Ambarella, bluebird bio, Tiffany Downgraded

Analysts are weighing in on chipmaker Ambarella Inc (NASDAQ:AMBA), biotech bluebird bio Inc (NASDAQ:BLUE), and retail stock Tiffany & Co. (NYSE:TIF). Here's a quick roundup of today's bearish brokerage notes on AMBA, BLUE, and TIF.

Ambarella Trades Lower After Negative Analyst Note

AMBA is down 1.3% at $50.89, after a Craig-Hallum price-target cut to $70 from $85. This is just more of the same, considering the stock has sunk 32% since topping out near $75 in early October. The shares could be vulnerable to additional negative notes, if they don't reverse course quickly. Seventy percent of analysts rate underperforming Ambarella Inc a "buy" or better, while not a single one has handed out a "sell" opinion.

Roth Capital Downgrades bluebird bio

Roth Capital downgraded BLUE to "neutral" from "buy" and lowered its price target to $71 from $87, despite the stock's recent gains. While the shares are down 1.8% today to trade at $77.25, they aren't far from their annual high of $79.70, notched in early December. On the sentiment front, short sellers have piled on bluebird bio Inc. One-fifth of the stock's float is sold short, and at its average daily trading level, it would take two weeks for those bears to cover.

CEO Exit Trounces Tiffany Shares

TIF has tanked 2.7% at $78.33, after CEO Frederic Cumenal announced his resignation, due in part to poor holiday sales. Citing concerns about executive turnover, Mizuho dropped its opinion to "neutral" from "buy," and slashed its price target to $74 from $90. That said, Tiffany & Co. remains 22% higher on a year-over-year basis, and could find a foothold at its ascending 80-day moving average. Meanwhile, options traders have been rolling the dice on a steeper slide. At the International Securities Exchange (ISE), Chicago Board Options Exchange (CBOE), and NASDAQ OMX PHLX (PHLX), TIF has racked up a 20-day put/call volume ratio of 3.61 -- with nearly four puts bought to open for every call in the last month.