Why do Birds Flock in Palo Verde?

The protected wetland area in Palo Verde National Park, home to thousands of resident and migratory birds

Study by Madison Deile, Alyssa Risch, & Mary Thelen

In wetlands, such as those in Palo Verde National Park, food resources are abundant for bird populations. Therefore, there is less competition between species and individuals so different species often forage together benefitting from the extra protection from predation. This leads to less vigilance in the birds as well, increasing foraging efficiency (Sridhar et al., 2009; Weller, 1999). The goal of this study was to determine how grouping patterns of species would vary depending on weather, time of day, and species’ diets. Our experiment involved the observation of birds in the wetland at Palo Verde National Park during the morning, afternoon, and evening. We recorded which species were present, grouping pattern (individual, same-species group, mixed-species group), and microhabitat (shore, mud, vegetation, open water). We used the data from the Organization for Tropical Studies to find the average scalar wind speed for each time period we observed. We also researched typical diets of every species present and grouped them into either mainly vegetation, invertebrates, or fish. We found that there was a higher percentage groups of species with completely different diets (53%) than there were groups of species with overlapping diets (47%), suggesting that birds which group together tend to have different diets, possibly to avoid competition. We found no significant difference between grouping patterns and wind speeds. There was also no significant difference between grouping patterns and time of day, but further tests suggested that more mixed species groups are present during the morning than other times of the day. Future studies could quantify abundance in each group to further learn about species and group behaviors. This study could also be repeated during the wet season to see how other biophysical variables affect bird grouping behavior.

(L) Alyssa Risch observes birds. (R) A Purple Gallinule, common in the wetlands of Palo Verde.