Yeah, the article linked there is nicely specific. From the article (and these are median):
Neurological surgeons had the highest median daily rate for providing on-call coverage, about $2,000 a day. Near the top of the pay scale were neurologists ($1,500), cardiovascular surgeons ($1,600), internists ($1,050), and anesthesiologists ($800).
Among the specialists earning lower median daily rates for on-call compensation were: psychiatry ($500), general surgery ($500) gastroenterology ($500), ophthalmology ($300), and family medicine without obstetrics ($300), according to the MGMA survey data.