By Roy Little
The Light-footed Ridgway’s Rail (LFRR) is on the endangered species list for both the Federal Govt and CA but there is a definite indication of problems locally as shown by the population crash of a factor of 10 according to the most recent 2016 census.
First I have to provide some background information to set the stage. The wetland is located west of Pacific Beach Drive and south of Crown Point Drive in the northeast corner of Mission Bay Park. The wetland area is roughly 40 acres, partly owned by UC and partly by the City of San Diego. Officially the wetland is called the Kendall-Frost/Northern Wildlife Reserve (K-F/NW.) Photo 1 shows part of the reserve when the tide is relatively high.
Photo 2 shows a pair of LFRR in the creek outside our condo unit which overlooks the K-F/NW Reserve, followed by a close-up of a rail (photo 3).
These endangered birds live only in saltwater marshes in Southern California and Baja CA. They look somewhat like a cross between a chicken and a duck, require cordgrass as a place to live, do not like to fly so are restricted to the wetlands they grew up in, and mainly eat crabs and snails.
The census data is collected in two ways: one is to kayak around the rail nests and the marsh edges at very high tides when the rails are restricted to such locations; and the other is to count rail calls by several observers, usually around dusk.
Rail calls are very obvious, unique and unmusical – they sound like rattling a stick on a fence! Pairs sing duets and single males and females give somewhat different calls which experienced observers can distinguish. Here are a few photos of census takers (photos 4, 5, 6). The nests shown are artificial because much of the cordgrass in the reserve is not tall enough or dense enough to provide natural nests. There are some 20 artificial nests that float up and down with the tide.
Annual census data is available for these birds in the roughly 20 coastal wetlands in SOCAL (defined roughly as Point Mugu as the northern limit and San Diego as the southern one). Dick Zembal and multiple collaborators have been providing data since 1980 and a summary from 1980 to 2016 is shown in figure 1.
This shows a gradual rise from roughly 200 pairs in 1980 to 650 pairs in 2016 with several peaks and valleys as a function of time, and overall is a success story. Part of the overall increase is due to improvements in counting techniques, part due to restoration efforts in several wetlands, part due to captive breeding and release of rails.
Figure 2 shows data for the local K-F/NW reserve, part of the total noted above, also from 1980 to 2016. The local data shows that in early summer of 2015 and 2016 the number of pairs counted was 33 and 30 respectively, a record. During the summer this year several local people noted that the rails had gone unusually quiet. A check census was done in November 2016 and found only 10 individual rails. This was sufficiently disturbing that another check was done in December 2016 and found only 6 individual rails. This is roughly a factor of 10 decrease in roughly 6 months.
The 2016 decrease is shown in figure 3, where I have divided by two the numbers of single rails seen to make the data somewhat compatible with the overall data.
Now of course interested people are wondering what has caused such a population crash and at present there is no answer. It is not difficult to come up with hypotheses but it is quite difficult to test those ideas.
So far one hypothesis is that something happened related to the El Nino event of this spring/early summer. This hypothesis could be associated with food poisoning, higher sea levels during critical breeding periods, unusual water temperatures. Presumably other wetlands should have seen major declines in rail population for such a cause.
Another hypothesis is food poisoning unrelated to the El Nino event.
Another hypothesis is unusual amounts of predation by hawks and/or raccoons though local people have not noticed unusual numbers of predators as far as I know. Photo 6 shows a Northern Harrier hunting above the marsh and photo 7 shows a Cooper’s Hawk with prey (probably a Mourning Dove).
Another hypothesis would be a disease specific to rails and Mission Bay. Clues could include the Red Tuna crab invasion or the Dungeness crabs that occurred in June 2016, but those events were tied to the El Nino conditions.
See photo 8 and 9.
There is some visual evidence that the Forster’s Terns that nest in the local marsh beside the Bay started nesting/breeding in spring 2016 but then abruptly stopped and disappeared.
If you have possible solutions to the puzzle above please contact firstname.lastname@example.org
If you are interested in this topic and our local wetlands in general come to the “Love Your Wetlands Day” event on February 4. It will be held from 9 a.m. to 4 p.m. at the UCSD trailer, located at 2055 Pacific Beach Drive.
This annual event is one of the few opportunities for the public to actually visit the wetland. You can learn about the marsh and its inhabitants, see some restoration in process, participate in interactive booths and animal presentations, learn about possible wetland expansions. There will also be a raffle, and a walk in the marsh.
There will be a set of morning activities, roughly 9am till noon and a repeat from 1pm till 4pm with some presentations in between. If you are interested in marsh walks be prepared for somewhat strenuous exercise, bring rubber boots if you have them and expect to get muddy. Even if you are not interested in the marsh walks wear sturdy foot ware as the area around the UCSD trailer is rough. Children need to be at least eight years old for marsh walking. For questions or to RSVP contact http://bit.ly/LoveYourWetlandsDay2017