Eared grebes keep their kids from getting wet by carrying them on the water
My children love being carried. Even at ages eight and four, they’d probably be perfectly happy to be hauled around as much as their mother and I could tolerate. For all the times I’ve worn myself out toting a kid around, I suppose I should be thankful to not be in the position of eared grebe (Podiceps nigricollis) parents, as their piggyback rides may be matters of life or death. It’s not that their kids are lazy per se, but that hatching grebes just aren’t prepared to venture out into the world the minute they leave their egg.
Grebes nest in huge colonies along the swampy shores of lakes, but they don’t stay put for too long. Once their young hatch, nearly every grebe parent can look forward to around 10 days of being a mobile bed, safety net and kitchen for their kids. Rather than stay in the nest, grebe hatchlings just go for a ride on their parents, switching between mom and dad when one adult needs a break from carrying the three to five chicks around. This means that babies may get a quick dip in the water as they switch from adult to the other, but the majority of their time is spent among the insulating feathers of their parents’ backs.
Swimming without getting soaked
This pattern suggests that staying out of the water is a key concern for grebe babies. This is likely due to the fact that, like many waterbird chicks, their feathers aren’t waterproof at birth. So while an adolescent grebe or duck can float along without getting cold water on its skin, a hatchling’s feathers will sop up water and leave the poor thing quite cold and waterlogged. From this perspective, staying on a parent’s warm back allows the kids to stay close to their mom and dad while also staying warm and dry. After about 10 days, a chick’s “preen,” or uropygial gland can start to do its job, providing the waterproofing oil that other waterbirds use to keep their feathers seaworthy.
Not all waterbirds adopt this strategy though, thanks to this amazing invention called land. Plenty of other bird species manage to keep their kids dry without carrying them around, although parents do sometimes share some oil from their own preening gland. The catch is that those waterfowl end up being anchored to the location of their nest, while grebes prefer to move around a lot. So in order to maintain their mobilized lifestyle, the parent grebes are essentially turning their backs into portable nesting sites.
Avoiding getting eaten
While not conclusively verified, there the grebes may gain one more advantage from the keeping their kids within wings reach all day. Hatchlings from other species may venture into the water before they’re really ready to handle things on their own, including being big enough to not look like prey to turtles and fish. While the grebes are competent enough swimmers, getting a ride on mom and dad helps keep them from putting themselves in harm’s way before they’re a little more adept at avoiding danger.
Source: Why Some Bird Babies Ride Piggyback by Elizabeth Preston, Inkfish