The Rufous Hummingbird (Selasphorus rufus) is a small, feisty bird that is known for being highly territorial and aggressive. Despite its tiny size, weighing just 3-6 grams, the Rufous Hummingbird will fiercely defend its feeding grounds from intruders.
During the breeding season, male Rufous Hummingbirds become especially aggressive as they compete for food and mates. They will chase away any other hummingbirds that enter their territory, even larger birds. Their aggressive behavior is driven by high testosterone levels during this time. The males will make fast, diving displays, produce buzzing sounds with their tail feathers and fight beak-to-beak to warn off intruders.
This raises the question – why is the Rufous Hummingbird so aggressive compared to other hummingbird species? There are several key reasons behind their competitive behavior.
Need to defend nectar resources
Hummingbirds have extremely high metabolism and must consume a lot of nectar to survive, particularly during high energy activities like breeding.
The availability of nectar sources is often limited and patchily distributed. Rufous Hummingbirds aggressively maintain feeding territories to ensure they have enough food. Research has shown that dominant, territorial males gain better access to food sources than subordinate males.
Males that control the best feeding areas are also more successful at attracting and mating with females. So aggression pays off in terms of reproduction – a key driver of behavior.
High testosterone
As mentioned before, Rufous Hummingbird males have very high testosterone levels during the breeding season, which leads to heightened aggression.
Their testosterone spikes in late winter and early spring as they migrate north into their breeding grounds in the Rocky Mountains, Pacific Northwest and Alaska.
Testosterone promotes behaviors related to reproduction, like defending a territory and attracting mates. Rufous Hummingbird testosterone levels have been measured at up to 5 times higher than their more peaceful tropical relatives during this period.
Protection of nesting sites
Male Rufous Hummingbirds will also aggressively defend nesting sites once they have mated with a female. The females build very small, cup-shaped nests high up in trees using spider silk and lichens.
Good nesting spots are limited, so the males will chase away other males or predators that get too close. They do this by diving at intruders at high speeds while making loud buzzing or chipping sounds.
Again, this behavior aims to maximize their reproductive success by protecting their mate and offspring.
How do Rufous Hummingbirds behave aggressively?
Rufous Hummingbirds display some classic aggressive strategies and combat moves:
Dive bombing
One of their most notable maneuvers is the steep, rapid dive bomb from up to 150 feet in the air. They zoom down at speeds over 60 mph, making a loud whizzing or popping noise with their tail feathers.
This dangerous dive is aimed at driving away intruders from their territory or food source. They will pull up at the last second to avoid collision. But the dive bomb often intimidates other birds into leaving.
Aerial dogfights
Rufous Hummingbirds will also engage in intense aerial dogfights with intruders that don’t retreat from their dive bombing. They fight beak-to-beak while flying, grappling each other with their feet.
These fast-moving aerial battles require excellent maneuverability and flying skills. The Rufous Hummingbird excels at these abilities, giving it an edge over opponents.
Loud vocalizations
In addition to aerial displays, Rufous Hummingbirds make frequent loud chirping, chattering and buzzing sounds during conflicts. These vocalizations communicate aggressiveness and reinforce their dominance.
Intimidating body posture
Rufous Hummingbirds will often puff up their bodies and fan out their tail feathers to appear larger and more imposing. This bluffing behavior works to intimidate other birds.
When are Rufous Hummingbirds most aggressive?
Rufous Hummingbirds display heightened aggression during two peak periods:
Spring migration and breeding
In late winter and early spring, male Rufous Hummingbirds become highly aggressive as they migrate north into breeding areas.
Their testosterone is rapidly rising during this time, leading to fierce competition for food, mates and nesting sites. Most conflicts occur between rival males.
Any other birds that interact with them, including larger species, may be chased out of territories. This ensures the males have the resources necessary for attracting a female and raising young.
Summer and fall migration
Interestingly, Rufous Hummingbirds remain very aggressive into the summer and fall, after the breeding season has ended.
During late summer, they continue defending feeding territories. As flowers become scarce in the fall, the competition for food intensifies.
The birds become feistier from July through September, during their southward migration. These periods of high aggression correspond with higher metabolic needs required for migration.
How does the aggression vary by sex and age?
Males are most aggressive
Male Rufous Hummingbirds are definitely the most pugnacious compared to females and juveniles. The aggression is driven largely by testosterone.
Adult males are intensely territorial as they compete for food, mates and nest sites. They instigate nearly all chases, dive bombings and physical conflicts with other birds.
Females and juveniles less aggressive
Females are generally far less aggressive than males, but they may still defend areas around their nests. Juveniles also show less aggression as they mature and disperse from their mothers’ territories.
However, in late summer, juvenile males start displaying territorial behavior as their hormones surge. The aggression prepares them for migration and breeding as adults.
How does the Rufous Hummingbird’s aggression compare to other species?
The Rufous Hummingbird is renowned for its aggressive behavior. But how does it compare to other North American hummingbirds?
More aggressive than other hummingbirds
Research has quantifiably shown Rufous Hummingbirds to be more aggressive than other species studied.
During 10 minute encounters at feeders, Rufous Hummingbirds instigated more chases and attacks than Broad-tailed, Calliope, Allen’s and Anna’s Hummingbirds.
They also dive bombed intruders at nearly twice the rate of these other species. Clearly, the Rufous is more domineering by nature.
Species | Chases / attacks per hour | Dive bombs per hour |
---|---|---|
Rufous Hummingbird | 24 | 4 |
Broad-tailed | 12 | 2 |
Calliope | 6 | 0.5 |
Allen’s | 2 | 0.5 |
Anna’s | 0.5 | 0 |
Less aggressive than tropical species
Despite being the most aggressive North American hummingbird, the Rufous is less domineering than some tropical species.
For example, the Fiery-throated Hummingbird and the Wedge-tailed Sabrewing are two Latin American species renowned for their extreme aggression.
The combination of higher food abundance and less seasonal breeding in the tropics allows these species to be perpetually territorial. The Rufous Hummingbird’s aggression peaks only during certain periods.
How does aggression help Rufous Hummingbird survival and reproduction?
The Rufous Hummingbird’s pugnacity appears to be an advantageous evolutionary strategy, helping the species thrive in several ways:
Increases access to food
Aggressively defending feeding territories ensures Rufous Hummingbirds have enough nectar and insects to meet their high metabolic needs.
Research shows dominant males gain nearly 2 times greater nectar intake at defended flowers compared to subordinate males.
Improves reproductive success
Males that control the best territories with abundant food resources are more successful at attracting and mating with females.
Their aggression directly translates into greater mating opportunities and production of offspring.
Discourages nest predators
Dive bombing nest intruders helps deter predators like squirrels, jays and hawks from raiding their nests and eating eggs or hatchlings. So it directly boosts nest survival rates.
Establishes dominance
Aggression establishes clear social hierarchies and territory boundaries between birds. This prevents endless fighting over resources and mates.
Conclusion
To summarize, Rufous Hummingbirds are the fieriest, most belligerent hummingbirds in North America. Their aggression peaks during migration and breeding when food, mates and nesting sites are limited.
Intense competition drives them to defend territories aggressively using dive bombs, vocalizations and aerial attacks. This pugnacity provides advantages in terms of food intake, reproduction and predator deterrence.
So their feisty, competitive spirit has evolved as an adaptation to thrive in challenging northern environments. The next time you encounter a fiery Rufous Hummingbird, appreciate its fighting spirit that has ensured the species’ success among the smallest birds.