Determining which bird species has the highest total population is not a straightforward task. There are over 10,000 recognized living species of birds, and obtaining accurate global population estimates for each one would be nearly impossible. However, by looking at the best available data, we can identify the bird species that likely have the largest numbers based on their widespread distributions and abundance.
In this article, we will look at the key factors that allow certain bird species to achieve very large populations across extensive ranges. We will also examine case studies of some of the most numerous bird species on Earth today. By better understanding the ecology and natural history of these highly successful avian species, we can gain insight into broader patterns of bird populations worldwide.
Key Factors Allowing Large Bird Populations
Certain intrinsic attributes of birds, along with favorable environmental conditions, enable some species to attain exceptionally high numbers and broad distributions. Here are some of the main factors that facilitate large populations:
Generalist Nature
Birds with generalized diets, habitat requirements, and other aspects of their ecological niche are better able to take advantage of diverse resources and environments. This allows their populations to grow across more extensive areas without being limited by specialized needs. Generalists like crows, gulls, and pigeons thrive alongside humans in developed areas, while other generalists like red-winged blackbirds exploit both wetlands and agricultural fields.
Rapid Reproduction
Species that mature quickly and produce many offspring per breeding attempt can rapidly grow their populations when conditions allow. Seabirds like gulls and terns have small bodies but lay up to three eggs per clutch and can breed multiple times per year. Passerines like sparrows and finches build open cup nests that allow for quick breeding cycles. These reproductive strategies result in exponential population growth when food, habitat, and other ecological needs are met.
Synanthropic Tendencies
Birds able to adapt well to human-altered environments gain access to abundant food and habitat provided inadvertently by human activities. Pigeons, house sparrows, European starlings, and other “synanthropic” species have achieved enormous global populations by associating with agricultural areas, cities, suburban neighborhoods, and other manmade environments. Their flexible diets and habits allow them to exploit these artificial resources.
Lack of Specialist Predators/Parasites
Specialist natural enemies like predators and parasites normally help keep prey populations in check. But some widespread generalist bird species experience relatively little predation or parasitism. With fewer checks on their numbers, fast-reproducing populations can grow enourmously. Hunting and egg-eating specialists have disappeared across much of invasive European starlings’ range, for example.
Mobility for Dispersal
The ability to fly allows birds to disperse over long distances and colonize new areas rapidly compared to flightless species. Seabirds like albatrosses and Arctic terns migrate enormous distances exploiting resources across global scales. Strong flying skills facilitate range expansions and population growth into new habitats and regions. Once established, large landbird populations spread further through short-distance dispersal.
By combining several of these traits, some bird species achieve populations numbering in the tens if not hundreds of millions across continents, oceans, and diverse ecosystems. Next, we will look at case studies of several bird species demonstrating this immense ecological success.
Case Studies of Highly Numerous Bird Species
The following bird species exemplify the largest global populations thanks to their generalist lifestyles, high reproduction, and other shared traits enabling exploitation of diverse habitat and resources.
Red-billed Quelea
Native to sub-Saharan Africa, the red-billed quelea or common quelea is likely the most numerous bird in the world. While lacking global population estimates, it forms enormous flocks of over 10 million individuals at shared roost sites across its broad range through central and southern Africa. A grain-eating specialist, it takes advantage of seasonal pulses in grass seed production, including cereal crops, to rapidly produce many offspring. With a short generation time, highly flexible breeding cycle and ability to migrate long distances, red-billed quelea populations can irrupt rapidly and exploit suitable habitat across Africa, becoming a major agricultural pest in the process.
European Starling
Native to Europe and parts of Asia, the European starling has been introduced across North America, Australia, New Zealand, and South Africa. It thrives in human-altered environments, forming large flocks and roosts in cities, suburbia, and farms exploiting abundant food from gardens, waste areas, and pastures. With few specialist predators in many regions where it has been introduced, and high annual reproduction of 5-8 eggs per clutch, enormous populations numbering over 200 million have arisen across the European starling’s globalized range.
Ring-billed Gull
The ring-billed gull breeds across northern North America from Alaska through Canada to the Great Lakes, northeastern USA, and Maritime provinces. Its global population likely exceeds 15 million, forming dense breeding colonies across inland lakes and coastal regions while exploiting fishery waste, garbage, and agricultural fields for food. Its generalist, opportunistic habits allow huge populations to exploit urban and suburban habitats successfully. Large-scale inland gull breeding is a relatively recent phenomenon facilitated by human activity and resource availability.
Barn Swallow
One of the world’s most widespread passerine species, the barn swallow occupies diverse habitat on all continents except Antarctica. Population estimates indicate 80-170 million individuals globally. Originally a cliff cavity nester, it has readily adapted to nesting on human structures like bridges, boathouses, and buildings, allowing it to exploit human-altered environments. Its aerial insectivore habits mean it can take advantage of swarming flying insects almost anywhere across its enormous range. The availability of nest sites facilitated by human infrastructure enables local-scale population irruptions.
Red-winged Blackbird
Abundant across North and Central America, the red-winged blackbird frequents both wetland and agricultural areas. Its global population likely exceeds over 200 million. Huge migratory flocks congregate in spring breeding grounds from temperate coastal to boreal wetlands, while other populations reside year-round in subtropical and tropical regions. It opportunistically exploits seasonal resources including grain crops, adapting its migration and breeding as needed. Despite habitat loss on wintering grounds, legal protection and abundant introduced foods maintain large populations.
Brown-headed Cowbird
Perhaps North America’s most abundant songbird, the brown-headed cowbird occupies diverse habitats across temperate North America. Unlike most passerines, it is an obligate brood parasite, laying eggs in other species’ nests. Without the need to raise its young directly, populations can focus energy on breeding, rather than parental care. Estimates suggest 70-150 million individuals exploit resources across agricultural land, pasture, and even urban areas through their broad generalist diet. Their reproductive strategy facilitates greater population growth than most native passerines.
Conclusion
While we lack definitive global census data to identify the single most populous bird species worldwide, the reviewed examples highlight shared traits facilitating huge populations. Species able to exploit human activity and food supplies readily, disperse widely, and reproduce prolifically sustain populations numbering in the tens if not hundreds of millions. Their flexible, generalist nature allows them to thrive across diverse regions and habitats. Examining these most successful bird species provides insight into the ecological factors driving avian populations to their enormous scales. Ongoing monitoring of population trends in these and related species will shed light on their continued success alongside human activities.
