Posted February 18, 2022
The Conservancy is making still further attempts to provide additional prey for the Swainson’s hawk, a “primary” species in the Natomas Basin Habitat Conservation Plan.
In this photo, the Conservancy is conducting aerial seeding of a Conservancy rice field. Except the seeds being placed are vetch, not rice. It is expected the vetch will climb the stalks of the harvested rice plants that are intentionally left in the field, ultimately creating a canopy. Underneath the canopy, soil moisture will be retained, and shade will prevail. It is hoped the Swainson’s hawk’s favored prey, meadow mice (microtus), will quickly populate the field’s 171 acres beneath this canopy.
When rice is harvested, between 100 and 300 pounds of rice per acre are typically lost to the harvester. The seeds remaining on the ground and are available to the meadow mice for consumption.
If successful, this prey production effort will be an example of how to afford greater foraging opportunities for the Swainson’s hawk. Throughout its range in the Central Valley, the hawk has seen decreased nesting success. This means fewer chicks fledging per nest. This reduction in nest success is also true in the Natomas Basin, based on extensive Conservancy biological monitoring records.
When scientists see the kinds of reductions in nest success, a leading suspect is nutritional deficit. The cause? Maybe the hawk has to burn more calories to find each prey. Maybe there are too few prey. Maybe the prey has changed in that it affords fewer calories per catch (e.g., smaller size).
The Conservancy’s experiment will help try to find solutions to some of these questions.