New Project: Rear and Release of the Mariana Crow on Rota Island

Over the past 23 years, the San Diego Zoo Global’s Hawaii Endangered Bird Conservation Program (HEBCP) has become expert in its work with ‘Alala, the critically endangered Hawaiian Crow.  HEBCP is excited to take this expertise and put it to use with another member of the corvid family:  the Aga.  The Aga, or Mariana Crow, is found on Rota, one of the islands that make up the Commonwealth of Northern Mariana Islands (CNMI) north of Guam, 11000 miles west of Hawaii.  Once common on both Rota and Guam, the Aga went extinct on Guam after the introduction of the brown tree snake, which decimated native bird populations.  On Rota, the Aga is classified as critically endangered and is in danger of extinction.  Loss of habitat due to deforestation on the island, predation by introduced mammals, and even an increase in intensity of seasonal typhoons are believed to be factors contributing to the population decline of this species. 

HEBCP is collaborating with the University of Washington, US Fish and Wildlife Service, and CNMI’s Department of Land and Natural Resources and Department of Fish and Wildlife to start a new project of collecting both eggs and chicks from wild Aga nests, caring for the chicks in a facility for a year, and then releasing them back out into their native habitat to help bolster the wild population.  Many wild nests fail before the eggs hatch or shortly thereafter; this project will help some of these nests through this critical time by bringing the eggs or chicks into our secure facility for artificial incubation and hand-rearing.  The wild Aga pairs will then have the opportunity to double clutch and lay another set of eggs.  This second nest will be left for the parents to raise.

For the past 11 years, the University of Washington has had a field crew on Rota to monitor and band wild Aga.  This year, the field crew got to add a new task to their fieldwork…nest collecting!  When an Aga nest is found, the field crew waits until the parents have incubated their eggs for at least two weeks of the three-week incubation period before collecting them.  On the day of collection, HEBCP staff hikes in with the field team to help collect the precious cargo of eggs and/or newly hatched chicks.  Several different collection techniques were discussed and rejected as not plausible due to the varied terrain of Rota’s forests.  As it turns out, the best method for collecting Aga nests is to just climb the trees!   Zoo staff relied on the field crew for this, as they are experienced tree climbers who are used to scaling the narrow trees used by Aga for their nest sites.  After collecting eggs and chicks from the nests they are placed into a container of millet and lowered down to HEBCP staff on the ground before getting carefully hiked out and then driven to the incubators waiting at the egg house.

It’s been 13 years since Aga eggs were last collected on Rota and there is little information regarding what has historically been used to feed these chicks.  Due to limitations on getting some food sources typically hand-fed to other species of chicks, HEBCP staff had to write an entirely new hand-rearing protocol for feeding the Aga on Rota.  Among other, more traditional food items, the Aga chicks are getting local geckos, crabs, and insects added to their diets.  Collecting local food is a great way to give the young Aga a taste for what they’ll be eating after they’re released. This year’s chicks will be closely monitored to ensure that they are thriving and growing properly on this new diet.

As our first nests came in, we were surprised by how many eggs were inviable at the time of collection.  Of the 12 eggs collected at the start of the season, only five were fertile and viable to put into our incubators for artificial incubation.  The other 7 were either infertile or had died when the embryo was only a few days old.  The cause of such low egg viability is unknown, but it could be related to inbreeding within such a small population (a study of Aga genetics is currently being conducted by our partners at CNMI). With less than 50% of our collected eggs alive when we received them it seems even more imperative that we collect as many eggs and chicks as possible in order to help this important part of Rota’s ecosystem be a part of the forest for generations to come.

Check back regularly for more blogs to complete the story!