Stories from the Field: Ecology of California Ridgway's Rails

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Notes from field biologists studying the endangered Ridgway's rail.

Story: Ecology of California Clapper Rails in the San Francisco Bay/Delta Region

WERC scientists tracking clapper rail nests

(Public domain.)

Field Notes - April 24, 2009 We are beginning our third field season of radio-tracking and continuing to gather data on clapper rails at four sites in San Francisco Bay. Winter captures were completed by early March during which we caught 39 California clapper rails including our first confirmed juvenile (caught in October before it completed molt). We also recaptured 4 individuals radio-marked previous year, and one that was has been radio-marked since the start of the project. Depredation has been high again over the winter, but rails have been surviving fairly well since the weather and tides have turned favorable. We have accumulated over 10,000 telemetry points. We completed our channel mapping efforts and are currently analyzing data from the first two years of study. We ended the trapping season with 10 birds marked at Colma, 10 birds at Arrowhead, 10 at Cogswell, and 3 at Laumeister.

On Thursday, April 23rd, we confirmed two of the largest movements of California Clapper Rails that have thus far been observed. One of the birds marked at Colma Creek was found to have moved to Santa Venetia Marsh in Marin County near San Rafael. Interestingly, the location that this bird moved to is within about one mile of the location that another marked California Clapper Rail moved to from Colma Creek two years ago. While confirming the location of this bird, we found a Virginia Rail nest in Santa Venetia Marsh. One of the birds marked at Cogswell Marsh was found to have moved to Ideal Marsh, just north of the Dumbarton Bridge. Both have been confirmed to be alive and well. We will continue to monitor the movements of these birds.

Colma Creek
Marking went well at Colma and completed in just a few days. Birds were captured on high tide events using small boats with electric motors and dip nets. Thanks to all those who came and helped! Three birds have turned up missing from Colma beginning in early April. We found one in the North Bay and continue to look for the other two. We currently have six marked rails at Colma Creek Marsh. One of the marked birds at Colma Creek has exhibited several large movements within the marsh complex during the past two weeks. The other marked rails at Colma Creek have been observed within relatively small ranges over the past few weeks and are likely starting to nest.

Laumeister
Trapping at Laumeister was shortened due to the onset of nesting and the time it took to get birds marked at other sites (the weather in March did not help either). One radio-marked bird disappeared over the last three days; the remaining two birds are in the northern portion of the marsh. Their movement patterns have been consistent with previously marked rails in this marsh.

Cogswell Marsh
Trapping went well at Cogswell with a combination of high tide trapping (primarily for replacing existing transmitters) and live traps placed in channels. Trapping was completed over a three week period. After one radio marked rail moved south to Ideal Marsh we are left with seven marked rails at Cogswell Marsh. One of the birds at Cogswell Marsh recently moved from the northern portion of the east marsh to the southern portion of the west marsh, a distance of nearly a kilometer and a relatively large within-marsh movement. One of our marked rails in Cogswell Marsh has been found to have initiated nest building and the depredated nest of an unmarked California Clapper Rail has been found, indicating that egg-laying has begun in Cogswell Marsh.

Arrowhead
Once again high tide trapping at Arrowhead Marsh was very successful. Thanks to all of those that made it out to help. We currently have seven marked rails at Arrowhead Marsh. Although a couple our marked birds at Arrowhead have exhibited behavior that would suggest to us that they have initiated nesting and one of the marked birds has been observed with a mate, we have not yet confirmed any nesting at Arrowhead. We continue to track these birds 4-5 times each week.

 

Field Notes - May 5, 2008

It's been a while. We apologize for the long lapse in updates, but here's a recap--

We currently have over 8400 locations. These are for the 32 originally radio-marked birds from early 2007, plus the newly marked birds in the late 2007/early 2008 trapping season. We currently have a total of 31 active radios deployed in our now *four* field sites. We added Arrowhead marsh this year, just north of Oakland Airport in Alameda County.

We trapped a total of 53 new birds this trapping season, though 7 of them at Arrowhead were only banded and not radio-tagged (see Arrowhead below for details). However, we also witnessed a very high predation rate through January and February totaling 15 birds. It may be that with the high tides, many of which are at night, coupled with a winter influx of diurnal and nocturnal predators, rails are at greatly increased threat by predation. There certainly may be other compounding factors, but at this point, this seems the most logical.

Colma Creek
We have 9 active radios at Colma Creek (5 males, 4 females). We still maintain 3 birds from the origin of the study, all of which have been remarked with new radios to ensure longer tracking of their movements. No nests have been found.

Laumeister
7 active marked birds are being tracked at Laumeister (2 males, 5 females). Multiple nests have been found at this site, though none are for marked birds. It looks like we may have 2 different pair, where both male and female are marked, so we are hopeful for nest finding.

Cogswell Marsh
6 active radios remain at Cogswell (2 males, 4 females). It appears that we may have a dual-marked pair at this site.

Over the course of 1 week in late January 2008, we were able to detect some interesting 1 km+ movements of one female who moved to the polar opposite portion of the marsh than where she'd been for the last few months. At the end of that week, she moved that entire distance back to 'usual haunt' in less than 20 hours. We have no idea what brought on the erratic behaviors, but it's nice to document. This is one of the birds we've been tracking since February 2007.

Arrowhead
Our newest addition to the study. Supporting one of the highest densities of rails in the Bay Area, this marsh is now a part of our study, and we captured 17 (!!!) birds on one high tide rush on 3/5/2008. We fitted 10 of these birds (4 males, 6 females) with radios. The remaining 7 birds (all females) were banded, measured, samples collected, and released.

Since then, 1 radioed bird has been predated, and one nest has been found for a pair that both male and female are radio-tagged. We now hopefully get to document the varied schedules of nest incubation between the parental sexes. So far (at least in other of our sites) we have seen mostly males fly off the nest, while it is generally thought that the female is the predominant diurnal incubator. This is a very interesting site, and could provide some wonderful insights as to how these birds breed, and how they respond to the ongoing invasive Spartina> treatment.

Other Endeavors

Channel Mapping

This has been fully underway since mid-March and is producing some amazing results. Having accurate marsh elevation, channel depth and width information could prove very interesting in characterizing rail movements and spatial use patterns. Laumeister has been completed, and despite being the smallest of our sites, supports over 40km of channels. Cogswell is underway, with approx 10km of channels mapped so far.

Vegetation Sampling

This season we have employed a new type of vegetation sampling to complement our previous efforts. Using the same sampling technique, we are sampling 10 set randomized points per marsh on a monthly basis to get a better understanding of the seasonal effects of vegetation and rail habitat use. These points are split per marsh to include more seasonally responsive areas (like native Spartina and invasive tracks) as well as more annually stabile areas. This is especially key when thinking of Spartina use (invasive and native). The other predominant vegetation in the marsh (gum plant, pickleweed, alkali heath, Jaumea) are seasonal in their growth and lushness, while Spartina foliosa can completely die back leaving mudflats in the winter, where tall vegetative cover was available for use in the summer.

Field Notes - January 11, 2008

We currently have over 6200 locations. These are for the 32 originally radio-marked birds, plus 10 newly marked birds. We currently have a total of 17 active radios deployed in our three field sites.

Trapping season is ongoing, with 4 new birds caught in Laumeister in December. However, a run of rain interrupted several days of potential trapping effort, and with new mortalities and radio failures, we continue the trapping season into January and possibly February if needed.

One interesting thing to note is it seems like pre-breeding behavior is fully underway. Birds are very vocal, and often observed in male/female pairs. On several instances, conspicuous males have been observed kekking and strutting in circles or figure-eights, seemingly beginning to mark out territories and solicit female attention. It will be nice to watch this behavior develop over the next couple months.

 

Colma Creek
We have 7 active radios at Colma Creek (4 males, 3 females). 3 birds have suffered predation in the last month, 2 due to feral cats that frequent a cat feeding station. The remaining bird was predated by a raptor. The remaining birds are behaving as usual, though a couple have explored new parts of the marsh through December, and then mostly returned to their 'typical' haunts.

Laumeister
7 active marked birds are being tracked at Laumeister (2 males, 5 females). 5 new rails have been tagged over the last two months, though one of these has already been predated by a mammal. We are just getting to know these new birds, and the 3 previously marked birds are occupying their usual haunts.

Cogswell Marsh
4 active radios remain at Cogswell (2 males, 2 females). The loss of two birds was due to one predation (source unknown) and one radio failure. We will begin trapping again at this site in the next few weeks and hope to re-trap the radio failure bird, since he was pretty reliable in location at high tides.

Over the course of a week, we were able to detect some interesting 1 km+ movements of one female who moved to the polar opposite portion of the marsh than where she's been for the last few months. At the end of this week, she moved that entire distance back to 'usual haunt' in less than 20 hours. We have no idea what brought on the erratic behaviors, but it's nice to document.

Other Endeavors
After delays due to the holidays, trapping schedule and weather, we are finally beginning to map the channels and elevations of the marsh using a Leica SmartPole GPS unit. This is going to be a large, time consumptive endeavor, and I'll provide updates as we figure out the details and an appropriate field protocol.

Field Notes - December 4, 2007

We currently have over 5700 locations. These are for the 32 originally radio-marked birds, plus 6 newly marked birds. We currently have a total of 19 active radios deployed in our three field sites.

Trapping this season has been drastically different from last January-March. Last season we spent a lot of time and effort to trap birds at Colma Creek by hand or in nets while using a boat during the high tide events. In contrast, trapping at Laumeister and Cogswell was relatively easy using drop-door traps during the low tides. This season, however, those trends have flipped entirely. Over 6 full days of trapping at Laumeister, we caught 1 new female, while last year we would have expected to have caught at least 5 during that time period. Then, 2 very short days spent at really high tide at Colma yielded 6 birds!!! In the past, we felt fortunate if we caught 1 in a day. Of those 6 birds, 5 are new (3 males, 2 females) and the remaining female was a recapture of an original study bird whose radio failed in October. We are very happy to have her back and actively marked again.

Colma Creek
We have a full 10 active radios at Colma Creek (5 males, 5 females), which is our target sample size per marsh. The 5 originally marked birds are behaving as they have over the last 11 months, and we're just getting to know the new 5 birds. The 10 birds are spread pretty evenly throughout the entire site. It will interesting to see any geographic differences in movement patterns through the winter.

Laumeister
3 active marked birds remain at Laumeister (1 male, 2 females). We were up to 4 for the week after we caught the new female, but then one of our remaining males was depredated by a cat (best guess). The remaining original 2 birds are acting as usual, and the new female is moving a lot around the northern ¼ of the marsh.

Cogswell Marsh
6 active radios remain at Cogswell (4 males, 2 females). Nothing new to report from this marsh-everything has been holding constant to last month.

Other Endeavors
Trapping continues to bring us up to the intended sample size of 10 birds per marsh. We need 7 more at Laumeister and 4 more at Cogswell. Additionally, we are also attempting to recapture all original birds so that we can replace their radios with new ones to carry them through next year.

We are also beginning to map the channels and elevations of the marsh using a Leica SmartPole GPS unit. This is going to be a large, time consumptive endeavor, and I'll provide updates as we figure out the details and an appropriate field protocol.

Field Notes - November 1, 2007

We currently have over 5200 locations for the 32 originally radio-marked birds. 13 birds remain in the study with active radios. We have been able to directly observe and confirm some radio failures, which helps explain some of the mystery disappearances from the study earlier in the year. It appears that the first batch of radios we deployed are failing fairly rapidly, and all of the mystery disappearances earlier in the year were of the same radio batch. We now have 4 cases of confirmed radio failures, either because the bird has later been found with a non-transmitting radio, or the signal dropped quickly over a couple days and then ceased.

Colma Creek
4 active radios remain at Colma Creek (2 males, 2 females). All birds are behaving similarly to how they have over the last 9 months. We lost 1 female from the study at this site due to observed radio failure.

Laumeister
3 active marked birds remain at Laumeister (2 males, 1 female), and all are being found in similar locations as those from the last month. 3 birds (2 males, 1 female) were lost from the study, all due initially to radio failures. The female's radio transmitted intermittently for a couple days and then failed completely. The radio of 1 male ceased suddenly without warning, but that bird was found 3 weeks later having been depredated within a few days. The other male's radio began transmitting a solid, unwavering tone (instead of beeping), and then was found predated by a mammal. A week later that radio died completely (in the lab).

Cogswell Marsh
6 active radios remain at Cogswell (4 males, 2 females). We suspect that two of these radios are beginning to fail... hopefully they can hold out as long as possible. One of the suspected failing radios is on a female that is currently using a portion of the marsh over 1 km from her core area during the breeding season. I especially hope that her radio holds out so we can see where she moves to next.

Other Endeavors
Vegetation sampling is almost completed, and trapping is underway. After 5 days of trapping using the drop-door traps at Laumeister, we have yet to catch a bird. This is extremely different from our experience trapping with this method in January and February, when we caught at least one bird per day. We are trying to figure out if there is simply a seasonal difference in marsh use by the rails or if there may be other behavioral differences causing our lack of trapping success. One theory is that birds could be much more congregated in the native Spartina bank on the bay edge, leaving the rest of the marsh (where we can trap) less densely populated. We may be able to see how this changes over the next month since the Spartina bank is actively dying and being washed away as wrack with the tides. Hopefully we will back up to 10 birds radio-marked in each marsh soon.

Field Notes - September 29, 2007

We currently have over 4860 locations for the 32 birds that were originally radio-marked. Clapper rails in general are very vocal and active in all sites. 17 birds remain in the study with active radios.

Colma Creek
5 active radios remain at Colma Creek. All birds are behaving similarly to how they have over the last 9 months.

Laumeister
6 active marked birds remain at Laumeister, and all are being found in similar locations as those from the last month. 3 birds continue to focus their time on the bay edge in the native Spartina bank, though as senescence is kicking in, it will be interesting to see where these birds move to once their vegetative cover dies off and disappears.

Cogswell Marsh
6 active radios remain at Cogswell (4 males, 2 females). Two birds are no longer a part of the tracking study, one due to mammalian predation, and the other because a harness was removed. Both of these birds have provided some very insightful information, however-

The carcass of the predated male was in mid molt, and we were able to document that Clapper Rails undergo a simultaneous flight molt. This type of molt has been suspected of all Rallids, but has rarely been documented and never (as far as we can find) for California Clapper Rails. This means that they undergo a period of about 3 weeks of flightlessness. They are possibly only slightly more vulnerable to predation during this period, since they rely on running and hiding much more than flushing/flying, but it could still have important ramifications on activity and movement patterns.

The female whose radio harness was removed was found submarining with only the top of her head exposed at eye level, with her bill out of water to breathe. She was on an inundated channel shelf during a very high tide event in a pickleweed plain with little available overstory vegetative cover. She was non-responsive and taken to International Bird Rescue Center in Cordelia, and by arrival time, was fully active and alert again. The IBRC ran tests and deemed her in full health, and the bird was released without a radio exactly 48 hours later. Although a couple scenarios could explain her non-responsiveness, it seems that she may have been in a torpor state to wait out the high tide, using the water as her cover from potential predators. We will be investigating bird responses to high tides to see if this is a common practice or if this was an anomaly.

Cogswell has also been turning up some nice migratory birds. In addition to the tons of 'usual' shorebird and waterfowl migrants, semi-rarities like Black Tern and Wandering Tattlers have also been spotted. : )

Other Endeavors
Vegetation sampling for all "bird-use" points has been completed, and we are now commencing on sampling "non-use" points in close proximity to core bird use areas. Beginning in December, we will start mapping the channels of the marsh to get an idea of how these potentially affect rail movements and home range configuration.

Additionally, we plan to begin trapping again in October to bring the sample size back up to 10 birds per marsh.

Field Notes - August 30, 2007

We currently have over 4500 locations for the 32 birds that were originally radio-marked. In all sites, especially Cogswell and Laumeister, birds have become much more vocal again after 2 months of relative silence. It's interesting to see the differences in behavior through the seasons, and I can't help but wonder if the birds were quiet post-breeding (and possibly chick-rearing), and are now reestablishing themselves and reacquainting themselves with each other.

Colma Creek
5 active radios remain at Colma Creek. The latest radio loss was of a male rail who mostly hung out on the island. We lost signal at the end of the first week of August, and have yet to relocate the bird. He may have dispersed, but we do not yet have information to substantiate this. We have a bay-wide flight scheduled to search for his frequency, and hopefully we can document another movement (from the same marsh) like the male that dispersed to Marin County. Time will tell.

The remaining 5 birds (3 females, 2 males) have been using their typical areas.

Laumeister
6 active marked birds remain at Laumeister, and some strong movements have been observed with more consistency. There are now three birds (2 males, 1 female) that are regularly using the native Spartina foliosa bank on the bay edge. One of those birds has moved over 200 meters from the marsh interior to now inhabit the native cordgrass bank along the bay edge. Noticeably, many other unmarked rails are also using the cordgrass bank and calling regularly.

On another note, at high tide bat rays and leopard sharks have been seen regularly working the bay edge. On August 20th, a school of three dozen leopard sharks were patrolling the area.

Cogswell Marsh
8 marked birds remain active at Cogswell. This marsh has shown some interesting movements throughout the study, including several 300+ meter daily movements in the past. Currently, a female that has previously been very constant in her core area in the southwestern portion of the marsh shifted over 300 meters to a more central portion of the marsh. In the last few days, she has been found over 500 meters north of her most recent locations for a cumulative 800+ meter movement over a week. I'm looking forward to seeing where she settles, as well as when she finally settles again.

Current Endeavors
In addition to tracking the birds on a regular basis, we are also sampling the vegetation to get an idea of how the plant structure affects birds' movements. This will be an ongoing process over the next month, and will be repeated again in the winter to better understand seasonal impacts of vegetative structure on rail movement patterns.

Field Notes - August 8, 2007

All in all not much has changed since the last update. All birds remain healthily active at all sites leaving us with 20 active radios. Laumeister and Colma each have 6, while Cogswell has 8 marked birds remaining. We currently have over 4,300 locations for marled rails.

The Invasive Spartina Project completed its herbicidal treatment at both Cogswell and Colma last week. Laumeister was not treated, since it has only minimal invasion by non-native cordgrass. It will be interesting to see if any movement patterns shift at the treated sites.

In other news, we have begun sampling for vegetation in the marshes to get at the question of preferential habitat use by the rails. Hopefully we'll be able to get this round of summer vegetation sampling completed in August, and then have a winter counterpart completed in January or February.

Lastly, fall migration has certainly begun. 100's of phalaropes (Wilson's and Red-necked) have been showing up, joined by waves of peeps and other shorebirds. The Least Terns at Cogswell have mostly completed their breeding cycle, and fledglings and adults are still around in good numbers.

Field Notes - July 12, 2007 We currently have 3800 locations for the 32 birds that were originally radio-marked.

Colma Creek
6 active radios remain at Colma Creek. One bird, the first bird fitted with a radio for the entire project, was found depredated on 5/27/2007.

Although chicks have been seen with adults along the mudflats, no evidence for breeding by study birds has been detected, despite a very obvious pair bond between one marked male and female.

Laumeister
6 active radios also remain at Laumeister. The most recent loss was of a male whose transmitter was found within an active northern harrier nest (with 1 chick) in the southeastern corner of the marsh. Maybe not so coincidentally, the only other 2 predations that have occurred in this marsh have been in the same general area.

Some interesting movements have been observed within the last couple weeks as the native Spartina has matured on the Bay edge of the marsh. Birds have been recently recorded using this area with consistency, where prior to the Spartina growth, no rails had been observed.

Cogswell Marsh
Cogswell currently is in the lead with 8 active transmitters remaining in the marsh. All birds seem to be moving consistently, and two birds have shown fairly dramatic shifts (greater than 200 meter change) in their core areas of use.

On another note, the least terns that are breeding just south of this site have been increasingly active, fishing in the channels to feed their young. It always provides some nice entertainment on slow days.

Marin Bird
Unfortunately, after wearing his radio for 6 months, traveling 28 miles to the north (from Colma Creek to north of San Rafael), and then being observed healthily going about his way in his new marsh, this radio was recovered on 6/23/2007. The harness was fully intact and in good condition with no signs of the bird. No signs of predation were detected, and so it is likely this bird slipped its harness.

Field Notes - May 17, 2007

Colma Creek
In the beginning of March, when full tracking began, we had 9 birds marked at Colma Creek marsh, with 7 radios still active within the site. Of biggest note, we had two neighboring males disappear without a trace within days of each other at the beginning of April, which remained unexplained until 5/17/2007. One of these birds has now been found alive and well in Marin, approximately 28 miles north of his trapping location; A very exciting movement to document. Otherwise, the remaining birds are behaving 'normally,' with breeding calls and copulation still being detected regularly. No nests have been found.

Laumeister
10 birds were marked at Laumeister Marsh, 8 of which are still active. Breeding calls are still heard daily, and one depredated nest (random bird) has been found. No nests have been found for marked birds.

Cogswell Marsh
10 birds were marked at Cogswell Marsh, all of which are still active.
Of note, two nests have been found for marked birds, one with eggs and one empty, but presumably in construction. Also of note, one of the males in the southeastern corner of the marsh abandoned his old, regular territory and remained for one week 300 meters to the southwest. Then he moved again, and has been occupying and area that is another 400 meters to the northeast, for a total of about 700 meters of cumulative movement in the last couple weeks. All other birds seem to be occupying fairly small areas.

Field Notes for 5/4/07

We started trapping in January of 2007 and were able to capture and mark rails at three study sites by the end of February. We are currently tracking 26 clapper rails in three different marshes. At Colma Creek Marsh we originally marked 9 individual rails. We are currently tracking 7 individuals there as two marked rails have not been found for several weeks. This may be due to radio-failure but since the birds were often located in close proximity to one another, we surmise that they were taken by a predator. We are still tracking 10 birds at Cogswell Marsh with one found incubating 8 eggs on Tuesday, May 1. We are currently tracking 9 out of 10 birds originally marked at Laumeister Marsh. We recovered one mortality on May 2, most likely caused by an avian predator.