Crimson-breasted Shrike chicks win a life-or-death race with Southern Pied Babbler chicks by fledging 5 days sooner, as predators arrive to check the nests. The little-noticed drama unfolds in the semi-arid, open acacia savannahs of southern Africa.
By Rex Graham
The shrike and babbler share the same breeding territory. Both eat the same prey and nest about the same time, and even build nests at about the same height in the same types of vegetation. However, the shrike chicks have an important edge when predators are attracted to a “honey pot” of spring nests.
Aside from their striking red and glossy black colors, Crimson-breasted Shrikes are known for their songs. Pairs sing loud duets – rapid vocal exchanges of sex-specific notes and phrases in strict codes and sequences. The duets cement pair bonds, but monogamous pairs become silent when they build nests and incubate eggs in October and November. The final silent days before their chicks fledge is particularly dangerous. (They resume the duets after their chicks hatch.)
Crimson-breasted Shrike Nest Hazards
The shrikes are devoted couples. The babblers, on the other hand, are “cooperative breeders.” Up to 8 sub-adult helpers pitch in to help the dominant pair raise their young. With all the extra help, babbler chicks fledge about 5 days sooner than the shrikes. (Cooperative breeding birds usually have significantly shorter nesting periods than similar non-cooperative breeders.)
Amanda R. Ridley and Irene M. van den Heuvel, researchers at the University of Western Australia, discovered that both species suffered the same nest mortality while incubating. However, the 5 extra days shrikes require to fledge their young makes a huge difference: 73 percent of babbler clutches hatched at least one chick, compared to only 57 percent for shrikes.
The babbler fledglings are clumsy. They learn to fly in the thorny undergrowth. The shrike chicks spend these awkward days growing and developing in the nest.
“By fedging their young significantly earlier than Crimson-breasted Shrikes, Pied Babblers suffer significantly lower predation rates during a time when Crimson-breasted Shrikes of the same age are still in the nest and exposed to heavy predation,” the researchers wrote in a paper in the journal Behaviour.
They went on to say that more study is needed to understand the breeding strategies of birds in harsh environments.