Field notes from Fairhill Nature Reserve, Western Cape province, South Africa, part 2: the ostrich (Struthio camelus)

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...continued from https://www.inaturalist.org/journal/milewski/81213-field-notes-from-fairhill-nature-reserve-western-cape-province-south-africa-part-1-the-common-eland-taurotragus-oryx#

I noted the following during my visit to Fairhill Nature Reserve (https://www.activities-south-africa.co.za/portal/business/17632/fairhill-guest-house-and-nature-reserve-stanford-7km) in August 2001.

Val Deverson had hand-raised three female individuals of the ostrich, which as adults remained habituated because they depended on being fed on a property where the natural vegetation, in its unburnt (mature) state, was unpalatable for this species. Two of the individuals were so habituated that they behaved more like pets than like wild animals.

DIET

As Val Deverson and I walked from the farmyard into the natural vegetation, burnt 8 months previously, the two individuals of the ostrich spontaneously followed us, and proceeded to forage continually, as I watched.

The birds ate mainly the soft (succulent), lax leaves of Trachyandra ciliata (https://www.inaturalist.org/taxa/595554-Trachyandra-ciliata), and the flower buds and inflorescences of Trachyandra divaricata and perhaps an additional species (https://www.inaturalist.org/observations?place_id=48641&taxon_id=180063&view=species).

They also, during the same foraging bout, ate

• Cotula discolor (https://www.inaturalist.org/taxa/582825-Cotula-discolor), in full flower at the time, which I take to be a post-fire annual; the birds took only the fresh, soft, yellow inflorescences, one at a time, each requiring a distinct back-and-forth movement of the beak, head, and neck; the leaves were ignored;
• the soft, brittle, bipinnatifid (see comment below) leaves of a form resembling Arctotheca prostrata (https://www.inaturalist.org/taxa/75549-Arctotheca-prostrata); this was growing vigorously post-fire; and
• Massonia longipes (https://www.inaturalist.org/taxa/862426-Massonia-longipes), plucking and swallowing the whole leaves, despite the ground-hugging growth-form; this species was even more common post-fire than in the mature vegetation, and the birds did not seem to be seeking this species out.

In the same vegetation at the same time, the birds completely ignored

• the abundant and easily available vegetative regrowth of Psoralea bracteolata (https://www.inaturalist.org/taxa/1434153-Psoralea-bracteolata), and
• the flowers of Hermannia and Babiana.

What I have identified as Arctotheca prostrata showed signs of also being eaten by the common eland, particularly along paths used by this ungulate. The repeated defoliation of the shoots had resulted in tough petiole-stumps at the centres of the rosettes.

Another species eaten by the ostrich was Gazania pectinata (https://www.inaturalist.org/taxa/567911-Gazania-pectinata).

Val Deverson told me that in the mature, unburnt areas of the same vegetation type at Fairhill (https://www.facebook.com/photo/?fbid=1332818170073904&set=a.920151795594782 and https://www.facebook.com/photo/?fbid=1109254330017860&set=a.920151795594782 and https://www.afristay.com/p/28394), these individuals of the ostrich had eaten only geophytes. However, in this 8-month old stand, the birds found the herbaceous stage of regeneration to be attractive.

At this time, these two individuals of the ostrich did still graze the farmyard lawn (where the grass was a few centimetres high), and received some supplementary food from Val. However, the third individual was foraging mainly on the natural vegetation, finding the post-fire regeneration to be sufficient nutritionally.

In the dusk of evening, I watched one of the individuals grazing uninterruptedly at the farmyard (https://www.facebook.com/photo/?fbid=5341407179214963&set=a.920151795594782), as if trying to fill up on roughage before bed. The short, fine-leafed, green grass that it was pecking looked like a winter annual, not a perennial species.

Val Deverson showed me a cultivated individual of Brassica napus (https://www.inaturalist.org/taxa/75869-Brassica-napus), in flower at the time, in her garden. What was odd was that this ornamental, from which the ostrich had repeatedly eaten when it was a juvenile plant, was now ignored by the birds.

I infer that this brassica is chemically-defended to the degree that, given the herbaceous food available in the natural vegetation at the time, even the flowers of the domestic plant became no longer worth eating.

ANTI-PREDATOR BEHAVIOUR

When still juvenile, the individuals of the ostrich had spent the nights together. However, upon becoming adult, their behaviour changed: they retired to separate places in the natural vegetation some distance from the farmyard.

Val's pet dog belonged to a large-bodied breed, with a father weighing 80 kg. At the time of my visit, it was still a boisterous, inexperienced 'puppy' (10 months old), with a body mass exceeding 50 kg. It interacted in an ambivalent way with the two most habituated individuals of the ostrich (adult females, with body mass probably about 80 kg).

When standing their ground and threatening the dog, the birds puffed out the throat ventral to the head (not extending to the neck), and made a slight hiss, while lifting and spreading the wings somewhat.

On one occasion, I watched this dog chase the birds in the farmyard. The birds sprinted for a short distance. They then turned and approached the dog, by walking towards it with head lowered to within 0.3 m of the ground, running at it when within a few metres. The dog took evasive action, but at least once in this brief game I saw it being caught and run over, with ambulatory kicks being delivered. The dog cringed on to its back/sides, to avoid the blows, without any whimpering or yelping.

This was the second time in my life that I have seen the domestic dog being trampled/kicked by the ostrich, and in both cases the carnivore arose unharmed.

My impression was that this game was enjoyable for the dog, but not for these individuals of the ostrich, which saw the carnivore as a nuisance and would have hurt it if possible. How does the domestic dog take kicks from the ostrich so lightly? Does it instinctively know how the feet of the ostrich work? Is it that the kicking mechanism is more injurious for humans than for canids?

One of the three individuals of the ostrich at Fairhill seemed to show vindictive behaviour towards this dog. Val Deverson told me that it would sneak up while the latter was asleep, apparently intending to harm it.

Val Deverson reported a quirk of behaviour, shared by the ostrich and the common eland on her property, possibly reflecting anti-predator psychology.

She had planted Thamnochortus insignis (https://www.inaturalist.org/taxa/595319-Thamnochortus-insignis) in the garden, initially as an ornamental. Inadvertently, she found that this stand of tall tussocks (up to 1.5 m high) served to protect her other ornamentals, among the tussocks, from herbivory by the ostrich and the common eland. The animals seemed to be instinctively (and, in this predator-free environment, unnecessarily) repelled by the presence of tall tussocks that impede vigilance while the heads are lowered.

The ostrich and the common eland had reacted differently to the baring and charring of the land by the fire. Val had continued her habit of leading the birds, on a daily basis, from the farmyard into the natural vegetation. However, when reaching the edge of the recently burnt area, the birds refused to proceed. They seemed to have an instinctive fear of the unaccustomed openness of the ground. By contrast, the common eland eagerly and immediately took to the recently burnt area, without any leading or encouragement.

SEXUAL BEHAVIOUR

One or more of the thoroughly habituated female individuals of the ostrich showed sexual behavior

• towards me, despite my being human and a stranger,
• towards Val, despite her being a woman and in a 'maternal' relationship with the bird, and
• towards Val's newly-parked Land Rover, despite this being a motor vehicle.

It/they did this repeatedly and frequently, during my visit, by lowering the head, snapping the beak in mock-foraging, and spreading and vibrating the wings, producing a surprisingly loud 'sail-billowing' sound.

All three individuals - despite remaining virginal - were also laying infertile eggs, at the time, here and there on the property. They had begun laying for the first time in their lives six weeks previously, indicating a spontaneous laying season starting approximately in June in the mediterranean-type climate of the southern Hemisphere.

The first egg produced by each individual had been laid with visible discomfort, just outside the farmhouse. This initial egg was small and lacked the usual gloss on the shell, but had proved to be perfectly edible.

Posted on June 16, 2023 08:31 PM by milewski