Poor weather and illegal persecution are two of the reasons why Hen harriers did not breed in Northumberland this year.
Only one pair was seen in Northumberland and their breeding was unsuccessful, according to the RSPB and Natural England's Hen harrier recovery project.
RSPB regional conservation manager, Peter Robertson said: "We had a very hard winter last year and more snow on the ground which would have knocked back food supply."
He also said "illegal persecution" may also be to blame.
Although the RSPB say they cannot pinpoint illegal activity, they have had cases of nests being stamped on.
Lowest ever
Some nests are also on grouse moors where shooting takes place and male birds have gone out to collect food and haven't returned.
This has led to concerns that birds have been injured or worse.
Peter said: "It is incredibly unusual for a male bird to abandon a nest."
Unsuccessful breeding hasn't just affected Northumberland, and the RSPB and Natural England have recorded the worst Hen harrier breeding figures since monitoring work began.
The future for Hen harrier in Northumberland does look better for 2010.
Peter said: "There is a pair that has bred in Northumberland for the last few years and they should be back next spring. We very much hope they will be back and try to breed next year."
The RSPCA have launched a bird of prey campaign and are asking people to sign a pledge, supporting the end of illegal killing.
For more information go to the RSPB website .
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