Peggy Pei-Wen Yen Undergraduate Researcher


Point Reyes Bird Observatory

4990 Shoreline Highway Stinson Beach, California 94970>




I completed my B.Sc. Honors in Ecology at Simon Fraser University. The past four years were made all the more interesting thanks to the invaluable guidance of many people at the Centre for Wildlife Ecology as well as the support of my ever-patient family. The opportunity to work on many of the projects in the CWE gave me many different perspectives and interesting approaches to behavioral ecology and conservation biology.


Projects Currently Studied:



Marbled Murrelet


Photo: Laura McFarlane Tranquilla

A large-scale model for the at-sea distribution of Marbled Murrelets (Brachyramphus marmoratus) for the breeding season in coastal British Columbia, Canada

P. Yen, F. Huettmann, and F. Cooke

Abstract The role that the marine environment plays in the distribution and abundance of Marbled Murrelets (Brachyramphus marmoratus) during the breeding season is not well understood. It was investigated how Marbled Murrelet marine distribution and abundance is affected by the abiotic and biotic components of the marine environment. Data on the marine distribution of Marbled Murrelets, in British Columbia (BC); densities (birds/km2), counts (no. of birds), and the pertinent environmental variables as identified from literature were compiled and then organized in a Geographic Information System (GIS, Arcview). Count surveys were found to be negatively correlated with density surveys signaling care to be used when interpreting the count data. First, significant predictors were identified with GLM (Generalized Linear Models) by evaluating their shortest distances from survey locations to the predictors and overlays in a multivariate scenario. Model predictors selected by using AIC and P values include sea surface temperature, herring spawn index, estuary locations, distribution of sand and fine gravel substrates (proxy for sand lance distribution), and proximity to glaciers. Second, spatially explicit large-scale distribution model algorithms uses this set of significant predictors to predict Marbled Murrelet abundance and distribution in coastal British Columbia (BC). The modelling algorithms used include GLM, Classification and Regression Trees (Tree from S-PLUS and CART from Salford System and Breiman et al. 1984), Multivariate Adaptive Regression Splines (MARS, Salford Systems), and Neural Networks (NNet, Venables and Ripley 1997). Model performances were evaluated by bootstrapping, and standardizing models. Using density of Marbled Murrelets, Tree was identified as the best performing model and therefore used to predict maximum carrying capacities for the marine habitat of BC. The remaining varianc e of the model was explained with shortest distance to old-growth forest, which led to the hypothesis of how the Marbled Murrelet distribution and abundance relates to proximity to old-growth forests.


A multiscale GIS model combining terrestrial and marine habitat for breeding Marbled Murrelets

P. Yen and F. Huettmann

We are further adding and expanding on the previous model (see above) by including biologically relevant terrestrial and marine habitat that may determine Marbled Murrelet abundance and distribution. Spatial modeling will be applied at various scales using ŽbinsČ to better capture the large-scale effect. We hope to better the understanding of their little-known marine foraging habitats in relation to the terrestrial nesting habitat during the breeding season. The compilation of survey data (densities, occupied detections and nest locations) will serve as the dependent variables for three different models to compare the validity of relying on only one aspect of MaMu biology.



Western Sandpiper



Photo: Guillermo J. Fernandez Aceves

The effect of Ultraviolet Radiation on Primary Flight Feathers of Western Sandpipers (Calidris mauri): an Unappreciated Cost of Long Distance Migration

P. Yen, P. O'Hara, D. Lank

Abstract Feather wear due to ultraviolet radiation may potentially present an additional cost to Western Sandpipers (Calidris mauri) that migrate to a southerly locality for the winter. Ultraviolet radiation has been known to degrade keratin, a fibrous protein molecule that is the main structural material in feathers which results in feather wear. Birds wintering farther south, closer to the equator, potentially have a faster rate of feather degradation due to an increase in UVR intensity, but may live in a more benign– site in other respects. Western Sandpiper 9th primary feathers were collected from wintering sites in Punta Banda, Mexico (31Ń52– N, 116Ń37– W), Bahia de Santa Maria, Mexico (25Ń00– N, 108Ń00– W), Panama (8Ń0– N, 80Ń50– W) and a stopover site in the Fraser River Delta, Canada (49Ń07' N, 123Ń11– W) and their wear due to ultraviolet radiation (UVR) evaluated. There are two major UVR costs associated with migrating further south, ( 1) the additional primary feather wear resulting from the prolonged flight, and (2) the additional wear incurred as a result of remaining on a more southern wintering location that receives relatively stronger UVR intensity. The wear due to UVR is isolated as the differential wear between the outer vane, which is exposed to UVR, and the inner vane, which is shaded by the adjacent outer vane. The juveniles grow their primaries on the breeding ground and so their 9th primary is used to look at the cost due to prolonged flight. Their primary differential wear was compared between the three sites and was found to vary with time (p=0.0018), and between countries (p=0.0007). The adults moult their primaries on the wintering ground and their 9th primary differential wear was used in examining the cost of wintering further south. When the adult differential wear was compared between Panama and Mexico with a latitudinal difference of 24 degrees, the differential wear varied significantly with time (p=0.005) but does n ot vary between the two countries. This is most likely due to an insufficient sample size since a trend does exist. In addition to UVR, other covarying factors are considered, such as differential pigmentation, the mechanics of flight, and environmental elements, that may also contribute to wear.


Latitudinal variation in Feather Pigmentation in Western Sandpipers

This study is a continuation of the notion birds accumulates an increasing amount of feather wear the closer to the equator they winter. It has been suggested that the darkness of feathers be dictated in part to the level of ultraviolet radiation intensity the feathers are exposed to. Melanin, a dark pigment found in feathers, not only provides bird with dark, cryptic plumages, it also increases abrasion resistance and hence decreases the amount of wear in feathers. For this reason, the primaries of many colorful passerines remain black due to the durability it imparts upon them.

The measure of the 9th primary feather darkness from birds wintering in three latitudinally distinct sites can be applied to the phenomena of differential migration in Western Sandpipers. Birds wintering further south can benefit from darker feathers to compensate for wear from both mechanical (migration) and the greater UVR intensity.




Yen, P., P. OČHara, (2001) The effect of ultraviolet radiation on primary flight feathers of Western Sandpipers (Calidris mauri): An unappreciated cost of long distance migration. Presented at the meeting of the 20th Annual meeting of American OrnithologistsČ Union, University of Washington, Seattle, Washington.

Yen, P., F. Huettmann, and F. Cooke, (2001) A large-scale model for the at-sea distribution of Marbled Murrelets (Brachyramphus marmoratus) in coastal British Columbia, Canada. Presented at the meeting of the Pacific Seabird Group, Kuaii, Hawaii.

Yen, P., P. OČHara, (2000) Geographical comparison of ultraviolet radiation wear in primary flight feathers in Western Sandpipers. Presented at the 6th Western Sandpiper Workshop, Center for Wildlife Ecology, Simon Fraser University, Vancouver, BC.



Yen, P., F. Huettmann, and F. Cooke, (submitted to Ecological Modeling.) A large-scale model for the at-sea distribution of Marbled Murrelets (Brachyramphus marmoratus) in coastal British Columbia, Canada.

Yen, P., P. OČHara, (MS in prep.) Geographical comparison of ultraviolet radiation wear in primary flight feathers in Western Sandpipers

O'Hara, P., P. Yen, B Haase, FS Delgado, DB Lank. (MS in prep). Primary feather wear as a cost of migrating to different latitudes for the winter.