Conservation of Neotropical migrants · Wood Thrush source-sink model Model combined population estimates based on point count censuses with productivity estimates based on 426 nests

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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