Ammocoetes being eaten by Green Heron; Eugene Delta Ponds

[Priscilla Sokolowski]

I am slightly out of the suggested geographical range of this group, but not by many miles and my topic might be of sufficient interest to make it worthy.  

The most exciting sighting of recent days, for me, was the discovery that an adult Green Heron I was watching at Delta Ponds on Tuesday morning, July 2, around 9am, was eating BROOK LAMPREY larvae (ammocoetes)! He caught four of these in less than six minutes! When he caught the first one I thought it was a small snake. Then he caught another one the same size. I looked closely at my photos and discovered the critter was flattened or progressively more keeled towards the "tail" end. About 1/3 of the creature was at least partially keeled that way. He caught two more and as I said, all this was in less than six minutes. The Heron could apparently see something the ammocoetes were doing because the Heron would run suddenly two or three feet and then grab one of these critters from the water. I couldn't see any movements of these things but the Heron could. 

I didn't know what these were at the time and thought they were Eels. Some research suggests there are two lampreys native to the Willamette Valley, the Brook Lamprey and the Pacific Lamprey. As their names suggest, the former remains in fresh water while the latter migrates to and from the Pacific Ocean.  The larval ammocoete stage lasts 2-7 years during which they remain submerged in soft silt and feed on organisms there. The two species are apparently so similar at these stage as to make it difficult for any but an experienced observer to sort out which is which. 

I have returned both in mornings and evenings several days since the day I caught this Heron eating them, but have not seen any further activity even though Green Herons are frequenting the general area. I'm sure if there were more ammocoetes there to be eaten, the Heron would be making short work of them.  I suspect the ammocoetes were emerging from the silt that morning -perhaps ready to metamorphose into adults or something, and it was only happening that one morning at that particular time. Or it could have been going on before sunrise as well. I wish I knew more about what was taking place and hope maybe someone in this group can add more to this story. 

I have four additional photos but only posted the clearest one because I am not sure if we are allowed to attach more than one photo with our posting.

Priscilla Sokolowski

[Lisa Millbank]

Hi Priscilla,

That's a great observation and a cool photo!  I had no idea that lampreys spend so many years as larvae. You can post multiple photos to this group, so feel free to post them if you have others you want to share.

Lisa Millbank

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[Priscilla Sokolowski]

Thanks Lisa!  Here are four more photos of the ammocoetes being sacrificed to the Green Heron.

Priscilla

[Ann Werner]

Also ... great images of the little green heron, particularly those snazzy orange legs 

Message flown by a lark

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[Priscilla Sokolowski]

Thank you. I'm glad you enjoyed the photos AND the crazy orange legs. :)