Ornithology Lecture 19

Species Decline and Conservation

Bird Species Trends

  • Not all bird species are declining; some aquatic species are increasing due to:

    • Legislation like the Clean Water Act

    • Wetland restoration efforts

  • Raptor populations are increasing due to:

    • Banning of DDT (dichlorodiphenyltrichloroethane)

    • Larger protection efforts

Major Causes of Species Loss

  • Four major causes of species loss:

    • Habitat loss

    • Overexploitation

    • Introduced/Invasive species

    • Climate change

  • These causes coincide with human population growth and the Industrial Revolution.

  • Climate change is a significant concern, but historically, land use conversion and habitat loss have been the primary drivers of species loss, leading to landscape fragmentation.

Land Use Conversion and Deforestation

  • Globally, there are intense areas of conversion from forest land to other uses, particularly agriculture.

    • This occurred in North America, especially Eastern North America.

  • In the history of North America, the establishment of the National Park System involved instituting protections, sometimes controversially.

  • Deforestation in the U.S. led to a situation where only around 3% of natural forest remained.

  • Deforestation was driven by land conversion and the use of wood for building structures, including boats.

Biological Hotspots

  • Areas near the Equator are biological hotspots, characterized by extremely high biological diversity.

  • Losing species in these areas has a disproportionately large impact.

  • Examples of areas experiencing significant loss include:

    • Atlantic Forest in coastal Brazil (agricultural conversion)

    • Sub-Saharan Africa (agricultural conversion)

    • Southeast Pacific, Indonesia, Borneo (deforestation for agricultural conversion, e.g., palm oil)

Agricultural Cropland Density

  • Many declining bird species, like sparrows, are affected by the conversion of grasslands to agricultural land.

  • Historically, the Great Plains in the U.S. were a massive land feature, but now only about 1% of the original prairie lands remain, having been converted into farmland.

  • This landscape conversion has contributed to the decline of many grassland bird species.

Population Trends

  • Data from the Breeding Bird Survey (1966-1996) shows percentage of decline per year of grassland bird species: red indicates severe declines, blue indicates increases.

Habitat Fragmentation

  • Habitat fragmentation results from progressive habitat loss.

  • Initial development, such as building a road, leads to easier access and further development, like farms and neighborhoods.

  • Satellite development occurs, branching off from initial access points, resulting in fragmented patches of habitat separated by land use development.

Edge Effects and Area-Sensitive Species

  • Fragmentation leads to edge effects.

  • Area-sensitive species require core forest and are intolerant of habitat change.

  • Edge species are more tolerant of change because they exist at the transition between habitats (ecotone).

  • As a landscape is fragmented, new edges form, reducing the interior core of the forest.

  • Patches of irregular forest that result from fragmentation may have effectively no core remaining.

  • The pattern of habitat loss is often centered on the edge; losing core area.

  • Increasing distance from the forest edge correlates with fledgling success.

  • Edge noise and other sublethal effects can decrease the foraging rate of birds, resulting in lower biomass and fewer fledglings.

Ecological Traps

  • Ecological traps are habitats that appear suitable but cannot support populations.

  • Remnant tracks of forest in a developed landscape may attract forest species but lack the resources to support them.

  • Species drawn to these areas may enter a downward spiral, and the only solution is to restore the habitat.

Source-Sink Dynamics

  • Corridors intended to connect protected lands can lead to source-sink dynamics.

  • A source population has a net positive population growth, leading to dispersal.

  • A sink population has a net negative growth rate, with death rates exceeding growth rates.

  • If the sink population is strong enough, it can cause a decline in the source population.

Other Reasons for Bird Declines

  • Overharvesting: legal hunting results in the death of around 20,000,000 birds per year.

  • Introduced species: cats are a significant cause of bird mortality.

    • Brown tree snakes eradicated endemic birds on islands like Guam.

  • Increasingly, urbanization has led to roadkill and window strikes.

  • Avian diseases like avian malaria can decimate bird populations.

  • Climate change poses an impending threat.

  • Illegal pet trade is another factor.

Climate Change Impacts

  • Climate change is showing effects such as altering the timing of migration, which is crucially important because this is offset with timing of food for birds.

  • Birds use temperature cues to time their migrations, but their food sources (e.g., insects) may rely on photoperiod, which is constant.

  • Warming temperatures cause birds to migrate earlier, while insect emergence remains the same, leading to a mismatch.

  • Birds arrive to breeding grounds, lay eggs, and by the time eggs hatch, there is a significant delay of those insects emergencies.

  • As a result, offspring have lower body mass, causing consequential effects during subsequent migration to overwintering ranges.

  • An example of this is termstones, which overwinter in the Arctic Circle. However, males are not getting enough body mass. They are not developing long enough beaks to reach the things like oysters, and they're having competition other birds.

  • Therefore, this is leading to a change in the male to female sex ratio.

  • Alpine habitats are also threatened by climate change.

  • Sky islands is to note that as lower land species, vegetation included, moves upwards, we see a depression of the original alpine species which can lead to escalator to extinction.

  • Pseudo habitat is also on the decline, which is really things that need more alpine types of habitat.

Citizen Science and Data Collection

  • Citizen science plays a crucial role in monitoring bird populations.

  • Christmas Bird Count: Organized by the Audubon Society, volunteers count birds in designated routes and compile data.

    • Inaugural count: 27 volunteers, 18,500 birds of 90 species.

    • 2023-2024 count: 83,000 volunteers in the U.S. and Canada counted just under 41,000 birds.

    • This data is publicly accessible.

  • Breeding Bird Survey: Run by the government with standardized procedures for survey methods.

    • Transects are 40 kilometers (24.5 miles) long.

    • Volunteers stop every half mile and do a point count of everything within a quarter mile radius for 3 minutes.

Population Trends

  • Grassland birds have declined due to the loss of grasslands/extreme loss of grasslands.

  • Some species like Merlins have done better around human habitats.

  • Model outputs are useful, based off breeding bird survey.

  • Birds are declining fastest where they were once common.

  • Common species are important for ecosystem functions, and their population declines can have collateral damage.

Data Compilation

  • Christmas Bird Count data is used in databases like eBird.

  • Breeding Bird Survey was established by the government with coordination with Cornell University, which now runs eBird, and there is a standardized protocol.

  • Eurasian Collared Dove spread through North America.

Extinctions

  • Examples of extinct species:

    • Dodo bird

    • Great auk: The bird that penguins get their name from

    • Moas (New Zealand)

    • Passenger pigeons: Once the most common bird species on the planet, eradicated by settlers because they were considered taking seeds and stuff on Aglands.

    • Carolina parakeet: Only parrot native to North America, extinct in 1918.

    • Ivory-billed woodpecker: Possibly extinct (largest woodpecker in North America).

  • Stephen's Island Wren: Eradicated by a lighthouse keeper's cat named Tibbles on a small island in New Zealand. And documented, visibly seen the cat in an introduced species wiping out the last individual species.
    * This species was thought to have been eradicated by a cat.
    * It was documented that the cat was visibily seen and that the species was introduced.

  • Hawaiian o’o: Extinct due to land use conversion, introduced species (rats, feral pigs), and avian malaria, basically taken out by a confluence of factors quite recently.

    • The last one was seen in 1985. And heard in 1987.

When listening to the last individual of what exists. It is hard, because you want to know if there will be somebody else out there.