MOBILE phone habits can change with the weather, a study has found.
When it is cold, or uncomfortably hot and sticky, people are more likely to make longer calls to close friends and family, scientists have discovered.
During unpleasant weather, callers tended to withdraw away from their wider network of acquaintances.
Lead researcher Dr Santi Phithakkitnukoon, from the University of Newcastle, said: "The fact that mobile phones have become an indispensable part of many people's lives means that they provide an opportunity to measure human behaviour and social dynamics like never before.
"The weather is well-known to influence human behaviour. Our mood, health and how active we are all vary with the weather.
"Our research suggests our mobile phone addiction is also susceptible to changes in the weather.
"We found that during uncomfortable weather our 'ringing anyone' behaviour declined."
The research was published in the online journal Public Library of Science ONE.
Dr Phithakkitnukoon's team analysed the call patterns of almost 23,000 mobile phone users in Lisbon, Portugal.
Examining anonymous data records, they categorised calls into "strong" and "weak" social ties.
"Strong ties are people who are socially close to us and whose social circles closely overlap with our own," Dr Phithakkitnukoon said.
"The key to this is not call length but reciprocal calls -- that is how often we call them and, crucially, how often they call us back.
"By factoring in the two-way 'chatter', we could determine not only strong and weak ties but also eliminate the random 'noise' such as business calls which are often long but are generally not returned."
Under uncomfortable weather conditions, there was an increased chance of calls exceeding six minutes, the study showed.