The Scottish government is facing calls to increase investment in bus services after new figures revealed a significant drop in passenger journeys.
Statistics published by Transport Scotland show that 409 million bus trips were made in Scotland last year, down from 487 million in 2007/8.
It also found that funding from local and national government dropped by 5% in real terms over five years.
Transport Scotland said it was "concerned" by the bus journey decline.
But a spokeswoman added that some parts of the country had seen an increase in bus use and a solution to the problem "must be local".
Despite the falling number of bus journeys, the report suggests they remain the most popular form of public transport in Scotland.
It found that buses are particularly well-used in Strathclyde, the south-west and south-east of Scotland.
But it also showed that rail trips are becoming an increasingly popular way of travelling.
A total of 93.2 million train journeys were made last year - an increase of more than a third (34%) since 2005/6.
Transform Scotland, which campaigns for sustainable transport, said the year-on-year decline in bus use was "very worrying".
Its director, Colin Howden, said: "Buses play an important role in reducing congestion in urban areas and providing services to lower-income groups who often don't have access to cars.
"It's deeply disappointing that the Scottish government continues to cut investment in bus services."
He added: "The government should instead be taking action to cut congestion by putting in place bus priority in urban areas, and protecting threatened rural bus services."
Bus services received funding totalling £301m from local and national government in 2015/16, according to the Transport Scotland.
It added that passengers have seen the price of their fares increase by 19%.
Mike Rumbles, the Scottish Liberal Democrats' transport spokesman, said Scotland's public transport system needed "action and real investment".
"The number of people using buses has dropped dramatically, as has the number of buses and journeys available to people," he said. "That means more traffic on our roads, less investment in public transport and missed targets on climate change.
He added: "We need action and real investment now in our bus and rail services so that we have infrastructure fit for the 21st Century."
The report also led to renewed calls for Scotland's bus industry to be re-regulated.
Long waits and delays
The Scottish Greens' transport spokesman, John Finnie, said: "What's made clear by these statistics is the Scottish government's continued emphasis on promoting private car use at the expense of public transport.
"Perhaps it's little wonder that there has been a steady decline in bus use throughout Scotland, given how many of us have come to expect long waits for delayed and non-existent buses and how poorly services here compare with other cities in the UK and Europe.
"The re-regulation of buses would stop companies cherry-picking profitable routes and leaving communities stranded."
Pat Rafferty, Scottish secretary of the united union, described Scotland's bus services as a "mess".
He said: "Without bus regulation, we will continue to have a free-for-all where the only thing that matters is profit - with people and passengers just being the mugs who pick up the tab.
"If the Scottish government fails to take the opportunity to regulate our buses and to seriously look at new models of common ownership, it will be a shameful example of putting big companies before working people."
Transport Scotland said it had no plans for "wholesale re-regulation".
A spokeswoman added: "The Scottish government is committed to improving bus services and the workings of the current regulatory framework through partnerships with bus operators and local transport authorities.
"We are concerned about the decline in bus patronage, something which has been continuing since at least the 1960s, well before de-regulation began in the mid-1980s.
"However, it is important to note that the decline is not seen in all areas. Indeed, some areas of Scotland have shown growth over the last five years whereas others see double figures in terms of percentage of decline.
"That is why the solution must be local. This government will bring forward a transport bill that will give local authorities the framework to work in partnership with bus operators to improve services. Whilst we have no plans for wholesale re-regulation, we do want to see more people using our public transport networks."
She added: "We continue to spend nearly a quarter of a billion pounds a year in grants to support the network, promote the take-up of new greener buses and reimburse operators for free bus travel provided to older and disabled people under the National Concessionary Travel Scheme.
"We are also investing over £1bn per year in public and sustainable transport to encourage people onto public transport and active travel modes."