Black Oystercatcher Disasters
Part of my Environment for the Americans (EFTA) internship is doing Black Oystercatcher monitoring to determine nesting success alongside the California Coastal National Monument (CCNM), Bureau of Land Management California (BLM). For the past few years, the BLOY pairs in Pacific Grove, CA have not been doing well with only an 8-11% fledging success. With beautiful beaches that have the rocky intertidal exposed, the City of Pacific Grove attracts a lot of tourism which often spells bad news for the BLOY pairs that mate for life, find and defend a territory, and live and nest in the rocky intertidal.
Earlier this spring with the help of CCNM Volunteer Manager Rick Hanks and EFTA Executive Director Susan Bonfield, I conducted a study quantifying the effectiveness of ropes and signs in decreasing the amount of human disturbance in BLOY nesting sites. In previous years, human disturbance seemed to be the cause of various nest failures and in one instance it is suspected that a family dog killed a BLOY chick. While the human disturbance study demonstrated a dramatic decrease in human disturbance in the two nesting sites I studied, nesting sites MP-4 and MP-5, the results of my last monitoring session were not positive.
Territory MP-11 is another nesting site that suffers from high human disturbance and is also in a very vulnerable place. BLOY eggs are often at the mercy of other birds (such as gulls, cormorants, and crows), mammals (foxes, squirrels, skunks, and raccoons), and the natural environment. In this particular case, the nesting site that the MP-11 pair chose is in a very low set of rocks when compared to the other nesting sites. When Hugo Ceja (Audubon consultant and previous EFTA intern) and I went out to look at the pair to count the number of eggs or to learn if any chicks were present I noticed that the BLOY pair was not in the usual spot. This isn’t rare because often when one mate is foraging, roosting, or preening, the other is incubating. When it is time to exchange duties the BLOY pair will occasionally go out on a little walk or flight before the other mate starts incubating. Though it is only for a few minutes, the eggs are exposed to a number of dangers. Knowing this we sat for a couple minutes waiting while listening and looking up at the sky for any BLOYs approaching the area. After a couple of minutes turned into many minutes, we suspected something was wrong. We walked closer and Hugo noticed puddles of water that were at the top of the rocks. Suspecting that the tide was high enough to reach the top of the rock, he walked directly to the nest site. Empty. All the rocks and twigs used to make a nest had been washed away. He headed one way and I the other in order to look for any egg pieces, and it wasn’t long before I found a broken BLOY egg.
While finding a broken BLOY is bad news in general, what Hugo found next was even worse while monitoring nesting site MP-4 and MP-5. These nests were located in sites where I conducted my human disturbance study and contain ropes and signs warning people not to enter the sites. We did not find the MP-4 BLOYs in their usual incubating location. Once again we waited for about 10 minutes before Hugo looked at the nest, and I stayed behind to monitor MP-5. Unfortunately, Hugo came back with the only egg left. However, this one looked like it had been pecked. A nesting seagull about 4 ft away from the BLOY nest is the prime suspect. A part of me couldn’t help but get particularly upset at this broken egg because it is in a site that was supposed to have increased in security.
This particular monitoring session reminded me that BLOYS and nesting birds in general suffer more than human disturbance. There are predation, environmental factors, and even BLOY behaviors that have to be considered when trying to determine the cause of nesting failure. Most of the time it is not easy to identify just a single cause. To make things more complicated, nesting failure can be caused by natural predation one year, but human disturbance the next. While it may not be easy to determine why a nest fails, this long-term monitoring will at least provide BLM and Audubon with data that will help researchers better understand BLOY reproductive success and the general rate of failure, as well as help to clarify what further questions need to be addressed.