Great news from Floreana

By Luis Ortiz-Catedral (CDF)

I have some great news to share. The breeding season of the Floreana mockingbirds has started! This has created a lot of excitement among staff from the Charles Darwin Foundation (CDF) and the Galápagos National Park (GNP). We have been very busy finding nests on Champion and Gardner and also keeping notes about the variety of items fed to the young. The Floreana mockingbirds have a fascinating breeding behaviour: they breed in what we call “family groups” which usually consist of the actual breeding pair plus some helpers. The size of the group varies from three to six. In previous months we did an extensive ringing of individuals, which has proven invaluable to assign group membership now that breeding has started.

Encountering mockingbirds nests is relatively easy, all one has to do is keep an eye out for birds carrying nesting material such as twigs, moss and lichens like the one you see in the photo. If the bird happens to be ringed, we would have a rough idea of the location of their territory. The nest is a neat cup placed on Opuntia, Croton or Cordia trees and commonly, mockingbirds would lay three eggs although we have found a number of nests with four eggs. The eggs are blue with brown spots and take about two weeks to hatch. Upon hatching, the chicks chirp constantly, which helps to locate nests that went missing during previous searches.

During the last five weeks, we have observed nests with chicks from a few metres away to record the food items brought by parents and helpers to the hungry offspring. Spiders, crickets, grasshoppers, moths and caterpillars are among the most common prey items fed to the young, plus the occasional fly. The whole family group seems busy harvesting prey and also keeping the nest tidy. Once a prey item has been delivered to the chicks, they inspect the nest and remove eggshells, droppings, leaves and twigs. From our observations, it appears that chicks leave the nest around two to three weeks after hatching and remain in the vicinity of the nest where they are fed by their family members for another three weeks or so.

Once they are fully feathered and able to fly, juveniles are easily lured into potter traps were we capture them and ring them to follow their development in the coming months. Some questions that intrigue me are: at what age do juvenile mockingbirds start their own nest? Do they split from their family group or do they stay within one for a few breeding seasons? What determines the size of a family group? Is the size related to the number of successful broods they can raise per season? I hope to provide answers to these questions in the coming months. Next week we are off to Champion and Gardner again as there are still a few nests with eggs due to hatch.

The weather has turned drier in the last few weeks and not a drop of rain has fallen in about a month. Water is indeed a scarce resource on these islets and whenever there were rain, animals and us researchers alike enjoyed the bounty. During the last heavy rain we even had the luxury of taking a shower! In spite of the brief rainy season, many plant species on Champion and Gardner completed their life cycle (from sprouting to producing seeds) during the brief rainy season. The islets looked different on every visit as the grass and some vines that were mere plantlets grew real fast and covered our tracks! There appears to be a greater abundance of fruits now including Cordia, Lantana and Physalis, which no doubt the mockingbirds will eat. Seeing these plants develop so fast is a timely reminder of the need to keep Champion and Gardner free of introduced plants. Prior to every trip we inspect our gear for seeds or invertebrate eggs to minimize the risk of accidentally introducing weeds to these fragile systems. Watch this space; I’ll post more photographs of juvenile mockingbirds in the coming weeks."