Heron Egret Rookery LKNWR

[rrip...@charter.net]

A few days ago I responded to an observation regarding the absence of nesting herons and egrets at the rookery along the old growth willow row at the exit of the tour route on the Lower Klamath National Wildlife Area. Although I hadn't been down there in a few weeks, I knew the condition of the refuge there, with its dry units, and suggested that the absence of nesting herons and egrets along that stretch was possibly due to lack of available food, and actually an abundance of food since hunting needs to sustain both adults and growing juveniles. 

Since then others have commented about being sad with the failure of the rookery. And I heard speculation that human disturbance, possibly with firearms, would seem more probable to cause the failure than the lack of food. So, that got my curiosity going and I went down there myself. 

In the end, I think the failure was due to avian egg predation, and most probably was done by one or more Common Ravens. 

I got down there and counted nests. There were 47 or more nests. I couldn't see them all as some toward the other side were hidden due to advanced leafing out. They were of various sizes, with some being obviously older with yearly stick additions. They were towards the tops of the trees, of different heights. When the herons were there it was almost like seeing a page from a Dr. Seuss book,  of weird characters in staggered positions on branches of questionable strengths. None were occupied. Although when I first began counting I observed a single Great Egret coast over the vacated rookery, cruising by as if going to land, or stop and feed its young. But it flew on. I drove on and went by the Bald Eagle nest, which was active, and saw a juvenile flapping its wings and jumping around the nest platform. The adult on the nest seemed annoyed and looked the other way.

 

I decided to venture down to the rookery nest trees. I did not come close to the eagle nest, but I did get under the now vacant rookery. I found egg shells, baby blue in color. They were under the canopies of the trees that had nests. The shell fragments were large and not near other parts of the same shell. It seemed like I could put together some of the fragments and the size of the egg would be a bit larger than a large chicken egg. Some fragments were under dense, now dead, stems from last year's ditch bank growth. Some hints suggested that the fragments were not mammal predation. I find that when a predatory mammal finds a nest, the entire nest is pillaged. This was not the case. The fragments seemed to be in random places. And the color of heron eggs? They are a baby blue color. I've included some photos. 

The unit along the tour route is dry, but the one on the other side of the willows has water, and there are currently waterfowl, and at least 27 Black-crowned Night Herons. I saw 8 Great Egrets while there. And although the rookery is now vacated, it probably wasn't vacated due to food. It was likely due to one or more opportunistic Common Raven, which are notorious nest robbers. I see them packing off hatchlings all the time when visiting a wetland during the nesting season. I don't know if herons and egrets will defend their nest. But in this case once one nest was successfully predated, they all were. It makes me wonder about the eagle nest. I think they would vigorously defend their nest against a raven; I don't know. But since the eagle's young is near fledging stage, it's also possible that it escaped the raven by being further along in nesting by the time the raven or ravens became desperate for food themselves and opted to hijack the eggs in the rookery. The ravens as far as I know, didn't have a big impact on the heron nesting there during previous years. But I am not sure about that. It will be interesting to see what happens to the rookery in the future. Corvids are smart, and I think they have good memories. I wonder if they will recall the eggs next year, even if the refuge returns. 

I've attached a few photos. Egg fragments: outside, inside, & random location on litter, and Unit 1 with Cliff Swallows.

Good Birding

Kevin Spencer

Klamath Falls

[kirsten potter]

Good job on this, Kevin.  Seems like you've got it right.   Could be more than just a couple [2] ravens since, as you said, they learn fast.     And I believe if an involved raven survives to next spring it will come back to hunt this area.

On one of the game warden shows - from back east - they were looking at a remains of dead pond turtles scattered on a little used forest road.  The state biologist figured out crows were killing and eating the meat out of the shells when the turtles are on land trying to lay eggs.   Myself, I saw a scrub jay pick off a California quail baby as the brood was crossing one of our residential streets in K. Falls.  I scared the brood across the road faster to stop the jay's repeat pass.  

Jays, crows, ravens and magpies are very intelligent birds.

                                                       Dave Potter

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[kirsten potter]

One last comment.   You can tell if a broken egg has hatched or been predated by looking at the membrane lining the inside of the egg.  If the membrane remains attached to the pieces of egg shell, it was predated.   If the membrane, or part of one, is laying detached from the shells [like in or near a nest] the egg has hatched.  This is a standard technique when recording duck nesting success in various habitats.  Did much of this.

                                          Dave Potter

[Barry West]

Thank. you for the informed observations.

Barry