Female bottlenose dolphins have to expend additional energy in carrying out parental care, e.g. infant carrying behavior. Dolphins don't physically hold their infants but line up in an echelon position with infants swimming beside them. This position creates a change of water flow pattern from the infant which minimizes separation between the mother and infant, but also increases the mother's surface area and creates a drag for the swimmer. This also leaves less energy to use in swimming speed, foraging, and predator evasion.