Birds are found worldwide, comprising over 10,000 different species. These feathered creatures inhabit diverse habitats, from deserts to rainforests, grasslands to frozen tundras. But how many birds exist globally? Getting an accurate count is challenging, but scientists estimate the total wild bird population to be between 50 to 428 billion.
Estimating the Global Bird Population
Calculating the global bird population is tricky for several reasons:
- Birds are highly mobile and dispersive animals that occupy expansive ranges.
- Many species are elusive, hard to detect, or live in remote areas.
- Population sizes fluctuate seasonally with breeding, migration, and mortality.
- There is a lack of systematic surveys and quantitative data for many species.
Scientists must therefore extrapolate population figures from limited sampling, making assumptions that introduce uncertainty. Estimates span a wide range depending on the methodology.
Lower-End Estimates
In 2018, a study tried counting total bird numbers by scaling up population density estimates from breeding bird survey data. Their tentative global estimate was 50 billion birds with a confidence range between 30 to 70 billion. However, this likely underestimates the true total.
Higher-End Estimates
Other researchers argue billions of non-breeding birds are missed, especially highly gregarious species. A 2020 paper estimated 428 billion birds globally based on citizen science checklists and spatial modeling of detection probabilities. They accounted for non-breeders plus cryptic and non-vocalizing birds overlooked in surveys.
While the upper figure may be inflated, the authors contend it represents the first empirically derived estimate of total global avian abundance.
Challenges in Monitoring Populations
Long-term monitoring is required to detect population trends over time. But comprehensive global surveys are logistically prohibitive. Scientists must therefore rely on proxies and sampling. Key challenges include:
- Incomplete geographic coverage: Most surveys focus on North America and Europe. Large swathes of Asia, Africa, and South America lack data.
- Research biases: Showy, vocal, diurnal species in open habitats are overstudied compared to cryptic, quiet, nocturnal forest birds.
- Irregular breeding: Species with sporadic, nomadic breeding are hard to sample during standard surveys.
- Shifting distributions: Migratory ranges are changing due to climate change, complicating trend analysis.
New technologies like acoustic monitoring, radar, drones, and crowdsourced citizen science data can enhance sampling. But a global monitoring framework with standardized methodology is still lacking.
Major Threats to Bird Populations
Both lower and higher estimates indicate an enormous bird population. But many species are declining under human pressures. The 2016 State of the World’s Birds report highlighted these major threats:
Habitat Loss and Degradation
- Agriculture, logging, urbanization destroys natural habitats
- Fragmentation isolates remaining habitat patches
- Climate change alters ecosystem composition and structure
Exploitation
- Hunting and trapping for food, pets, medicine, feathers
- Incidental bycatch in fisheries
Invasive Species
- Displacement by introduced species competing for resources
- Nest parasitism from cowbirds reduces reproductive success
- Predation by cats, rats, snakes etc.
Pollution
- Oil spills coat feathers causing hypothermia
- Pesticides accumulate in tissues, reducing fertility
- Plastic ingestion blocks digestive tracts
Other issues like collisions with buildings and vehicles take minor tolls. But overall, human impacts have made agriculture one of the most hazardous habitats for birds compared to natural ecosystems.
Global Declines in Bird Populations
Scientific evidence reveals many bird populations are decreasing. A 2019 study analyzed decades of survey data on North American breeding birds representing over 90% of avian biomass. They found:
- Populations declined by 29% (around 3 billion birds) between 1970-2014
- Declines affected most biomes, including grasslands, shrublands, forests
- 90% of losses came from 12 families including sparrows, warblers, blackbirds
- Long-distance migrants suffered steepest drops, but even common birds declined
These trends mirror global patterns per the 2016 State of the World’s Birds report:
- 44% of extant bird species worldwide are declining
- Agricultural and forest species show greatest declines
- Habitat specialists and long-distance migrants are disproportionately threatened
However, some adaptive generalists like ravens, gulls and egrets have increased with human landscapes. But overall, industrial agriculture coupled with climate change poseexistential threats for many birds worldwide.
IUCN Red List Bird Status
The IUCN Red List categorizes extinction risk of all bird species based on population trends. Of the over 10,400 extant species, the 2020 Red List status breakdown is:
IUCN Category | Number of Species | Percentage of Extant Species |
---|---|---|
Least Concern | 6,657 | 64% |
Near Threatened | 869 | 8% |
Vulnerable | 774 | 7% |
Endangered | 461 | 4% |
Critically Endangered | 191 | 2% |
Extinct in Wild | 5 | <0.1% |
Extinct | 158 | n/a |
TOTAL | 10,115 | 100% |
While most species are still relatively secure, over 1,300 species face heightened extinction risk warranting conservation action. Habitat protection, sustainable agriculture, mitigating climate change, and reducing exploitation will be critical for bird conservation worldwide.
Citizen Science for Monitoring Birds
Citizen science programs engage public volunteers in scientific research. For birds, these projects can exponentially increase data collection on distributions, migrations, breeding, survival and threats. Some major citizen science initiatives include:
Christmas Bird Count
- Annual winter bird census started in 1900, now globally coordinated by Audubon
- Over 70,000 volunteers conduct counts following standardized protocol
- Provides long-term data on population trends, shifts in winter ranges
Breeding Bird Survey
- Breeding season surveys started in 1966 across North America
- Over 3,200 skilled birders conduct roadside point counts
- Monitors status, trends, distributions of >420 native species
eBird
- Worldwide citizen science database of bird sightings launched 2002
- Over 600,000 participants contributed >1 billion entries to date
- Data repositories for distribution, abundance, migration, breeding
These massive datasets advance avian research and conservation. Anyone can contribute to scientific knowledge by reporting local bird observations.
Technology for Bird Monitoring
Innovative technologies are also facilitating bird population monitoring, including:
GPS Tracking
- Miniaturized units attached to birds reveal migratory paths and habits
- Tags transmit locational data via satellite or radio
- Provides detailed individual movement and behavioral data
Remote Sensing
- Aerial and satellite imagery used to survey habitats and detect birds
- Drones, camera traps and audio recorders gather data remotely
- Can cover inhospitable terrain lacking ground access
Radar and Acoustics
- Weather radar detects flocks, provides broad biomass measures
- Acoustic sensors record calls, estimate occupancy rates
- Passive, continuous data collection independent of weather/light
Integrating these technologies with traditional surveys and citizen science will enhance avian research, guiding conservation efforts worldwide.
Conclusion
Determining Earth’s total bird population remains an imperfect science due to the inherent challenges of surveying highly mobile, disparate species inhabiting diverse global biomes. However, scientists estimate global numbers in the tens to hundreds of billions, comprising over 10,000 different species. While most species are still secure, over one-quarter face heightened extinction risk from human impacts like habitat loss, exploitation, pollution, and climate change. Expanding protected areas, practicing sustainable agriculture, reducing emissions, and monitoring populations through technological and citizen science advances will be key to ensuring birds remain a vibrant part of ecosystems worldwide.