Question

why are fruits attractive and colourful

Answer 1

As to the birds, plenty of plants haveattractive fruits that are packaged in a way that is very attractive to birds. ... Strawberries are not actually fruits at all, but modified flower parts. The truefruits (called achenes) are the husks of the tiny seeds scattered across the surface of what is known as a receptacle.

Answer 2

Not all plants have fruits that attract animals. Humans have however cultivated many plants to have larger, sweeter, more colorful fruit. But if you think about a plum or a peach for example, birds are unlikely to help with seed dispersal; they simply peck at the fruit on the tree (or ground) taking some calories, but leaving the part the plant “would like” to have dispersed away from the parent plant.

Even if you go back to the parent species before being selectively bred for humans, a lot of fruits are too large for the passerine birds that feed on them. The largest parrots are an exception to this, but primarily in the tropics. More temperate zones don’t support many, if any birds that are capable of plucking and flying off with a large fruit. There are several species of fruit-eating bats, and many mammals that are attracted to those same fruits. The bats, although some (e.g. flying fox) are large, they consume fruits where they are on the plant, although some may distribute small seeds that become stuck to them as they feed. Saguaro cactus (Carnegie gigantea), while not everyone’s image of a “fruit tree” is an example of this. They are pollinated primarily by the long-nosed bat, which is adapted to reaching well into the large flowers.