Fig 1.
Refugio oil spill site and distribution of post-spill pelican field sightings.
Locations of Refugio spill green banded pelican sightings from August 2015 through November 2016 are shown (N = 190 sightings). North and south limits of field surveys are indicated by triangles. Base map credit: Esri, HERE, Garmin, OpenStreetMap contributors, and the GIS users community.
Fig 2.
Configuration of GPS-PTT tags on brown pelicans observed in the field.
Dorsal (A) and ventral (B) views shown on Z11, 17 March 2016, after about 9 months of wearing the equipment.
Fig 3.
California brown pelican crown and nape index scoring system.
The scores shown were the numbers used for the crown and neck molt indices (CMI and NMI).
Fig 4.
California brown pelican gular pouch scoring system.
The gular redness index (GRI) was based primarily on extent of red; other characteristics that typically accompany each score are also included here.
Fig 5.
Field encounters of post-spill brown pelicans by season (2015–2016).
Data are separated for previously oiled birds released with only leg bands (BAND), equipped with GPS-PTT transmitters (PTT) and birds that shed transmitters but retained bands (PTT LOST). N = 190 sightings of 33 individual post spill birds of all ages.
Fig 6.
Crown scores compared for non-oiled and oiled pelicans, showing monthly mean and standard deviation.
The oiled group includes pelicans released with band-only and GPS-PTT tags (N = 21). The non-oiled group includes only unmarked pelicans (N = 135) and does not include pelicans bearing PTT tags. Data are from September 15-December 15, 2015. Statistical analysis results are presented in Table 1.
Table 1.
Results of generalized loglinear analysis of crown molt showing interaction terms.
Fig 7.
Hindneck scores compared for non-oiled and oiled pelicans, showing monthly mean and standard deviation.
The oiled group includes pelicans released with band-only and GPS-PTT tags (N = 21). The non-oiled group includes only unmarked pelicans (N = 135) and does not include pelicans bearing GPS-PTT tags. Data are from September 15-December 15, 2015. Differences in neck molt between groups were not significant according to loglinear analysis (see text).
Fig 8.
Mid-November brown pelican plumage aspect comparison, lagged versus typical.
This example shows lagged molt of a post-spill bird carrying a GPS-PTT tag photographed 6 months after the spill (A) versus seasonally typical molt status in a post-spill bird marked with band-only, photographed 18 months after the spill (B).
Fig 9.
Gular redness scores for non-oiled, previously oiled, and non-oiled GPS-PTT bearing pelicans.
Shown are medians, quartiles, and outliers across months. Sample sizes are as follows: non-oiled (N = 135), oiled (N = 17), non-oiled with GPS-PTT (N = 9). Data are from September 15, 2015-March 21, 2016.
Table 2.
Results of generalized loglinear analysis of gular pouch redness with interaction terms shown.
Table 3.
Distribution of gular redness scores, separating the effects of previous oiling and wearing electronic tags for loglinear modeling.
Fig 10.
Gular pouch redness index and number of days that previously oiled pelicans were known to survive post-release.
Gular redness index (GRI) is the highest score observed in the field (0–3) in the first 18 months after oil contamination; ‘Survive’ is the number of days elapsed between the last sighting of the bird and its release date following rehabilitation. All data (N = 16) are from ATY pelicans. GRI and the survival index were positively correlated (S = 138.7, rS = 0.796, p = 0.0002).