LONG REEF is the best place on Sydney’s Northern Beaches for a migratory shorebird encounter. It’s a brilliantly fascinating and vibrant intertidal, ecological hotspot: a real nature lover magnet! So it’s not unusual to find me stalking about the reef with scope and bins and magnifying glass, as I was yesterday, during a brief break in our welcome wet weather.

I’ve had to abandon the Ruddy Turnstone limpet predation survey for the winter, as there are so few juvenile turnstones on the reef this year that the sample is statistically way too small to be of any use (check out the “Ruddy Turnstone study” category in the sidebar). The project is almost at an end, with enough data to start moving things towards the laboratory, so it’s a disappointment that we wont be able to capture some juv – adult comparisons to determine if the rejection of siphonaria limpets has any basis in age cohorts. I was pondering this yesterday whilst observing a lone Ruddy Turnstone amid a foraging party of 20 Red-necked Stints and a couple of Double-banded Plovers, when some Sooty Oystercatchers landed not too distant from me.

A small portion of an oystercatcher's feast. The arrow points to a rejected siphonaria limpet amid the predated cellana limpets. A couple of the limpets bare the hallmarks of this oystercatcher's foraging guild: a "hammerer". © 2009 Ricki Coughlan.

I GAVE the oystercatchers a bit of time to settle and then strolled across the reef and began to observe their foraging. What unfolded in the next half hour has added considerable interest to my work on limpet predation on Long Reef. The oystercatchers were taking a large number of Cellana tramoserica limpets: nothing unusual about that. What was unusual was that the limpets they were feasting on were much smaller than usual and they were also sampling – and rejecting – Siphonaria furniculata limpets. There was not just a few either: after 5 minutes of observing, I moved in and counted 34 rejected siphonaria limpets and 16 predated cellana limpets in a 5 square metre area. Up until now, I have not observed Sooty Oystercatchers rejecting siphonaria limpets, as they generally take limpets which are larger than the average siphonarias and I have presumed that the siphonaria limpets have not been targeted as they’re smaller than their usually predated limpets.

A Sooty Oystercatcher on Long Reef with a cellana limpet of the size which we are generally accustomed to seeing this species take. © 2009 Ricki Coughlan.

DETECTIVE WORK in nature requires great diligence, finding all the tiny puzzle pieces and building a picture which works. What I now have is evidence that turnstones are not alone in their rejection of siphonaria limpets – further pointing to foul taste, foul odour or toxicity (or all three). I’m pretty certain now that we can rule out that the flesh is too difficult to remove from the shell as a reason for rejection, as surely there’s no way that these masters of muscle removal would be thwarted by a mere siphonaria. Although we don’t have statistical data on siphonaria limpet rejection by age cohort, we can probably rule out inexperience as a factor in flipping the siphonaria limpets in the first place as it goes across species and my oystercatchers were adult birds.

I’m now certain that all will be revealed when we get some samples of cellana limpets and both species of siphonaria limpets (S. furniculata & S. denticulata) into the laboratory for analysis.

As I strolled back up the steep hillside overlooking Long Reef I couldn’t help but wonder at the massive numbers of siphonaria limpets which are flipped and left to die each day and, indeed, the massive numbers of cellana limpets which are gorged upon by the turnstones and the oystercatchers. The rate of recruitment, of replenishment, must be enormous, further pointing to the extraordinary vibrancy of habitats like these and the need for us all to ensure that they remain inviolate, in order for the fantastic play of life to continue to unfold in this little spark of magic on Sydney’s coast line.

Until next time . . . Happy birding!

Filed under:
Birding, Ruddy Turnstone study, Shorebirds by Ricki