UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13G

Under the Securities Exchange Act of 1934

(Amendment No. 1)*

(Name of issuer)

(Title of class of securities)

(CUSIP number)

(Date of event which requires filing of this statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

x Rule 13d-1(b)

¨ Rule 13d-1(c)

¨ Rule 13d-1(d)

The information required in the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

SCHEDULE 13G

SCHEDULE 13G

SCHEDULE 13G

SCHEDULE 13G

SCHEDULE 13G/A

Armour Residential REIT, Inc. (the “Issuer”)

3001 Ocean Drive, Suite 201, Vero Beach, FL 32963

This statement is filed on behalf of each of the following person (collectively, the “Reporting Persons”):

This statement relates to Shares (as defined herein) held for accounts of Magnetar Equity Opportunities Master Fund, a Cayman Island exempted company (“MEOM”) and Magnetar Global Event Driven Master Fund, a Cayman Island exempted company (“MGED”) and warrants to purchase common stock, $0.001 par value, of Armour Residential REIT, Inc. (“Warrants”) held for the accounts of Magnetar Capital Master Fund, Ltd, a Cayman Islands exempted company (“Magnetar Capital Master Fund”) and Hipparchus Master Fund, Ltd, a Cayman Islands exempted company (“HMFL”). Magnetar Financial is a registered investment adviser under Section 203 of the Investment Advisers Act of 1940, as amended. Magnetar Financial serves as investment adviser to MEOM, MGED, Magnetar Capital Master Fund and HMFL. In such capacity, Magnetar Financial exercises voting and investment power over the Shares held for the account of MEOM, MGED, Magnetar Capital Master Fund and HMFL. Magnetar Capital Partners serves as the sole member and parent holding company of Magnetar Financial. Supernova Management is the general partner of Magnetar Capital Partners. The manager of Supernova Management is Mr. Litowitz.

The address of the principal business office of each of Magnetar Financial, Magnetar Capital Partners, Supernova Management, and Mr. Litowitz is 1603 Orrington Avenue, 13^th Floor, Evanston, Illinois 60201.

Common Stock, $0.001 par value per share (the “Shares”)

04231510

(e) [X ] An investment adviser in accordance with §240.13d–1(b)(1)(ii)(E)

(g) [ X] A parent holding company or control person in accordance with §240.13d–1(b)(1)(ii)(G)

As of December 31, 2011, each of Magnetar Financial, Magnetar Capital Partners, Supernova Management, and Mr. Litowitz held 274,100 Shares and 4,458,651 Warrants, which represents approximately 4.81% (calculated pursuant to Rule 13d-3(d)(1)(i)) of the outstanding Shares of the Issuer.

As of December 31, 2011, the number of shares of which each of Magnetar Financial, Magnetar Capital Partners, Supernova Management and Mr. Litowitz were deemed to be the beneficial owner constituted approximately 4.81% of the total number of Shares outstanding (based upon the information provided by the Issuer in its most recently filed registration statement on Form 8-K, there were approximately 93,969,468 shares outstanding as of December 14, 2011).

Item4(c) Number of Shares of which such person has:

Magnetar Financial , Magnetar Capital Partners, Supernova Management, and Mr. Litowitz:

If this statement is being filed to report the fact that as of the date hereof the reporting person has ceased to be the beneficial owner of more than 5 percent of the class of securities, check the following [ X ].

This Item 6 is not applicable.

This Item 7 is not applicable.

This Item 8 is not applicable.

This Item 9 is not applicable.

By signing below the Reporting Persons certifies that, to the best of their knowledge and belief, the securities referred to above were acquired and are held in the ordinary course of business and were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect.

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

EXHIBIT INDEX

EXHIBIT A

JOINT FILING AGREEMENT

The undersigned hereby agree that the statement on Schedule 13G with respect to the Common Stock of Armour Residential REIT, Inc. dated as of February 14, 2012 is, and any amendments thereto (including amendments on Schedule 13D) signed by each of the undersigned shall be, filed on behalf of each of us pursuant to and in accordance with the previsions of Rule 13d-1(k) under the Securities Exchange Act of 1934, as amended.