"Online casinos don't face the same dramatic seasonal variances as sports betting does, so they act as a steadying force for the industry," said Jessica Welman, analyst for PlayMichigan.com. "On the other hand, sportsbooks have been hit by the seasonality of sports betting and struggling local teams. It appears they will have to wait until the end of summer before substantial growth can be expected again."

Michigan sportsbooks took in $237.6 million in online wagers through the 31 days of May, down 4.9% from $249.9 million over the 30 days of April, according to official data released Tuesday. Combined with $20.2 million in retail handle, Michigan's online and retail sportsbooks took in $257.7 million in bets. That total is down 6.0% from $274.2 million in bets in April.

Gross operator revenue from online betting fell 4.5% to $19.5 million in May from $20.4 million in April. That produced $9.9 million in taxable revenue, down from $10.9 million, yielding $993,784 in state taxes.

With its 28.5% drop in wagering, Michigan's 28.5% decline in April handle represented the steepest month-over-month decline among major U.S. markets. And May's results so far lag behind other states that have reported April data, including Indiana (up 7.6%) and Iowa (down 2.9%).

Michigan's decline has been more pronounced because as the initial enthusiasm that came from the launch of online betting began to settle, the sports schedule also waned. Even more, all of Detroit's professional teams that were in action in April and May struggled mightily.

"A lack of success from Detroit teams naturally saps interest, and Michigan is facing too many short-term factors to overcome completely," said Matt Schoch, analyst for PlayMichigan.com. "Despite the declines in betting volume, there aren't any systemic issues. Even if the Lions' prospects are equally dim, substantial growth will almost certainly return with the beginning of football season."

FanDuel/MotorCity Casino led all online sportsbooks with $71.2 million in wagering, down from $74.2 million in April.

"The next few months should help bring innovation from sportsbooks, as each operator experiments with ways to spur interest during the slow season," Schoch said.

Online casinos and poker

Revenue for Michigan's online casinos and poker rooms hit $94.9 million in May, essentially even with April. May's win breaks down to $3.1 million per day of the 31 days of the month, down slightly from $3.2 million per day over the 30 days of April.

The win produced adjusted gross receipts of $89.1 million, up from $88.9 million in April. That total yielded $18.1 million in state taxes and $7.1 million in local taxes. Since January, online casinos and poker have generated $393.9 million in revenue and $99.7 million in state and local taxes.

"Online casinos have become a powerhouse of revenue generation," Welman said. "Revenue has remained high, even as retail casinos around Detroit have become more accessible. Looking ahead, the popularity of these games should remain — and likely expand — over the next few months, even as retail casinos' operations continue to steady."

BetMGM/MGM Grand Detroit led with $36.1 million in gross receipts, yielding $10.6 million in state and local taxes.