Context Integrating Population and Housing Censuses with Agricultural Censuses
Conservation of Neotropical migrants · Wood Thrush source-sink model Model combined population...
Transcript of Conservation of Neotropical migrants · Wood Thrush source-sink model Model combined population...
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Conservation of Neotropical migrants
• Over 80% of North American birds are migratory during some phase of their annual cycle
• Neotropical migrants include a diversity of species but most attention has focused on terrestrial insectivores
Proportion of Neotropical Migrants
NeotropicalMigrants
Other Species
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Southern Appalachian Neotropical Migrants Breeding and wintering ranges
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Percent of Migratory Bird Species Showing Population Declines 1978 -1987
Robbins, C.S, J.R. Sauer, R.S. Greenberg and S. Droege. 1989. Population declines in North American birds that migrate to the Neotropics. Proc. Natl. Acad. Sci. USA. 86:7658-7662.
Forest Songbirds
The Breeding Bird Survey is a point count based abundance index
• Began by Chandler Robbins USFWS in 1966
• 3000 Roadside Routes in the US and Canada
• 25 miles, 50 points/route
• 3-minute unlimited radius point counts
Wood Thrush
BBS Trend Map, 1966 ‐ 2003
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BBS Trend Map, 1966 ‐ 2003
BBS Trends 1966 - 1992• Long distance Neotropical migrant
• Common breeder in deciduous forests of eastern North America
• Consistent population declines across range
• Increased rates of nest predation and Cowbird parasitism associated with forest fragmentation
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Breeding and wintering ranges
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Historic trends in forest coverHabitat loss
Fragmentation Fragmentation effects
Wilcove, D.S. 1985. Nest predation in forest tracts and the decline of migratory songbirds. Ecology 66:1211-1214.
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Fragmentation effects Great Smoky Mountains National Park
• Established 1935, 2057 km2
• Part of largest protected forested landscape in the eastern United States
• Internationally recognized refugia of temperate forest biodiversity
• High floral diversity• Over 100 breeding bird species,
75% Neotropical migrants• Largest remaining stands of
primary forest in the eastern United States
Methods
• Point counts– Variable circular plot
– 10 minute interval
– Single observer
– Distance sampling
• Point locations– Low use hiking trails
– Stratified by vegetation type
Industrial Logging
• 18% of Park (376 km2)• 1900 - 1930• Highly Mechanized• Clear Cuts• Substantial Erosion
A Comparison of Breeding Bird Communities in Primary and Secondary Eastern Deciduous Forests
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Secondary Forest at Industrial Logging Sites
• 75 Years Old• Smaller Trees• Even-aged Stands• Few Canopy Gaps• Lack of Woody Debris
Primary Forest
• 23% of Park (469 km2)• Big Trees• Forest Gaps• Uneven Canopy• Woody Debris
Primary and Secondary Forest Census Points
# Census PointIndustrial Logging (376 km2)Undisturbed (469 km2)
Forest Type
Northern Hardwood (195 km2)
Cove Hardwood Mixed Mesic (1025 km2)
All Mesic Forest Points
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More Abundant on Primary Forest Sites
Factors
• Forest succession -hemlock
• Decaying large trees and snags
• Forest floor with woody debris, pits and mounds
• Organic soils -invertebrates
Wood Thrush source-sink model
Model combined population estimates based on point count censuses with productivity estimates based on 426 nests to evaluate the significance of the park as a population source
Estimated annual Wood Thrush productivity in Great Smoky Mountains National Park
Adult survival
Juvenile survival
Equilibrium fecundity
Surplusfecundity
Population surplus (low-high)
0.60 0.30 1.33 0.05 500 (350-650)
0.67 0.30 1.10 0.28 2,800 (1,960-3,640)
0.74 0.30 0.87 0.51 5,100 (3,570-6,630)
Seasonal fecundity = 1.38 females per breeding pair
Breeding population = 7,000 - 13,000 breeding pairs
Estimated minimum size of the continental Wood Thrush population
0 0 32,523,613 0
2 0.0318 35,448,778 112,536
4 0.0635 50,617,417 321,380
11 0.1746 52,426,797 915,389
31 0.4921 2,729,149 134,291
Relative abundance
Density(pairs/10 ha)
Habitat area (ha)
Population estimate
Total 173,745,754 1,483,596
Great Smoky Mountains National Park = 2000 km2 = 0.5% of breeding rangeExports ~6,630 surplus females (max), of which ~2,000 survive to breed on ~400 km2 of habitat Therefore the National Park is a source for maximum area ~20% the size of the parkTheory (Pulliam 1988) predicts that some source areas support up to 10X their area
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Conservation lessonsCanaries in a coal mine?
“Whenever a man hears it he is young, and Nature is in her spring; whenever he hears it, it is a new world and a free country, and the gates of heaven are not shut against him.”
Thoreau
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Oil, Seabirds, and ScienceThe effects of the Exxon Valdez oil spill
• 24 March 1989
• 10 million gallons
• Largest spill in U.S. history
• Oil traveled 900 km and covered 2100 km shoreline
Effects of the spill
• 30,000 dead birds retrieved, 74% murres
• First estimate (USFWS), 60%-70% killed based on carcasses
• Wiens/Boersma (Exxon), conclude no effect using counts at colony
1996 BioScience 46: 587-596
The “advocacy trap”• Counts indicate that
populations recover quickly– Are northern seabirds “resilient”?
– Have floaters moved in?
– Debate over long term effects continues. 20 year analysis of Harlequin Duck populations
• Who is in the trap?
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Deepwater Horizon spill
• 20 April -15 July 2010
• 210 million gallons
• 68,000 sq miles
• Direct mortality of birds limited
• Long term effects unknown
Seabirds and Longlines
Mobile protected areas for marine birds
Shorebird conservation• 31 species migrate from the
Arctic to South America– Species that breed farther
north winter farther south– Birds concentrate on
stopover and breeding sites so population estimates fairly precise
• Morrison et al. 2001. Estimates of shorebird populations in North America. Occasional paper #104, Canadian Wildlife service
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Shorebird conservation• Fragile life histories
– Low reproductive rates
– Single brood, short breeding season
– K-selected, sensitive to changes in adult mortality
• Stopover sites limited– Birds have high energy
demands during migration
– Stopover sites under pressure from humans
Western Hemisphere shorebird reserve network
• The network, established by a international consortium of public and private organizations, currently consists of more than 90 sites divided into two categories: hemispheric reserves defined by an international panel of biologists as supporting either more than 500,000 birds or at least 30% of a species’population, international sites supporting more than 100,000 birds or at least 10% of a population, and regional reserves defined as supporting more than 20,000 birds or 5% of a species’ population