Oystercatcher Questions...

[Arthur Morris]

In this thread, http://www.birdphotographers.net/forums/showthread.php?p=114365#post114365, Grace Scalzo wrote, "As an aside to the photography discussion, there are probably 40 adult oystercatchers at Nickerson, yet only 3 chicks." Axel responded by suggesting that this was not a very good adult to chick ratio, and that is surely true.

I made the point that it was highly likely that only the one pair attempted to nest there and that the rest were just roosting there, possibly as failed or finished nesters or as non-nesting birds. Oystercatchers do not nest colonially, i.e., in groups and are often but not only found nesting in the vicinity of tern or skimmer colonies. It;s the same with Piping Plover.

Now surely our beach nesting birds are under tremendous pressure from human development, beach-goers, fisherman, and the rest.

My point was that oystercatchers often gather in large groups in areas where they do not nest.

Any additional light that might be shed on such situations would be appreciated. Thanks.

[Barry Goggin]

I found some figures for successful Oystercatcher nesters :
"George (2001) estimated extremely low American Oystercatcher’s nesting success in the egg stage (12-27%) and in success at fledging young (0-6%) in recent studies along the Georgia coast. In North Carolina from 1997-1999, Davis et al. (2001) found that only 13% of the nests hatched at least one egg (n = 245 nests). Prior to these two studies, Nol (1989) also found low hatching success (13-14%) for American Oystercatchers in Virginia."

If you take the fledging young success rate at 6% (the high end) and assume all 40 birds were breeding pairs, then you get 2.4 chicks. However honestly the number (40) is too low for statistics to be meaningful. Probably a few tried to nest there and only one or two succeeded.

Data from USGS Patuxent Wildlife Research Center
http://www.pwrc.usgs.gov/products/sciencebriefs/sb%2015%20amoy%20science%20brief.pdf

[Axel Hildebrandt]

Thanks for this information, Barry! Very interesting, maybe the low success rate is reflected in the relative low number of oystercatchers. I remember reading that there are about 7000 birds on the East Coast.

[John Chardine]

A fledging rate (assume this means chicks fledged per egg laid or something similar) of 6% is extraordinarily low and would quickly produce population extinction unless adults were virtually immortal (in fact annual survivorship for adult oystercatchers is about 85%, so they are not). Breeding success varies between years and locations and is difficult to characterise at the species level. The Birds of North America account for this species, authored by Nol and Humphrey give 48% and 71% for hatching success from two states, and 34% and 36% for fledging success (chicks fledged per egg hatched).

I agree with Artie that this was likely a case where a lot of the birds were non-breeders, loafing around.