After a year of planning and 53 hours of travelling I arrived on Mo’orea; the first of five French Polynesian islands that I will be visiting over a two-month period as part of my DPhil. I am here to study the silvereye, Zosterops lateralis, a small passerine bird that was introduced to French Polynesia in 1937 by Eastham Guild, a prolific aviculturalist who attempted to introduce over 40 species to the nearby island of Tahiti; although very few of these species successfully established.
Since its introduction the silvereye has spread to 10 other islands and over the coming weeks I will be visiting five of these (Mo’orea, Huahine, Raiatea, Maupiti and Tahiti) in order to understand how this species has diverged from its source population (New Zealand) since its introduction less than 90 years ago; and to measure the genetic and morphological variation that exists between these islands.
For the past two weeks I have been staying at the University of California’s Gump South Pacific Research Station with my supervisor Dr Sonya Clegg. Sonya has lots of experience sampling silvereyes across the Pacific and has accompanied me to Mo’orea in order to train me to collect the small blood samples required to do the genetic work. After a few days recovering from the long journey, getting used to the 11-hour time difference, and getting relevant permissions; we were soon catching silvereyes (pictured below).
Like most passerines (perching birds), silvereyes are easily caught with mist-nets (fine nylon mesh nets, that are difficult to see from a distance). When strung between vertical poles, un-expectant birds fly into these near-invisible nets falling into the net’s pockets. Nets are then periodically checked and caught birds carefully disentangled, before being placed in soft cotton bird-bags ready for processing.
Processing caught birds involves the collection of morphological data including wing, tail, tarsus, and head length, as well as weight and bill length, depth and width. Collecting these measurements will allow us to see how French Polynesian silvereyes have physically changed from the their New Zealand ancestors; with such changes potentially representing responses to the different selective pressures here on French Polynesia.
Given the relatively low number of bird species present on these islands, French Polynesian silvereyes are likely to experience less competition from other species (interspecific competition); but due to their large numbers increased competition within species (intraspecific competition). In response to these changes in inter and intraspecific competition, we would expect French Polynesian silvereyes to have evolved a larger body size. The reason behind this expectation being that a larger body size facilitates the exploitation of a greater breadth of resources (which is favoured in the absence of competitors) and also confers an advantage when protecting resources from other silvereyes (favoured when intraspecific competition is high). Such a shift towards larger body size has been frequently observed in other island bird populations, including silvereyes elsewhere, and is therefore a well founded expectation!
But the morphological data is only one part of the story – we also collect small blood samples from each silvereye we catch, to allow us to study changes at the genetic level. Collecting blood samples is a simple procedure and is done by pricking the brachial vein using a sterile needle while the wing is gently extended (this vein is in fact the same one from which you would give blood). The resulting small blood droplet is then collected using a tiny glass capillary tube and transferred to a storage tube containing lysis buffer. The whole procedure is done in mere minutes and after checking that bleeding has stopped and offering the silvereye sugar water they are released to go about their day.
As well as catching silvereyes, other introduced species also fall into our nets. On Mo’orea there are five other species of introduced bird: red-vented bulbul, common myna, zebra dove, chestnut-breasted mannikin, red-browed firetail (pictured below) and common waxbill. We also collect morphological data and blood samples from these other species, which, along with silvereye samples, we will be screening for avian malaria (I will explain why in a later blog).
Getting enough samples for our study is hard work particularly in a tropical climate but our two-weeks on Mo’orea have been extremely successful; having caught and sampled 74 silvereyes (more than our target of 30 for this island!). Here’s hoping that catching on my next island stop, Huahine, will be equally as successful! – I will update you soon.
This blog was originally published at www.ashsendellprice.com
“”I am a PhD student in the Department of Zoology where I conduct genomics based research exploring various aspects of diversification in the silvereye bird. My interests are broadly centred around understanding how organisms adapt to environmental change, with a particular interest in the evolutionary changes that occur during the early stages of adaptation.”