Shares of online travel-services provider Expedia Group Inc. were heading for their best day in two months on Thursday, as activist investor Starboard Value disclosed a large stake in its smaller rival, Tripadvisor Inc.

Activist investor Starboard Value has built an over 9% stake in online travel firm Tripadvisor , a person familiar with the matter said on Wednesday.

While Tripadvisor posted better-than-expected results in the first quarter, its core business remains under pressure from factors including increased competition and weaker travel demand.