Searching for the Zigzag Heron

It has been some time since the last post, very busy with many things and three months travel, but I’ll try to catch up with some of the highlights from this summer.

The Zigzag Heron (Zebrilus undulates) is a widespread but poorly known species found throughout the Amazon basin. The species prefers slow moving creeks, lagoons, and swamps within undisturbed tropical forests. It forages within dense cover along the water edge and builds a stick platform nest in trees overhanging lagoons and rivers. Generally, it is a shy species and often only detected by its distinctive cooing calls given frequently at dawn and dusk. If seen, the bird is strikingly small, in fact one of the smallest Ardeids in the world, and is most closely related to bitterns. The adult is slate gray on the upperparts with fine vermiculations, forming distinct zigzag patterns. The underparts are a lighter gray to whitish. The overall shape is compact with stout legs, comparatively heavy bill, and large eyes. On first glance, a crouching Zigzag Heron could give the appearance of anything but a heron. Young birds are browner overall with a rufous wash to the breast, neck, and face. Also, the back and crown have brown feathers infusing the slate gray color, giving the overall appearance of warmer plumage compared to the adult.

I spent three months birding and guiding at the Cristalino Jungle Lodge in Mato Grosso, Brazil. While the species reaches its southeastern limits of distribution in the area, Zigzag Heron sightings are relatively frequent and the species is considered uncommon in the Rio Cristalino Private Natural Heritage Preserve. I realized the dry season, May through September, was not the best time of year to look for this difficult species and Zigzag Herons are vocal mainly during the breeding season beginning October. Yet, with three months from May to August and plenty of time in the field, I could still hope to catch a glimpse of this elusive heron.

It looked promising in May, when after just a few days at the lodge and already dozens of great species and sightings on the list, I heard the unmistakable “oooop” call of a Zigzag Heron at dusk, while we were idling in a boat along the Rio Cristalino upstream from the lodge. The bird was calling from a swamp or lagoon deep within igapo forest and there was no hope of actually seeing it, but the species was here. As the dry season progressed, streams in the forest slowed to trickles and pools of standing water, and lagoons along the river receded, eventually leaving nothing but a few moist leaves and open expanses of forest.

For nearly two and a half months I was distracted with over 400 other bird species, tracking down low density antbirds, having luck with some rare raptors, finally seeing a tinamou or two, and keeping my hopes up for a quetzal. By August the dry season was in full swing, with hot sunny days and the forest relatively quiet. Any puddles remaining in the forest were visited by large numbers of bird in the afternoons and evenings. With less than a week left I was getting anxious to find some of the species that had so far eluded me, which not surprisingly included Zigzag Heron. The chances of seeing one before I left were poor at best. The last sighting I knew off was from February, when another guide had spotted one at dusk along the river. Despite hoping to spot one during one of the night boat tours, they always turned out to be the larger Striated Heron.

On a free morning another guide and I struck out for the Cacao Trail, one of our favorites at the lodge. The trail started on the opposite bank of the lodge and we had to paddle across and upstream for a few minutes in the weak early morning light. The dawn chorus was in full swing with Glossy Antshrikes and Buff-breasted Wrens competing in the riverside vegetation, flycatchers, pihas, and mourners calling from the canopy, and commuting parrots screeching above.

As soon as we landed and had walked down the trail a few meters we sorted mentally thought the calls, White-bellied Tody-Tyrant at its usual spot, Rufous-winged Antwren calling from high up, Silvered Antbird in the flooded section of the forest, and somewhere in the dense understory the up and down whistle of a Spot-backed Antbird. Our plan was to walk the trail in the early hours, carefully check each mixed flock and listen for anything new or unusual. The trail winds through beautiful terra firme forest and cuts through a large stand of bamboo that was always full of specialties. Right at the start I was sidetracked as the trail skirted a large densely vegetated lagoon that still held substantial water. I knew it was a great place to see Band-tailed, Dot-backed, and Silvered Antbirds and it looked as promising as any spot I had found at the reserve for the small heron.

We walked down the small slope to the water’s edge and took a close look. Fallen logs, vines, and dense tangles were interspersed by areas of open water. On a whim we decided to investigate further and walk around the lagoon. The igapo forest was relatively open with a thick layer of fallen leaves and essentially no understory. We followed a peccary trail, clearly left by herds regularly visiting to drink, and even found fresh tapir tracks. The lagoon was larger than it had first appeared, broadening as we followed the edge. At a promising looking spot I played a recording of the “oooop” and “ahnnn” calls of Zigzag Heron. We waited quietly for a response and as we expected no answer came from the flooded tangles. At the far end of the lagoon, where we could see dry land wrapping around the water, I played the calls again and we waited. I was about to take a step to continue when an answer came from somewhere in the forest “ahnnn”. The response was brief, but we were certain we had found our bird. Looking at each other in disbelief, I played again briefly and another answer came from far off in the tangles. We spent a few moments going back and forth, with the bird possibly coming closer and MR even spotting some movement. As we had learned on earlier occasions the best strategy was often to just wait silently and we found a log along the water’s edge that was relatively ant free and crouched down. Staring into the dark forest and black water of the lagoon, hoping for a subtle movement, straining for a clue of the bird’s exact whereabouts, we waited.

Not even blinking an eye we waited some more. It was quiet, the bird had not called for several minutes, and nothing was moving, but we sat frozen near the water’s edge. After at least fifteen minutes a Zigzag Heron flew in out of nowhere, perching on an exposed log completely out in the open no more than four meters distant. Even though we sat still, it took off and disappeared behind the buttress root of a large tree. We waited and eventually spotted the head of the bird peaking above one of the roots, disappear, and almost immediately reappear. The bird jumped onto the muddy ground near the root and we were able to see it well. This continued for several minutes with the bird disappearing behind the roots, popping up its small head, and jumping back and forth unlike any other species of heron I had observed previously.

We could see that it was a young bird, with extensive rufous on its underparts, face, and neck. At one point it ran a short distance and appeared to snap at some flying insect. It constantly flicked its short tail and at one point extended its neck, holding its bill almost vertical. Eventually the heron flew off into a thicker tangle and was lost from sight. By now the morning chorus in the forest around us was subsiding and we decided to track along the lagoon. Within minutes we found the bird again, this time it hopped along thin branches in a dense thicket overlying standing water. We watched it for another thirty minutes as it bounced back and forth. At one point it plunged head first into the water much like a kingfisher, but emerged without anything in its bill. It also appeared to be gleaning from leaves and carefully investigated the muddy margins. The bird worked its way deeper into the tangle and finally disappeared.

Elated we wandered around the lagoon. Walked through some nice open forest and were back on the trail with the majority of the morning gone. We walked the entire trail anyway, knowing that the rest of the day would be anticlimactic after such a privileged sighting and despite finding several mixed flocks, a fruiting tree full of birds, nothing could match the special Zigzag Heron.

Zigzag Heron Cristalino Lodge Brazil Photo Stephan Lorenz

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One response to this post.

  1. Very cool, Stephan. One of my “must see” birds..

    Reply

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