"Ornithologists estimate the diversity of living bird species in the entire world to be around 10,380. . . . That number almost doubles the number of extant mammal species (5,416) and is almost 3,000 more than extant amphibian species (7,509). The number of reptile species is the closest to the bird number with a current count of 10,272 extant species. Because most of these vertebrates are terrestrial, we have about 33,500 different species of terrestrial vertebrates on earth today. I am leaving out the aquatic vertebrates (mainly the fishes) because they would not have been represented on the Ark (33,200 fish species have been described, and the implications of that are important for creation scientists who are trying to model the diversity of all life from the Flood to the present).
How Did All Those Animals Fit on the Ark?
The answer to this question is more easily answered once we distinguish between biblical kinds and species. In Genesis 6:1–20 we read that Noah was commanded to take two of every animal kind into the Ark. Verse 20 makes clear that those animals would include two of every kind of bird. Later, God clarified that seven individuals of the clean animals, including some birds, would be on the Ark (Genesis 7:2–3). Does that mean that Noah had two (or seven) of all 10,380 extant bird species (more if you count extinct species)? If a biblical kind and a species were equivalent, then yes. But they are not the same; many species are categorized under each biblical kind.
Dr. Jean Lightner [a retired doctor of veterinary preventive medicine] has conservatively estimated that birds are comprised of about 196 created kinds. If we round that up to 200 bird kinds, we could account for all 10,380 extant species by each species diverging into two species just once every 750 years—just six times (200 to 400 to 800 to 1,600 to 3,200 to 6,400 to 12,800). That would even give us 2,420 more bird species to account for some extinction events. That is a very simplistic view and does not account for many variables, but it does provide us with a quick way to estimate if simple speciation (doubling) could account for all the birds we have today.
What Is a Species?
A group of sexually reproducing organisms that produce viable offspring is considered a biological species. Often this definition is clarified with the phrase “potentially reproducing”
Robins produce more robins. Bluebirds produce bluebirds. Could a male robin and a female bluebird produce a hybrid like a bluebin? No, they are different biological species.
To some people, what I just described [speciation] sounds too much like evolution. The evolutionary process definitely includes the idea of speciation, but the formation of species in response to geographic (or habitat) differences is consistent with a biblical worldview. Having over 10,000 different species of birds (not to mention mammals, reptiles, and amphibians), especially two of every kind and seven of the clean animals (many of the birds), would have been too much for Noah and his family to care for—not to mention house. The efforts of those involved with the Ark Encounter are providing us with realistic figures about the number of animals on the Ark. Having two of every bird kind and seven of every clean bird kind fits nicely.
[An example of the post-ark speciation]
If we follow the thrush kind out of the Ark, they could quickly scatter in many different directions. As they reproduced and their populations grew, they would find habitats that fit their needs. The variation potential in the Ark population would be displayed when different populations settled into different habitats. The populations would continue to grow and the variations inherent in their populations would allow them to quickly adapt to the new and developing habitats around the world. New species would form as geographic barriers isolated different populations.
Eventually one of the populations of the thrush kind that migrated to what is now North America has diversified into at least three species of bluebirds. One species is thriving in eastern North America, and the other two species are thriving in western North America. However, these three species can hybridize where their populations overlap, which indicates that the speciation process is not complete. However, if I ever see a mountain bluebird or a western bluebird, you can guarantee that I will put them on my life list as different species.
That was following just one lineage of the thrush kind. Now think of other lineages to other regions of the world. Then add to that all the other bird kinds, all originating from the Ark and migrating away from the modern day country of Turkey or one of the surrounding countries in the region. Variation among all the populations enabled spreading into various habitats in which to thrive. Populations continued diversifying as new habitats become available, thriving in those newer locations and filling the earth with birds and more birds so that today we have over 10,000 birds to enjoy and to add to our bird list.
source
