What is the effect of the type of food available on the frequency of different types of bird beaks? ”

Why do they exist different types of beaks?

Well as the question indicates, it is all about food. Think of the beak as a tool, and you use the best tool to ease the job you have in front of you, so do birds, depending on the type of food we have:

These birds feed on meat, and the beaks are strong and hooked with the upper part longer than the lower, hooking down. This works to tear and pull flesh from their prey. Examples are eagles, falcons, and vultures.

This diet is based mainly on seeds. The beaks are short, robust and end in a conical shape, making it easy to break seeds. Goldfinches, sparrows and canaries are examples.

These are birds that feed on fruit, and sometimes on seeds. Their beaks are short and curved with a specialized sharp tip for extracting the edible part of the seeds.  The lower part is flat and sharp, for cutting into hard fruits.

Beaks for hunting insects. These vary, if they are for hunting them in the air the beak is usually short, wide and flat. Like the swallow and the swift. If the bird catch insects when they are still, their beaks are short, straight and thin beaks, such as the robin.  If the insect lives deep underground or inside bark, the beaks have thin, elongated shapes, and are very strong, like the woodpecker.

These have long beaks, to eat invertebrates at the bottom of ponds and marshes, while keeping their heads out of the water, like the stork.

These birds feed on fish, usually by water diving. They have large, strong beaks with a curved tip or serrated ridges to secure their prey, like seagulls.

An example would be flamingos, with wide, flat beaks. These have adapted to help obtaining food from pond and riverbeds, the beaks also have holes to filter their prey from water.

These birds feed on flower nectar by inserting their beaks inside them. The beaks are thin and long usually adapted to the shape of the most common flower in the area, an example would be the hummingbird.