So this series of very unusual events is an extreme example of parental instincts gone into overdrive! What we presume happened was that the Common Tern adults had laid an egg near this nestbox but their egg got stolen, crushed, or lost somehow. They then mistook the nearest egg for their own, which just so happened to be a Roseate Tern egg in an open-fronted nestbox. We don't know how the Roseate Tern parents took to this, but we know Commons can be quite aggressive so presumably saw them off fairly quickly!
We see plenty of less-extreme examples of parental instinct-induced silliness around the colony every year. We usually come across Common Tern nest where eggs have been stolen from their neighbours. Common Terns uusally lay 2-3 eggs, but we've found a few clutches that jumped from 3 to 5 to 7 eggs in a short space of time, and even one with 9 eggs, all at the expense of neighbouring nests. Unfortunately it's not possible for a Common Tern to incubate such a large clutch and most of the extra eggs go cold and are rolled out of the nest.
|Parental instinct led this Common Tern to kleptomania! She laid three eggs, then stole another four!! (Picture taken under NPWS license)|
We also had another inter-species mix-up, similar to the above where an adult Common Tern saw a neighbouring egg and hurridly rolled it in with their own eggs, not realising that it belonged to a neighbouring Roseate Tern!
|Spot the odd one out! Two Common Tern eggs, with a Roseate Tern egg in the middle! (picture taken under NPWS license)|
|The same nest after hatching - again, spot the odd one out! Note how welll camouflaged the chicks are too. (picture taken under NPWS license)|
The above clutch hatched successfully and all three chicks were progressing as normal. Unlike the video above, the Roseate Tern in this clutch had to make-do with sitting in a a nest that was out in the open, as opposed to a shaded or covered area that a Roseate Tern would usually lay eggs and raise chicks in. Unfortunately the chicks from this clutch succumbed to poor weather earlier in the summer.
Of course, the most obvious (painfully obvious sometimes!) example of parental behaviour we beare witness to is the Common Terns attacking the wardens and anyone else who gets too close to a nest! They'll defend their eggs at almost all cost and will continue to be like this until the chicks are close to fledging. They invest a lot of time and energy into flying to Rockabill from Africa, laying eggs and looking after them until they hatch, then feeding them and keeping them out of trouble until they're able to fly and fend for themselves. So they don't want to lose all of that evolutionary investment, not without a fight! And of course, we want them to succeed too, so we can't be angry with them - just begrudgingly admire them as we duck and dive out of their way!
|Andrew suffering at the hands (and beaks!) of some angry parents!|
|Tern wardening - sponsored by Panadol! (?)|
|Of course, they don't just peck us.....|
|...plenty of good clothes ruined over the years....|