Sotheby’s, the New York-based auctioneer of art and collectibles, reported a 13 per cent decrease in second- quarter profit that fell below analyst expectations because of a change in the sales calendar and a loss on a painting sold during the period.

Net income was $67.6 million, or 96 cents a share, in the quarter ended June 30th, compared with $77.6 million, or $1.11, in the same period last year.

The company was expected to report earnings of $1.22 a share, according to the average of five analysts in a Bloomberg survey.

Prices for art have reached records, fueled by a surge in private wealth and a six-year rally in financial markets. Sotheby's and rival auction house Christie's are under pressure to boost profitability that's been eroded in the competition for top consignments.

Sotheby’s reported earnings before the start of regular trading.

The shares have declined 6.2 per cent this year through yesterday, compared with a 1.2 per cent gain for the Standard and Poor’s 500 Stock Index.

The auction house also announced a $250 million share buyback, up from $125 million in a prior authorisation. The company said it will complete the purchases in the next 12 to 18 months.

Evening Sale Revenue in the quarter fell 1 per cent to $332 million. Sotheby’s biggest auctions are held in the second and fourth quarters.

The decline “is largely due to a change in the timing of the summer evening sale of contemporary art in London, which was held in the third quarter in 2015 after being held in the second quarter in 2014, as well as unfavorable movements in foreign currency exchange rates,” Sotheby’s said in a statement.

The London evening sale of contemporary art took place in the third quarter on July 1st.

Last month Sotheby’s said its preliminary sales for the first half were $3.2 billion, the same total as for the period last year. Christie’s tally for the same period rose to a record £2.9 billion.

In May, Sotheby’s sold $894.6 million of art in New York, boosted by demand from Asian buyers.

Wang Jianlin, Asia's richest man and chairman of China's Dalian Wanda Group, bought a Claude Monet painting for $20.4 million at Sotheby's Impressionist and modern art sale on May 5th. Chinese movie mogul Wang Zhongjun bought a Picasso for $29.9 million at the same sale.

Bloomberg