Avian foraging


Avian foraging refers to the range of activities and behaviours exhibited by birds in their quest for food. In addition to their unique body adaptations, birds have a range of described behaviours that differ from the foraging behaviours of other animal groups. According to the foraging habitat, birds may be grouped into foraging guilds. Foraging includes a range of activities, starting with the search for food, making use of sensory abilities, and which may involve one or more birds either of a single or even of multiple species. This is followed by locomotion and movements to obtain or capture the food, followed by the processing or handling of the foods prior to ingestion. Like all organisms foraging entails balancing the energy spent and energy gained. The high metabolic rate of birds, among the highest in the homoeotherm groups, constrains them to ensure a net positive gain in energy and have led evolutionary ethologists to develop the idea of optimal foraging.

Energetics

Foraging involves expending energy and seeking food can be both time and energy consuming. Birds make use of a variety of approaches to improve the efficiency of their foraging. These include foraging in flocks which provides many eyes to seek patches rich in food while also reducing the risk of predation by increasing the efficiency of detecting predators, increasing time spent on handling food, and by reducing individual risk. It has been suggested that individuals may exchange information for instance at communal roosts.

Foraging guilds

Assemblages of bird species that share common habitats or substrate from which food is gathered, and to some extent foraging technique are conceptual grouped within in foraging or trophic guilds. Various attempts have been made to classify foraging guilds for ecological studies and universal and undisputed classifications do not exist. It must also be noted that species may belong to multiple foraging guilds depending on situation. Specific classifications are used in ecological and behavioural studies. The classifications are often made according to multiple hierarchical criteria and a full classification may include multiple terms. To take an example a bird may be described as "nocturnal gleaning insectivore" with parts of the classification dealing with the time of day, the diet and the technique used to obtain food.
Guild classification on food type based mainly on terms used by North American ornithologists includes:
Guild classification based on habitat or substrate from which food is gathered includes:
Guild classifications based on foraging technique include the following. These may also involve other associated behaviours.
Other miscellaneous foraging behaviours include:Foot trembling movements may be used by waders such as plovers and lapwings. They are used mainly on wet soil or while wading in shallow water. Some waders move around rapidly in circles, these include the phalaropes, best known for their pirouetting movements, often in deeper water that reaches until their body. Among the first to document the behaviour was the German ornithologist Oskar Heinroth who described it in 1915.
Foot paddling is a foraging behaviour unique to gulls. The behaviour is exhibited while perched in shallow water, and sometimes on dry land, over short grass or bare soil. The gulls rapidly move their feet up and down while staying at a spot and it is thought that this flushes subterranean prey that they then detect and feed on although there is no definite evidence. Other terms describing the term have included paddling, puddling, pumping, stamping, thumping, tramping, trampling, treading and trembling. The behaviour is found in young gulls and is considered to be innate and does not require learning. The behaviour has been compared by lay observers to rapid dancing moves.