When hovering during fasting, rufous hummingbirds oxidize fatty acids to support metabolism and food energy requirements, but can rapidly switch to carbohydrate metabolism (within 40 minutes) after feeding on flower nectar. Both male and female "S. rufus" are territorial; however, they defend different types of territories. The more aggressive males fight to defend areas with dense flowers, pushing females into areas with more sparsely populated flowers. Males generally have shorter wings than females, therefore their metabolic cost for hovering is higher. This allows males to beat their wings at high frequencies, giving them the ability to chase and attack other birds to defend their territory. The metabolic cost of short wings is compensated for by the fact that these males do not need to waste energy foraging for food, because their defended territory provides plenty of sustenance. Females on the other hand are not given access to the high concentration food sources, because the males fight them off. Therefore, females generally defend larger territories, where flowers are more sparsely populated, forcing them to fly farther between food sources. The metabolic cost of flying farther is compensated for with longer wings providing more efficient flight for females. The differences in wing length for "S. rufus" demonstrate a distinct sexual dimorphism, allowing each sex to best exploit resources in an area. In 2018, the rufous hummingbird was uplisted from least concern to near threatened on the IUCN Red List, on the basis that due to its reliance on insect prey during the wintering season, it will be heavily affected by the global decline in insect populations due to pesticides and intensified agriculture. Due to climate change, many flowers that the rufous hummingbird feeds on during the breeding season have started blooming two weeks prior to the birds' arrival to their breeding locations, which may lead to rufous hummingbirds arriving too late to feed on them.