2015 Western Sandpiper Survey Update
3 years of counting
As 2015 draws to a close I wanted to thank you all for your hard work in this year and in previous years. We have asked a lot of you in methodology and in time. David Bradley at Bird Studies Canada, Ron Ydenberg at Simon Fraser University and I thank you very much for your continuing support. Without you this project would not exist and with you, we have been much more successful than we had originally envisioned. We will be conducting a final season of surveys in 2016, if you’re interested in potentially surveying again, you can sign up at the project webpage.
We have a project update in Bird Study Canada’s Coastal Programs newsletter and I have some more specific results for each of the survey regions below. More results will come in the next few months and I will update the webpage as they come in.
Once again, thank you all. It has been a very successful three years and they have already provided us with some fascinating preliminary results.
Sincerely,
WESA foraging in Tofino
A note about the graphs; they are all in colour, but if you click on the image it will take you to a greyscale image.
Results overview
The surveys showed us that juveniles are making use of a wider distribution of sties, while the adults tend to congregate primarily at the largest sites. The pattern across sites varied between years, possibly due to timing of peregrine migration.
Over the past three years we had over 105 groups of observers conduct 450 surveys at 40 sites. Over 500 000 birds were recorded, everywhere from ponds to lagoons, to river deltas.
As mentioned in BSC’s Coastal newsletter, the number of birds counted varied substantially each year. More surprisingly, between years the distribution of the birds across all the sites shifted based on site size. The figure below outlines the shift in total numbers and the shift between large, medium and small sites. In 2013, overall numbers were very low, especially during the adult migration. As those of you who surveyed that year can attest to, surveying when numbers were so low, can be demoralizing. However, the distribution across site sizes, remained similar to the following two years. Thus even in the low abundance years, the data from surveys can provide useful information about the sandpiper population. Of note, the number of juveniles counted has increased in the three years of study, while the number of adults has not.
Our work focuses primarily on the distribution of sandpipers across sitea, not their total numbers. If you look at part A of the graph, you see that a greater proportion of juvenile sandpipers are making use of the smallest sites, while adults tend to be found almost entirely at the large and medium sites. This distribution changed during the years we have been surveying, and appears to shift towards larger, safer sites in 2014. 2014 was also a year of early snow melt in Alaska, which has been established as the primary factor that leads to earlier migration of peregrine falcons. While the results are preliminary, it does lend support to the idea that migrating sandpipers’ behaviour is sensitive to conditions experience on migration.
Regional Summary
So, where were the birds we observed? To examine this I assigned each site to one of the following regions:
- Eastern Vancouver Island (EVanIs)
- Fraser River Delta, and Lower Mainland (FRD)
- Malcom Island (Malc)
- Puget Sound (Puget)
- Southern Vancouver Island and Gulf Islands (SVanIs)
- Tofino Mudflats (Tofino)
The regions are based on geographic proximity, despite being often a hundred kilometres or more apart, they group together more than with other sites. The figure below shows how each year’s counts breakdown by region. The two regions that are consistently important are the Fraser River Delta and Puget Sound. This isn’t surprising as they hold the largest mudflats. Tofino and southern Vancouver Island appear to be more heavily used during juvenile migration than adult migration, though this also varies by year. Interestingly, eastern Vancouver Island is consistently avoided by adult sandpipers.
Regional Breakdown
1. Eastern Vancouver Island
While this region is fortunate to have many survey sites, the numbers are very low in adult migration across all sites. In the juvenile migration, birds visited Comox Harbour regularly and Cowichan Bay and San Malo Bay with less regularity. The contrast here between the two age classes is dramatic and very intriguing.
Cowichan Bay will be an important site to watch as it’s hydrology will change with the recent addition of a culvert to allow water movement between the two sites of the dyke that divides the bay.
2. Fraser River Delta, and Lower Mainland
As expected the sites at Boundary Bay and Roberts Bank dominate this region. That said, the numbers counted at Boundary Bay were quite low in 2013 and 2015. This could have been a result of timing, tides or weather, but could also be indicative of site usage by birds. Roberts Bank is consistently well used, as is the outflow near 92nd Street. Low usage at Iona Island remains an striking comparison with Roberts Bank. The distribution across the region is very inconsistent between years, perhaps as a result of patches of high food abundance within the large expansive mudflats.
3. Malcom Island
Malcom Island is an outlier compared with the other sites, lying north of all other sites. Nonetheless, it has regular usage, with higher numbers in the juvenile migration.
4. Puget Sound
Puget Sound is a large and diverse region, and we could recreate the study just within this region. However, the sites you have surveyed have shown themselves to be very unique. The Eide Road ponds near Stanwood have had several thousand birds counted there, despite being just over a hectare in size and surrounded by low cover. The dykes in this location are being removed in the next few years and the data collected here will provide a good baseline for monitoring.
Crockett Lake has also provided good numbers. As a saline lake, it likely collects birds at high tide as Eide Rd. does.
Kennedy Creek is another outlier, being much further south than the other sites, but saw good numbers of juveniles in 2014 and 2015.
5. Southern Vancouver Island and Gulf Islands
The southern Vancouver Island region holds many small sites that are used regularly. This use is masked somewhat by the relatively large numbers that visit Sidney Island. However, as we saw in 2015, sites that had previously only had extremely low usage, such as View Royal, saw birds in good numbers. This region does attract a larger proportion of LESA, so these numbers will change as the analysis progresses. The results do highlight the importance of small sites that may be used intermittently.
6. Tofino Mudflats
The Tofino mudflats remain one of the last relatively intact and undisturbed mudflat complexes remaining in the study region. It has been a treat to be able to survey there these past few years. Usage has remained relatively low during the adult migration, but this August saw extremely large flocks making use of the Jensen’s Bay flats.
Why a fourth season?
When we started the project, we had hoped to be able to conduct three seasons and come out with a strong result. Through your hard work, we have three years of strong data. The variance in conditions between years increases the likelihood that we can develop a distinctive ‘fingerprint’ of sandpiper usage under different scenarios. The aim was always to develop a protocol whereby migrant populations can be quickly assessed and identified as a population that requires further monitoring. To develop the ‘leading indicator’ we need as many years, with as much variation as possible in order to test the strength of the indicator’s predictions. Three years is the absolute minimum for such a process and a fourth year will ensure the previous three years survey effort is not lost in an ambiguous result.
I recognize a fourth year requires a great deal of effort from you, our volunteers. The project has asked a lot of you, our surveyors, and you have accomplished so much already, but if you are willing, a fourth year will ensure we can develop a strong leading indicator of the Western Sandpiper population and hopefully a protocol for implementing the indicator for other populations.
If you are interested in signing up, you can do so here: www.sfu.ca/~dhope/volunter.html
Thank you again for your hard work. Have a great winter, and I will speak to you as the birds return.
Disclaimer
As I mention above, the results here are very preliminary. For example, I have not accounted for LESA yet, and have not included site size estimates in these results. It is likely the results will change as the covariates are taken into account. In addition the model of migratory behaviour has yet to be confronted by the data, so we cannot yet gauge the support for a particular scenario of population status.
Stay tuned, as more results are soon to come.