Uninviting nest surface
The equality – or ambivalence – extends beyond courtship. Most birders will have noticed that it is difficult or impossible to tell the sexes of grebes apart, although the males are usually fractionally larger and heavier. Even the birds cannot always tell. An individual may start displaying and realise, with red faces all round, that the targeted object was not of the desired gender. Perhaps the most extraordinary aspect, though, is that, during copulation, the female will sometimes mount the male, instead of the other way round. As far as I am aware, nobody has confirmed whether these reverse mountings result in egg fertilization, but they are a consistent feature among grebes. Very few other birds ever do this, unless extremely drunk on a night out.
The equality of grebe reproduction goes well beyond the baby-making stage, too. Indeed, it pervades all through the stages of breeding. Take nest-building. You might not think that it is earth-shattering that both male and female Slavonian Grebes build the nest together, but the female Robin in your garden builds the nest almost entirely by herself, and this is common, especially among smaller birds.
Grebe nests are not among the marvels of bird architecture, but they do have the distinction of being able to float, which is useful on a small waterbody that might fluctuate in depth. Affixed to emergent vegetation, often hidden in thick marshy mush, they are little more than piles of the most common plant material in the vicinity.
Slavonian Grebe nests can be built in just a few hours, although, as seems to be common in the construction industry, work can expand to fill several days. The cup of the nest is a distinctly uninviting surface of wet and rotting vegetation, damp and chilly, similar to the experience of staycation camping. Grebe chicks earn their Duke of Edinburgh award schemes before they even hatch.
In traditional style, Slavonian Grebes share incubation duties, taking turns to sit
on the clutch of anything between one and eight eggs. In one study, a male babysat for 45% of the time. Both adults cover the eggs during brief off-duty forays, loading bundles of sludgy vegetation over them, presumably to keep them from chilling excessively. This carries on for 22-25 days.
Once the eggs hatch, the young take one look at their insalubrious surroundings and evacuate the nest for their five-star accommodation, on top of a parent’s back. They can swim and dive almost from hatching, but naturally they are reluctant to take the plunge, and revel in their floating luxury for at least a week, and often longer. It must be something of a shock to them when the adult dives with the brood still on its back, which happens frequently.
During these salad days, the young receive food packages from whichever parent is not providing accommodation. The food they receive is a snapshot of whatever invertebrates are available in the surroundings of the nest – beetle larvae, dragonfly larvae, mayflies and caddisflies and perhaps the odd fish. In winter, most Slavonian Grebes switch their diet almost entirely to fish, often taking these from the bottom of shallow water.
You might think that a Slavonian Grebe chick has the perfect start to life, but a curious feature of grebe behaviour is that each parent may take a liking or disliking to one or more of its brood. Once the back-riding is over, the brood is then split into two. Each parent apparently has its own in-chicks and out-chicks, which seems rather harsh for such an egalitarian species.
Nevertheless, the brood is divided between the adults, which then go their separate ways, each with their own consignment of chicks.
It is the final and complete statement of gender equality.