If the earth were not tilted in its orbit how would the climates and seasons be affected at the equator and between 30 north and south latitudes

There would be one season (summer), and it would be always hot

Explanation:

What causes climates and seasons is the tilted orbit of Earth, this is caused by sunlights which come to Earth with different angles all over the Earth. The last palce to get sunlight with 90 degrees are 23 degrees 27 minutes N and S latitudes. When sunlight comes directly to the Earth longtitude between 30 N and S would get sunlights with 90 degrees all year.

The bird populations will decrease due to competition for resources such as food and nesting sites.

Explanation:

Ecological succession can be defined as the process by which the biological structure of a community, i.e., the group of interacting populations of species that occupy a particular area, changes over time. Human activities such as, for example, deforestation in order to develop an urban ecosystem, can dramatically alter the process of succession and literally destroy the natural balance of biological communities. In this case, it is expected that human activities have a negative impact on bird populations by increasing intra and interspecific competence with other organisms for limited resources (i.e., food and nesting sites).