What is courtship behaviour? The acts it encompasses are as varied as life itself; a sound, a gesture, an action, etc. The overarching and general attribute all these behaviours have (which makes them courtship) is whether they appear to be connected to successful mating.
The first feature of courtship behaviour is that it enables organisms to identify members of their own species. The central part of the definition of a species is the members’ ability to produce viable offspring. Hence, attempting to mate with members of a different species is not an advantageous behavioural trait in the context of reproductive success.
Courtship behaviours also allow organisms to approach one another without aggression or invasion of their personal space.
Sometimes the outcome of courtship behaviour is the formation of a pair bond. This bond results in a better reproductive success, due to the increased survival probability of the offspring. In some species this is the case, while in others it isn’t. This is tightly related to a specific organism’s physiology. Fish are able to lay a huge number of eggs, while pigeons only lay one or two. Therefore, it is more likely that pigeons would from a pair bond, rather than fish.
Last, but by no means least, is the nature of courtship behaviour which makes it a tool for sexual selection. This is not a mere test of survival (natural selection takes care of that), but a test of relative superiority in a variety of attributes which vary between species, at different times, and even between individual organisms. These attributes can be anything, and in many cases they seem random or peculiar. In others, they seem very much expected.
Territoriality is another key facet of sexual selection and courtship behaviour. The location, resources, food and bells and whistles associated with the period leading up to mating is strongly dependent on territory. It is a base definer of the available resources to the individuals and the success of their subsequent offspring.
Only a minority of species are strictly territorial, as defined by not only pertaining to a defined territory, but actually actively defending it. Usually, animals only defend the smallest part of a territory needed for their survival, as defending any larger a territory would not make sense in their cost-benefit analysis.
Benefits associated with territorial behaviour include the resources found therein e.g. food, the suitability for the territory to serve as a nesting ground, as well as the presence of mates within the territory. In this sense, an individual behaving territorially may be defending the resources present within, the potential of the territory for their future, or indeed other individuals found in their territory.