Orni 11 PDF: Population and Conservation (Lecture 11)

Population and Conservation (Lecture 11) Population — group interbreeding individuals and their offsprings o May refer to individual populations within a species o Or population of entire species Many bird population sizes fluctuate dramaticall...

Population and Conservation (Lecture 11) Population — group interbreeding individuals and their offsprings o May refer to individual populations within a species o Or population of entire species Many bird population sizes fluctuate dramatically between years (short term) o Storms, drought, etc. can lead to short term changes o Often recover quickly from these events o Annuals fluctuations in Scaled Quail driven by rainfall Some birds populations show large populations changes over longer periods (long-term) o Gradual decline in Scaled Quail over 80 years o Introduction of House Finch to eastern North American: rapid population growth followed by decline Growth of Population Birds species often have potential for explosive population growth o Large-bodied species with slow reproductive rates: 10-30% o Small-bodied with fast reproductive rates: 50-100% Introduced species provide an example: European Starlings o 100 starlings released from Central Park NYC in 1896 o Over the next century increased dramatically in population size (200 mill) and geographic range o Today a major invasive pest -- compete with native species for tree cavities for nesting Limitation and Regulation Population limitation – any ceiling on population growth - Habitat - Food - Disease - Predation Population regulation – effects of population density on population size (negative density dependence) o - Survival and reproductive rates often regulated by population o - Regulation buffers short-term fluctuations in population size Example: Great Tits o - Mean clutch size and number of fledglings related to population density o - Lay fewer eggs with population density high o - 60% of variation in clutch size due to population density o - Survival and reproductive rates often regulated by population o - Regulation buffers short-term fluctuations in population size  Example: Black-throated Blue Warblers o - Density-dependent stabilization on breeding grounds o - Young fledged decreased as population density increased o - Rate of population growth (r) negatively related to population density (low pop density pops increase, high pops density decrease) o - Experimental removal neighbors = increase in young fledged Population Trends Some of the best data on populations fluctuations in the wild comes from birds o - Fish and Game departments (gamebirds) o - Extensive and lengthy record of citizen science o - Christmas birds counts, eBird Population regulation and limitation interplay to determine population size changes o - Food limitation may reduce population size and density o - But reduced density will reduce negative density dependence (results in population growth) Example: Waterfowl o - Ducks declined severely in the 1960s o - Northern Pintails dropped from 10 million breeding pairs to 1 million  o - Canada, Mexico and US organized management plan – recovery occurring Citizen science has played a crucial role in documenting populations trends of non-game species - Audubon Christmas Bird count – started in 1900 - 1900: 25 counts, 18,500 birds, 90 species - 2016: 2,505 counts, > 58 million birds, 2,607 species - Similar, more formal long-term counts hosted by government (Breeding Bird Survey) - eBird – year-round recordings of bird sightings Document changes in populations of individual species - Eastern Meadowlark – decreasing - Merlin – increasing Document geographic changes in population trends o - Black-throated Blue Warbler o - Changes in local density from 1960 o - Loss of old-field habitat Red Grouse cycles o - Gamebird of moorlands of Scotland o - Strongly managed o - Shows show-term fluctuations and long-term trends o - Most populations show 4- or 8-year short-term cycles Variety of factors combine to dictate short-term population cycles o - Food availability o - Social behavior (density-dependent territorial behavior) o - Parasite loads (nematode worms; density dependent) o - Predation (influenced by worm load) Long-term trend: Populations have declined 50% over last century - Driven by loss of moorland habitat Population Crashes, Bottlenecks, and Inbreeding Population bottleneck – severe and rapid loss of population size (population crash) o - Reduces genetic diversity o - Increase inbreeding Example: Birds populations in New Zealand - Hatching failure increases with bottleneck severity Bottlenecks increase inbreeding after the event, but can also cull highly inbreed individuals - Example: Song Sparrows - Crashes in 1979/80 and 1988/89 reduced population mean inbreeding coefficient State of Birds Today Many bird species are threatened, endangered, or in decline o - Greatest threats in high-diversity tropical areas (often developing countries with high human population pressure) o - In the US, 1/3 of species need urgent conservation action o - Signs of danger in Neotropical migrants, grassland species, migratory shorebirds, and songbirds with small ranges Species associated with humans are often increasing o - Rock Pigeons, European Starlings, House Sparrows o - Red-tail Hawks, Turkey Vultures o - 200 years ago American Crows were shy, rural birds – now common in suburban settings Endangered Species International Union for the Conservation of Nature (IUCN) Red List o - Classifies species by risk of extinction o - Globally 673 endangered o - 787 vulnerable o - 66 species data deficient Example: Parrots o - 28% of species threatened o - 56% in decline o - Only 9% increasing o - Threatened by agriculture, hunting, trapping, logging Threats Bird species are threatened by numerous human induced factors - Habitat loss (widespread) - Climate change (slow but huge impacts) - Disease (human introduced – avian malaria via mosquito introduction to Hawaii) - Chemicals (pesticides, pain-killers, pollutants) - Collisions (building, towers, windmills) - Hunting and fishing (by-catch) - Also benefits from some human structures (nest sights) Birds and DDT  Pesticide application, especially DDT, responsible for bird population declines o - Directly kill birds o - DDT interferes with eggshell production Bald Eagles went into steep decline during peak use of DDT in North America o - Fledged many few young because eggshells would become damaged prior to hatching o - Occurred in many other predator species as well o - Increased population size after DDT was banned Brown Pelicans also suffered eggshell deformities and were placed on endangered species list in 1973 - Have recovered well and are populations are expanding; no longer on endangered list Habitat Loss Habitat loss is the greatest threat to birds today o - Direct losses via habitat destruction o - Reduction of habitat quality through fragmentation, invasive species, etc. o - Loss of habitat with changing climate Deforestation particularly damaging, especially in the tropics - Many endemic species with small ranges Grassland species declining as well Water management o - Reduction of wetlands impacts ducks, shorebirds o - Levees and dams in the south drained many bottomland forests where Ivory-billed Woodpeckers specialized Fragmentation Fragmentation of habitat has detrimental impacts on bird populations - Widely studied in birds Fragmentation increases mortality and decreases dispersal o - Edge effects – negative impacts of nesting close to a forest edge o - Increased nest predation Corridors can play a critical role in fragmented landscape o - Provide connectivity o - Dispersal, gene flow o - Aid local migrations Connectivity From a conservation perspective, birds are unique in their ability to connect distant locations o - Complicates conservation efforts for migratory species o - Must work to conserve breeding and wintering grounds (often different pressures) o - Sometimes within a continent (Resplendent Quetzals migrate within Central America) o - Between continents (many species) Connectivity key to both local conservation efforts (corridors) and global conservation (migration flyways) Extinction Sadly, humans caused extinction is commonplace in birds, including in North America o - Passenger Pigeon o - Carolina Parakeet Island species particularly vulnerable o - Hawaiian Honeycreepers (avian malaria) – 10 species lost in last 15 years; remaining species face extinction o - New Zealand Moas (9 species) – driven extinct by hunting, within 200 years of human arrival o - Dodo (hunting) o - Elephant Bird of Madagascar (largest bird in history) o - Estimated 2,000 island species lost since human arrivals Reintroductions We have been successful with reintroduction programs for some species that were near extinction o - Whooping Cranes o - Peregrine Falcons o - California Condors DDT drove Peregrine Falcon populations towards extinction in eastern Northern America o - Virtually disappeared from East in 1950s and 1960s o - Major effort to raise young in captivity and then released o - Nesting boxes built in many cities o - Population has been steadily increasing California Condor saved by reintroduction program  o - Largest vulture in North America; was once widespread o - Last individual captured from wild in 1987 o - Raised in captivity, first reintroduction in 1992 o - Slow but successful recovery – 488 living wild in 2018 Frightening Reality Over the past 50 years, the total population of North American birds has decreased by one third! - Loss of ~ 3 billion birds These huge losses are expected to continue without intervention o - Habitat loss important (breeding and wintering grounds) o - But climate change likely important, but will become increasingly critical factor The loss of species will have impacts beyond birds themselves - Ecosystem services - Human enjoyment