OF HEAT AND HUMIDITY DURING A RACE
By Dr Colin Walker BSc, BVSc, MRCVS, MACVSc
Pigeons do not have sweat glands and so cannot lose body heat
through sweating. In birds, body heat is lost by evaporative cooling
from the air sacs. When birds become hot, they start to pant. This
increases air flow over the air sacs, in the process increasing evaporative
loss, leading to cooling. Lost moisture is replaced by drinking.
In this way, a normal body temperature and normal level of hydration
What we do know is that at 250C, if deprived of water, pigeons
become 5% dehydrated in only 24 hours. To put this in perspective,
birds that are 5% dehydrated become quiet and fluffed up and will
readily drink if water is provided. When 10% dehydrated, these
symptoms become more exaggerated. When 15% dehydrated, there has
been such a reduction in the circulating blood volume that various
organs are inadequately perfused with blood to function normally
and there is interference with the level of consciousness. Over
15% dehydrated, deaths start to occur.
We also know, importantly, that at 250C
no dehydration will occur if birds are provided with water.
On races conducted on days over 250C, it can be assumed that
unless birds drink along the way, they will arrive at their lofts
suffering a degree of dehydration. Upon return, in health, a bird
will drink readily, in the process replacing lost fluid reserves
and a normal hydration status quickly reestablishes.
Problems arise in a number of situations.
High temperature – Temperatures over 250C require larger
amounts of fluids to be evaporated from the air sacs to maintain
normal body temperature, leading to a quicker onset of dehydration
unless drinking occurs.
Either very high or very low humidity – Low humidity has
a similar effect on the air sacs as high temperature. Low humidity
tends to more readily dry the air sacs, leading to a more rapid
fluid loss. Conversely, high humidity decreases evaporative cooling,
leading to hyperthermia (high body temperature).
Head winds – The extra exertion involved in flying in to
a head wind leads to an increased level of carbon dioxide in the
blood stream, which increases respiratory rate. This increases
fluid loss from the air sacs and also predisposes the birds to
Races conducted in areas where surface water is not available to
competing birds – Normal hydration can be maintained under
quite extreme levels of temperature and humidity provided the birds
have access to water. Lack of surface water means the birds have
no way of replacing lost fluid reserves if they become dehydrated.
The combination of hot winds that are also dry and face the birds,
with no access to water is a deadly one for pigeons. With exertion
and heat, large amounts of fluid are lost from the system through
evaporative cooling, leading to dehydration. As fluid reserves
become depleted, evaporation from the air sacs can no longer occur.
This means that the pigeon has lost its only method of cooling
itself and so secondary hyperthermia starts to occur. As dehydration
levels approach 15%, normal metabolic systems are disrupted and
a decreased level of awareness occurs. In this situation, heavy
losses can be expected.
It is worth noting that even on cool days the temperature within
a race unit can quickly reach 25??q C because of the heat that pigeons
generate (normal body temperature is 41.7??q C). This means that
birds, if not offered water from the start of basketing until arrival
at a race point the next morning, will already be suffering some
degree of dehydration. The importance of insuring that birds have
access to water whenever possible so they are fully hydrated at
release cannot be overstated.