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Right whales forced to shout over people’s noise, scientists say

July 7, 2010
Courtesy of Penn State University
and World Science staff

Just like peo­ple in a crowd­ed bar, North Amer­i­can right whales in­crease the vol­ume of their calls to be heard over noise caused by hu­mans, sci­en­tists have found.

And just like hu­mans, at some it may be­come too costly to con­tin­ue to shout.

“The im­pacts of in­creases in ocean noise from hu­man ac­ti­vi­ties are a con­cern for the con­serva­t­ion of ma­rine an­i­mals like right whales,” said Su­san Parks, an ac­ous­ti­cian at Penn­syl­va­nia State Uni­vers­ity. “The abil­ity to change vo­cal­iz­a­tions to com­pen­sate for en­vi­ron­men­tal noise is crit­i­cal for suc­cess­ful com­mu­nica­t­ion in an in­creas­ingly noisy ocean.”

A North Atlantic right whale div­ing with tail in the air. (Cred­it: Sus­an Parks, Penn State)
Right whales are large ba­leen whales—the term ba­leen refers to a fil­ter­ing struc­ture in the mouth—that of­ten come close to shore. They may have been giv­en the name right whales be­cause they were the “right” whales to hunt as they are rich in blub­ber, slow swim­ming and re­main afloat af­ter death. Con­se­quent­ly, whalers nearly hunt­ed these whales to ex­tinc­tion. 

Right whales are mon­i­tored to­day to de­ter­mine the health and size of the popula­t­ion. The north­ern and south­ern right whales are on the en­dan­gered spe­cies list.

Whales make sounds known as up­calls, or con­tact calls, when alone or in the pro­cess of join­ing oth­er whales. The most fre­quent call by right whales, an up­call be­gins low and rises in pitch.

Parks and col­leagues stud­ied North At­lantic right whales us­ing re­cord­ing de­vices at­tached to the whales by suc­tion cups. The find­ings are pub­lished in the July 6 is­sue of the research journal Bi­ol­o­gy Let­ters.

The scientists lis­tened to re­cord­ings of 107 calls from sev­en male and sev­en female whales. The team looked at re­ceived lev­el, dura­t­ion and fun­da­men­tal fre­quen­cy, or pitch, of the calls. They al­so com­pared back­ground noise lev­els with the call-re­ceived lev­els of in­di­vid­ual calls.

It seems right whales in­crease the am­pli­tude, or en­er­gy, in their calls di­rectly as back­ground noise lev­els in­crease, with­out chang­ing the pitch, Parks said. Much of the in­crease in back­ground ocean noise in right whale hab­i­tat is be­lieved to be due to com­mer­cial ship­ping.

“To our knowl­edge, this is the first ev­i­dence for noise-dependent am­pli­tude modifica­t­ion [vol­ume in­crease] of calls pro­duced by a ba­leen whale,” said Parks.

Chang­ing call­ing pat­terns can, how­ev­er, in­cur costs in­clud­ing in­creased en­er­gy ex­pend­i­ture, al­tera­t­ion of the sig­nal and the in­forma­t­ion it con­tains, and in­creased pred­a­to­ry risks, the re­search­ers not­ed. With in­creased noise the ef­fec­tive com­mu­nica­t­ion range for feed­ing or mat­ing will shrink and stress lev­els on in­di­vid­ual an­i­mals may rise.

“Whether they can main­tain their com­mu­nica­t­ion range in nois­i­er en­vi­ronments still needs to be test­ed,” said Parks. “O­cean sound lev­els will probably con­tin­ue to in­crease due to hu­man ac­ti­vi­ties and there is a phys­i­cal lim­it to the max­i­mum source lev­el that an an­i­mal can pro­duce.”

Anoth­er im­plica­t­ion for po­ten­tial changes in whale calls is that up­calls are the whale calls that con­serva­t­ion­ists use to mon­i­tor right whale popula­t­ions. They do this us­ing au­to­mat­ed acous­tic sen­sors that are look­ing for spe­cif­ic char­ac­ter­is­tics to tease out the whale calls from oth­er noises.

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Just like people in a crowded bar, North American right whales increase the volume of their calls to be heard over environmental noise caused by humans, scientists have found. And just like humans, at some it may become too costly to continue to shout. “The impacts of increases in ocean noise from human activities are a concern for the conservation of marine animals like right whales,“ said Susan Parks, an acoustician at Pennsylvania State University. “The ability to change vocalizations to compensate for environmental noise is critical for successful communication in an increasingly noisy ocean.“ Right whales are large baleen whales—the term baleen refers to a filtering structure in the mouth—that often come close to shore. They may have been given the name right whales because they were the “right“ whales to hunt as they are rich in blubber, slow swimming and remain afloat after death. Consequently, whalers nearly hunted these whales to extinction. Right whales are monitored today to determine the health and size of the population. The northern and southern right whales are on the endangered species list. Whales produce upcalls, sometimes called contact calls, when they are alone or in the process of joining other whales. The most frequent call by right whales, an upcall begins low and rises in pitch. Parks and colleagues studied North Atlantic right whales using recording devices attached to the whales by suction cups. The findings are published in the July 6 issue of the Biology Letters. The researchers listened to recordings from seven male and seven female whales totaling 107 calls. The tags recorded from 2 to 18 calls each. The team looked at received level, duration and fundamental frequency, or pitch, of the calls. They also compared background noise levels with the call-received levels of individual calls. It seems right whales increase the amplitude, or the energy in their calls, directly as background noise levels increase, without changing the pitch, Parks said. Much of the increase in background ocean noise in right whale habitat is believed to be due to commercial shipping. “To our knowledge, this is the first evidence for noise-dependent amplitude modification [volume increase] of calls produced by a baleen whale,“ said Parks. Changing calling patterns can, however, incur costs including increased energy expenditure, alteration of the signal and the information it contains, and increased predatory risks, the researchers noted. With increased noise the effective communication range for feeding or mating will shrink and stress levels on individual animals may rise. “Whether they can maintain their communication range in noisier environments still needs to be tested,“ said Parks. “Ocean sound levels will probably continue to increase due to human activities and there is a physical limit to the maximum source level that an animal can produce.“ Another implication for potential changes in whale calls is that upcalls are the whale calls that conservationists use to monitor right whale populations. They do this using automated acoustic sensors that are looking for specific characteristics to tease out the whale calls from other noises.