Quantifying Hummingbird Territory Defense Behaviors

We used the following criteria to determine that a floral patch of B. ternifolia was an actively defended feeding territory: (1) the territory owner always returned to the same perch near the patch, (2) foraged within the patch, and (3) actively defended the patch through chases (Camfield, 2006 (link); Mendiola-Islas et al., 2016 (link); Márquez-Luna et al., 2019 (link); Márquez-Luna et al., 2022 (link)). A chase implies persecutions and aggressions towards an intruder to try to force it away from the territory. In our field observations, we did not tag hummingbirds because the tiny size of the permanent bands commonly used to tag hummingbirds makes it impossible to identify them individually (Márquez-Luna et al., 2022 (link)). Instead, during the behavioral recording, each territory owner was recognized based on the fact that chases started from a certain perch and that the same perch was frequented. Twenty-one territories of adult male Broad-tailed hummingbird were monitored in an area of about 50 hectares.
In each territory, the territory owner’s behavior was observed and recorded for a period of four continuous hours (from 8:00 to 12:00 h), when hummingbirds are more active foraging and nectar production is high in this plant species (Torres et al., 2008 (link)). Each territory had the same sampling effort on weekdays and weekends from June to August. Due to the size of the territories (see below), the observations were carried out using binoculars (10 × 42), standing from different points 10 m away from each territory. We detected no apparent approach or avoidance behaviors by birds in response to the observers. We recorded: (1) the number of times the territory owners chased an intruder, and (2) the number of intruders that were not chased and were able to forage in the territory. Additionally, (3) we recorded the number of flowers visited by the owners inside their territories during the entire observation period.