4 am: with thermos in hand I close the front door behind me with a click, hop into the car, and after a short drive arrive at my destination – a water treatment facility at the foot of the Malvern Hills. Every two weeks I make the same journey to join my local bird ringing group where we are in the middle of the year’s Constant Effort Site (CES) survey.
4:20 am: once the whole group has assembled in the carpark we adorn hard hats and high-vis jackets, before making our way to the site’s biodiversity area with poles and nets in hand – birdy folk wouldn’t normally want to look this conspicuous but we must follow the stringent rules set by the facility owners! Splitting into groups we unravel and suspend fine nylon mist nets between lightweight metal poles in suitable locations. Such suitable locations include alongside bushes, and clearings between tree patches. With six nets up, chairs are unfolded, thermoses opened, and the wait begins.
5 am: the dawn feeding frenzy commences, and it isn’t long until tits, finches, thrushes and warblers begin to fall into the nets’ “shelves”. Every 20 minutes birds are carefully extracted from nets, placed into fabric bags and hung in rows at the work bench. Birds are then processed, meaning their species, sex and age is determined, and weight and wing length recorded.
Except for ‘cryptic’ species such as garden warblers and chiffchaffs that look, at least to me, practically the same, determining species is more often than not a quick process, as is determining sex in sexually dimorphic species (where males and females are different in size or appearance). For example, male blackcaps are easily identified by their glossy black crowns (or caps – hence the name) which females lack; instead female crowns are red-brown.
In contrast, sexing species with less prominent plumage differences requires some detective work, using subtle and at times hard-to-see differences. For example, male and female greenfinches differ in that for males the yellow of the outer webs of their primary feathers reaches the dark feather shaft; whereas in females this yellow does not extend as far as the feather shaft – a difference of millimetres1.
Proximity of yellow webbing to the central feather shaft of the primary feathers in male (left) and female (right) greenfinches. Source: birdingfrontiers.com and jenlynch.wordpress.com.
For many species, obvious plumage differences exist between juvenile and adult forms, allowing a rough age (juvenile, 1st year, 2nd year etc.) to be determined; but as juveniles begin to sequentially moult out their plumage these differences become less pronounced. An understanding of the moulting process and feather development is therefore required to understand how and when juvenile plumage is transformed. For example, the distinctive red-orange breast, throat and forehead of the European robin is developed during a partial post-juvenile moult of body feathers, lesser and median and the inner most greater coverts (see diagram for feather types) that takes place during the first-year post fledging2. This partial moult allows three age classes to be identified for robins: juveniles which lack the distinctive red-orange plumage of adults, 1st years that have undergone a partial moult but retain juvenile outer greater coverts, and adults where all juvenile greater coverts are replaced following a second moult. However, in reality much variation occurs between individuals and differences in one feature may not be so clear-cut. As a result, becoming a bird ringer is not a quick process; instead many hours must be spent with bird in hand to learn the variety that exists between and within species.
By 11 am catching has slowed and with 30+ birds caught, ringed, measured and released, nets are carefully packed away, chairs folded and equipment returned to car boots before driving home with the sound of bird song still in the air.
- Svensson, L. Identification Guide to European Passerines. Thetford: British Trust for Ornithology.
- Zumeta, J. B. 2004. Robin: Erithacus rubecula. [Online]. Available at: http://aulaenred.ibercaja.es/wp-content/uploads/327_RobinErubecula.pdf
“”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.”