SELECTION OF COLONY SITES AND NEST SITES BY COMMON TERNS STERNA HIRUNDO IN OCEAN COUNTY, NEW JERSEY

Abstract

SUMMARY Common Terns nested on 34 of 259 saltmarsh islands along 46 miles of Ocean County coastline, New Jersey. They nested on low islands of Spartina with less than 12%, windrow ranging in size from 0.6 to 108 acres. All islands selected by terns faced at least two miles of open water from at least one direction. Selection of islands seemed a response to vegetation, size, distance to the nearest island, distance to the nearest shore and exposure to open water. Of the 225 islands without nesting terns, only three fulfilled appropriate criteria. Eighty per cent of nests were situated on windrow. Terns laid larger clutches on windrow compated to those nesting in Spartina. Nearest neighbour distance on islands with low predation varied from 85 to 485 cm and was a function of space, vegetation, and the size of the island. Terns nested closer together on windrow compared with Spartina. Considering all colonies, the mean nearest neighbour distance negatively correlated with the number of nests. Skimmers, Oystercatchers, Laughing Gulls, and Herring Gulls nested in some of the tern colonies. All tern colonies on islands also occupied by nesting Herring Gulls suffered over 10% egg‐loss by predation. Proportionally more nests were preyed upon in windrow than in Spartina. Clutch sizes in nests in windrow on islands with predation were significantly lower than those in windrow on islands without predation, even though clutch sizes in Spartina were similar on islands with and without predation. Flooding by exceptional high tides destroyed significantly more nests in Spartina than in windrow. The nests that survived in Spartina were built deeper, and their rim heights were higher than nests destroyed by tides. Choice of colony and nest sites is discussed in terms of the balance of two selection pressures: predation and tidal flooding. Tern nests on windrow are more exposed to predators, but safer from flooding, whereas those nests in Spartina are more susceptible to flooding and less vulnerable to predators. The recent invasion of Herring Gulls into Ocean County has significantly increased the rate of nest predation among affected colonies of Common Terns. It is possible that in future years the terns' behaviour may be modified in response to this new selective pressure.

The role of behavior in tern conservation

“…If site fidelity is low (see Philopatry and Dispersal, below) it may also be important to protect currently unoccupied but suitable sites (Erwin et al, 1998). If site fidelity is high, then protecting existing sites takes on added urgency because the terns may be unlikely to colonize new locations (Burger and Lesser, 1978;Heinänen et al, 2008).…”

“…In many locations habitat is successfully managed for common terns by removing vegetation or inhibiting succession (Burgess and Hirons, 1992;Morris et al, 1992;Becker, 1996;Kress, 2000;Cabot and Nisbet, 2013; but see Cook-Haley and Millenbah, 2002), but in saltmarsh colonies instead by adding dead eelgrass (Zostera) and other wrack, the preferred nesting substrate at these sites (Burger and Lesser, 1978;Burger and Gochfeld, 1991;Rounds et al, 2004;Palestis, 2009b). Adding wrack or moving it farther from the water's edge provides nesting substrate that is less susceptible to flooding (Palestis, 2009b).…”

“…There have been many observational and experimental studies of nest site selection in terns (e.g. Burger and Lesser, 1978;Becker and Anlauf, 1988;Burger and Gochfeld, 1988Fasola and Canova, 1992;Neubauer, 1998;Guicking et al, 2001;Cook-Haley and Millenbah, 2002;Rounds et al, 2004;Colchero et al, 2010;Hu et al, 2013) that have led to improvements in management techniques, such as vegetation control, manipulation of water regimes, and the construction of nest boxes for particular species (reviewed in Kress, 2000;Cabot and Nisbet, 2013). Wide variation in preferred nesting substrate occurs across species, from mats of floating vegetation in marshes to low terrestrial vegetation to cobble beaches to bare sand.…”

“…It is important that restoration sites are selected carefully (Nisbet and Spendelow, 1999;Ward et al, 2011) and that the determinants of habitat quality are well understood, so terns do not fall into an ecological trap by being attracted to suboptimal habitat that causes further population declines (Battin, 2004;Reed, 2004;Sih, 2013). Selection of colony and nest sites reflect trade-offs (which vary among species) between predation risk, flooding risk, and proximity to preferred foraging sites (Burger and Lesser, 1978;Becker and Anlauf, 1988;Gochfeld, 1990, 1991;O'Connell and Beck, 2003;Rounds et al, 2004;Cruz et al, 2013). For example, low-lying islands without trees or shrubs are less likely to harbor predators but are more susceptible to flooding.…”

Island shape, size, and isolation affect nest-site selection by Little Terns

“…Within breeding colonies, nest density and abundance can be influenced by a variety of social, ecological, and landscape factors, and for any particular species these factors may differ from those that determine occurrence at potential breeding sites (Heinänen et al 2008). Ecological factors include predation risk (Burger and Lesser 1978, Quinn et al 2003), competition (Dawson et al 2011), and proximity to food resources (Duhem et al 2007). Landscape factors that may affect nest densities include slope (Punta et al 2003) and topography.…”