Like many other animals in the ocean, whales have complex patterns of movement. In order to make sense of these movements, scientists break them down into several categories, based on factors such as consistency of direction, distance, speed, and duration of travel.

In ascending order of size (in both space and time), the main categories are:

• meandering
• commuting
• ranging
• migrating

When we plot the paths ('tracklines') of satellite-tagged whales onto a map, meandering segments appear as a scribble: a cluster of locations with lines criss-crossing in random directions.

Foraging is a kind of meandering during which a whale changes direction frequently, moving back and forth within an area where prey is available. The size of the area over which this foraging extends is often a good indicator of prey abundance and patchiness. If food is abundant in a small area, the whale does not have to go far in order to eat. However, if prey is not very concentrated, the whale has to move further away to find the next meal.

Whales also have meandering movement patterns when they are not foraging but searching for things other than food - including other whales. For example, whales may have a meandering path when they are in the breeding areas looking for mates.

However, if prey is not very concentrated, the whale has to move further away to find the next meal.

Commuting is the movement between adjacent foraging areas within the same general region. A whale may decide to try looking for food in another patch if it is proving scarce. Next up in the scale is movement between these regions, referred to as ranging. This might involve a journey of a few hundred kilometres.

The category that describes the most extensive movement is migration - where a whale journeys between summer and winter areas. In the case of humpbacks this is from the high latitudes (for example, Antarctic Peninsula, Alaska, Nova Scotia) to the tropics (for example, Hawaii, Baja California, Costa Rica, Caribbean Sea) and vice versa.

Here's an example to illustrate how the humpbacks that we tagged in their Antarctic feeding grounds might demonstrate the four basic movement patterns (this map shows the locations mentioned):

A whale may spend some time foraging in the south end of Hughes Bay, before commuting to the adjacent Charlotte Bay and continuing to forage. After a couple of days the whale may start ranging and move 500km south to Marguerite Bay. By the time the summer feeding season comes to an end the humpback will be in prime condition. It will then migrate north back to the winter breeding and calving grounds - perhaps 8,000km away in the tropics.

Observations of whale movements from satellite-tracking data are limited by how often we receive transmissions that are good enough to determine locations (temporal resolution), and by the accuracy of the estimated location (spatial resolution). Location data usually comes in at intervals that can range from minutes to days. So, in most cases we do not have the complete sequence of locations, but instead get a snapshot of the whale's true path from just a few locations.

It is important to keep in mind that when we connect locations on a map to produce a trackline, the whale's true route was probably not straight and so the true distance it has travelled is much greater. As a result, the travel distances and speeds that we obtain from the data are minimum estimates only. Distance and speed under-estimation is greater during meandering movement (like foraging) than during constant directional movement (like migration).

In any given period of analysis, there is a difference between a whale's total distance travelled and its net displacement. Total distance travelled may be estimated by adding the distance between the consecutive points of a trackline, while net displacement is the straight line distance between the first and the last locations of each week.

Two whales could also have travelled the same total distance in a particular week, but have different net displacements. A whale that stays within a small area, like a bay or a strait, will have a small net displacement; one that ranges between areas will have a high net displacement. Total distance travelled and net displacement have similar values when a whale is migrating or ranging long distances, but they have different values when the whale is meandering. 

More about Joel and our whales:

• Learn about Joel's work at the OSU Marine Mammal Institute, his colleagues and why it's important to track humpbacks.