Hummingbird migration and flowering synchrony in the temperate forests of northwestern Mexico.

BACKGROUND

Many species of birds are morphologically and physiologically adapted for migration. Migratory movements of birds can range from thousands of kilometers, such as when birds migrate from wintering to breeding sites in summer, to several kilometers, such as when birds migrate among habitats in a single mountain system. The main factor that influences bird migration is the seasonal fluctuation of food resources; climate, predation, competition for resources and endogenous programming are also important factors. Hummingbirds are highly dependent on nectar, so their migration is likely correlated with the blooming of plant species. The ecological implications of altitudinal migration in the mountains of North America as well as the latitudinal migration of through Mexico are still poorly understood. To explore these issues, over three non-consecutive years, we evaluated interannual variation in the phenologies of a latitudinal migrant () and an altitudinal migrant () and their visited plants.

METHODS

We assessed the relationship between two migratory hummingbirds and flower abundance in 20 fixed-radius plots (25 m radius). All available flowers were counted along transects (40 × 5 m) inside each fixed-radius plot. Sampling was performed every 10 days from November 12 through February 20 of 2010-2011, 2013-2014 and 2015-2016, resulting in a total of 11 samples of each plot per period. Phenological variation and the relationships among hummingbird abundance, flower abundance and vegetation type were evaluated using a generalized additive mixed model.

RESULTS

abundance was related to sampling time in the first and third periods; this relationship was not significant in the second period. abundance was related with the sampling time over all three periods. The abundance of hummingbirds was significantly related to the number of flowers. The abundance of hummingbirds was related to the number of and flowers and the total number of flowers. We found a non-significant correlation between and abundance and vegetation types.

CONCLUSION

Contrary to expectations, the long-distance migration of was not consistent over the sampling periods. The migration of through the study region may be altered by changes in climate, as has occurred with other species of migratory birds. In the present study, the migration of was correlated with the blooming of . In comparison, the altitudinal migrant responded to the availability of floral resources but was not associated with a particular plant. The migration of this latter species in the area probably depends on multiple factors, including climatic and demographic factors, but is particularly dependent on the supply of floral resources and competition for these resources.