"Ares Capital’s dividend is generally not a “qualified dividend” for tax purposes and therefore generally is not eligible for the lower qualified dividend tax rate. As a regulated investment company, Ares Capital generally does not pay income taxes on its earnings at the corporate level, but passes its income through to shareholders in the nature that it was earned. Therefore, a portion of our dividend is usually taxable to our shareholders at their ordinary income tax rates and a portion may qualify for the long-term capital gains tax rates. For more information about the tax treatment of our dividend, please visit our Tax Information page. For information about taxes in respect of dividends received by you, you should consult your own tax advisor."
Their Tax Information page gives you a breakdown of how the dividend is taxed, which differs from year to year. Look under Investor Resouces - Tax Information.