One of the reasons we get "goopy" over bluebirds is their family orientation. Fledglings will sometimes assist or help their parents by feeding a subsequent brood, helping to defend the nest, and removing fecal sacs. In this fantastic video, Kenn of St. Louis, MO captures fledglings falling all over themselves to feed five young from a third brood. He says "It's like an assembly line with everybody (parents and kids alike) bringing bugs and standing in line to be the next one at the hole. And though we've not captured it with the camera yet, we saw the fledges carrying out fecal sacs...."
In the video, fledglings enter the box to feed. It also shows a bird "beaking off" (vs. handing off :-) a morsel to another bird (fledging or parent) inside the box. Kenn and Temple are convinced that fledglings from both previous broods (the first and second) are assisting. Mealworms are being provided, which may slightly increase the likelihood that helping occurs.
One study indicated that 2-14% of Western Bluebirds were assisted by helpers feeding and defense of the nest. (Keyser 2004) Another study indicated that helpers are typically male, and are usually related to the breeding pair (70% sons, 16% brothers, 6% daughters, and 8% unrelated or unknown relationship.) (Charmantier 2007.) There may be a genetic factor that increases the propensity to help, or it may be learned behavior (called "social inheritance.")
Benefits of Cooperative Breeding (where individuals other than the male–female pair help to raise a single brood - Brown 1987).
Helping provides younger bluebirds with experience that is likely to improve their odds of successfully breeding as adults the following season.
Helping reduces the workload of the parent, which improves their fitness, and thus can increase their chances of surviving to breed again. Helping may be more common when weather is poor and food is scarce, or predation rates are high.
Adults receiving help lay more eggs, hatch more young, and produce more fledglings and more recruits than birds that do not receive help. (Charmantier, 2007)
Other species: Bluebirds are not the only species that engage in this behavior. It has been documented in 9% of bird species (Cockburn 2006.) Red-cockaded woodpecker young are also known to "help." On occasion, adults that had failed on a previous nesting attempt will also engage in "cooperative breeding," by helping feed the young of another pair. Mammals and insects may help others before producing their own offspring.
Video filmed by Kenn (with Temple by his side) using a Canon S3-IS with a Sony DH1758 teleconverter.
