Research In Motion's head of developer relations, Mike Kirkup, has resigned, the latest in a string of departures as the BlackBerry maker seeks to claw back ground lost to Apple and Google.

Kirkup, long a presence at RIM's outreach events for developers, made the announcement on his personal blog on Tuesday.

This seems like a great time to step back and consider my next steps, Kirkup said in a blog entry that cited immense change in the industry including Google's $12.5 billion bid for Motorola Mobility, Hewlett-Packard's shutting down of webOS and Steve Jobs' resignation as Apple CEO.

RIM, for its part, has struggled to convince developers writing code for devices from Apple and those running Google's Android software to also produce products for its BlackBerry smartphones and PlayBook tablet.

Its app store, where developers hawk their wares, is much smaller than either Apple's or Google's equivalent offering.

Kirkup had worked at RIM since 2001, after graduating from co-CEO Mike Lazaridis' alma mater, the University of Waterloo.

His departure follows two defections from RIM's marketing department to Samsung, which relies heavily on Google's Android software.

RIM's head of marketing, Keith Pardy, and one of its chief operating officers, Don Morrison, also resigned this year.

In July, the Canadian smartphone maker said it was slashing about 11 percent of its workforce, amid falling sales and profit.

The company's shares rose 1 percent early on Wednesday and have jumped from a trough in early August. They are still down almost 50 percent since the start of the year.

(Reporting by Alastair Sharp; editing by Janet Guttsman)