Why are relatively few procellariiform birds found in calm equatorial waters?

Relatively few procellariiform birds are found in calm equatorial waters primarily due to two environmental factors:

• Lack of Wind: Procellariiforms are highly adapted for dynamic soaring, a flight technique that relies on steady horizontal winds to provide lift for their long, narrow wings. The equatorial region, often referred to as the doldrums, is characterized by light winds and calm conditions, which provide insufficient lift for these birds to travel efficiently.123
• Food Scarcity: These birds are largely dependent on pelagic (open-ocean) crustaceans. The calm equatorial waters generally lack the abundance of these food sources compared to the windier, nutrient-rich zones of higher latitudes, such as the areas of upwelling water near the Antarctic convergence.1

Because of these limitations, most procellariiforms occupy windier latitudes where they can effectively utilize their specialized wing anatomy to forage and travel.41