Chase Lake National Wildlife Refuge (NWR) in south-central North Dakota is home to one of the largest colonies of ground-nesting waterbirds in the northern Great Plains.
The waterbird colony at Chase Lake NWR has changed dramatically during the past two decades, increasing both in species composition and in overall numbers. In recent years, the Chase Lake islands supported 20,000-30,000 nests of 40,000-60,000 breeding birds (12+ species), making this one of the most significant mixed-species waterbird colonies in the northern plains and certainly one of the most important colonies managed by the U.S. Fish & Wildlife Service (USFWS) in this region. Such a large concentration makes the breeding birds especially vulnerable to multiple factors (e.g., predation, weather events, disease) that can influence their productivity and survival. Access to reliable population data is crucial for effective conservation and management of the Chase Lake waterbird colony and other colonies in the region.
Ground surveys by walking observers were used at Chase Lake NWR in the 1970s when the waterbird colony was much smaller. Ground surveys are not recommended because this technique is known to cause disturbance and nest abandonment of American White Pelicans and other waterbirds. Annual aerial surveys of nesting pelicans using manned fixed-wing aircraft (e.g., Cessna 172) have proven critical in documenting the increases and decreases in American White Pelican populations at Chase Lake and other regional pelican colonies in recent years. However, aerial surveys using manned aircrafts have potential complications, including safety, costs, and logistics. For example, the ideal timing (i.e., late May or early June) of the aerial imagery from manned aircraft often conflicts with other refuge priorities (e.g., easement assessments, law enforcement, etc.) and schedules for USFWS pilots. For safety, pilots often avoid low-altitude flights. The resolution of the photography from manned aircrafts often is insufficient to identify individuals of smaller waterbird species such as gulls. The aerial surveys using fixed wing aircraft did not utilize remote sensing with high resolution color or infrared imagery, which would allow better detection of individual birds on nests.
Monitoring of waterbirds is essential to detect and evaluate changes in waterbird distribution and abundance. At present, there is some urgency to continue to develop reliable methods for estimating population sizes of ground-nesting waterbirds at Chase Lake NWR. Reliable baseline information on breeding population sizes and changes over time would allow the USFWS to evaluate population levels and changes and to make informed decisions. Unmanned aircraft systems (UAS) are proving to be a useful alternative to manned aircrafts for wildlife surveys and have the potential to be more economical, less obtrusive, safer, and a more efficient and versatile means to survey nesting pelicans and other ground-nesting waterbirds. High-resolution color images and infrared images will provide detection of individual nesting pelicans and other ground-nesting waterbirds.