The Vermont Common Tern Recovery Project
Audubon Vermont (2011). The Vermont Common Tern Recovery Project (Final Report). Grand Isle, VT: Lake Champlain Basin Program.
This report provides an account of the Vermont Common Tern Recovery Project’s 2011 field season. Since 1897 Common Terns, a Vermont state endangered species, have been monitored on several small islands on Lake Champlain and management efforts have been undertaken to restore the breeding population to pre-1970’s levels. In 2011 this work continued using well established monitoring and management practices. The objectives of the 2011 field season included providing Common Terns with adequate nesting habitat, increasing the number of adult breeders and aiding the survivorship of tern chicks. To this end we conducted weekly surveys of the nesting islands, collecting evidence of adult numbers and reproductive success and implementing management actions such as chick shelters, warning buoys and a grid system to prevent competition from gulls and cormorants. Work was conducted from early May to mid-September, 2011.
The 2011 field season had mixed results. Lake Champlain saw record high water levels in April and May 2011. This pushed back our first visits to the island from late April to early May. In addition, one of the nesting islands, Rock, was inundated with water, limiting available nesting space at that site. Other early season complications included higher than usual gull nesting on Popasquash and Rock islands and the presence of a Peregrine Falcon on Popasquash Island in early May. These resulted in a late start to the nesting season. Despite all this we recorded the highest peak nest count (203 nests, all on Popasquash Island) in more than 2 decades and estimated the breeding population at roughly 225 pairs. This number is similar to 2010 and is above the 200 pair level required for downlisting this species from endangered to threatened. Shortly after this peak count was recorded, however, Great Horned Owl predation was documented on Popasquash Island and newly hatched chicks began disappearing. This combined with excessive vegetative growth resulted in extensive abandonment of nests. The vegetation also prevented researchers from collecting nest and chick data as both nests and chicks were obscured by the vegetation. As a result we were unable to determine the exact number of nests that hatched and the numbers of chicks that fledged. A very rough estimate of chicks that fledged based on banding data was between 40 and 50 chicks. This represents very low productivity levels.
Overall the number of Common Terns nesting on Lake Champlain remained at high levels. This will be the 3rd consecutive year numbers were above 200 nesting pairs. An average of 200 nesting pairs over 5 years is needed for downlisting this species to threatened. The low productivity documented in 2011 may be offset by relatively high productivity levels in previous years. Continued low productivity, could however, result in declining adult numbers. The 2011 field season saw a number of new factors effecting Common Terns on Lake Champlain. Whether these factors will continue to impact the terns is uncertain and continued monitoring and management will be needed in the future.