Date: 201807
Local time of day: 0001-0600
Location: ZZZ.Airport, US
Light: Dawn
Aircraft: B737-800
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Takeoff / Launch
Airspace: Class B ZZZ
ATC / advisory: Tower ZZZ
Aircraft component: Turbine Engine
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Human factors: Situational Awareness; Time Pressure; Workload
Second reporter function: Pilot Not Flying; First Officer
Anomaly: Aircraft Equipment Problem Critical; Ground Event / Encounter Person / Animal / Bird
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Aircraft Aircraft Damaged; Flight Crew Landed in Emergency Condition; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Returned To Departure Airport; General Maintenance Action
Contributing factors: Environment - Non Weather Related; Airport
Primary problem: Environment - Non Weather Related

Narrative: From the gate to conducting the takeoff roll all was normal operations. During the takeoff roll after 80 knots (100 knots or so) we noticed a discoloration on the runway. We had no idea what is was; maybe just a visual anomaly. After V1 we realized that it could be birds; however not until we began rotation (moving at 250 fps) did the birds start flying. We flew into the middle of the flock of birds; hard to say how many; but it was a big flock. We heard the numerous bird strikes hit the aircraft; at this time we assumed that both sides of the aircraft took strikes; as we could not tell the exact locations. The landing gear was left down. Shortly after takeoff the right engine vibration meter; as well as physical vibration was indicated.The Number 1 engine was stable; Number 2 engine was indicating vibration of 5.6 (on the VIB meter) with reverse highlighting and box around engine parameters. We informed the Tower of the bird strike; requested return to the airport and [advised ATC]. At 400 feet N1; N2 and EGT seemed to be stable on both engines; although the vibration indication was high on the Number 2 engine. We discussed possible shut down; however we had no idea as to the condition of the Number 1 engine. We continued to 1;000 feet and at this time our gear was down and flaps were set at 10 degrees. We elected to leave the flaps at 10 degrees not knowing of any damage sustained during the bird encounter. We reduce thrust; continued to climb to 2;000 feet and began left turn for left traffic to XXR.As we reduced the thrust the VIB meter lowered to around 2.5 and we noticed the physical vibration reduced as well. F/A (flight attendants) and passengers were notified and told our intentions. We consulted the QRH vibration issue and possible engine shut down if conditions changed; we still did not know if the Number 1 engine was affected. We elected to continue and land at ZZZ; although our options remained open as condition warranted. We both agreed to land on XXR. Knowing that the Number 2 engine and possibly the Number 1 engine were affected by the strike; getting back on the ground safely was our goal. Either of our alternate options was extending our air time; by our estimate five to ten minutes. Runway XXR had positive stopping margins; however if flaps had problems or a shutdown of an engine was required ZZZ1 or ZZZ2 were our options.On base flaps were lowered to 15; the FO (First Officer) informed me that no abnormal indications were noticed; we continued as discussed. Turning final; flaps 30 were selected with no adverse effect or control issues. Upon reaching 1;000 feet all stable indications were observed and we continued for landing. Touchdown was smooth and braking normal as auto brake was selected. As we turned off runway nose wheel steering was difficult at first; after re-centering it perform normally. Rescue trucks were off to the east side north of our turnoff; we taxied up to and shut both engines down to have the rescue crews to clear and check the aircraft. FA and Passengers were notified of our current condition and a delay back to the gate.


Second narrative: [Report narrative contained no additional information.]


Synopsis: B737-800 flight crew reported striking a large flock of birds during takeoff; resulting in damage to the Number 2 engine; and an immediate return to the departure airport.