The S&P/ASX 200 Index (ASX: XJO) is on course to record a small decline ahead of the Christmas break. At the time of writing, the benchmark index is down slightly to 8,198.9 points.

Four ASX shares that are falling more than most today are listed below. Here's why they are dropping:

Charter Hall Retail REIT (ASX: CQR)

The Charter Hall Retail REIT share price is down 3% to $3.15. This has been driven by the property company's shares going ex-dividend this morning. Earlier this month, the company announced plans to pay a 12.4 cents per share interim dividend. This represents an attractive 3.8% dividend yield based on yesterday's close price. Eligible shareholders can look forward to receiving this dividend in a couple of months on 28 February.

DroneShield Ltd (ASX: DRO)

The DroneShield share price is down 3.5% to 63.2 cents. Except for a nice rebound on Monday, this counterdrone technology company's shares have fallen heavily in recent months. So much so, DroneShield's shares are now down 75% from their mid-July high. A softer than expected performance in the second half of FY 2024 has weighed heavily on sentiment. And with its shares trading on sky high multiples, it seemed inevitable that its shares would be shot down like a drone. Though, some brokers think this could be a buying opportunity now. For example, Bell Potter has a buy rating and $1.20 price target on its shares.

FBR Ltd (ASX: FBR)

The FBR share price is down 5% to 3.7 cents. This may have been driven by profit taking after some strong gains from the robotics company's shares. Since this time six months ago, the company's shares have risen by approximately 85%. Investors appear optimistic about its potential in the US market after successfully demonstrating its brick-laying robot.

St Barbara Ltd (ASX: SBM)

The St Barbara share price is down 34% to 20.2 cents. Investors have been hitting the sell button after the Papua New Guinea Internal Revenue Commission (IRC) delivered correspondence to Simberi Gold's tax agent containing details of tax assessments. The IRC correspondence contains an assessment of additional taxes, inclusive of a 200% penalty imposition, that amount to PGK 523 million. This is the equivalent to approximately A$210 million. CEO Andrew Strelein said "The receipt of this IRC Amended Assessment, backdating changes to 2008 and earlier, just as IRC were closing down its office for Christmas was disappointing – particularly when such positive progress has been made with Mineral Resources Authority and with Kumul Minerals Holdings Limited on the development of the Simberi Sulphides."