Circadian rhythms: crepuscular

The last couple of blogs I wrote cover nocturnal and diurnal activity patterns. Day and night. However, this is not the end of the story. There is a brief moment just before the sun rises and just before it sets. These are the twilight hours and some animals have chosen this time to be active. They are called crepuscular animals.

So why might these animals choose then to wake and work?

The light during twilight hours is different to full day and this can make it difficult for both diurnal and nocturnal animals. The most obvious reason for crepuscular creatures to adopt this period is hunting. Predators can stalk their prey easier There’s just enough light to see but long shadows to hide behind and ambush their prey. For prey again, they have enough light to see predators but they too are able to keep out of sight.

For a lot of species it may have been driven by competition. With so many animals vying for day and night some may have moved to just before or just after their usual activity cycle in order to avoid competing with them.

In the desert it is incredibly hot during the day and very cold at night so it only makes sense that many choose twilight to avoid these extremes. The morning dew is only present for a very brief moment and some insects for example, will travel to the top of dunes to collect it before it evaporates. It is too late to drink like this once the sun has risen.

Crepuscular can also be broken down into subcategories.

is when the animal is awake at dusk and matutinal which covers the time just before Dawn.

Cathemeral

Some animals may have an irregular pattern of activity and are awake at different times day and night. This is likely due to resources or lack of them. This in turn may be largely due to where that animal is found.

If the species has a large habitat range then different areas will have different levels of resources. So where in one area food is plentiful, they may only be diurnal. In another, food may be scarcer or there may be more competition for it. These may then adopt a random habit and come out day and night. This would make the species cathemeral.

So next time you are at the park, if you get to us first thing why not see who’s already awake or now we are in winter and the days are shorter, who is just getting up as the sun is almost set.

Source: winghamwildlifepark.co.uk