Is birds and mammals are usually present only in the later stages of succession?

That statement is not entirely accurate. While it's true that birds and mammals often become more diverse and abundant in later stages of ecological succession, it's not always the case that they are only present in later stages.

Here's why:

* Early Succession: Birds and mammals can play a role even in early stages of succession. For example, some birds may be pioneer species, establishing themselves on bare ground or in newly disturbed areas. Small mammals like rodents can also colonize early successional habitats.

* Habitat Specificity: The specific species of birds and mammals present will depend on the habitat type and its stage of succession. Some birds and mammals are adapted to early successional habitats, while others prefer mature forests or grasslands.

* Flexibility: Many bird and mammal species are adaptable and can thrive in a variety of successional stages. They may shift their habitat use depending on the availability of resources.

Here's a better way to understand the relationship between birds/mammals and succession:

* Early Stages: May be dominated by generalist, adaptable species that can tolerate harsh conditions.

* Mid Stages: Increasing habitat diversity and resources lead to more specialized species.

* Late Stages: Mature ecosystems often support the highest diversity of birds and mammals, as well as a greater abundance of particular species.

Overall, it's more accurate to say that the diversity and abundance of birds and mammals generally increases as succession progresses, rather than them being entirely absent in the early stages.