mdahlem.net

Home About Contact us Related links No AI

Birds Australia

Top Species list A-Z Family groups 1-26 Plumage Nests Habitats Key plants Passerines v non-passerines Glossary Sponsors Credits Photos Aboriginal information General information

Birds Europe

Top Species list A-Z Family groups 1-26 Plumage Glossary Credits General information

Birds Oman

Top Species list A-Z Family groups 1-26 Plumage Glossary Credits General information

Nat'l Parks

Top Australia Chile/Argentina Germany/Netherlands USA/Canada

Impressions

Top Australia Chile/Argentina Germany/Netherlands

Photos

Top Favourites Birds of Australia Australian weather shots Dew drops Dew drop animations How dew drop lenses work Birds of Oman Astronomical telescopes Art in nature

Astronomy

Top Scientific research Popular-scientific pages Credits

Birds of Australia: Wing loading

"Wing loading", generally speaking (this can refer to either flying animals, including birds, or airplanes), is the ratio of body mass over levitating surface area.

There are two substantially different ways of calculating the levitating area. Either one counts only the surface area of the combined wings or one also takes into account the uplift created by the body itself, and therefore counts the surface area of the body together with that of the wings.

An extreme example of this can be found in the literature, in which data of one collected specimen of a Great Bustard (Otis tarda) are used in two different ways. In both cases, the body mass is listed as 8.95 kg. However, one team of authors uses the combined surface area of the two wings (and ONLY the wings), of 5,728 cm², whereas another author used the combined wing surface area, PLUS the surface of the bird's body (which also contributes to the uplift), leading to a total surface area of 15,897 cm². NB: The body contributes almost 2/3 of the total surface area! The first method uses what is called an "isolated anatomical area" (wings only). The second makes use of the "aeronautical planform area". The use of either method makes sense in different contexts. To study wing performance, one will want to use the wing surface area only. In order to determine the total uplift, including the body's surface area, on top of the wing surface area, leads to the best results.

The two vastly different areas, for the same total body mass, lead to two equally different values for the wing loading, of 1.56 g/cm² (isolated anatomical area) vs. 0.56 g/cm² (aeronautical planform area).

This makes it abundantly clear that, in order to compare the flight capabilities of different species of birds, one must stick to one way of measuring the surface area providing lift. If not explicitly stated otherwise, we use here only surface areas of the two wings combined, i.e. the "isolated anatomical area" method (NOT including the body).

What levels of wing loading can one expect from birds?

What determines the level of wing loading, i.e., why doesn't every bird species have low wing loading (low body mass AND large wings) so as to be excellent fliers? What compromises are being made and why?

1. Wing size

• Agility/maneuverability: Large wings with enormous lift compromise a bird's ability to make quick turns.
• Need for speed: The largest wings are not necessarily the fastest.
• Diving under water for prey: Wings to be used as flippers tend to be shorter and made of harder material, leading to lower airlift.
• Need for stealth: Silent wings, as e.g. owls', are made of softer feathers which compromises lift. Corvids, on the other hand, don't care who can hear their wingbeats.
• High metabolic rates: Birds that need a lot of fuel must be excellent fliers to quickly find sufficient food.
• Moulting: Worn feathers need to be replaced; while the new feathers grow/develop, airlift is compromised. This can range from minor effects (in partial moults) to rendering species flightless (especially in synchronous complete wing moults).

2. Body mass

• Need for food reserves: Long-distance migrants need fat reserves which increase their wing loading until consumed.
• Need to take on a lot of food: Scavengers such as vultures may not find food on a daily basis, so when there is food available they will gorge themselves and thereby increase their wing loading drastically, to the point at which they struggle to take off.
• Egg-laying: Females about to lay eggs carry extra weight.

These pages are largely based on our own observations and those of our contributors. The structure of these bird pages is explained HERE. For more salient facts on any bird species please refer to a field guide.