Re-appearing Characteristics

When birds started to evolve, over 100 million years ago, the environment offered many possibilities and the random nature of the evolutionary process was such that a large variety of very different birds developed. Some were the ancestors of the birds we know today.

A broad-brush review of three periods during which these birds evolved enables me to highlight some of the characteristics which are subsequently seen again and again in the birds of the world. It is almost as if they were forecasting the vast range that was to come!

Evolutionary periods.

Period 100 to 65 mya.

Much of the land was heavily forested but large rivers and inland fresh-water lakes as well as desert areas existed. Dinosaurs roamed the earth and the seas and oceans were populated by predatory reptiles and fish. The extinction of the dinosaurs and other giant reptiles about 65 mya paved the way for small mammals to evolve:-

• On the land various plants provided food for ground foragers such as Tinamous and Ostrich and early Game birds like Guans and other members of the Cracidae family.

• Vegetation in inland waters favoured the evolution of aquatic grazing birds which became the Ducks, Geese and Swans which we know today.

• In the seas and oceans fish eating Penguins and Albatross evolved.

Period 65 to 50 mya.

Rising temperatures across the planet led to a period of global warming and by 55 mya the overall climate was wetter and sea levels had started to rise. Forests thrived and trees grew even in Polar regions. By 50 mya a further group of distinctive birds had evolved including:-

• Fish eating Cormorants, fruit eating Parrots and nocturnal hunting Owls. Three very distinctively different birds !

• Development of “dagger- beak” feeders such as the Heron and Bittern and the Rails each with its own behaviour pattern.

Trogons, Rollers and Woodpeckers which are all so obviously different in appearance, feeding technique and behaviour.

Swifts demonstrating agility in the aerial environment catching insects.

Falcons used the aerial environment in a different way to catch small mammals. This led to the development of carnivores with hooked beaks and talons which we call Birds of Prey.

Period 50 to 25 mya.

Towards the end of this period forests diminished to some extent being replaced by open grasslands. Further birds which evolved in this period included:-

  • Cranes and Storks which probably evolved about 35 mya.
  • Grebes and Flamingos.
  • Cuckoos may also have evolved about 35 mya.
  • Kingfishers.
  • Sandpipers.
  • Gulls evolved somewhere in the period 30 to 35 mya.
  • Pigeons and Doves were present and may have even evolved in an earlier period.

Body form variations.

Summarising the birds mentioned above in relation to the three evolutionary time periods, they can be represented by 25 to 30 groups, each of which are well known and can be defined by readily observable characteristics. The phrase "if it looks like a Duck and behaves like a Duck, it is a Duck" comes to mind. We can replace the word Duck by Flamingo, Heron, Gull, Pigeon etc, by any of the common names used above.

What all these birds have in common is a body, head, neck, two legs, two wings and a tail but this over-simplified view requires extension to include the type and nature of beak in relation to the head and the type and size of the feet and claws in relation to the legs. The variation of these physical features is considerable.

In general terms, birds which favour a terrestrial environment tend to be large and robust, often preferring to stand their ground or run when danger threatens. Medium sized birds often rely on camouflage to hide from predators.

Characteristics which re-appear.

Characteristics which are highlighted in the above groups and which re-appear, often several times, in later groups are:-

  • Large bodied birds - flightless, reluctant fliers, camouflage.

• Dagger-beaks – Herons, Bitterns, Rails, Kingfishers, Sandpipers, Gannets, Anhingas.
• Hooked tip beaks – Cormorants, Merganser, Frigatebird, Pelican, Hamerkop, Shoebill, some Rollers.
• Hooked beak and talons – Falcons, Vultures, Hawks, Eagles.
• Nocturnal hunters – Owls, Owlet- Nightjars, Nightjars, Potoos, Frogmouths.
• Agile fliers which feed on insects – Swifts, Tree-swifts, Swallows, Martins, Tropicbirds.
• Ground foragers – Bustards, Cranes, Thick-knees.
• Sea and Ocean birds – Petrels.
• Scavengers – Gulls, Pigeons,
• Ground camouflage - Sandgrouse

New characteristics to be added to this list are high-lighted in bold.

Large bodied birds.

Large, robust birds such as the Ostrich and Rhea mentioned above preferred to run and became flightless. Medium sized birds became reluctant fliers and some relied on camouflage for protection. These characteristics appeared again with the evolution of Emu, Megapodes, Chachalacas, Guineafowl, New World Quail, Pheasants and related birds.

Where birds were evolving in aquatic environments

2. Aquatic - swimmers with webbed feet - Ducks, Geese, Swans.
Aquatic - swimmers with long-lobed toes - Coot, Grebes.
Aquatic - swamps and reed-bed foragers - Swamphens, Moorhens.