UAS Pilot reported that while conducting a mission with the assistance of a visual observer a flock of birds flew towards the UAS and one struck the UAS causing a crash.

Narrative

We were conducting a normal UAS scan at the Location. We had a crew of two for this operation. I was acting as RPIC and maintained visual contact with the UAS during this operation. I had my operator who's job was to manipulate controls for the operation and monitor the data that was coming back from the UAS. Before the operation we went through our pre-flight checks on our checklists; ensure that the drone was fully operational and check the flight automated software. We check the weather; winds were from the east; clear skies; and 10 SM visibility. We both went through the IMSAFE checklists and determined we were safe to conduct the UAS operation at the site. We attached an additional anti-collision strobe light that we use to help us keep track of the drone and assists in making the UAS more visible. When we first started the operation we didn't have many birds in the area; we had a group of crows to the south of the site but it wasn't a factor to the operation. We had successfully brought the UAS back to the Takeoff/Landing area to swap batteries in it. About 40 minutes into the operation and with the 90 percent of the scan complete a flock of thousands of seagulls started moving toward the flight path of the UAS. It seemed that most of the seagulls flew away from the UAS and were going to fly at a higher altitude than the UAS. We started calling the UAS back to the Landing/Takeoff area and getting away from the column of birds. About 30 seconds of the birds moving into the area; a seagull made the decision that it wanted to attack the UAS. So the UAS was attacked and in the process the propellers were broken and the bird was wounded. I watched as this all happened so quickly; and watched as both the UAS and the bird fell 400 feet to [the] ground. We noted where the last location of the UAS and cleaned up the staging area. After arriving to the last location of the UAS we could see that it had fell hard and hit some rocks. All four propellers were broken; the camera had been broken off the frame of the UAS and the battery had ejected itself about 25 feet from the drone. The seagull was dead and the UAS was broken beyond repair. We took photos of the site and the UAS before we picked up the pieces. We notified the site managers of what had happened and we would be back in a few days to attempt another scan with another UAS. We were able to go back and accomplish our goal of finishing the scan for the client. I was able to meet two workers at the site who uses falcons; hawks and RC planes to keep the seagulls out of the Location. I will be coordinating with them next time before I arrive on site so they can move the seagulls at of the area. Hope you are able to learn from this experience as we did.