Metabolism and Survival Key Area 5b Avoiding Adverse Conditions

By the end of this topic you should be able to: State that some animals avoid adverse conditions by migration Understand why migration is important for some organisms Explain how innate and learned behaviour influences migratory behaviour

Avoiding Adverse Conditions

Migration Migration is a relatively long-distance movement by members of a species on a regular (usually seasonal) basis. It allows the organism to avoid adverse conditions by expending energy to relocate to a more suitable environment. In times when there will be a shortage of food and low temperatures, it is better for the organism to expend the energy required to move than to stay in the conditions of metabolic adversity.

Migration Migration can be innate (inherited) but it is also influenced by learning ie. it can be gained by experience such as specific stop points on long journeys A lot of information on migration has been obtained by tracking migrants over large distances and a range of techniques are involved Migration is a response to an external trigger stimulus such as day length, local climate, availability of food, season of the year, mating reasons, hormone changes…

Migration - Birds Some birds will migrate from one hemisphere to another whilst others cover less distance and migrate from one region to another in the same hemisphere

Migration - Mammals Mammals migrate for a variety of reasons. Humpback whales, for example, are found in polar regions in the summer as there is an abundance of food for them to build up layers of blubber They then migrate to subtropical waters for the female to give birth. If they did not, the young would lose too much body heat in the winter polar regions

Migration - Invertebrates Not many invertebrates migrate but one of the ones that do is the Monarch butterfly. They migrate from Mexico to the USA and Canada as these areas contain their exclusive food source (milkweed plant). They migrate back to Mexico to avoid the cold winter conditions

Tracking Migration Information on when migration occurs, where organisms migrate to, whether they return to their original regions and how long organisms live has been obtained by tracking migration A range of specialised tracking techniques have been developed to help track migrants over large distances which include: Individual Marking Transmitters

Individual Marking - Ringing Ringing (also called banding) involves placing a metal band with a unique identifying number around a birds leg. If the bird is recaptured this information (place, date, time…) is reported and used to plot an overall picture of the birds movement

Individual Marking - Tagging Similar to ringing, tagging involves attaching a small circular tag with a code to the underwing of butterflies. Again, if recaptured it allows the route and distance of the butterfly to be recorded

Transmitters Most recently, birds and mammals have been fitted with transmitters (glued or implanted into body) that emit a signal which is picked up by orbiting satellites This provides a more precise picture of migratory routes and also means the organism does not need to be recaptured However, it is much more expensive and can cause a drag effect on smaller birds

Innate and Learned Migration Innate behaviour is inherited and inflexible – an organism responds to an external stimulus and migrates in the same way as every member of its species Learned behaviour is a result of watching and learning from experience. It is flexible and involves trial and error and the knowledge gained is transmitted amongst the members of a social group.

Displacement Experiment Starlings An experiment was designed to look at the effect of displacement – taking birds from their normal region of habitat to a different one and seeing if they will still migrate to where they normally would. Starlings usually migrate from Eastern Europe to Northern France. A large number of starlings were caught in the middle of migration in Holland, taken from Holland to Switzerland, tagged and released

Displacement Experiment Starlings The results found: Adult birds that had migrated at least once before found their way to Northern France showing both innate and learned behaviour (to correct their navigation) Young, inexperienced birds continued in the direction they had been travelling and so arrive in Spain instead of France showing purely innate behaviour

Although not showing the correct countries, the same principle applies – the young displaced birds continue in the same direction as they originally travelled but in a parallel line to the original

Directional Tendencies Experiment A second experiment looked at the flight path taken by 2 distinct populations of blackcap warbler birds. One population always heads south-west; the second population always heads south-east. Members of each population were hand-reared and the direction in which they flew was monitored Each population chose what would be their normal, typical direction which indicates the young birds have inherited genetic information (innate behaviour) about the direction in which they have to migrate

Cross-fostering Experiment In another experiment, eggs from birds that migrate (lesser black-backed gulls) were placed into the nests of non-migratory birds (herring gulls), and vice versa The results showed: Black-backed gulls raised by non-migratory birds did migrate as they normally would – innate behaviour Herring gulls raised by migrating birds did migrate when they wouldn’t normally – thought to have been just following the adults in a learned type behaviour