HAVE you ever wondered about the effects aircraft noise may have on animals, especially your cattle – more so, pregnant cows and the effects of noise on milk production?

In 1956, a study found that the reactions of dairy and beef cattle to noise from low-altitude or subsonic aircraft were similar to those caused by paper blowing about, strange persons and other moving objects.

While adverse effects have been found in a few studies, similar adverse effects have not been reproduced in other comparable studies.

In response to farmers’ concerns, the US Air Force prepared a handbook for environmental protection. 

The report that included specific case studies conducted in airspaces across the country summarises the literature on the impacts of low-altitude flights on livestock and poultry. 

A further study suggested that two out of 10 cows in late pregnancy aborted after showing rising estrogen and falling progesterone levels. 

These increased hormonal levels were reported as being linked to 59 aircraft overflights. 

The remaining eight cows showed no changes in their blood concentrations and, in due course, these calved normally.

A similar study reported abortions occurred in three out of five pregnant cows. This was after exposing them to flyovers by six different US Air Force aircraft.

In 1987, no effects of low-altitude and supersonic flights were noted by seven livestock operators who were contacted for production of the data.  

Yet, in another study, three out of 43 cattle previously exposed to low-altitude flights showed a startle response to US Air Force aircraft flying overhead and travelling at 400 knots

The startled cattle, the report said, “… ran for less than 10 metres, then within one minute, they resumed normal activity.”    

Another study proposed that feedlot cattle could stampede and injure themselves when exposed to low-level overflights. 

In fact, as early as 1983, a study carried out found that helicopters caused more reaction than other low-aircraft overflights.  

However, the US study found that helicopters low-flying overhead did not affect milk production and pregnancies in cows and heifers.

Contrary to this report, in Zimbabwe, during the course of the war of liberation in the late 1970s, the noise pollution caused by low-flying Rhodesian helicopters wreaked havoc on many communal MaShona breed cattle and other livestock and affected rural beef production during their raids on targeted African villages. 

The cardiac function, breeding rates and hormonal rates of the MaShona cattle  were affected by the strange mechanical noise of the low-flying helicopters.

Several other studies investigated the effects of noise from overhead jet aircraft and sonic booms on the milk production of dairy cows and determined that milk yields were not affected. This was particularly evident in those cows that had been previously exposed to jet aircraft noise.

A study carried out in Wisconsin, US, to examine the causes of 1 763 dairy cattle abortions over a one-year period found that none were associated with aircraft disturbances. 

Five pregnant dairy cows in a pasture, according to the study, did not exhibit ‘flight-fright’ tendencies and did not interrupt their pregnancies after fly-past by 79 low-altitude helicopters and four low-altitude US Air Force subsonic jet aircraft flights.

The United States Forest Service, in a report to Congress, concluded that evidence showed the risks of damage, when aircraft approached at 50 to 100 metres, are minimal.

The report concluded that, there was no evidence that cows and their calves are separated, or that animals collide with obstructions (unless confined), or that they travel over dangerous ground at too high a rate, due to excessive aircraft noise. 

However, results of these varied studies suggest that the confining of cattle could increase animal response to aircraft overflight noise. 

But, there is no proven cause-and-effect link between startling cattle from aircraft overflights and abortion rates or lower milk production.

Several studies, however, also report a varied response of horses to low-altitude aircraft overflights, though no injuries or abortions occurred.  

Studies, focused specifically on any changes in behaviour, pregnancy success, cardiac function, hormonal production, rate of habituation.

Levels of anxiety and mass body movements in horses were the highest after initial exposure. The intensities of responses decreased after the initial exposure. 

There were no differences in pregnancy success when compared to a control group of horses.

The findings for pigs generally appeared to be similar to those for cows and horses; with effects from aircraft noise reported to be minor.  

However, continuous noise exposure was reported to influence on short-term hormonal production and release in pigs.

Additionally, constant exposure to noise indicated the observation of stress reactions, hypertension and electrolyte imbalances.

Another study demonstrated no adverse effects on feeding efficiency, weight gain, ear physiology thyroid and adrenal gland condition in pigs, though heart rate increases were recorded. However, the heart rate returned to normal after the noise had stopped. Conception rates and offspring survival did not appear to be influenced by exposure to aircraft noise.

Studies using simulated aircraft noise at levels of 100 decibels (dB) to 135 dB, found only minor effects on the rate of feed utilisation, food intake, weight gain and reproduction rates of boars and sows.

The effects of low-altitude overflights (below 1 000 ft) showed to have minor effects on domestic fowls. Although given certain circumstances, harmful effects can be serious.  

Some effects include panic reactions, reduced productivity and effects on marketability; for example, bruising of the meat caused during ‘pile-up’ situations as a result of excessive noise.

A short-term startle response is the typical reaction. This response stops as soon as the noise stops and all activity returns to normal within a few minutes.  

More severe responses are possible depending on the number of birds, the frequency of exposure and environmental conditions.

Egg productivity was not badly affected by infrequent noise bursts. This was seen even at exposure levels as high as 120 to 130 dB. 

Between 1956-1988, there were 100 recorded claims against the Navy in the US for alleged damage to domestic fowls. 

The claims were filed for the following alleged damages:

λ 55 percent for panic reactions

λ 31 percent for decreased production

λ six percent for reduced hatchability

λ six percent for weight loss

λ less than one percent for reduced fertility

In the early 1960s, the number of claims peaked following publications of studies on the topic. Many of the claims were disproved or did not have sufficient supporting evidence. 

Studies of low-altitude overflights revealed that turkey flocks kept inside turkey houses occasionally cause ‘pile up’.  They experience high mortality rates due to the aircraft noise as well as a variety of disturbances unrelated to aircraft. 

One cannot help but wonder what impact and adverse effects excessive noise, especially of such events as the annual Carnival, with their attendant ubiquitous fireworks, has on livestock and the wild animals in Victoria Falls! 

Dr Tony Monda holds a PhD in Art Theory and Philosophy and a DBA (Doctorate in Business Administration) and Post-Colonial Heritage Studies. He is a writer, lecturer and a specialist Post-Colonial Scholar, Zimbabwean Socio-Economic analyst and researcher. E-mail: tonym.MONDA@gmail.com