Wildflowers growing in the Rocky Mountains have shifted their bloom pattern to cope with climate change, according to a new study based on data from two million flowers collected over a four decade period.

The study, conducted by David Inouye from the University of Maryland and colleagues, found that the bloom season has extended; from May to early September a few decades back to late April to late September now. The change in bloom season can have a negative impact on insects and birds that depend on flowers for nectar.

Previous research has shown that climate change has advanced early flowering in British plants. Other studies have shown that spring in the U.S. is now arriving earlier than in the last few decades.

According to Inouye and team, the dataset collected by them is the most comprehensive record of wildflower bloom in the region. Over the years, studies on flowering patterns have relied on just the date of flowers' first bloom, which doesn't show the entire effect of climate change.

"Most studies rely on first dates of events like flowering or migration, because they use historical data sets that were not intended as scientific studies," Inouye said in a news release. "First flowering is easy to observe. You don't have to take the time to count flowers. So that's often the only information available. It has taken a lot of effort to get the comprehensive insights needed for this analysis, which helps us understand how ecological communities are going to change in the future."

The current study began in 1974 when Inouye was a graduate student. Since then, he and his colleagues- his students- have counted blooms in each of 30 plots every other day for nearly five months a year. The data n the 2 million flowers was collected over period of forty years.

Data analysis showed that the date of the first spring bloom has advanced more than six days every decade. The peak of spring when a majority of flowers are in bloom has also extended by five days per decade.

Researchers studied some 60 plant species. They found that seven species have changed their entire flowering cycle. Nearly half of the plants have started blooming earlier than usual, Livescience reported.

 "The flowering season is about one month longer than it used to be" Amy M. Iler said in a news release, "which is a big change for a mountain ecosystem with a short growing season."

The change in plant behavior in the region has a ripple effect on several birds and insects. For example, hummingbirds' nesting time is in tune with the flowering of certain species of flowers. Change in climate has lengthened the blooming season but not the number of flowers produced by  the plants, meaning that the chicks of these birds might not have enough nectar.

The shift in the blooming cycle has even brought new species of animals in the region, researchers found.

The study is published in the journal Proceedings of the National Academy of Sciences.