Winners and losers in the population game
(http://www.ccbbirds.org/2014/03/31/winners-and-losers-in-the-population-game/)
see link for population table
By Bryan Watts
Through time, the fortunes of species rise and fall reflecting the underlying
conditions and demographic fundamentals. Tracking populations through time
allows the conservation community to see which species are in trouble and which
species are in need of research to determine root causes. Understanding causal
factors is a first step toward either developing remedies or acknowledging that
the declines are beyond management influence. The Center for Conservation
Biology (CCB) has recently compiled the results of the 2013 colonial waterbird
survey for Virginia. The broad community-wide findings identify some clear-cut
winners and losers over the past twenty years.
Within the winners' camp are primarily species that have colonized the state in
the past forty years, including double-crested cormorant, brown pelican, white
ibis, and great black-backed gull. Double-crested cormorants have increased
from 6 pairs in 1978 to 2,876 pairs in 2013 and have increased eight-fold over
the past twenty years alone. Similarly, brown pelicans have increased from 30
pairs in 1987 to 2,454 pairs in 2013 and have increased nearly seven-fold over
the past twenty years. Great black-backed gulls have increased from a first
breeding attempt in 1970 to 1,172 pairs in 2013 and have more than doubled over
the past twenty years. The white ibis, a recent colonizer of Virginia, has
increased from just 3 pairs in 1993 to 369 pairs in 2013.
The losers' camp includes several species that should be considered for life
support and several others that continue to experience a slow-burn decline.
Species that should receive immediate life support include cattle egret, little
blue heron, glossy ibis, and gull-billed tern. The cattle egret stands out as
having experienced a greater than 96% decline in only twenty years (1,459 to 56
pairs). Both little blue herons and glossy ibis have declined from thousands
in the 1970s to just 162 and 430 pairs, respectively, including a 57% decline
since 1993. The gull-billed tern continues a long decline reaching a low of
only 294 pairs in 2013. Many other species have experienced much shallower
declines, including snowy egret, tricolored heron, black-crowned night heron,
herring gull, least tern, and black skimmer.
Sea-level rise is a clear factor contributing to declines of several species.
This is highlighted in the laughing gull population that has declined more than
46% in just ten years. Most of the wader species that have experienced deep
declines have lost nesting habitat on bay islands that are rapidly eroding
away. These islands represent significant and unique nesting areas for these
species and are in jeopardy of being washed away completely over the next two
decades.
Colonial waterbirds are top consumers within aquatic ecosystems and are
considered by many to be some of the most effective sentinels for aquatic
health. As a group, the community has declined by 36% in Virginia since 1993
(94,947 pairs in 1993 to 60,460 pairs in 2013). We should continue to press
toward a broader understanding of the underlying causes for this decline.
The 2013 colonial waterbird survey was a collaborative, multi-agency effort
lead by Bryan Watts and Bart Paxton of CCB and included the help of the
Virginia Department of Game & Inland Fisheries, the United States Fish and
Wildlife Service, The Nature Conservancy, the Virginia Department of
Conservation and Recreation, the Virginia Department of Transportation, and the
Army Corps of Engineers. We thank all of the many individuals who contributed
time and expertise to the effort.
Michael Wilson
Center for Conservation Biology
College of William and Mary & Virginia Commonwealth University
P.O. Box 8795
Williamsburg, VA 23187-8795
phone: 757-221-1649
fax: 757-221-1650
email: mdwils@xxxxxx
web: www.ccbbirds.org
