Striated Herons

Striated Herons (Butorides striata), stocky bittern-like herons, are strongly associated with mangroves and tidal estuaries and rivers. 

Please click on photos to enlarge.

Morcombe notes they can be secretive, skulking in shadowy mangroves and emerging at low tide to forage. However they can become relatively tame around manmade structures such as marinas, sea walls and oyster farms for example.

Striated Herons in Victoria are probably best regarded as rare vagrants with just 23 records in Birdata from the Mallacoota – Gypsy Point area between 2008 and 2014 with a peak of sighting records in 2010. There may have been unrecorded sightings since 2014 and eBird may contain additional records.

There are several Striated Herons on the Brunswick River in northern NSW where I found two birds using oyster farm racks to hunt fish on a rising tide. When hunting, the birds adopt a crouched posture. They often crouch low and rigid with intense concentration and focus while waiting for hapless prey to swim into the range of their surprisingly long necks and beaks which they use to make lightning fast lunges to capture fish and other small aquatic prey such as crabs and shrimp. They also stalk prey, once again in a crouched posture – I assume this makes it hard for their prey to see them. When not hunting they adopt a much more relaxed and upright stance. 

When not in hunting mode the Herons are relaxed and assume an upright posture.

In hunting mode they adopt a crouched posture and stalk with intense concentration.

Hunting from on top of the oyster racks required them to have good grip with their strong feet and legs to make vertical downward lunges at the fish below.

All the fish I saw caught were very small – these seemed to be targeted as a preference as there looked to be larger fish present.

A view of the Heron’s back.

A relaxed upright non-hunting posture.

 

The Striated Herons on the Brunswick River certainly make good use of the oyster growing infrastructure. They also forage along constructed rock sea walls and look for fish from mooring lines in the marina.

Oyster farms may be a physical blight on scenic tidal environments however they are an important aquaculture industry and they do provide very useful habitat for roosting/resting and foraging water birds including migrant shorebirds. Also small fish use them as shelters and sources of food.

Great Egret attraction to excavator?

On a recent Saturday morning birding walk at the Byron Wetlands I came across a parked bright orange Kubota excavator which had been used to do some vegetation clearing around water management infrastructure. (1)

To my surprise there was a Great Egret (Ardea alba) standing on the left hand rubber track of the excavator. Even though the bird was quite close, and from my experience well inside the distance within which this species would normally not tolerate human presence, it showed no sign of moving. 

Please click on photos to enlarge.

I took a couple of photos and then moved a couple of paces forward and the bird then flew up to a hydraulic hose on the excavator arm.

The bird perched on the hose for a few minutes before dropping down to the ground beside the excavator.

After a minute or two on the ground by the machine the bird then flew up to the roof.

I observed the Egret on the roof for over ten minutes. While it was on the roof an Intermediate Egret (Egretta intermedia) flew in quite close over the Great Egret to land nearby on the mown grass of a lagoon bank. (2)  The Intermediate had not noticed me at first, I suspect because it was focused on the Great. However when it did notice me its head feathers were erected in alarm and then it ejected an impressive stream of white liquid.

The Intermediate soon flew off to the adjacent lagoon where it commenced foraging. The Great remained on the roof of the excavator so I decided I would see how close I could get before the bird flew. I moved to about 10 metres from the bird before it flew, however when it did fly it did tight circuits around me and the excavator with hoarse croaks of displeasure,  landing on the roof couple of times and then eventually on the nearby lagoon bank before flying 100 metres or so to a dead tree in the lagoon.

By this time I had observed the Great Egret for just over 20 minutes. The bird clearly showed it did not want to leave the excavator in spite of my close presence which was well within the bird’s normal FID (flight initiation distance). I was left wondering what it was that attracted the bird. My only explanation is the bird had been attracted to its reflection in the excavator cabin plastic screens which are highly reflective. 

I did not see the bird pecking at the screens as many male birds do when they see their own reflection and take it to be a competing male in their territory. This is often seen during the breeding season. I have seen birds attacking car external rear view mirrors and house windows. The attacks can in the case of house windows go on for many days. Species I have seen doing this include Superb Fairy-wrens, White-browed Scrubwrens, Willie Wagtails, Magpie-larks, Rufous Whistlers and others. So I do not think the Great Egret was responding as it might to another male competitor and I’m thinking it may have seen its reflection as a potential mate.

Great Egrets must see their own reflection a lot as they stalk prey in still water. In this case the reflection was in the  vertical surface of the excavator windows and not the usual horizontal surface of water. Perhaps the novelty of a vertical surface led the Egret to see its reflection differently. 

I had a close look in and around the machine to see if there was any food item or other attraction for the Egret but could find nothing to explain the attraction.

As I ended my walk about an hour later I noticed I had a distant view of the excavator so checked with my binoculars and there was the Egret, still on the excavator roof.

Note 1: The formal title for the Byron Wetlands is the Byron Bay Integrated Water Management Reserve which is run by the Byron Shire Council.  Access is provided only by obtaining an electronic gate key.

Note 2: Identification of Great and Intermediate Egrets in the field can be tricky at times. While the two species are quite different with respect to size they do look very similar and their hunting styles can be similar. One way to separate the two species is via their gapes which in the case of the Great E extends to behind the eye whereas the Intermediate’s gape stops short of the back of the eye. The following two photos of the subject egrets show this potential ID feature.