Posts Tagged ‘Snowy Egret’

I went for a walk along Putah Creek yesterday at the South Fork Preserve.  The early morning was windy and not yet hot, but the sky was clear and the sun was bright.  When I got to the first creek access point, I was treated to a view downstream of the creek scattered with egrets and herons (all members of the family Ciconiiformes).  Usually there are one or two, but I have never seen this many along the creek before.  About half-a-dozen Black-crowned Night Herons were perched in some dead and fallen branches just above the water line.  Three Snowy Egrets were just beyond them foraging in the shallows skittering their feet around in the mud and silt and darting off after food when it was disturbed by the egret’s agitated foot movements.  A bit farther into the channel, stood 5 Great Egrets.  They were all hunting through an area of the creek that was thick with aquatic plants and alga.  They stood almost motionless, waiting for some unsuspecting prey to swim by.  Out in the deeper water in the center of the channel were the 3 Great Blue Herons using the same hunting strategy as the Great Egrets, they stood waiting.

Watching these birds all crowded into the same area got me thinking on how each species utilizes a different part of the habitat and has characteristic behavioral differences that help then to do so, a concept known as niche partitioning.  But which came first, the different species or the different behaviors?  Perhaps populations of ancestral Ciconiiforms became somehow reproductively isolated and so became different species, and then these different species developed different behaviors.  Alternatively, perhaps different behaviors arose in that ancestral species that allowed some members to use one part of the habitat better, and other members use a different part of the habitat better, and this then led to assortative mating and speciation.  And the answer is not necessarily the same for all species, in fact it is almost certainly not.  But how often does reproductive isolation come first?  How often is behavioral differentiation the inciting incident?  No one is really sure, but I find it fascinating to think about.  Gaining a greater understanding of how these different processes work and interact will give us a greater understanding of evolution and natural selection as a whole.

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