used to establish nesting populations of the federally-threated Least and the Illinois state-endangered Forster s Terns in Illinois and Missouri. We then monitored these populations from two to four years, respectively, to evaluate how the productivity of these colonies changed through time. In the context of this study, we discuss the implications of using conspecific attraction to establish and manage species of conservation concern. METHODS Conspecific Attraction of Forster s Terns Between 2002 and 2008, we investigated whether conspecific vocalizations and models could be used in the re-establishment of Forster s Tern colonies in northeastern Illinois. While Forster s Terns had been reported breeding in northeastern Illinois for over 100 years (Ridgway 1889), they had infrequently fledged young, and had been extirpated as a nesting species in Illinois for over six years prior to this study. Four large inland glacial lakes were selected as study sites because they represented typical wetland nesting habitat for this species (McNicholl et al. 2001). The Grass Lake site was an artificial island recently created using geotextile fabric and spoil dredged from nearby navigational channels ( N W). The Lake Elizabeth study site consisted of two islands of floating vegetation ( N W). At the final two sites, Redwing Slough ( N W) and Fourth Lake ( N W), no islands were CONSEQUENCES OF CONSPECIFIC ATTRACTION 477 present, so we deployed twelve artificial floating nesting platforms similar to the ones used for Black Terns (Chlidonias niger) in Wisconsin (Shealer et al. 2006). The platforms were secured to concrete blocks and located near duck blinds that provided loafing sites and additional nesting habitat. Both the duck blinds and platforms were approximately 120 meters from the shore and the islands at the other two sites were over 250 meters from the shore. At these study sites twelve models of Forster s Terns were deployed, together with two call boxes, just prior to the anticipated return of migrating birds in mid- April. The plastic-resin decoys were crafted to resemble the terns. The call boxes were solar-powered CD players (see Ward and Scholssberg 2004 for details) that broadcast a series of Forster s Tern vocalizations (National Geographic Bird Songs). Calls were played from 05:00-07:00, 09:00-12:00, and 17:00-19:00 hours. The conspecific attraction techniques were used between 2003 and 2006 and all sites were monitored weekly from 2002 to Conspecific Attraction of Least Terns From 2008 to 2010, we investigated the use of conspecific vocalizations and models in the re-establishment of the interior Least Tern. We created a floating sandbar using two deck barges (~140 m), which provided protection from flooding and mammalian predators. The sandbar was located just north of the confluence of the Missouri and Mississippi Rivers, at the US Army Corps of Engineers, Riverlands Migratory Bird Sanctuary ( N W). We used game callers (Foxpro, Lewistown, PA) powered by a solar-charged deep-cycle battery to broadcast Least Tern vocalizations over the entire 24-hr period. Commercially available Least Tern vocalizations (National Geographic) were used, as well as recordings from Least Terns in Yucatan, Mexico (A. Celis-Murillo). The vocalizations from birds in Mexico were used to supplement the array of vocalizations and under ideal situations vocalizations from local individuals may be warranted. Twenty Least Tern models were positioned on the barges prior to spring migration in mid-april. Tern models were purchased from Mad River Decoy (Waitsfield, VT). The location of the project site is within the historical breeding range of the species (Thompson et al. 1997), but 75 km north of the most recently-documented breeding location of the species along the Mississippi River. Monitoring and Observations of Forster s and Least Terns Both the Forster s and Least Tern study sites were monitored every four to five days to determine if individuals were attracted to the conspecific cues and to document attempted breeding efforts. Once tern activity was noted, the site continued to be monitored every four to five days to determine nesting success. The sites were most often monitored from boats and the colonies were only entered to investigate potential nest predation events or at the end of the season to band fledg-

4 478 WATEBIRDS lings with USGS leg bands and unique color bands. In the case of the Forster s Tern colonies trail-master cameras were used to identify mammalian and avian predators. We used a Fisher Exact test to compare the difference in fledging success between the initial year of conspecific attraction and the subsequent year. RESULTS Forster s Terns Forster s Terns were readily attracted to the areas where conspecific models and vocalizations were deployed. The population of Forster s Terns increased from two individuals at the four sites the year prior to the study, to at least 100 individuals (Table 1). Forster s Terns experienced high initial reproductive success, although the probability of fledging young decreased significantly in the second year of colony establishment (G adj = 89.44, df=1, P <0.01, Table 1). In year two at all sites, nest predation became a significant factor. In each case it was not only a single species, but rather a suite of predators that eliminated all reproductive effort in the colony. Predators identified by trail cameras, observations, scat, foot prints, and necropsy included Ring-billed Gulls (Larus delawarensis), Herring Gulls (Larus argentatus), Great-horned Owl (Bubo virginianus), Sandhill Crane (Grus canadensis), Black-crowned Night-heron (Nycticorax nycticorax), Great Blue Heron (Ardea herodias), and American Mink (Neovison vison). Other sources of nest failure included floods, usurpation of nesting sites by Mallards (Anas platyrhynchos) and competition with Black Terns for limited nest platforms. Least Terns Least Terns increased from no birds present in 2008 to 32 individuals in 2009, the first year of conspecific attraction. Twelve nests were also found in 2009, producing 27 fledglings. In 2010, the second year conspecific cues were used the number of adults increased to 41 individuals and there were 37 nests. However, in 2010 no nests were successful because a Great Blue Heron depredated 19 young resulting in the colony being deserted, and at least 31 eggs were abandoned. Consequently, the probability of fledging young decreased from the initial year to the second year of the study (G adj = 15.92, df=1, P <0.01). DISCUSSION Forster s and Least Terns responded strongly to the presence of conspecific models and vocalizations. In three of the four Forster s Tern study sites and at the Least Tern site, individuals settled and nested, where no or one pair had previously bred. In addition, reproductive success in the initial year of conspecific attraction was high for both species. While terns appeared to respond to conspecific attraction, allowing managers to establish colonies at predetermined locations, this technique as a management tool presents several challenges. Nest predators often use parental activity when searching for nests (Martin et al. 2000) and while models and playbacks appear to be unlikely to attract predators over the course of a breeding season, it is likely predators will eventually detect a large col- Table 1. Site-specific information on the Forster s Terns study sites. The dark shaded areas are the initial year of conspecific attraction at a site, the lightly shaded areas are years after the initial year when conspecific attraction techniques were used. The first number is the maximum number of adults observed at one point in time at a site, the second number is the number of nests located at the site, and the final number is the number of young produced (i.e., capable of flight) at a site. More than 57 nests were likely present at Grass Lake in However, there were so many, nest searching was halted due to the high density of nests and the possibility of damaging nests while searching for new nests. Site Grass Lake 2 /0 /0 65/ 57 / / 131 / 0 35 / 17 / / 41 / 0 36 / 19 /0 16 / 8 /0 Lake Elizabeth 0 / 0 / 0 0 / 0 / 0 8 / 4 / 0 2 / 0 / 0 0 / 0 / 0 0 / 0 / 0 0 / 0 / 0 Fourth Lake 0 / 0 / 0 0 / 0 / 0 0 / 0 / 0 20 / 10 / / 7 / 0 0 / 0 / 0 0 / 0 / 0 Redwing Slough 0 / 0 / 0 2 / 0 / 0 0 / 0 / 0 0 / 0 / 0 7 / 0 / 0 0 / 0 / 0 0 / 0 / 0

5 ony of breeding birds. Previous research has suggested that one of the benefits of colonial breeding is protection from nest predators via mobbing (Wittenberger and Hunt 1985; Danchin and Wagner 1997) and increased vigilance against potential nest predators (Picman et al., 2002). In the case of Least Terns, the floating sandbar effectively removed flooding as a source of nest failure and prevented access by mammalian predators; however in the second year of the study avian predators avoid the lattice of rope, used to dissuade avian predators, and depredated 19 nestlings in the colony. If terns are unable to defend their colony from nest predators, the tactic (in addition to mobbing) the terns may employ to maximize reproductive success is to use the presence of conspecifics to quickly colonize a new site. Once a colony has been detected by a predator, and predators have entered the colony, individuals within the colony may benefit from abandoning their nests and dispersing from the colony. Both in this study and other studies (Jackson and Jackson 1985; Burger 1989; Fraser 1997) Least Terns have been observed quickly abandoning colonies. Due to the high probability of a predator returning and depredating more nests individuals may benefit from abandoning their nest, and beginning to search for a new colony. At least two studies have suggested that the ephemeral nature of Least Terns colonies is due in part to nest predation forcing individuals to locate new colonies (Burger 1989; Brunton 1997). Terns may be staying one step ahead of nest predators by using the presence of conspecifics to locate new breeding areas. However, in order for this to be an effective strategy, individuals must locate and colonize sites rapidly. We observed both species in this study rapidly colonize a site. For Least Terns the time from which the first individuals were detected at the site to when the first egg was laid was often less than five days. Forster s Terns had a more protracted period typically 14 days from the arrival of the first birds to the start of egg laying. At the Grass Lake site a colony of over 100 individuals was established in 14 days. For both species the CONSEQUENCES OF CONSPECIFIC ATTRACTION 479 rapid establishment of a colony suggests that either there was a population of local nonbreeders foraging in the area, or this technique attracted individuals that may have nested in other locations (Ward and Schlossberg 2004). In the case of Forster s Terns the location of the study on the southern edge of the species range likely helped recruit birds that would have otherwise continued north to breed. In the case of Least Terns the location of the study was at the northern edge of the species range. The northern location of the colony may have resulted in relatively fewer individuals encountering the site. Also, Least Terns colonized the site later (mid-june) in the breeding season relative to other breeding locations in the area (mid-may) suggesting that some of the individuals may have attempted to nest in other locations or due to its location it is taking longer for the Least Terns to locate the site. If terns are attempting to stay one step ahead of nest predators by dispersing to new colonies and using the presence of conspecifics to locate these colonies conspecific attraction can provide a powerful conservation tool for managers. Managers can establish colonies of species of conservation concern at protected, high-quality nesting sites. However, recovery of most species of conservation concern is only possible through addressing a wide-range of ecological factors (Walk et al., 2011), in the case of Least Terns factors such as altered hydrology of large rivers, protection of sand bar habitat, and wintering foraging sites. Because these are significant factors that will require years to address, conspecific attraction can provide a short-term management tool. In addition to establishing new protected colonies, one potential application is the use of conspecific attraction is as a safety net at known natural colonies. For example, if a colony of Least Terns is destroyed due to flooding, conspecific attraction could be used to establish a colony at a safe location nearby. As this study illustrates, colonial waterbirds such as terns may readily exhibit conspecific attraction. However, while this behavior could be used to manage populations, understanding why species exhibit

6 480 WATEBIRDS this behavior will ultimately be important in developing long-term recovery plans. ACKNOWLEDGMENTS Funding was provided by the Illinois Department of Natural Resources, Zoos for Environmental Conservation, and the U.S. Army Corps of Engineers. We thank the McHenry County Conservation District and the Lake County Forest Preserve District for access to their natural areas, and the Fox Waterway Agency for creating the island at Grass Lake. We thank two anonymous reviewers for comments on the manuscript. LITERATURE CITED Ahlering, M. A., D. Arlt, M. G. Betts, R. J. Jr. Fletcher, J. J. Nocera and M. P. Ward Research needs and recommendations for the use of conspecificattraction methods in the conservation of migratory songbirds. Condor 112: Brunton, D. H Impacts of predators: Center nests are less successful than edge nests in a large nesting colony of Least Terns. Condor 99: Burger, J Colony stability in Least Terns. Condor 86: Burger, J, Social attraction in nesting Least Terns: Effects of numbers, spacing, and pair bonds. Condor 90: Burger, J Least Tern populations in coastal New Jersey: Monitoring and management of a regionallyendangered species. Journal of Coastal Research 5: Danchin, E. and R. H. Wagner The evolution of coloniality: The emergence of new perspectives. Trends in Ecology and Evolution 12: Dittmann, T. and P. H. Becker Sex, age, experience and conditions as factors affecting arrival date in prospecting common terns Sterna hirundo. Animal Behavior 65: Fraser, G. S Feeding ecology of Forster s Terns on Lake Osakis, Minnesota. Colonial Waterbirds 20: Jackson, J. A. and B. J. S. Jackson Status, dispersion, and population changes of the Least Tern in coastal Mississippi. Colonial Waterbirds 8: Kress, S. W The use of decoys, sound recording and gull control for re-establishing a tern colony in Maine. Colonial Waterbirds 6: Kotliar, N. B. and J. Burger The use of decoys to attract Least Terns (Sterna antillarum) to abandoned colony sites in New Jersey. Colonial Waterbirds 7: Martin, T. E., J. Scott and C. Menge Nest predation increases with parental activity: separating nest site and parental activity effects. Proceeding of the Royal Society of London B 267: McNicholl, M. K., P. E. Lowther and J. A. Hall Forster s Tern (Sterna forsteri). In The Birds of North America, No. 595 (A. Poole and F. Gill, Eds.). The Birds of North America, Inc., Philadelphia, Pennsylvania. Nisbet, I. C. T. and E. Cam Test for age-specificity in survival of the Common Tern. Journal of Applied Statistics 29: Picman, J., S. Pribil, and A. Isabell Antipredator value of colonial nesting in Yellow-headed Blackbirds (Xanthocephalus xanthocephalus). Auk 119: Renken, R. B. and J. W. Smith Interior Least Tern site fidelity and dispersal. Colonial Waterbirds 18: Ridgway, R The Ornithology of Illinois, Vol. 1. State Laboratory of Natural History. Bloomington, Illinois. Rimmer, D. W. and R. D. DeBlinger Use of fencing to limit terrestrial predator movements into Least Tern colonies. Colonial Waterbirds 15: Shealer, D. A., J. M. Buzzell and J. P. Heiar Effects of floating nest platforms on the breeding performance of black terns. Journal of Field Ornithology 77: Sidle, J. G., D. E. Carlson, E. M. Kirsch and J. J. Dinan Flooding: Mortality and habitat renewal for Least Terns and Piping Plovers. Colonial Waterbirds 15: Thompson, B. C., J. A. Jackson, J. Burger, L. A. Hill, E. M. Kirsch and J. L. Atwood Least Tern (Sternula antillarum). In The Birds of North America, No. 290 (A. Poole and F. Gill, Eds.). The Birds of North America, Inc., Philadelphia, Pennsylvania. Visser, J. M. and G. W. Peterson Breeding populations and colony site dynamics of seabirds nesting in Louisiana. Colonial Waterbirds 17: Walk, J. W., M. P. Ward, T. J. Benson, J. L. Deppe, S. A. Lischka, S. D. Bailey and J. D. Brawn Illinois Birds; A century of change. Illinois Natural History Survey Special Publication 31, Champaign, Illinois. Ward, M. P. and S. Schlossberg Conspecific attraction and the conservation of territorial songbirds. Conservation Biology 18: Ward, M. P., C. Jablonski, B. Semel and D. Soucek The biological pathway and effect of PCBs on Common Terns in Lake Michigan. Ecotoxicology 19: Wittenberger J. F. and G. L. Hunt The adaptive significance of coloniality in birds. (D. S. Farner, J. R. King and K. C. Parkes, Eds.). Avian Biology Vol. III, Academic Press, New York, New York.