Promoting Change in Common Tern (Sterna hirundo) Nest Site Selection to Minimize Construction Related Disturbance

Due to the many challenges facing waterbird populations (Jia et al. 2018, Wetlands International 2018), it has become common practice to limit disturbance to breeding colonies whenever possible to maximize reproductive success. While this may require often unpopular management techniques including beach closures (Jorgensen et al. 2015, Mayo et al. 2015) and predator removal (Neuman et al. 2004, Stocking et al. 2017), such actions are sometimes necessary for the success of the colony. However, there are instances when eliminating disturbance is not possible and birds must be attracted to a new site. A common method for attracting waterbirds to a desired location is paired auditory and visual attractants such as decoys and conspecific calls, a highly effective approach for terns (Jeffries and Brunton 2001, Roby et al. 2002, Arnold et al. 2011), murres (Sawyer and Fogle 2013), and other colonial nesting waterbirds (see Friesen et al. 2017 for a review).

Figure 1.

Map of Poplar Island showing areas of lateral expansion (the area of construction activity), historical Sterna hirundo colony nesting site, and colony relocation site (image courtesy of U.S Army Corps of Engineers).

While attracting breeding populations to desired locations is an important step in colony relocation, managers must also ensure that individuals do not nest at the historical nesting site. One approach is to reduce the quality or quantity of breeding habitat at the historical colony and create or improve habitat at a desired location (Roby et al. 2002, Hartman et al. 2018). However, this jeopardizes the colony if the new site is not adopted. Another option is the use of overhead lines and flagging. This approach is commonly used to deter nuisance species (Pochop et al. 1990) but has also been successful for preventing nesting of various tern species (Roby et al. 2002, Marcus et al. 2007).

The goal of our study was to evaluate the use of a paired attractant and deterrent to facilitate the relocation of a Sterna hirundo (Common Tern) breeding colony from its historical nesting location in the face of extensive disturbance. We hypothesized that the paired use of attractants placed in suitable breeding habitat and deterrents covering the entirety of the historical nesting colony would result in complete relocation of the breeding population to the new target area.

The Paul S. Sarbanes Ecosystem Restoration Project at Poplar Island (Poplar Island), located in Talbot County, Maryland (38°46'01" N, 76°22'54" W), is a U.S. Army Corps of Engineers (USACE) and Maryland Port Administration (MPA) beneficial use of dredged material project (USACE 2005). Poplar Island serves as the largest of only two S. hirundo nesting sites within the Maryland portion of the Chesapeake Bay. The largest S. hirundo colony present on Poplar Island is traditionally located at the north end of the island within the northeast corner of a dredge containment unit (elevation: eight meters above sea level, Figure 1). The historical nesting site was a narrow linear parcel of land encompassing approximately 0.70 ha. The nesting substrate was composed of a sand/clay/shell mixture, interspersed with vegetation that grows to increasing density as the breeding season progresses (May through August). Similar habitat is found in abundance throughout this area of the island.

At times, on-site conflicts arise between avian use and construction activities. For example, during the 2017 and 2018 S. hirundo nesting seasons ongoing construction activity increased heavy equipment and foot traffic near the historical nesting site (Figure 1). However, continuation of the project was necessary to avoid significant complications and delayed habitat development. Due to the negative impacts disturbance would have on nesting terns and the need to continue construction, the decision was made to promote nesting approximately 200 m northwest of the historical site. Nesting substrate within the relocation site was sandier than the historical site due to the recent deposition of fresh sand used for dike construction, but the area was comparable...