Birds are survivors.


Many birds, or at least their ancestors, were already in existence tens of millions of years ago. In the following table I list the earliest time (mya) in which some of the ancestors of birds of birds we know today are believed to have existed:-

65 60 55 50 45 40 35 25
Tinamou Albatross Roller Falcon Stork Kingfisher Flamingo Pigeon
Ostrich Loon Trogon Swift Cuckoo
Guan Cormorant Woodpecker Rail Sandpiper
Waterfowl Heron Gull
Penguin Owl

This implies is that, having evolved in a suitable habitat, these birds and their offspring have been able to survive the many changes that have taken place between the time they evolved and the present day. So how have they managed to do this?

Habitat changes.

The explanation is to be found in the long time period involved and the fact that the evolutionary activity has taken place over a world-wide geographical area. The mobility of most birds means that they can access a variety of habitats over very large geographical areas. Opportunities for geographical isolation of populations, brought about by long term tectonic plate movements, volcanic events, glacial or climatic events and human activities, have facilitated the evolution of new species or sub-species which were better adapted to the new conditions which prevailed.

  • In the period 65 to 55 mya much of the land was covered by dense forests with beech trees, oaks and conifers. Dinosaurs and other giant reptiles lived there until they became extinct following the K/T event 65 mya. This paved the way for mammals and plant eating birds to evolve. Much of what we now know as dry land was underwater, since sea levels reached their highest ever during this time. Plant materials, fish and aquatic invertebrates were available in the seas and provided food for ancestors of birds such as Waterfowl, Penguin, Albatross, Loon, Cormorant and Heron which evolved in aquatic environments.
  • In the period 55 to 35 mya forests thrived and trees grew even in polar regions. This provided a good habitat for birds like the ancestors of the Roller, Trogon and Woodpecker to evolve. Eventually the climate became cooler and drier.
  • The period 35 to 25was the time when grasslands began to expand and forests - especially tropical ones - shrank correspondingly. Animals evolved to fit the new, open landscape and many fast-running prey and predator species arose as a result. This, I believe, was when the Ostrich adapted from being a forest dweller to favour the open areas of grassland and scrub where it could see potential predators and run fast to escape. It had certainly become flightless by then.
  • In the period 25 to 5 mya grasslands continued to expand and forests to dwindle in extent. Flood basalt eruptions, a type of large-scale volcanic activity, both in terms of extent and duration, that can occur on land or on the ocean floor frequently occurred during this period so the landscape in general gradually changed from tropical heat and steamy jungles to searing deserts. In the seas, kelp forests made their first appearance.
  • In the last 2.5 million yearsfossil evidence has shown that ancestral land-birds maintained broadly similar habitat preferences to those exhibited by the species we know today.

Roughly half of the birds listed in the table above favour an aquatic environment. Oceans, seas and inland waters were available to various extents throughout the period 65 mya to the present day. Waterfowl, Penguin, Albatross, Loon, Cormorant, Heron, Gull, Flamingo and Kingfisher always had the environment they needed although the habitats within it will have varied.

Habitats ancient and modern.

In looking at ancient habitats it has been argued that prehistoric British forests and their bird life were similar to those persisting in a near-primeval condition in the Białowieża Forest on the Polish/Belarussian border. It has been favourably compared to the primary Amazon rain-forest. While birding in Poland in May 2004 and were fortunate to be able to visit the forest with an accredited guide. A very memorable visit.

The Common Swift, which elsewhere nests entirely in buildings in towns and villages and is absent from woods, still nests in tree holes in old growth in the Bialowieza forest. The Common Buzzard which now nests in mature woodlands and forages in open country, nests high in the forest trees and forages under the canopy in Bialowieza.

Some birds have profited considerably in modern habitats. The Common Wood Pigeon which used to nest in old growth forest and had poor nest success due to predators, now has very good nest success nesting in urban parks with very few predators.

The Mute Swan used to breed on large open lakes but has now started to breed on smaller water bodies closer to human habitation.