Bird populations have been declining at an alarming rate in recent decades. According to the North American Breeding Bird Survey, nearly 3 billion birds have been lost in the United States and Canada since 1970, representing a 29% decline in total bird numbers[1]. This loss of avian biodiversity is a cause for serious concern, as birds play vital ecological roles including pollination, pest control, and seed dispersal. Understanding the key threats facing bird populations is crucial to developing conservation strategies to reverse ongoing declines.
Why are birds declining?
The reasons for declining bird numbers are complex, but several major factors have been identified by ornithologists:
Habitat loss and degradation
Habitat loss due to human activities is the number one threat to birds globally. Development, urbanization, agriculture, resource extraction, and infrastructure projects destroy or alter natural habitats needed by birds for nesting, feeding, and migrating. Fragmentation of remaining habitat can also have detrimental effects by increasing predation and creating barriers to dispersal. Up to 75% of temperate and boreal forests have been degraded by human activity over the past 200 years[2]. Grassland habitats have seen even greater losses, with only 3% of tallgrass prairie remaining intact in the U.S.[3] Deforestation in the tropics, often for palm oil or soy production, threatens species rich rainforests that serve as wintering grounds for many migratory birds. Overall, habitat loss disproportionately affects species with specialized habitat requirements.
Climate change
Climate change poses a severe and growing threat to many bird species. Rising temperatures are causing shifts in natural ranges, mismatch between migration timing and food availability, increased drought and wildfires, sea level rise threatening coastal nesting habitats, and extreme weather events. The Intergovernmental Panel on Climate Change estimates that a 1.5°C rise in global average temperature will put 9% of bird species worldwide at risk for extinction[4]. Some severely affected groups include seabirds reliant on localized food sources, Arctic shorebirds and waterfowl with rapidly changing breeding habitat, and desert species already living near temperature thresholds. Climate change exacerbates existing stressors like habitat loss, compounding extinction risk for vulnerable species.
Agricultural intensification
Increasing mechanization, chemical inputs, field consolidation, and loss of non-crop habitat have made agricultural landscapes inhospitable for many bird species. Pesticides reduce insect food sources and can accumulate in the bodies of birds leading to poisoning or reproductive effects. For example, Neonicotinoid pesticides have been implicated in declines of aerial insectivores like swallows and swifts[5]. The transition to monoculture crops lacking plant diversity removes vital seed and cover resources for granivorous and ground-nesting birds. Draining wetlands and converting grasslands to row crops destroys important habitats outright. Agricultural intensification reduces biodiversity and bird numbers across whole landscapes.
Invasive species
Invasive animal and plant species often outcompete or threaten native bird communities. Introduced birds like European starlings compete with native cavity nesters for limited nesting sites. Invasive snakes, rats, and cats prey on eggs and chicks, decimating ground-nesting populations. Non-native plants displace diverse native vegetation relied on for food and cover. For example, Eurasian Phragmites grasses overtake coastal wetlands and decrease habitat quality for endangered birds like the Saltmarsh Sparrow[6]. Invasive species are more likely to become established and spread in degraded habitats, compounding habitat loss issues. Island species lacking coevolved defenses are especially vulnerable.
Overexploitation
Direct overexploitation of birds remains a problem in some areas despite protections. Harvesting of adults and eggs for food, pets, feathers, or medicinal use has extirpated or endangered vultures, parrots, and other prized species over much of their range. Large terrestrial bird species sensitive to hunting pressure, like pheasants, grouse, and curassows, have experienced population declines even in regulated contexts due to difficulty enforcing poaching bans. Indiscriminate trapping techniques also pose risks to non-target species. Bycatch from fisheries is another additive mortality source for seabirds globally. While now illegal in many countries, overexploitation still threatens bird populations in some regions.
Other threats
Additional factors contributing to bird mortality and population declines include:
- Collisions with buildings, transmission towers, and other structures
- Vehicle strikes
- Predation and nest parasitism by species associated with human activity, like corvids and brown-headed cowbirds
- Disease outbreaks which may increase with climate change and habitat fragmentation
- Air pollution that can poison or cause injury
- Noise pollution that interferes with communication
Though less severe than the largest drivers, cumulative impacts from these threats further endanger birdlife.
Which species are most affected?
While bird populations have declined alarmingly overall, some groups have been harder hit than others:
Grassland birds
Grassland species have experienced some of the steepest declines, with population losses of over 50% since 1970. Intensive row crop agriculture has destroyed native prairie and converted grasslands to unsuitable habitat. Affected species include meadowlarks, bobolinks, dickcissels, and many sparrows.
Shorebirds
Many shorebird species that migrate long distances and rely on sensitive coastal or wetland habitats have seen precipitous declines. Destruction of stopover habitat and breeding grounds through development is a major cause. Examples include red knots, dunlins, Western sandpipers, and sanderlings.
Aerial insectivores
Swallows, swifts, flycatchers, and nightjars that feed aerially on insects have exhibited widespread declines, likely due to pesticides reducing prey numbers. The common nighthawk population, for instance, dropped by over 60% since 1970. Even traditionally common species like chimney swifts are rapidly decreasing.
Boreal forest birds
Species breeding in northern boreal forests, like wood warblers, have declining populations as climate change degrades habitat and alters food webs. Half of all North American boreal birds are currently decreasing. Rusty blackbird numbers have fallen 85-99% in some regions.
Western forest birds
Habitat loss and fragmentation in western forests have put species like the spotted owl in jeopardy. Other populations in decline include Lewis’s woodpecker and Williamson’s sapsucker as old-growth habitats shrink.
Arctic birds
Tundra habitat is disappearing rapidly due to climate change, impacting birds like red-throated loons and buff-breasted sandpipers that breed in Arctic and subarctic regions. Snowy owls are also struggling with lemming population crashes linked to warming.
Hawaiian birds
Island species are inherently more vulnerable, and Hawaii has lost most of its native bird diversity. Over 75% of Hawaiian birds have gone extinct since human colonization, primarily from habitat loss compounded by invasive species impacts. Surviving species remain critically endangered.
Bird Group | Example Species | Population Trend |
---|---|---|
Grassland birds | Eastern meadowlark, bobolink, Savannah sparrow | 53% decline since 1970 |
Shorebirds | Ruddy turnstone, semipalmated sandpiper, short-billed dowitcher | Average 37% decline |
Aerial insectivores | Barn swallow, common nighthawk, chimney swift | 59% decline |
Boreal forest birds | Magnolia warbler, bay-breasted warbler, rusty blackbird | 50% of species declining |
Western forest birds | Spotted owl, Lewis’s woodpecker, pygmy nuthatch | Moderate to steep declines |
Arctic birds | Snowy owl, buff-breasted sandpiper, red knot | High vulnerability |
Hawaiian birds | ‘Akiapōlā’au, kiwikiu, nene goose | 75% extinct, survivors endangered |
What can be done?
Given the ongoing bird crisis, action must be taken to reverse population declines. Here are some priority conservation strategies:
Habitat protection and restoration
Preserving intact habitat and restoring degraded areas is essential for protecting bird populations. This requires initiatives like designating protected areas, managing public lands appropriately, reducing fragmentation, restoring wetlands, removing invasive plants, and planting native vegetation. Particular focus should be placed on safeguarding habitats needed by declining grassland and boreal species. Financial incentives for landowners can aid conservation on private property.
Sustainable agriculture
Making farmland more bird-friendly through regenerative agriculture practices can counteract biodiversity declines in agricultural regions. Strategies include planting hedgerows and cover crops, using integrated pest management, retaining wetlands and fallow fields, reducing chemical inputs, and implementing agroecological farming models. Government policies and food industry initiatives can encourage sustainability.
Threatened species recovery
Endangered birds require direct management interventions to avoid extinction. This can involve captive breeding, control of invasive predators, protecting nest sites, supplementing food sources, and translocations to suitable habitat. Continued monitoring is necessary to assess effectiveness. Legal protections should aim to preserve critical habitat. Prioritizing Hawaii’s endemic birds is especially important.
Urban habitat development
Creating green spaces, parks, green roofs, and bird-friendly yards and gardens in cities can aid declining urban-adapted and migratory species. Reducing building collisions through treatments such as tape, UV-reflective glass, and lights-out programs also helps. Planning guidelines should promote vegetation and reduce threats. Engaging the public in citizen science monitoring and habitat projects builds awareness.
Climate change mitigation and adaptation
Reducing greenhouse gas emissions is needed to contain global warming to levels tolerable for birds and other wildlife. At the same time, facilitating bird adaptation through enhancing habitat connectivity and protecting climate refugia creates resilience. Planning for anticipated range and distribution shifts allows successful conservation across changing conditions.
Reducing exploitation
Banning hunting, nest poaching, and trapping where still practiced unsustainably controls a direct threat. Eliminating illegal international trade in wild birds through enforcement and cooperation between nations is also impactful. Implementing solutions like better fisheries bycatch mitigation reduces non-target mortality.
Funding and policy reform
Expanded funding for bird research and conservation programs can deliver needed action. Legislative protections like the Neotropical Migratory Bird Conservation Act and Endangered Species Act must be maintained or strengthened. Policy reforms promoting wetland protection, pesticide regulation, sustainable land management, and natural resource planning can benefit birds indirectly.
Education and monitoring
Monitoring bird population trends allows assessing conservation outcomes over time. Engaging citizen scientists in surveys expands data collection capabilities. Environmental education programs and public outreach raise awareness on birds, threats like invasive species, and ways to help. Building human connections to nature this way fosters broader support.
The future of birds
With sustained commitment from governments, businesses, communities, and individuals to implement science-based conservation strategies, recovery of imperiled birds remains achievable. However, lack of action will lead to continued net loss of avian biodiversity and essential ecosystem services. Preventing extinctions and fostering thriving, resilient bird populations for generations to come requires society to address the key threats driving declines. Each small step matters, but meeting the magnitude of the extinction crisis calls for bold, transformative change across political, economic, and social systems. Our shared future with birds depends on the choices made today. There is still hope, but time is running out.
References
1. Rosenberg, K.V., Dokter, A.M., Blancher, P.J., Sauer, J.R., Smith, A.C., Smith, P.A., Stanton, J.C., Panjabi, A., Helft, L., Parr, M. and Marra, P.P., 2019. Decline of the North American avifauna. Science, 366(6461), pp.120-124.
2. Watson, J.E., Shanahan, D.F., Di Marco, M., Allan, J., Laurance, W.F., Sanderson, E.W., Mackey, B. and Venter, O., 2016. Catastrophic declines in wilderness areas undermine global environment targets. Current Biology, 26(21), pp.2929-2934.
3. Samson, F.B., Knopf, F.L. and Ostlie, W.R., 2004. Great Plains ecosystems: past, present, and future. Wildlife Society Bulletin, 32(1), pp.6-15.
4. Warren, R., Price, J., Graham, E., Forstenhaeusler, N. and VanDerWal, J., 2018. The projected effect on insects, vertebrates, and plants of limiting global warming to 1.5° C rather than 2° C. Science, 360(6390), pp.791-795.
5. Hallmann, C.A., Foppen, R.P., Van Turnhout, C.A., De Kroon, H. and Jongejans, E., 2014. Declines in insectivorous birds are associated with high neonicotinoid concentrations. Nature, 511(7509), pp.341-343.
6. Benoit, L.K. and Askins, R.A., 2002. Relationship between habitat area and the distribution of tidal marsh birds. The Wilson Bulletin, 114(3), pp.314-323.