One of the most fundamental questions about birds is, “How many birds are there?” But that question is not as simple to answer as it seems. For one thing, it lacks the precision necessary to tackle what is, and has been for over a hundred years, the difficult problem of determining exactly how many birds are present on earth.

So, we need to divide the problem into two more precise questions: “How many different bird species are there?, and “How many different individual birds are there?’

Of these two questions, the number of bird species is the one which most occupies the efforts of biologists and birdwatchers alike. In many places around the world, the high number of birdwatchers has ensured that there is literally an army of eyes watching the birds and keeping close track of them.

The result is that in those areas, which include North America, Europe, Australia and New Zealand, and many other scattered regions of the world, there is a pretty good idea of which bird species breed in an area, which are migratory, and which are only rarely sighted.

From the records kept by these biologists and birdwatchers, there is a very good knowledge base about how many species can be found in an area at different times of the year. However, there are still large areas of our planet where the bird community is not well known. Examples of these areas include the remote Amazon River basin in Brazil, the island of Papua New Guinea and the remote jungle islands of the south-east Pacific Ocean.

The end result is a fair amount of uncertainty about just how many bird species there are on earth. But the current, and most widely accepted number, is about 9,800 bird species.

This number is considerably higher than even estimates made in the recent past. In 1982, it was believed that there was a world total of between 8,600 and 8,700 species, with the belief that there were only about 50-100 birds left to be discovered. That was obviously a huge miscalculation on the part of the bird biologists.

There are several reasons why there was such a huge change in the total number of species over the past 25 years, and why that total number keeps slowly changing.

1 – Each year, new bird species are discovered, or in the case of species which were thought to have gone extinct, they are re-discovered. These happy discoveries are not all that common and in some years, add only 3 to 8 new species to the total. However, they indicate the possibility that there are still other new species out there, a fact which drives many scientists to continue the search.

2 – New areas are opened for exploration. In some cases, this can result from something as simple as a new road being built into a previously inaccessible area. This has lead to increased exploration of areas like the Amazon rain forests of South America.

In other countries, newly opened areas may have resulted from shifting political agreements. This was the case in Vietnam, a country which remained tightly closed to much of the world since the end of the Vietnam war in 1975. As the country slowly opened its borders to tourists and travellers, scientists and birdwatchers alike found that the Annamese Mountains which run along the length of the country were a virtual treasure trove of undiscovered species.

3 – Birdwatching is one of the most popular hobbies in many parts of the world. In North America, it ranks second behind gardening as a pastime. And the number of birdwatchers with the interest and income to travel for their hobby will only increase as the members of the Baby Boom generation start to retire in large numbers.

The result will be more people spending more time learning about birds and contributing information to the overall global database about birds. It is inevitable that with more knowledgeable birdwatchers tramping around the planet, more new species will be discovered.

4- Scientists who specialise in organizing birds into related groups and keeping track of the description of each species are known as taxonomists. As their understanding of the biology of each species increases, so does their ability to determine which bird is a separate species and which are, for example, simply two different color variations of the same species.

Every year, taxonomists publish updates of their discoveries about the relationships between closely related groups of birds. As a result, two birds which were previously thought to be separate species could now be considered as a single species. The opposite situation also happens; what was once believed to be a single species is now found to be actually two (or more) separate species.

A recent example of this taxonomic change occurred with the very common Canada Goose. For many years, scientists argued about whether there was just a single species of Canada Goose or whether the size range and color variations in its plumage meant that there were actually 21 different goose species.

The end result, after much study and even more arguments, was the splitting of the Canada Goose into two separate species: the larger birds remained known as the Canada Goose whereas the smaller-sized geese are now known officially as the Cackling Goose.

This kind of change in the number of bird species, regardless of how the number is changed, is reflected in the Clements Checklist of Birds of the World. This checklist is considered by most scientists to be the authoritative list for birds on Earth and the most recent edition (the 6th edition, which was published in 2005), incorporated hundreds of changes. And the final word from that authority was that the Earth now has, as far as we can tell, just over 9,800 different species of birds.