Birds’ struggle to survive and reproduce is not only waged in the elements (as we were recently reminded) but also in the midst of other birds and animals. There is limited space in this world. Species are bound to interact with one another. Predators eat prey, small birds make way for the bigger ones and so on. However, bigger isn’t always necessarily tougher. Take, for example, the cute docile little Piping Plover. This species is mentioned frequently on this blog because it is state and federally-listed as threatened, and we work on it quite a bit. Piping Plovers nest on sandy beaches adjacent to water and on river sandbars. The closely-related Killdeer, also a plover, often nests at the same sites. Killdeer are noticeably larger than Piping Plovers and have about twice as much mass. However, it is the Piping Plover that often pushes around the Killdeer as evidenced by the photo series, below.
So what was going on here? Are Piping Plovers aggressive jerks harassing peace-loving Killdeer for a cheap thrill? Are Killdeer wimps that need to stand up for themselves? Such anthropomorphizing is of limited value. Actually, the Piping Plover had a brood in the area. The adult was merely being very protective of its young chicks. Piping Plovers will also behave aggressively toward much larger predatory species, such as Ring-billed Gulls or American Crows, when they’re defending their own flesh (feathers) and blood. Predatory birds will prey on Piping Plover chicks. Killdeer do not eat other birds, and they would not prey on Piping Plover chicks. As I mentioned, the two species nest in close proximity and are closely related. Thus, these two plovers compete for resources. If Killdeer (or other similar species) are eating all the nutritious invertebrates, fewer remain for Piping Plover chicks. The Killdeer in the photos was likely just passing through. Killdeer can also turn the tables on the smaller Piping Plover when they are defending progeny. Maxson (2000) studied interspecific interactions and provided this summary about Piping Plover-Killdeer relations in the discussion:
“While Piping Plovers could routinely displace non-breeding Killdeers, Killdeers with nests or especially chicks were much more aggressive. Breeding Killdeers were as likely to initiate agonistic encounters as were Piping Plovers and, when both species were equally motivated, the larger Killdeers prevailed. Haig (1992) reported an injury to a Killdeer during a confrontation with a Piping Plover. Based on the level of aggression that I observed, it is conceivable that a brood-rearing Killdeer could attack and kill small Piping Plover chicks. This would most likely occur where Killdeers and Piping Plovers have adjacent or overlapping territories and both species are tending chicks.”
Even though such observations may appear frivolous or even comical to us humans, this is serious business for these battling birds and there are potentially life and death consequences.