Objectives should be clear both in a general sense and in terms of specific questions to be answered. Studies commenced without going through this step rarely come to anything. It is important to list these questions at an early stage so as to ensure that the right data are collected to answer them.
What are objectives?
Objectives might be (a) questions to be answered, (b) theories or hypotheses to be tested, or (c) variables to be estimated.
- to investigate the causes of reverse sexual dichromism in Eclectus Parrots (i.e. to find out why females are more brightly coloured than males. The language doesn't have to be full of jargon; the important thing is saying what we want to find out.)
- to investigate whether the presence of Noisy Miner colonies is associated with reduced densities in other forest-dwelling bird species.
- to estimate annual survival rate for juveniles and adults of each sex in a population of White-browed Scrubwrens in the Brindabella Ranges, ACT.
Many current examples are given in Flightlines, the banding office newsletter.
Data (a plural noun) means observations, measurements or any items of information. What data do we need to answer our questions, test our theories, or estimate the variables of interest?
Core banding data
To start with we might consider whether we will need more than the 'core banding data'. This is the data which the ABBBS requires banders to provide for every bird captured or retrapped. The data required is :
Band number, whether banded or retrapped, species, number, species name, age, how aged, sex, how sexed, date, location code, method of encounter, status of bird and band.
This data had its origin in one of the earliest objectives of bird banding studies: the investigation of movements of different bird species. The banding office could provide information, for each bird recovered, on species, age and sex if known, date and place of banding and recovery, banding interval, and distance and direction moved. Plotting such data can reveal what, if any, movements are undertaken by different species of birds.
This approach has been spectacularly successful in elucidating movements in species such as Short-tailed Shearwaters, whose migration between southern Australia and Alaska has been traced in some detail.
In some other species this approach has been no use at all, as in Yellow-faced Honeyeaters where 65,000 birds banded have yielded only 2 remote recoveries.
Other data that we might consider collecting includes measurements, plumage patterns, moult scores, observations of behaviour of individuals using colour-marks or radio- or satellite-transmitters, nest details, clutch size, laying dates, food eaten, habitat description or measurement, rainfall, song pattern, flowering dates of different plants, etc., etc.
No one is likely to need all this information but we should give careful consideration to what we should record and what techniques are likely to help us answer our questions.
How much data and when?
One versus multiple sites.
A single site can be studied more intensively, several sites allow us to make inferences to a wider environment or population.
How many birds to be banded/colour-marked/given a transmitter?
It depends! Observation of 30 colour-marked birds may give us reasonable information on breeding behaviour and annual survival rate. Banding of 100,000 migratory waders may not be enough to show exact migration routes, because the band recovery rate is less than 1 in 5,000. Information from just 16 Eastern Curlews banded in 1997 has produced a wealth of detailed information on their migratory movements and strategies as each bird was also fitted with a satellite transmitter.
The principle appears to be that we will get more information from studying a small number of birds intensively rather than banding a large number and hoping for recoveries.
How often do we catch/retrap/observe our subjects?
Again it depends on what we are trying to find out. If we want to know whether Silvereyes are sedentary at site A, we might consider monthly banding or counting, determining age and sex of all birds trapped. This would allow us to investigate seasonal variation in abundance (or catchability?), and ageing birds might show if trends are similar for juveniles and adults. If we cannot age birds more than a few weeks old, we probably need to supplement our study with searches for nests, observations of breeding birds and/or study of records from a Nest Record Scheme to incorporate information on time and duration of breeding.
Do we need to standardise our banding effort in terms of net-hours per month?
Can we get away with different levels of intensity as long as we record what our net-hours were each month? If we simply band til we have caught a few birds, does this allow us to draw any conclusions at all about monthly abundance?
Can we draw conclusions from a very few birds caught each month?
As the numbers are likely to be variable we might need to aim at a degree of net effort that guarantees us a catch of at least 100 (or 50 or 200) birds over a each twelve month period.
- make an assessment of the data and project duration that will be needed
- make a realistic assessment of the effort required to collect those data
- establish a clear methodology for collecting the data
- build in review of progress towards objectives
- seek professional advice
Manly, B.F.J. (1992). The design and analysis of research studies Cambridge University Press, Cambridge.
Fowler, J. and Cohen, L. (undated) Statistics for Ornithologists, 2nd Edition, BTO Guide No.22 British Trust for Ornithology, England