Between the May 15 and May 29 settlement dates, biotech stock MannKind continued its climb up the ranks of the most heavily shorted stocks traded on the Nasdaq. It threatens to unseat Sirius XM from the top spot, with less than 9 million shares difference between them at the end of the period.

Note that the five most shorted Nasdaq stocks all had more than 110,000 shares short at the end of the month.

The number of Sirius XM Holdings Inc. (NASDAQ: SIRI) shares short tumbled by almost 16 million to about 139.91 million late in the month. That was 6.1% of the total float, and it ended a three-period streak of rising short interest. At the current average daily volume, it would still take less than eight days to cover all short positions. Sirius was one of our back from the dead stocks during the period. Short sellers watched the share price pull back about 3% during the two weeks between settlement dates, but it is now up about 8% year to date. Shares closed Tuesday at $3.78, in a 52-week trading range of $3.14 to $4.04.

MannKind Corp.’s (NASDAQ: MNKD) short interest, at almost 131.16 million shares as of May 29, was up 16.1% from the previous period. Note that it was more than half, 51.2%, of the total float, as well as the highest short interest in at least a year. The days to cover dropped from more than 14 to less than 13. In late May, it looked like Mannkind shares had found bottom. Shares ended Tuesday at $6.70, in a 52-week range of $3.46 to $11.48. The stock saw a share price increase of more than 41% in the two-week short-interest period, and another 43% or so since.

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The short interest in Frontier Communications Corp. (NASDAQ: FTR) rose 8.0% from the previous period to more than 120.85 million shares, or 12.1% of the telecom’s float. That was the second increase in a row, after the number of shares short had been on the decline since last December. The days to cover remained more than six, on the highest daily volume since February. Even with shares at 52-week lows, Morgan Stanley upgraded the stock. During the short interest period, the stock more than 5%. It is down more than 25% year to date. Shares closed Tuesday at $4.96 and have a 52-week trading range of $4.90 to $8.46.

Advanced Micro Devices Inc. (NASDAQ: AMD) had around 118.03 million shares short by the end of the month, down 1.3% from the previous settlement date. The most recent reading totaled 18.7% of the company’s float, and the days to cover jumped to almost 12, the highest number so far this year. AMD continues to live in the shadow of rival Intel. The share price ended the two weeks more than 3% lower than where it began, though it has been relatively flat since. The stock closed at $2.29 on Tuesday, and the 52-week range is $2.14 to $4.80.

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A 5.1% bump in short interest brought Intel Corp. (NASDAQ: INTC) to around 116.08 million shares short at the end of the period. That totaled 2.4% of the company’s float and was still the greatest number of shares short since March. The days to cover remained more than four. The Altera merger was announced at the very end of the period. Shares rose less than 3% in the short interest period, while the S&P 500 was essentially flat. The stock is now down almost 14% year to date and closed most recently at $31.25. Shares have traded between $27.72 and $37.90 in the past year.

BlackBerry Ltd.’s (NASDAQ: BBRY) short interest, at more than 87.10 million shares as of the end of May, was 1.8% lower than in the previous period, and 17.7% of the total float. Short interest has been smaller in just one period so far this year. The days to cover rose from less than 10 to more than 13 as the average daily volume declined. BlackBerry announced share buybacks during the period. Shares closed Tuesday at $9.54, in a 52-week range of $7.77 to $12.63. They fell more than 3% in the two-week period and more than 4% further since.

Rounding out the top 10 were Express Scripts Holding Co. (NASDAQ: ESRX), Qualcomm Inc. (NASDAQ: QCOM), Microsoft Corp. (NASDAQ: MSFT) and Groupon Inc. (NASDAQ: GRPN). The notable mover among these was Qualcomm, shooting up from less than 20 million shares short to around 69 million by month’s end. And an almost 21% decline in short interest dropped Apple Inc. (NASDAQ: AAPL) out of the top 10.

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