the background, history, the circumstances under which the birds were found, the
species (and sex/age ratio) and a multiplicity of other aspects (e.g. weather, repro-
ductive activity) that may have played a part.
Sometimes the interpretation of findings presents few difficulties. For example,
a swan that has flown into a power-line and broken its neck will show characteristic
gross postmortemlesions—mainly hemorrhage. At other times, however, interpre-
tation can be problematic or require lateral thinking. The swan that has struck a
power-line may have done so because of an underlying infectious disease, such as
avian tuberculosis, which has made it more susceptible to accident. For this reason,
biologists often separate the proximate from the ultimate causes of death.
The finding of micro- or macroparasites on or in a bird can be misleading.
Sometimes they have been acquired from elsewhere—for instance, prey species
(e.g. lice from corvids on falcons) or contamination from other carcasses in the
postmortemroom. Even when such organisms are bona fideisolates, their relevance
may not be clear. Intestinal worms associated with ulceration of a bird’s intestine,
or bacteria isolated from a swollen eye, are clearly of some significance, but what
about the findings of these organisms withoutassociated lesions? Are they of sig-
nificance or not? Much remains to be learned about the biology of pathogens
(Reece 1989) and host–parasite relations in birds (Cooper 2001) and, until reli-
able data are available, the best that can usually be done is to record the finding,
both qualitatively and quantitatively, and to attempt to relate it to the bird’s body
condition and systemic health. Data on captive birds have proved of some value,
as have findings in wild bird causalities (Cooper 2003a).
Useful publications regarding interpretation of laboratory findings in birds
include those on histopathology by Randall and Reece (1996), on hematology
(Campbell 1995; Hawkey and Dennett 1989) and on microbiology by Scullion
(1989) and Cooper (2000).
Situations where birds are found dead or dying and where gross postmortem
findings and laboratory investigations are unrevealing or confusing, often pre-
sent a dilemma. For instance, gross necropsy, together with standard laboratory
tests, may offer no specific diagnosis (cause of death) for a group of parrots found
dead in a South American suburb. Additional tests may also provide no specific
cause of death; heavy metal values, for example, might be elevated, but not to the
extent that they can be considered lethal. In such cases, careful analysis of all the
findings, together with extraneous factors such as climate, are essential but might
still be inconclusive. The available data should be stored—as should a selection
of samples—because later studies, perhaps using more sophisticated investi-
gations, may provide an answer.
200 |Information from dead and dying birds