This is an interesting question that many people may wonder about. At first glance, it seems like there could be more birds, since we often see flocks of birds flying overhead. However, the world’s oceans cover over 70% of the planet’s surface, suggesting there is a vast habitat available for fish populations. To truly determine whether fish or birds are more numerous, we need to consider the global populations of the major groups in each category.
Fish Populations
According to research, there are approximately 33,100 species of fish worldwide. This includes both saltwater and freshwater species. The four most diverse groups of fish are:
- Ray-finned fish – This is the dominant group, comprising nearly 99% of all fish species. There are about 31,300 ray-finned fish species.
- Sharks and rays – There are over 1,000 species of cartilaginous fish, including sharks, rays, and chimaeras.
- Lobe-finned fish – This rare ancient group contains under 10 species, including coelacanths and lungfish.
- Jawless fish – The most primitive group, hagfish and lampreys make up around 120 species.
In terms of numbers, a 2021 estimate put the global fish population at around 950 billion to 2.7 trillion. However, estimating fish populations precisely is challenging due to their aquatic habitat and elusive nature. The most abundant groups are small, fast-reproducing species like herrings, anchovies, and sardines.
Saltwater Fish
The ocean contains over 250,000 known marine fish species across a diverse range of habitats, from coral reefs to the deep sea. Small species that produce huge numbers of eggs, like bristlemouths, dominate the biomass. Though less numerous, open ocean predators like tuna can reach weights over 1,500 pounds.
Some of the major groups of saltwater fish include:
- Herrings and anchovies – Extremely abundant, with over 400 species.
- Gobies – Over 2,000 species, common on coral reefs.
- Bristlemouths – Tiny midwater fish, likely Earth’s most abundant vertebrates.
- Lanternfish – Bioluminescent mesopelagic fish, with over 250 species.
- Salmons and smelts – Important commercial and ecological species, around 160 types.
- Cods – Including Atlantic and Pacific cod, hakes, around 200 species.
- Snipefish – Strange-looking deep sea dwellers, over 90 species.
Though less diverse, large open ocean hunters like marlins, swordfish, and tuna are keystone species in marine food webs.
Freshwater Fish
While less extensive than the oceans, freshwater lakes and rivers also support huge numbers of fish. Nearly 41% of the world’s fish species are found exclusively in freshwater. Major groups include:
- Carp and minnows – Over 3,000 species, found worldwide.
- Catfish – Ranging from tiny parasites to giant predators, around 3,000 species.
- Perch – Familiar species like bass and walleye, over 210 species.
- Pike – Voracious ambush predators, about 50 species.
- Killifish – Thousands of small species, often found in temporary pools.
- Sturgeon – Ancient giants like beluga sturgeon, 29 species.
- Eels – Catadromous fish that migrate between rivers and the sea, 800+ species.
Though smaller than the oceans, lakes and rivers clearly hold an enormous diversity of fish adapted to freshwater habitats.
Bird Populations
In comparison to fish, estimating global bird populations presents similar challenges. However, we have a clearer sense of total species diversity, with around 10,000 known living species of birds according to most experts. The main groups of birds include:
- Passerines – Perching songbirds make up over half of all bird species, around 5,700 types.
- Parrots – With macaws, cockatoos and budgerigars, roughly 400 species.
- Hawks and eagles – Raptors like hawks, eagles, kites, around 250 species.
- Hummingbirds – Specialized nectar-feeders, around 340 species.
- Loons – Divers like loons and grebes, about 40 species.
- Kingfishers – Fish-eating birds like kingfishers and kookaburras, around 120 species.
- Herons – Wading birds like egrets and bitterns, around 90 species.
- Pelicans – Large waterbirds, about 10 species.
- Penguins – Flightless aquatic birds of the southern hemisphere, around 20 species.
The global population of birds is estimated to be 50 to 400 billion, though only roughly 13 billion individual breeding birds. The most abundant types of birds by far are smaller species like sparrows, finches, and warblers.
Comparison
Based on these numbers, there are likely far more fish in the world than birds. While both estimates are rough, fish populations seem to outnumber birds by at least an order of magnitude. There are over 30,000 fish species encompassing habitats from coral reefs to the deep sea, while birds occupy mainly terrestrial and wetland environments. The tiny bristlemouth may be Earth’s single most abundant vertebrate. While small passerine birds are certainly numerous, they do not seem to compare with the huge numbers of fast-reproducing fish occupying the world’s oceans. Lake and river habitats harbor an enormous additional diversity of fish as well. Overall, the preponderance of evidence points to global fish populations dwarfing birds in terms of biomass and number of individuals.
Challenges in Estimating Global Populations
Estimating global populations of fish and birds both present unique challenges that make precision difficult.
For marine fish, the obstacles include:
- Aquatic habitat – Sampling the open ocean at depth is logistically difficult.
- Patchy distributions – Fish concentrate in shifting schools and clusters.
- Elusive species – Many fish exhibit camouflage or are nocturnal.
- Microscopic larvae – Early life stages are abundant but extremely hard to quantify.
- Undescribed species – New marine fish are still being discovered.
For birds, the main difficulties are:
- Migration – Birds migrate and have shifting ranges making counts challenging.
- Forest habitat – Canopy-dwelling birds are hard to survey systematically.
- Cryptic species – Camouflaged birds are easily overlooked.
- Irregular breeding – Breeding periodicity depends on food availability.
- Vast ranges – Birds like albatrosses range across whole oceans.
These factors limit our ability to make precise global estimates. However, approximations using conservative assumptions still reveal far higher fish abundance compared to birds.
Geographic Patterns
Beyond just global numbers, looking at geographic patterns also reveals clues about the relative abundance of fish versus birds.
Fish Biogeography
For fish, biomass and diversity peaks in warm shallow ocean waters near coastlines and around coral reefs. Key geographic patterns include:
- Tropical coastal seas – Habitats like mangroves and lagoons harbor huge fish biomass.
- Upwelling zones – Cold upwelled water creates blooms of krill and forage fish.
- Reefs – Coral reefs support extremely high fish diversity and abundance.
- Deep sea – While less productive, the deep sea still harbors many unique fish.
- Lake hotspots – African rift lakes harbor hundreds of endemic cichlid species.
- Large rivers – Amazon and Mekong rivers have incredibly diverse freshwater fish.
So while present across the oceans, fish biomass concentrates in the highly productive tropics and subtropics near coasts.
Bird Biogeography
For birds, diversity peaks in tropical regions, while seasonal concentrations occur at higher latitudes:
- Lowland tropics – Flocks of colorful tanagers, antbirds, etc. fill neo-tropical forests.
- Coral islands – Seabirds aggregate in huge numbers to breed on remote islands.
- Wetlands – Marshes and mudflats harbor huge migratory shorebird concentrations.
- Montane forests – Tropical mountain forests are filled with endemic hummingbirds, honeycreepers, etc.
- Boreal forests – Seasonal concentrations of ducks, warblers, sparrows migrate here to breed.
Birds occur across most of world, but unlike fish do not have marine habitats and endemic Antarctic species. Their diversity peaks in tropical regions.
Ecological Roles
Beyond diversity and numbers, fish and birds also play very different ecological roles within their environments.
Fish Ecology
As primarily aquatic animals, fish interact with their environments in unique ways:
- Mobile links – Fish link food webs from corals to open oceans.
- Nutrient recycling – Fish excretion and migration promote nutrient cycling.
- Habitat engineering – Many fish shape their environments through browsing, digging, etc.
- Predator-prey – Fish are key prey for marine mammals, seabirds, larger fish.
- Grazers – Herbivorous fish graze on algae and maintain reef health.
- Seed dispersers – Fish dispersal helps spread aquatic vegetation.
- Scavengers – Deep sea fish scavenge falling carcasses.
Fish essentially help drive the ecology of the world’s oceans and freshwaters through these diverse interactions.
Bird Ecology
As terrestrial vertebrates, birds interact with their environments in contrasting ways:
- Mobile links – Birds connect habitats by dispersing seeds and nutrients.
- Pollinators – Hummingbirds, sunbirds, honeycreepers pollinate tropical plants.
- Insectivores – Many birds help regulate insect populations.
- Scavengers – Vultures and seabirds clean up carcasses and waste.
- Seed dispersers – Berries adapted for bird ingestion help plant dispersal.
- Predator-prey – Birds of prey help regulate small mammal populations.
- Soil turnover – Through digging, large seabirds enrich breeding islands with guano.
Birds fill parallel niches on land, air, and water to fish in marine ecosystems.
Significance for Conservation
The enormous populations yet fragile nature of many fish and bird species are important considerations for conservation.
Fish Conservation Importance
Key conservation concerns for fish include:
- Overfishing – Commercial fishing threatens whales, tuna, sharks, and other large species.
- Habitat loss – Development, pollution, dams threaten lakes, rivers, wetlands, and reefs.
- Invasive species – Introduced fish outcompete native species.
- Climate change – Warming and acidification impact fish physiology and habitats.
- Bycatch – Wasteful net fishing catches and discards immense numbers of fish.
Urgent reforms of fishing practices and habitat protections are needed to preserve fish abundance and diversity.
Bird Conservation Importance
Major concerns impacting bird populations include:
- Habitat loss – Agriculture and urbanization destroy forests and grasslands.
- Hunting and poaching – Raptors, parrots, and shorebirds are still over-hunted in many regions.
- Invasive species – Introduced predators like rats and cats threaten island birds.
- Climate change – Disrupting migration, breeding, and insect food-chains.
- Pollution – Pesticides accumulate in birds, killing raptors and seabirds.
Conserving habitats and outlawing unsustainable hunting are priorities for preserving endangered birds worldwide.
Clearly, maintaining both fish and bird populations is crucial for sustaining functioning ecosystems. Their futures are intertwined through aquatic and terrestrial food webs. Only through thoughtful stewardship can we ensure their abundance is preserved.
Conclusion
While exact numbers are uncertain, current evidence suggests there are far more fish than birds globally. The world’s oceans, lakes, and rivers support enormous biomass of fish, from tiny bristlemouths to giant tuna. While less productive, tropical terrestrial habitats harbor extremely high avian diversity. However, birds occupy a smaller range of primarily terrestrial environments. Ultimately, fish dominate vertebrate abundance on Earth largely thanks to their expansive ocean habitats. However, both fish and birds play vital ecological roles through unique interactions in their respective environments. Conserving both groups is crucial for maintaining functioning ecosystems. In summary, while birds are more visible creatures, fish comprise the larger portion of global vertebrate biomass and diversity.
