Reproductive success of the interior least tern (Sterna antillarum) in relation to hydrology on the Lower Mississippi River

The annual hydrograph of large rivers, including flood pulses and low‐flow periods, is believed to play a primary role in the productivity of biota associated with these ecosystems. We investigated the relationship between river hydrology and Interior least tern (Sterna antillarum) reproductive success on the Lower Mississippi River from April to July 1986–1993. The number of fledglings produced per adult pair was negatively correlated with July mean (r=?0.95, p=0.0004) and July maximum river elevation (r=?0.97, p=0.0001), but no other aspects of river hydrology were related to tern reproduction. Low‐water elevations in July may benefit least tern reproductive success by increasing sand island area or the area of shallow‐water habitat that surrounds islands. Loss of deep‐water habitats in conjunction with an increase in shallow habitat during stage decreases may concentrate fish prey in shallow‐water habitats and backwater areas, thereby increasing food availability during chick‐rearing. Copyright © 2002 John Wiley & Sons, Ltd.     

Distribution and abundance of nesting common and Caspian terns on the North American Great Lakes, 1976 to 1999

Canadian and US federal wildlife agencies completed three surveys (1976–1980, 1989–1991, and 1997–2000) to census colonial waterbirds breeding on the Great Lakes. We here summarize and comment on nest numbers and colony site distribution of common terns (Sterna hirundo) and Caspian terns (Hydroprogne caspia). Common terns are in serious trouble on the Great Lakes. Numbers declined with substantial losses in nests (− 19.1%) and colony sites (− 23.2%) between the first and third censuses. An increase in numbers at US sites (+ 26.6%) did not compensate for losses (− 33.1%) at Canadian sites. Caspian terns increased in nest numbers (+ 65.9%) and colony sites (+ 50.0%) over the same period. The increase at US sites (136.5%) was greater than at Canadian sites (11.5%). Most (70.7%, n = 186) common tern sites had nests during only one census; 17 sites (6.5%) had nests during all censuses. In contrast, 9 of 33 (27.2%) Caspian tern sites had nests during all censuses and contained a majority of nests (50–82%) in each census. Pairs of both species nested on natural substrates across the Great Lakes. Common terns nested mostly on artificial (human-constructed) substrates on the lower Great Lakes. We identify site characteristics that may have contributed to long-term (three census) occupancy by common terns (small size, artificial substrates, absence of ring-billed gulls) and Caspian terns (natural substrates on large, remote islands). We suggest an urgent need for protection and conservation of common tern colonies and identify specific priority sites for implementation of management protocols.     

The influence of river stage on endangered least terns and their fish prey in the Mississippi River (USA)

Spatial and temporal availability of small fishes, as forage for interior least terns (Sterna antillarum), was compared to the least tern reproductive period during 1993 and 1994 in the lower Mississippi River, Missouri. Timing of forage availability and least tern reproduction was also related to river stage and temperature regimes. Four deep-water habitats (main channel, secondary channel, side channel, and connected slough) and two shallow-water habitats (main-channel interface and side-channel interface) were sampled using a seine and neuston net, yielding 67 245 fish≤10 cm. Catch-per-volume and richness were highest in shallow-water habitats in both years. Highest catches in deep- and shallow-water habitats occurred between 56 and 64 days after peak spring flows in both years. Water temperature was increasing rapidly during the spring flood peak each year. About 80% of total fish catch consisted of taxa known to spawn in floodplain habitats, supporting the connection between the spring flood and the timing and amount of forage available for nesting least terns. Timing of least tern reproduction was related to falling river stages in May and increased forage–fish availability in June. A conceptual model integrates the abiotic factors of hydrology and sand island area to least tern reproduction and small fish availability. © 1998 John Wiley & Sons, Ltd.