I was at a breeding site on Wednesday; the Falcon was incubating when an intruding bird showed up, in London nowadays more or less a daily occurrence for most pairs. It appears more so at this time of year as migrant peregrines add to home grown nationwide movement.
The intruder, an immature female was unringed and was instantly attacked by the resident male, being smaller he cannot directly close with her as he would come off 2nd best and possibly be injured, as it was he tried to usher her out of his territory. Sometimes it’s hard to work out the Tiercel’s behaviour due to their tendency to flirt.
|Intruding immature female - as you can see some wing damage|
The resident female, incubating, hearing the kafuffle exited the nest box at a rate of knots and went straight at the intruding female. Another female is another matter, and an angry one protecting a nest site from a rival is to be avoided, the intruder high tailed it south with the pair hot on her heels. It did occur to me that being unringed it could have been their own female offspring from last year; they had a male and female juvenile. But given the reaction to this immature and the level of aggression shown I would say not, I do believe that they do recognise their own off spring, even 9 months later. Over the years I have seen territorial adults receive immatures the following year and there has not been the reaction I expected, to an extent they have been tolerated ,I can only surmise that they were the previous year’s offspring.
|Tiercel behind shepherding her out|
|Tiercel just dived her|
|Lining her up again|
|The direct approach - Tiercel on right|
Back to the chase, all 3 were lost to view heading south which now meant the eggs were totally unguarded, minutes went by, it’s at times like this that they lose eggs to Crows but thankfully she came back after 2 minutes and resumed incubating.
The intruder was very much the worse for wear with some wing damage so I suspect that she had tangled with other territorial pairs, possibly trying to usurp a pair or find a territory of her own, prime sites are strongly defended all year round.
I may have seen this bird before and will check back on photos.