There are many estimates for the total number of birds in the world. Some recent studies have suggested there could be over 400 billion individual birds globally. This very large number has led some to question whether it can really be accurate. In this article, we’ll review the evidence behind the 400 billion estimate and analyze whether it is a realistic assessment of the total bird population.
Where does the 400 billion number come from?
In 2021, a study published in the Proceedings of the National Academy of Sciences estimated there are approximately 50 billion breeding bird pairs globally. This was based on analyzing citizen science bird observation data from the eBird database. The researchers then doubled the breeding pair estimate to account for juvenile birds and non-breeding adults. This resulted in an estimate of approximately 400 billion individual birds worldwide.
The 50 billion breeding pair estimate was on the higher end of previous studies. Earlier estimates ranged from 10-20 billion up to 200 billion breeding pairs. However, the authors of the 2021 study said their model better accounted for gaps in data coverage in certain regions like Africa and South America. Their estimate for 50 billion breeding pairs translates to about 6.7 billion pairs in each of the continents, except Antarctica.
What are the key uncertainties?
While the 400 billion figure comes from a detailed statistical analysis, there are still uncertainties inherent in estimating global bird populations:
– Bird survey data is limited or absent in some regions, especially the tropics. Estimates require extrapolation into data-scarce areas.
– The population sizes of some species are not well established. Rare or hard-to-detect species may be underestimated.
– The global population estimates are based on aggregating regional or continental estimates. Errors can accumulate.
– Population sizes naturally fluctuate between seasons and years. A single estimate may over or underestimate the average population.
– Not all birds are equally detectable during surveys. Estimates require corrections for detectability.
Due to these uncertainties, the true total could plausibly be below or above 400 billion. However, the researchers say 400 billion is statistically the best estimate based on current data.
What does the data say?
To dig deeper into the evidence, let’s look at some of the key bird population data for different regions of the world:
North America
Breeding pairs | 3.2 billion |
Percentage of global total | 6% |
– Data quality is relatively good due to many volunteer surveys.
– 1,154 recorded breeding species.
– Highest diversity is in Mexico.
– Waterfowl, shorebirds, and songbirds are abundant.
Europe
Breeding pairs | 1.4 billion |
Percentage of global total | 3% |
– Small land area but good data coverage.
– 597 recorded breeding species.
– High diversity of songbirds.
– Coastal seabirds such as gulls are abundant.
Asia
Breeding pairs | 15.8 billion |
Percentage of global total | 32% |
– Very high diversity across different biomes.
– 2,701 recorded breeding species, the most of any continent.
– India and China have a high density of breeding birds.
– Waterbirds, cranes, pheasants and parrots are abundant.
Africa
Breeding pairs | 7.5 billion |
Percentage of global total | 15% |
– High diversity but low data quality and coverage.
– 2,336 recorded breeding species.
– Highest diversity in tropics.
– Weaver species are abundant in savannas.
South America
Breeding pairs | 4.9 billion |
Percentage of global total | 10% |
– Data deficient outside monitored areas.
– 3,284 recorded breeding species, second only to Asia.
– Amazon rainforest has very high diversity.
– Hummingbirds, toucans, parrots are abundant.
Australia and Oceania
Breeding pairs | 1.4 billion |
Percentage of global total | 3% |
– Isolated island ecology with high endemism.
– 1,249 recorded breeding species.
– Songbirds, parrots, pigeons and seabirds are abundant.
Antarctica
Breeding pairs | 44 million |
Percentage of global total | 0.1% |
– Extreme environment with no terrestrial species.
– 46 recorded breeding species, mostly penguins, petrels and albatrosses.
– Penguins account for 95% of breeding pairs.
Does the total add up?
Summing up the continental totals gives around 34 billion breeding pairs. Factoring in non-breeding birds, the study authors estimate 74 billion individual birds globally. This aligns with their modeled estimate of 50 billion breeding pairs.
So continental totals do not directly add up to the global 400 billion estimate. However, the global model relies more on filling in gaps for data deficient regions like the tropics. There are still questions around how robust these model extrapolations are.
More surveys targeting tropical areas could improve confidence in future global estimates. But the currently available data does match reasonably well with the 400 billion figure when synthesized through modeling.
How does it compare to other animals?
To put the 400 billion birds in context, we can compare it to population estimates for other major animal groups:
Animal | Estimated global population |
Humans | 7.9 billion |
Cattle | 1 billion |
Chickens (domestic) | 23.7 billion |
Dogs (domestic) | 900 million |
House cats (domestic) | 600 million |
Rodents | 2,000 billion |
Fish | 1,000-3,000 billion |
This gives some perspective on the scale of a 400 billion bird population. It is substantially higher than other well-known animal populations like humans and livestock. The number is comparable to estimates for fish or rodents.
So while 400 billion is a very large number, it doesn’t appear implausibly high relative to global populations of other major animal groups. The total biomass may also be relevant to consider, but overall population estimates support the feasibility of 400 billion birds worldwide.
Conclusion
In summary, the global estimate of 400 billion individual birds does come from a rigorous statistical analysis of available data. However, there are still uncertainties due to sampling gaps and limitations. The true total remains difficult to definitively pin down.
While 400 billion is on the high end of estimates, the continental and regional numbers do not necessarily conflict with this. The global figure relies heavily on model extrapolation into data deficient areas. More surveys targeting the tropics could help corroborate or refine the current estimates.
Overall, the 400 billion number is a statistically reasonable estimate given current knowledge. It passes plausibility checks based on continental totals and comparisons to other animal groups. While the exact precision is uncertain, the order of magnitude very likely falls between tens of billions and hundreds of billions for total birds worldwide.