available to count as new. This is replicated several times. Target list lengths might
be as small as 10 species in poor habitats or perhaps 20 in richer ones. The advan-
tage of this method is that it allows to an extent for the fact that some people will
accumulate lists faster than others. If hourly lists are being recorded, any time given
to trying to catch sight of a strange call to identify it will detract from finding other
species in the time. With McKinnon lists, you can take as long as you need to iden-
tify individual birds. A more skilled observer will simply collect more lists in a given
time period.
Not many people have actually taken up this attractive method. Perhaps the
idea of frequency on lists from a fixed time period has the inherent appeal of
greater simplicity. Additionally, it could be argued that the benefit of helping less
skilled observers is unnecessary or inappropriate. It is possible to stop the clock
and to identity a mystery bird during a fixed time sample (provided the clock
really is stopped and you do not record anything else). If your skills in identify-
ing the birds of a study area leave you taking a lot of time on identification then
perhaps they need to be improved with more practice.
1.6 Atlas studies
Atlas studies have proved to be a very effective way of documenting the avifauna of
a region. The aim is simply to map the distribution of occurrence of species. Target
areas are divided into grid cells. Squares of side 2, 10, or 50 km on the UTM grid
have been used in Europe, with the smaller being used to cover smaller areas.
Elsewhere, latitude and longitude cells have been used with sides of one-eighth,
quarter, or half a degree. Half a degree at the equator is approximately 55 km but
cells become narrower toward the poles. An important practical consideration is
that the grid needs to be marked on commonly available maps, although with
cheap access to Global Positioning Systems (GPS) this constraint may not last
much longer. So far, it seems that a few thousand grid cells is plenty of work to
administer which is probably why bigger regions have used a less fine resolution.
At its simplest, fieldwork consists of accumulating lists of species in grid
cells. Most atlases have classified some information on the breeding status of the
species. Broadly similar criteria for doing this have been standardized in Europe
and North America (summarized in Table 1.2). Some of the details look subtle
but there are significantly different interpretations between different atlases.
The second atlas in the United Kingdom, for instance, did not distinguish
records of summering according to whether birds were in suitable breeding
habitat or not on the grounds that this is an arbitrary decision especially if
habitat boundaries are poorly known or a new habitat use is emerging.
8 |Bird diversity survey methods