Bird occupancy dynamics in Alaskan wetlands: Why different size ponds matter?

Background/Question/Methods:

The rate of temperature increase in the Arctic region has been approximately double the global average. These temperature increases have been affecting all ecosystems and biomes, from terrestrial to marine, and yet the responses of these systems have been diverse. Recent studies indicate a decreasing trend in abundance and area of permanent water bodies of Arctic. It is therefore crucial to understand the relation between pond systems and associated species because any change in pond size due to warming may have implications for the diversity of species dependent upon this habitat for reproduction and survival.   

This study focuses on assessing relationships between pond size and temporal components of bird community dynamics, including phenology of bird occupancy, species diversity, and species abundance. Our study site, Izembek National Wildlife Refuge, is located on the southwestern tip of the Alaska Peninsula. We sampled 9 sites in 2011 [three of each size class (small, medium and large)], 12 sites in 2012 [three of each size class (extra small, small, medium and large)] and 16 sites in 2013 [four of each size class (extra small, small, medium and large)] for assessment of bird diversity and abundance, and arrival phenology in order to understand the dynamics between pond size and bird occupancy. Data were collected on use of ponds by different bird groups, including presence/absence and abundance, using spotting scopes and binoculars, from May through August. This period covers arrival of migratory birds to the area and their breeding season.

Results/Conclusions:

The findings of this study indicate that bird occupancy dynamics change due to pond size. In comparison to large ponds, small ponds host fewer migratory bird species and are occupied by these bird species more rapidly. The same pattern is also observed between species abundance and pond size. Larger ponds support higher numbers of individuals than smaller ponds; however, species accumulation rates in larger ponds are lower than small ponds. 

Considering the current rate of temperature increases in Arctic, it is very important to understand how ecosystems respond to this rapid change. The disappearance of high latitude ponds due to warming also shows the urgent need for information in order to understand the relations between pond systems and associated species.