Some judgment is involved with many habitat measures, so thorough training
is needed before the survey work begins. Ideally all the data should be collected
by the same researcher and, if that is not possible, a pilot study should be carried
out, after initial training is complete, in which all researchers collect at least
30 data points independently in the same area. Analysis of these data can identi-
fy how strongly the measures by different researchers are intercorrelated and
estimate correction factors to make the results comparable.
11.3 Physical environment
Abiotic aspects of a bird’s environment can be important influences on distribution,
abundance, reproductive success, and behavior. The technology for measuring
abiotic variables is continually improving. In particular it has become routine to
place sensors in the environment linked to dataloggers so that measurements can
be taken and stored automatically at specified intervals for later transfer to a
computer. Examining catalogs or websites of distributors is often a good way to
get ideas for appropriate methods for measuring abiotic variables of interest.
Distributors include Alana (alanaecology.com) in the United Kingdom,
Ben Meadows (benmeadows.com) and Forestry Suppliers, (forestry-suppiers.com)
in the United States. If ordering American equipment ensure it does not use
imperial measures or Fahrenheit! Sophisticated instruments and automatic mea-
suring and logging devices are usually expensive, so there may be a trade-off
between measuring variables of interest in great detail at a few sites and doing this
more crudely with simple equipment at many more sites.
11.3.1Temperature and thermoregulation
Thermoregulation is an important cost for birds and depends upon ambient
temperature and exposure to wind. Temperature also affects birds indirectly via
their food supply, especially for insectivorous species. A study may require the
placement of portable meteorological recording equipment in a site using small
sensors to record the microhabitats of particular importance to birds, such as nest
or roost sites. While some studies may require recording temperature at frequent
intervals with a thermistor and datalogger, in others it may be sufficient to
measure an integrated average temperature over a longer period with much
cheaper equipment. For example, glucose in solution changes into fructose at a
rate determined by temperature. By placing containers of glucose solution in
nest boxes for ten-day periods and measuring the amount converted to fructose
with a polarimeter, O’Connor (1978) was able to measure the mean temperature
within the boxes with a precision of 0.1C. Instrumented models of birds can be
254 |Habitat assessment