How Water Level and Irrigation Practices Affect Waterbird Community,
Nesting, and Foraging Habitat Use on the Duck Valley Indian Reservation
Authors: Burke Jamie L. 
Published: June 2020

Loss of habitat continues to threaten all bird populations. Despite efforts for conservation
of wetlands, waterbirds continue to face habitat threats especially in western North America
where water resources are limited across the landscape. The White-faced Ibis (Plegadis chihi)
is a colonial nesting waterbird of conservation concern that builds nests in
emergent vegetation of freshwater wetlands throughout the western United States. An ibis breeding
colony site located at the Blue Creek Wetland complex on Duck Valley Indian Reservation may face
habitat threats in the future due to plans intended to increase irrigation water use efficiency.
Plans include manipulation of water levels in the wetland and conversion of flood irrigation
practices to sprinkler irrigation which may alter nesting and foraging habitat quality and
availability for waterbirds. We conducted an assessment of waterbird populations, especially
including the White-faced Ibis, to add critical information that could help conservation planning
at this important bird site. We compared secretive marsh bird density, local nesting habitat
changes, and ibis breeding success during two years with naturally different water levels, and in
2019, we modeled ibis nesting success with habitat variables we predicted might influence nesting
success. We did not see a difference in density of secretive marsh birds or abundance of ibis from
2018 to 2019. However, higher natural water levels in 2019 decreased availability of emergent
vegetation in the wetland needed by ibis for nest building and we observed catastrophic nest failures
due to exposure to harsh weather events. As a result, apparent nest survival for ibis was lower in
2019 than 2018. Additionally, we investigated foraging habitat selection by ibis of agricultural
fields with different irrigation practices surrounding the breeding colony. We found ibis foraged
most often in the natural wetland areas but frequently used flooded agricultural fields as additional
foraging sites. We modeled habitat selection and our results suggest the presence of water, resulting
in saturation of a field with standing water, is the main predictor of selection. We also investigated
differences in macro-invertebrate abundance and diversity of agricultural fields with different irrigation
practices which may also drive foraging habitat selection. Our results suggest no differences in diversity
between irrigation practices, but abundance was higher in naturally flooded areas and in flood-irrigated
fields than sprinkler irrigated fields. Given the importance of this wetland site to a variety of wetland
birds, understanding the effects of changes to irrigation practices and water management on waterbird
community structure, nesting habitat, and foraging habitat availability is necessary to help shape
adaptive management practices. Overall, our results provide information for future waterbird conservation
planning and will be especially informative in increasingly human-controlled environments.