Lazy Birds May 3, 2010Posted by Kyle in Behavior, Biology, Ecology, Evolution.
Being a bird can be extremely difficult, especially when it comes to raising offspring. The best way to pass on your genes, and at the same time spend no energy in doing so, is to let another bird do the work!
Brood parasites get around the huge investment of raising offspring by tricking another bird into doing it. Brood parasitism is not a very common reproductive strategy across species (although rates of brood parasitism are high), but it definitely has its benefits. The less time a bird is spending incubating eggs, the more time that individual can spend on foraging or mating. The handful of species that use this strategy to gain an edge are constantly trying to trick the host birds, while the host birds are always on the lookout for parasitic eggs. This has led to an evolutionary arms race, with both sides working hard to win.
The costs of being fooled by brood parasites are huge. Not only does the fooled bird have to spend time raising someone else’s offspring, usually it’s not even the same species of offspring. There is no genetic benefit in raising someone else’s young. There is also the possibility that the parasitic chick out-competes the host’s chicks. This is the case with the Cuckoo Finch (Anomalospiza imberbis) and the Tawny-flanked Prinia (Prinia subflava). If the Cuckoo Finch egg is not discovered by the host, the Cuckoo Finch chick will hatch first and grow larger than the host’s chicks, out-competing its “siblings” for food and space until the host’s chicks eventually die. The cost associated with this relationship has led to a complicated defense system used by Prinias.
In a study done by Dr Claire Spottiswoode and Dr Martin Stevens of the University of Cambridge, the researchers worked on the two tropical African species to determine what strategies are used by both sides to win the battle. The back and forth struggle between the two species has resulted in Cuckoo eggs being almost identical to those of the Prinia. Researchers tested how Prinias detect impostures by taking eggs from Prinia nests and putting them in other Prinia nests. They then observed whether or not the eggs were rejected. The results showed that the Prinia are extremely talented when it comes to distinguishing between their own eggs and those of another bird. By using color and pattern the host birds are able to distinguish among their eggs and those of the parasite birds. Although this sounds like a great plan, the reason it isn’t so popular is because it doesn’t really work that well. In another study researchers used Zebra Finches (Taeniopygia guttata) to look at brood parasitism, and found that only one-third of the eggs laid by brood parasites are actually reared.