Watching the Great Blue Heron harvesting voles in Mud Lake
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Deliberately, the predator slowly went step by step as it approached a small tunnel where faint sounds were coming from. For 15 minutes, the Great blue heron remained motionless, staring at the ground before every muscle, including the wings, exploded to drive its seven-inch dagger-like bill into the dirt. Bingo! Pay dirt as the bill held a wiggling adult vole.
Turning away from the burrow, the heron dropped the hapless rodent three times spearing it each time before positioning it headfirst. Down the hatch it started, but stopped half in and half out, too big to go down easily. The heron tried up-chucking the rodent. No dice. So it started shaking its whole body and finally got it to go down. Some herons have choked to death because the prey was too large to be swallowed.
That was not the only Great blue in the hayfields along the dike road that runs along the south side of Mud Lake. Last week, I counted 52 of them dotting the fields within a half of a mile from the water. I stopped for an hour to observe 11 herons just north of Dobson Farms and the canal running to their irrigation pump. In the hour, I observed the herons harvesting and eating 18 voles and I also observed seven missed strikes by them. It appeared to me that after a heron had swallowed three to four rodents, they flew to the water for a drink. I also observed a heron capture and eat a small perch as it hunted the shallow water.
Great blue herons are known for their love of fish, but they will eat anything, including snakes, small birds and frogs. Several studies indicate that 25 to 40% of their diet in Idaho are voles. Hayfields are often a haven for voles because the ground is not plowed or worked each year. The fields near Mud Lake, that have the herons harvesting voles are also the fields that had hundreds of raptors working last fall.
While watching the herons, a flock of about 5,000 Snow and Ross’s geese landed in the field and methodically marched across, eating new growth and depositing little balls of nutrients along the route. It looks to me like the hay farmers are getting free rodent control, along with free fertilizer for a better crop of cattle feed.
Great blue herons are lonely birds, rarely being seen close to another heron. They need their space to practice their patience in stalking and harvesting food. Many of them even migrate as singles or in a loose group. The only time they are near each other is during nesting season. They are colony nesters as they gather in a rookery known as “heronry” of up to 500 birds. Most of the heronries in southeastern Idaho have about 40 to 50 nests or couples, but they can nest anywhere, including on the ground.
Herons are mostly monogamists but are only together for a season and build their nest as partners with the male gathering the material while the female is the carpenter. Once the nest is finished and two to six eggs are ready to be incubated, both will sit on the eggs. After the eggs hatch, the babes are fed regurgitated puree by both parents. It is believed that adults will consume four times more food to fill the demand for themselves and their kids.
Raising kids is a huge commitment for herons as they grow rapidly and do not learn to fly until they are two months old. The parents must feed the fledglings for another two months while the kids learn the art of harvesting their own food. The art of stalking — patience must be learned and the ability to strike the target must all be learned.
This summer, I hope to be able to find where the young herons are hunting and see how many strikes it takes for them to harvest a vole. Last week, I watched as one missed three strikes before it finally harvested a small rodent while I watched another heron harvest four in a row. I also noticed that fewer herons were working the fields as the canals began filling with them, switching to a fish diet.
If you are interested in watching a Great blue heron hunt or fish, you must also develop patience. After a long wait, you may miss the strike, which is over in a fraction of a second. Good Luck and have fun.
