In any release program in which we reintroduce captive propagated birds to the wild, we consider four basic steps that must be reached in order to determine that the overall program has been successful. The first step is breeding enough birds in captivity to form a release cohort. The second step is to release the cohort and support the birds to the point where they are independent in the wild and live long enough to support themselves in their new habitat (every parent’s dream for their child anxious to leave home).
Step three is the birds should live long enough to enter into a breeding season and breed successfully. The fourth step is that enough birds, both release birds and their progeny, reproduce with enough success to actually establish a flock that is more than simply self-sustaining but expands to the point of reaching the “carrying capacity” of the new habitat.
Of course, there are many, many factors that are required that are supernumerary to the actual propagation and release of captive birds that support the success of such an effort, such as; predator control, disease control, elimination of invasive plant and animal pests, and forest rehabilitation, just to name a few.
In late 2003, we released the very first two cohorts of 10 palila on Puu Mali, Mauna Kea (Step #1 completed). Of the 10 birds we now know that the majority of the birds survived to independence and indeed, two of the birds nested and laid an egg (the egg was later determined infertile). Step #2 and #3 nearly completed. We are in the process of bolstering the release by putting a new cohort of five palila in the Puu Mali habitat. This will hasten the maturation of the flock and hopefully will successfully complete the critical and final Step #4. This last step will require many generations of palila reproduction and several more seasons of releases.
Perhaps the most rewarding event that has occurred at this year’s release of the five palila is the return to the release aviary of four of the eight (we know that seven or eight of the birds survived the first release) palila that we released over a year ago. All four look great, now being truly savvy warriors of the mamane fields that surround the site. They have returned to the aviary to not only introduce themselves to the new release candidates, but to take advantage of the food treats which are fed to support the new release birds. It’s like old friends dropping by for Happy Hour (except in this case Happy Hour starts at sunrise!).
It is very encouraging to see these old friends looking so healthy. It is very polite of them to show us that, although reared in a captive environment, they are fully capable of surviving (and breeding) long term in recovering native habitat when given the support of resource management that will always be required at some level to minimize the limiting factors. Welcome back, old friends. It’s great to see you all!
Alan Lieberman is the program director for the San Diego Zoo’s Hawaii Endangered Bird Conservation Program.