A new argument has been put forward as to whether penguins are disturbed by the presence of tourists in Antarctica. Previous research by scientists from Keil University in Germany monitored Adelie penguins and noted that the birds' heart rates increased dramatically at the sight of a human as far as 30 meters away.  But new research using an artificial egg, which is equipped to measure heart rates, disputes this.  Scientists from the Scott Polar Research Institute at Cambridge say that a slow moving human who does not approach the nest too closely, is not viewed as a threat by penguins. The earlier findings have been used to partly explain the 20 per cent drop in populations of certain types of penguins near tourist sites.  However, tour operators have continued to insist that their activities do not adversely affect wildlife in Antarctica, saying they encourage non-disruptive behavior in tourists, and that the decline in penguin numbers is caused by other factors. Amanda Nimon of the Scott Polar Research Institute spent three southern hemisphere summers at Cuverville Island in Antarctica studying penguin behavior towards humans.  "A nesting penguin will react very differently to a person rapidly and closely approaching the nest," says Nimon.  "First they exhibit large and prolonged heart rate changes and then they often flee the nest leaving it open for predators   to fly in and remove eggs or chicks."  The artificial egg, specially for the project, monitored both the parent who had been 'disturbed' when the egg was placed in the nest and the other parent as they both took it in turns to guard the nest. However, Boris Culik, who monitored the Adelie penguins, believes that Nimon's findings do not invalidate his own research.  He points out that species behave differently - and Nimon's work was with Gentoo penguins.  Nimon and her colleagues believe that Culik's research was methodologically flawed because the monitoring of penguins' responses needed capturing and restraining the birds and fitting them with beart-rate transmitters.  Therefore, argues Nimon, it would not be surprising if they became stressed on seeing a human _ . Which ONE argument of the following is stated in the passage?
Penguins are harder to research when they have young. Tour operators should encourage tourists to avoid Antarctica. Not all penguins behave in the same way. Penguins need better protection from tourists.