Ruby-throated hummingbirds (Archilochus colubris) are one of the most widespread and commonly seen hummingbird species in North America. They are known for their aggressive behavior, especially when it comes to defending food sources and mating territories. One of the most conspicuous behaviors exhibited by male ruby-throats during the breeding season is chasing other males that may encroach on their territory.
Territory Defense
Male ruby-throated hummingbirds are extremely territorial. They establish breeding territories in the spring, which they aggressively defend from intruders. These territories contain food resources, such as nectar-producing flowers and insect populations, that are necessary to attract potential mates and sustain themselves and their future offspring. When another male hummingbird enters a territory, the resident male will chase the intruder out. These aerial chases often involve rapid diving, climbing, and zig-zagging motions as the birds try to drive off the intruder.
By chasing away intruders, male ruby-throats can ensure continued access to the food resources in their territories needed for successful breeding. They can also maintain their territorial boundaries, providing an exclusive area to court potential mates. Studies have shown that male hummingbirds with the largest and most nutrient-rich territories are more successful at attracting mates and producing offspring. As such, defending territories through chasing is an important component of maximizing reproductive success for male ruby-throated hummingbirds.
When Does Chasing Occur?
The frequency of territorial chases peaks in late spring and early summer during the height of the breeding season. This is when males are actively courting females and mating. Some chasing may still occur into mid and late summer, but becomes less common as fewer females remain receptive and the number of intruders decreases. Chasing is primarily initiated by resident males against other males that pose a threat to their territories and reproductive success.
How Long Does Chasing Last?
Most chases are brief, lasting only a few seconds or minutes before one bird retreats. However, in some cases, prolonged chases can persist for up to an hour or more before one bird finally leaves the territory. The longer an intruder remains and continues to pose a threat, the more aggressive and persistent the territorial male will be in trying to remove it.
Resource Competition
In addition to territory defense, competition over limited food resources is another reason male ruby-throats frequently chase each other. Hummingbirds have very high metabolisms and must consume significant amounts of energy-rich nectar each day to meet their nutritional needs, especially while breeding. However, flowers and nectar are not infinite resources within a habitat, which leads to frequent conflicts over access to prime energy supplies.
When a hummingbird finds a concentrated food source, such as a cluster of flowers or a feeder, it is in its best interest to keep other birds away so it can maximize its own energy intake. Chasing is used to claim priority access to these limited resources. The outcome of these competitive chases determines which bird has priority access to the food source after the original defender. Nearby breeding territories may also be temporarily abandoned in favor of particularly rich feeding areas in what is known as a “site-dependent” territorial system.
When Does Resource Competition Occur?
Resource competition and chasing at prime feeding sites occurs throughout the entire breeding season and into fall migration as flower availability changes. It may escalate at certain times of year when food becomes limited, such as during late summer when many spring flowers have already gone to seed. Successful competitors gain better body condition and fat reserves which can increase their chances of survival and future reproductive success.
Mate Guarding
Male ruby-throats also chase other males that get too close to their mate. Once a female chooses a male partner, he will aggressively guard her and try to disrupt any potential threat from other males that might try to mate with her. This mate-guarding helps ensure that the offspring the female bears will be his own genetic descendants. A male that is unable to sufficiently guard his mate risks being cuckolded and expending energy raising offspring that do not actually carry his genes.
Chasing during mate guarding occurs most frequently in the brief window when the female is sexually receptive and ready to mate. The male will stay close to her, following her closely from flower to flower, and chasing away any male that approaches her. He may also make frequent copulation attempts during this time to help cement paternity by passing along sperm that can outcompete any potential rival’s sperm.
How Does the Female React?
Interestingly, the female often does not appear bothered or frightened by males chasing around her during mate guarding. She may simply continue foraging as normal while the territorial disputes occur over her head. This is likely because she already chose her preferred mate, so the male-male competition does not directly impact her as long as her selected mate remains near her and able to mate.
Establishing Dominance
Chasing serves as more than just protecting critical resources and mates for male ruby-throated hummingbirds. It also establishes a clear “pecking order” of dominance between males within and even beyond a single territory. Birds have surprisingly good memories, and regular aggressive chasing helps reinforce which individuals are dominant and subordinate males within the local population. This reduces unnecessary conflicts in the future, since subordinate birds will consistently and quickly defer to known dominant individuals.
In both territorial and feeding site chases, the initial aggressor tends to be the dominant bird, while the retreating bird becomes subordinate. However, prolonged, evenly-matched chasing may occur occasionally between two dominant males of similar status and motivation before one backs down. The outcome helps re-establish which one holds higher dominance during that season.
How is Dominance Expressed?
Dominant male ruby-throats typically occupy the most favorable central territories with the highest quality resources. They are able to displace subordinates to the outer fringes. Dominance may also be evident through behaviors like prolonged hovering in front of other birds to force their retreat. Consistent winners of both territorial and feeding chases across days and weeks continually reinforce their status over subordinate birds.
Practice Honing Skills
Young male ruby-throated hummingbirds that have not yet established a territory or bred may also participate in chasing. While they have no resources or mates to defend, chasing provides vital practice to develop skills for future survival and reproduction. Males that hone their stamina, speed, and maneuverability through regular chasing will be better prepared when it comes time to breed in future seasons and defend real territories.
Juvenile males may initiate practice chases with each other or even adult breeding males. Adults are often tolerant of these interactions as long as the young birds do not become a true threat. These practice sessions help the young males learn when to escalate conflicts versus back down against more dominant opponents. This social feedback allows them to gauge their own abilities and develop strategies for future success after they mature.
What Do Juveniles Chase Each Other Over?
Unlike adults, juvenile males do not chase each other over territories, mates, or even concentrated food sources. Rather, their practice chases are more play-like jockeying for position as they fly through open air space. The chase instigator may dive at another young bird, initiating a twisting reaction flight as the opponent tries to evade a direct collision. The goal appears to be honing reflexes and control rather than establishing dominance or claiming resources at this stage.
Conclusion
In summary, multiple factors drive chasing and aerial fighting behaviors between male ruby-throated hummingbirds during the breeding season. Territorial defense, competition over limited food resources, mate guarding, establishing dominance, and skill practice all contribute to the frequent mid-air skirmishes observed between intensely territorial, feisty males of this species. Understanding the evolutionary roots of these behaviors provides insight into how competition and conflict play integral roles in hummingbird reproductive strategies and ecology.
Key Takeaways
- Male ruby-throated hummingbirds chase each other to defend breeding territories containing necessary food resources for attracting mates and feeding themselves and offspring.
- They also engage in chases at prime nectar sources as limited food availability leads to heightened competition over access to quality feeding sites.
- Mate guarding chasing occurs as males try to prevent rivals from approaching and potentially mating with their female partner.
- Chases establish clear dominance hierarchies between males that reduce future conflicts within and between territories.
- Juvenile males practice chasing skills for future application in breeding contests.
Frequently Asked Questions
Do female hummingbirds also chase each other?
Female ruby-throated hummingbirds are much less aggressive than males. They may occasionally chase each other, but almost never participate in the prolonged, aerial dive-bombing chases observed between males. Female energy is instead focused more on nesting and caring for offspring than on defending territories.
How close do the birds get during chases?
Chasing birds may get quite close, sometimes nearly touching, as they buzz by each other in midair. However, actual physical contact is rare as both birds maneuver actively to avoid collision. The tip of the tail is sometimes snapped sharply by the aggressor to signal dominance.
Do chasing behaviors make hummingbirds more vulnerable to predators?
Surprisingly, the aerial acrobatics and speed involved in chasing seem to reduce predation risk. The erratic movements and quick dashes make it difficult for birds of prey to successfully target and strike the small, fast-moving hummingbirds. Spending more time sitting still feeding rather than engaged in chases may actually increase predation risk.
How can you provide for hummingbirds in your own yard?
You can encourage hummingbirds to visit your yard by providing a nectar feeder, planting native flowers and shrubs that attract hummingbirds, and including elements like running water or perches to make your landscape more appealing. However, be aware increased competition at your feeder may lead to more chasing as dominant birds try to claim priority access.
References
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