Saturday, July 17, 2010

Sure They’re Pretty, but So’s Deadly Nightshade: The Dark Side of Black-Crowned Night Herons


I was surprised and delighted to discover that wild black-crowned night herons nest in the trees surrounding the bird exhibits at the zoo. I was also impressed to discover how unafraid they seem to be; unlike the ones I’ve seen in the wild, which have always been shy and retiring birds, these guys are fearless and raucous, flying low above visitors’ heads, flapping and crashing through the trees, and producing a cacophony of honks and squeals and yowls and groans that can be really alarming.


[this is the way their throats look
when they're making their strange noises]

As it turns out, they’re also quite aggressive and something of a nuisance.

A few times now I’ve seen them fighting with one another over food:




And, speaking of food, one day I was surprised to see night herons flapping down to gather around a pile of little dead fish. Being a trained marine biologist, I cleverly deduced that these fish had not appeared naturally on the grass beneath an oak tree.


So I asked two volunteers who were recording kori-bustard behavior (more on that another day) if it was zoo policy to feed these wild birds. They explained to me that the night herons have a tendency to steal the food of legitimate zoo animals; every now and then this kleptoparasitism gets so bad that the zookeepers put out some food as a distraction for the herons in the hopes that they’ll leave the captive birds’ food alone. Apparently it doesn’t work all that well; the herons scarf up their offering and then go back to stealing from the storks (and others).

[a night heron taking food from a stork's food box]

It seems as if even the young juveniles harbor dark secrets: I was told that some young appear to push others out of their high nests—or at least, zookeepers and volunteers have seen the young shrieking and shoving and have found fallen, dead fledglings on the ground from time to time. (Mind you, this is to some degree a tried-and-true technique for a lot of bird species—so even if it’s happening, it’s a species thing, not a sign of deliberately fratricidal birds.)


One of the volunteers, who also works near the cheetah exhibit, told me that one year the zoo tried to prevent the herons from nesting, as they usually do, around the bird house. In response, the herons moved over to the cheetah area, where they made a huge noise and mess and generally fouled (fowled?) things up. So now the zoo’s given up, it seems, and just gives them some food and hopes for the best.


[they do look kind of malevolent when they're eating, don't they?]

It works out well for me: they’re a lot of fun to watch and photograph. And they’re not eating my food.


3 comments:

Adrian said...

"Being a trained marine biologist, I cleverly deduced that these fish had not appeared naturally on the grass beneath an oak tree." Brilliant!

They do look like maniacal little beasts in some of these photos! What do you think makes these black-crowned night herons less shy than the others you've seen in the wild? It's kind of fascinating...is it just something that city life does to them?

Olivia V. Ambrogio said...

It could be; I think some populations of animals habituate to humans if they live in areas with a lot of people. Or it could be that they feel a particular sense of safety in the zoo because of the fencing; I don't know how good they are at logic, but they may have noticed that people can't or don't enter certain areas.

Anca said...

And what have you got against deadly nightshade, I'd like to know? Beautiful flowers, pretty berries that the birds love, and a outlet for revenge fantasies :).

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