Friday, August 22, 2014

Know Thy Herons

[SW Florida. August 2014]

The definitive word on the family Ardeidae is the highly scholarly (and equally expensive) "The Herons" (recommended for all birders who are not averse to occasionally dabbling in Ornithology).  In this definitive 400-page treatise, in addition to individual species accounts, some fascinating facts about the heron family emerge:
  • The first herons arrived on the scene in the Eocene period 60 million years ago
  • There are 64 species of herons extant today ranging in size from the Least Bittern to the Goliath Heron (the former barely reaching the latter's ankles)
  • Linnaeus was the first to group all the herons under one genus (Ardea) in 1788. Today the family includes 21 genera comprising day herons, egrets, bitterns, pond herons, cattle egrets, tiger herons, night herons and more
  • Long and slender -- everything about a heron is long and slender; from overall body shape to the shape of individual body parts such as the neck, bill, legs, and toes
  • The kink in the heron's neck is a distinctive evolutionary adaptation and is a result of an elongated 6th cervical vertebra. This unique "anatomical hinge" is what gives the heron its powerful fish-catching strike.
We begin with a quick review of the features that make a heron a heron:

Tricolored Heron seen at Tigertail Beach. This side view does justice to its long, spear-like bill.

The Tricolored Heron is, in many ways, the archetype heron. The first thing that stands out is the impressively long, spear-shaped bill. The more aquatic and fish-dependent the heron, the longer and slimmer the bill. In counter example, the Cattle Egret has a much shorter bill -- which is perfect for an insect eating "ground heron".

Great Blue Heron seen at Bunche Beach

Our next heron, the Great Blue, also fits into the typical heron mold: the flexible, long neck with the prominent kink; the bill here, while proportionally not as long as the Tricolored's, is still long but appreciably stouter -- a feature that helps it catch larger fish.
 
Yellow-crowned Night Heron seen at Ding Darling (Nov 2013). Note the powerful bill.

It is the serial crab predator, the Yellow-crowned Night Heron, however, that typifies food-based bill specialization in the herons. Compared with the Tricolored's, the night heron's bill is much more compact as well as thicker -- a powerful bill that is perfectly suited for preying on crabs and crayfish.

Little Blue Heron seen at Tigertail Beach

Compared to the Yellow-crowned night Heron, both the Little Blue Heron and the Reddish Egret display the typical characteristics of fish-eating herons -- long necks and slender bills.

Reddish Egret seen at Tigertail Beach

While the basic anatomy of both the Little Blue Heron and the Reddish Egret is similar, their foraging habits are not.


 Little Blue Heron foraging at Little Estero Lagoon (Sept. 2012)

The Little Blue Heron is a slow and deliberate hunter and uses "Head Swinging" (see above) -- its long neck swaying over the water not unlike the movement of a snake. Compare this with the foraging antics of the Tricolored Heron and Reddish Egret.

The Tricolored Heron (as the text explains) frequently uses Open Wing Feeding which is preceded by Stalk, Hop, Run and then with Open Wings, Lunge and Strike.



Tricolored Heron feeding sequence observed at Tigertail Lagoon

When it comes to foraging, however, no American heron is perhaps as energetically entertaining as the Reddish Egret. While the stoic hunters like the Great Egret and Great Blue Heron use a lethargic "wait for the prey" technique, the Reddish Egret is an active forager -- employing all of the techniques of the Tricolored plus Canopy Feeding.





Reddish Egret at Bunche Beach in feeding sequence

The white morph of the Reddish Egret displays exactly the same behaviors. It is a little known fact that the occurrence of the white morph varies by geography -- from a low of 5% for Reddish Egrets found on the Texas coast to a high of 90% for those on Great Inagua in the Bahamas.




Reddish Egret at Bunche Beach in feeding sequence

About 15% of the Reddish Egrets in Florida are white morphs (incidentally, compare this to less than 1% for the occurrence of Great White Herons among Great Blues).

The scientific study of our avifauna sheds tremendous insights into the world of birding; and, as a consequence, the pursuit of birds whether as a sport, recreational obsession, or photographic quest is greatly enriched when supplemented by Ornithological accounts that are now more accessible than ever to the birding enthusiast.

Other members of the heron family:

 Indian Pond Heron seen at Sultanpur, India, July 2009


Least Bittern seen at Wakodahatchee Wetlands, July 2009

Little Bittern seen at Dal Lake, India, July 2012

Purple Heron seen at Bhindawas Bird Sanctuary, India, July 2012

White-faced Heron seen at Anglesea Beach, Victoria, Australia. February 2012

2 comments:

  1. It was a nice surprise to see your herons outside of the Gulf Coast, Hemant. Wondrous variety.

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  2. I enjoyed reading your Heron story - love the pics too. Thanks.

    ReplyDelete