r/megafaunarewilding • u/Psilopterus • 4h ago
Magpies and megafauna
There are plenty of cases of megafauna-mutualisms in birds, with oxpeckers (Buphagus) in Africa being a classic example, and it is interesting to think about how living birds may have had a relationship with extinct large herbivores in the past. Perhaps the best example of this in the Holarctic is in the true magpies (Pica sp.), a group of corvids characterized by contrasting black-and white plumage and long tails. Like many corvids (e.g. crows - Corvus) magpies are intelligent and socially complex birds that can easily take advantage of human-dominated habitats, but their preferences within that characterization are interesting.
Magpies generally prefer short-grass communities where they can forage for insects and other small animals, habitats that are common in urban areas but which were originally (and still in many cases) predominantly created by grazing megafauna, first as wild ungulates and later as livestock. Magpies in North America were historically associated with bison herds, not only for this reason but also because herbivores flush small animals as they move and serve as a constant sources of food in the form of ectoparasites (ticks, botflies) and carrion- or dung-associated invertebrates.
It has been observed before that magpie’s share several qualities with an African corvid that is also strongly megafauna-associated - the piapiac (Ptilostomus afer). The two are not particularly close phylogenetically, but have developed similar traits - both have long and rigid tails that may allow them to better stabilize themselves on the backs of moving ungulates, both have bright underwing plumage at an angle that would alert their hosts to their approach while alighting, and both are more capable of running and hopping quickly across the ground.
Magpies as a group arose sometime between 4.1 and 6.2 mya, i.e. the former being the estimated split for the most basal species in the genus (Pica mauritanica) and the latter being the split for the genus and the most closely related corvids (Coloeus, Corvus, Nucifraga). The fact that the most basal magpies come from North Africa suggest that the genus may have originated there, but the fossil record for magpies is as poor as for most birds and all known fossils come from after the estimated split. I’ve attached a figure below that describes what we currently know about intrageneric magpie phylogeny and their limited fossil distribution. Notable is their current absence from much of eastern North America compared to their fossil presence.
The timing of magpie colonization of North America is interesting. The split between American and Eurasian magpies (Pica pica) occurred around 1.5 mya but the oldest magpie fossils from the continent are about 1.0 mya. Both substantially predate the estimated split for the two American species at 0.2 mya. It is likely that magpies were able to cross Beringia when it was exposed at some point during the Early Pleistocene. This predates the formation of what we now call the mammoth-steppe as a biome, and the landscape at the time might have more closely resembled the forest-steppe landscape that modern magpies find most appealing, with both short grasses and trees for nesting. The separation of mitochondrial lineages for magpies on either side of the bridge today may suggest they did not thrive in later Beringia, though it is worth noting that studies on magpie hybridization elsewhere suggest it is male-dominated.
An Early Pleistocene arrival of magpies in North America also suggest that their association with bison there is relatively recent, as bison arrived less than 0.2 mya. Instead, magpies may have been associating with mammoths, horses, sloths, etc.
https://doi.org/10.4081/rio.2017.295
https://doi.org/10.2108/zs160119
https://doi.org/10.1007/s13127-022-00568-6
