Sunday, 23 April 2017

A Hunting Heron - Voles and Fish

Over the past several years I have been fortunate to see Grey Heron on many occasions. I have monitored a colony in Warwick and often see them at St. Nicholas Park and on my patch.

This morning I watched an individual Heron for some time as it hunted on the mill pond at the Saxon Mill. I watched as it stood stock still waiting for prey. It dived forward several times and failed each time, it got me thinking about what the Herons success rate was.
As I continued to watch a marveled at how controlled and stealthy such a large bird is. It places its feet carefully and lifts them to minimise splashes. It turns its head carefully watching multiple angles and once it detects a prey moves into position to start foraging.

The heron moved from the reeded central area where it was being unsuccessful to the bank side where over hanging trees might have improved visibility.

Whilst fishing here it saw something in the rocks on the bank side and quickly darted in to grab what seemed to be a vole. In the following sequence of photos you can see that it grabbed it with the tip of its beak and then rather than swallowing immediately it took it to the water and dipped it into the river. I do not think this was to drown the prey as it was too short a time but could have made swallowing easier as straight after it gulped the vole down.

The Heron grabs the vole side on from the rocks to the left

The Heron re-orientates the vole by gripping it by the head and neck
The Heron then dips the vole into the river
The Heron the swallows the vole whole, note the bulge in the neck as it passes down the crop.

Following this meal the Heron moved out of site under some low hanging branches. Here it spent 5 or 6 minutes before a splash could be heard and it emerged on the bank carrying a substantially sized Perch. Again the Heron did not immediately swallow its prey. Instead it moved swiftly away from the bank side and quickly flew across the river to thicker reeds where it then ate the fish. It was likely worried that another predator would try and steal his food and so relocated to better cover in order to keep it.

Interested by the herons feeding habits I found a paper in Bird Study which looked at how successful herons could be. The article indicated a basic frequency of prey at 1 per 55 mins with a 50% success rate.

I reckon I watched the heron for about 20 minutes and estimated it also to have a 50% success rate but a frequency of 1 per 12.5 mins.