At first thought, it might seem that any tropical bird could appear anywhere along the U.S./Mexico border. But, in fact, distinct patterns emerge about where these birds appear.
It’s worthwhile to spend time studying maps of northern Mexico to understand why certain birds show up where they do. For example, relatively few tropical land birds wander north into California. Why? Because immediately south of that state is the peninsula of Baja California. Baja has some distinctive endemics but far fewer tropical species than the adjacent mainland of Mexico.
The Mexican mainland just south of the border features lowlands along both coasts
