Changes in Waterbird Numbers Before and After the 1983 Oil Spill at Yaquina Estuary, Oregon

As published in: Bayer, R. D. 1988. Changes in Waterbird Numbers Before and After the 1983 Oil Spill at Yaquina Estuary, Oregon. Oregon Birds 14(2):157-161.

(I thank Owen Schmidt, Oregon Birds editor, for his assistance in preparing the original article and this web page.)

During a heavy storm on the night of 19 November 1983, the "Blue Magpie," a 350-foot general cargo freighter, slammed into the ocean side of the north jetty (Fig. 1) as it tried to enter Yaquina Estuary. The fuel tanks of the freighter ruptured, releasing as much as 60,000 gallons of "bunker C" oil within 5 days and 10,000 gallons of diesel fuel within the first 3 days after the wreck (Rosemary 1983a, Sleeth 1983).

More than 8,000 gallons of bunker oil were skimmed from Yaquina Estuary (Rosemary 1983b), but the total amount that entered the Yaquina is unknown. Most of the bunker oil and diesel was thought to have been carried out to sea by winds and wave action, but pockets of oil were still found in Yaquina Bay in mid-December (Anonymous 1983). Bunker oil was found at the estuary mouth, at embayments, and more than 5 miles upstream to Coquille Point (Monroe 1983, Sleeth 1983)(see Fig. 1).

Oil and oiled birds were found not only in Yaquina Estuary but also along the coastline, perhaps as far as 100 miles to the north (Rosemary 1983a). As of 30 November 1983, a total of 365 oiled birds had been found at Yaquina Estuary and at adjacent beaches; 248 were found dead and another 28 died while they were being held to be cleaned (Rosemary 1983b). Thirty-two of the oiled birds were Brown Pelicans, at least 7 of which died (Monroe 1983). Many of the pelicans were emaciated before the oil spill, probably because of poor feeding conditions associated with the 1983 El Nino (Snow 1983). Many other birds may have been oiled but were not recorded because they sank (see Speich and Thompson 1987), were not reported to oil spill coordinators, or were swept out to sea.

When an oil spill occurs, it would be worthwhile to know how many birds are present and likely to be affected. Although numbers of oiled birds have been tallied for several Pacific Northwest oil spills (Speich and Thompson 1987, and references therein), I have been unable to find any references to an oil spill where the number of birds in the affected area was known before the oil spill and also shortly afterward.

In the case of the "Blue Magpie" oil spill, I had by chance conducted a census the day before the wreck (Table 1). I had also made 2 other censuses within 21 days before the wreck and 4 censuses within 22 days after the wreck (Table 1). I minimized the possibility of recounting birds by counting during a single, continuous sweep with a 20x telescope only when glare, heat waves, and water conditions did not obscure birds. All these censuses were at the embayments shown in Fig. 1.

Counts of some birds remained relatively unchanged after the oil spill, but the numbers of Pied-billed Grebes, Western Grebes, Brown Pelicans, dabbling ducks, coots, and total waterbirds declined significantly (Table 1). The average number of scaup and scoters also declined an average of 187 birds and 59 birds, respectively, after the wreck, but these declines were not statistically significant, perhaps because there were too few censuses. In contrast, Canvasbacks, Black Brant, Common Goldeneye, and Ruddy Duck numbers increased significantly (Table 1).

It would be easy to jump to the conclusion that the oil spill influenced bird numbers. Insurance adjusters for the freighter might argue that the oil actually helped increase bird numbers, while environmentalists could argue that several bird species decreased in response to the oil.

In fact, the effect, if any, of the oil spill on Yaquina Estuary bird numbers is impossible to separate from normal fall migration or lingering effects of the 1983 El Nino. The marked decrease of Western Grebes is consistent with the late fall decrease of Western Grebes at Yaquina embayments documented in 1980 (Bayer 1983:82). Similarly, the decline in Pied-billed Grebes, pelicans, and dabbling ducks is consistent with a late fall decrease in the numbers of these birds in other years at Yaquina embayments (unpubl. data).

The increase in Brant after the oil spill is concurrent with their normal fall increase at the Yaquina (Bayer 1983). Canvasbacks, Common Goldeneyes, and Ruddy Ducks also normally increase in numbers at Yaquina Bay in mid- to late November (unpubl. data).

The only species that changed in numbers differently at embayments in 1983 compared to other years was the American Coot, which decreased significantly after the oil spill (Table 1). In 1982 and 1984, over 275 coots were still counted in mid-December (unpubl. data), but there were less than 30 in 1983 after the oil spill (Table 1). Nevertheless, it is not possible to ascribe the abnormal coot decrease after the oil spill to the effects of oil because the coots may have also been negatively influenced by the 1983 El Nino, which effected many other bird species along the Oregon Coast (Snow 1983, Bayer 1984, 1985, 1986a, 1986b; Hodder and Graybill 1985). Further, the decrease may also have resulted from increased human activity in embayment areas to clean up the oil spill or from yearly variation in the timing of coot fall emigration.

In conclusion, I was fortunate enough to be able to make censuses before and after an oil spill. However, even with these censuses, it is not possible to conclusively determine whether bird numbers changed in response to the oil spill, or if bird numbers just continued to change as they normally would with migration. The censuses simply allow one to estimate how many birds may be susceptible to being oiled, not how bird numbers were influenced by oil.

Although I continued to make censuses after those given in Table 1, determining longer term changes in bird numbers as a result of the oil spill is also tenuous because even more emigration and immigration occurs, the lingering effects of El Nino may also be important, and the 1983-1984 winter was abnormally cold at the Yaquina Estuary.

I am grateful to Mark Stern and Paul Sullivan for reviewing the manuscript.


Anonymous. 1983. More oil cleaned up. News-Times (Newport, Oregon newspaper). Dec. 28, p. A-10, col. 1.

Bayer, R. D. 1983. Seasonal occurrences of ten waterbird species at Yaquina Estuary, Oregon. Murrelet 64:78-86.

Bayer, R. D. 1984. Oversummering of Whimbrels, Bonaparte's Gulls, and Caspian Terns at Yaquina Estuary, Oregon. Murrelet 65:87-90.

Bayer, R. D. 1985. Nearshore flights of seabirds past Yaquina Estuary, Oregon, during the 1982 and 1983 summers. Western Birds 16:169-173.

Bayer, R. D. 1986a. Breeding success of seabirds along the mid-Oregon Coast concurrent with the 1983 El Nino. Murrelet 67:23-26.

Bayer, R. D. 1986b. Seabirds near an Oregon estuarine salmon hatchery in 1982 and during the 1983 El Nino. Fishery Bulletin 84:279-286.

Hodder, J. and M. R. Graybill. 1985. Reproduction and survival of seabirds in Oregon during the 1982-1983 El Nino. Condor 87:535-541.

Monroe, B. 1983. Oil ring-around-the-bathtub doesn't preclude fishing, crabbing. Oregonian (Portland, Oregon newspaper). Nov. 27, p. E-10, col. 1.

Rosemary, K. 1983a. 100-mile shoreline watch for freighter oil continuing. Oregonian (Portland, Oregon newspaper). Nov. 28, p. B-1, col. 2.

Rosemary, K. 1983b. Oil spill cleanup sticks crew with surprise. Oregonian (Portland, Oregon newspaper). Nov. 30, p. C-3, col. 1.

Sleeth, P. 1983. Ship's oil tanks will be allowed to drain. News-Times (Newport, Oregon newspaper). Nov. 25, p. A-1, col. 1.

Snow, C. D. 1983. Thanks Oregonians! Oregon Wildlife 38(12):6.

Speich, S. M. and S. P. Thompson. 1987. Impacts on waterbirds from the 1984 Columbia River and Whidbey Island, Washington, oil spills. Western Birds 18:109-116.

TABLE 1. Number of waterbirds at embayments of Yaquina Estuary within 22 days of the 19 November 1983 oil spill. Embayments censused are shown in Fig. 1. The only waterbirds censused that are not included below are Double-crested Cormorants and gulls (see footnote c); shorebirds were also not censused. PSTime is the time at the start of a census by the 24 hour clock (i.e., 1 PM=1300). Censuses took about 35-100 min, depending upon how many birds were present. LoTime is the time at the start of a census relative to the time of the nearest low tide measured at the Marine Science Center dock shown in Fig. 1 (i.e., a LoTime of +1.3 means that a census started 1.3 hr after the time of low tide). Net Change in Means=(Post-oil mean)-(pre-oil mean). P=probability (which was calculated with the Mann-Whitney test), NS=Not statistically Significant, *=two-tailed P<0.10.

Double-crested Cormorants and gulls were present but are not included here because their numbers are reduced at these embayments near high tides, so the two post-oil censuses more than 3.5 hr from low tide are not comparable to other censuses.

               Before Oil Spill_____  After Oil Spill____________  Net
Date           10/29 11/5 11/18       11/24 11/26 11/29 12/6       Change
PSTime          1343 0802  1355        1305  1019  1348 1320       in
LoTime          +1.3 +2.3  -3.1 Mean   +4.5  -0.7  -0.4 +6.0 Mean  Means   P
Red./Pac. Loon@    2    5     2    3      7    35     5    1   12     +9  NS
Common Loon        3   15     9    9     24    11     4    9   12     +3  NS
Pied-b. Grebe     39    9    11   20      0     0     1    0   <1    -19  *
Horned Grebe      29   32    32   31     14    21    33   22   23     -8  NS
Eared Grebe        3    1     2    2      0     0     2    4    2      0  NS
Western Grebe    227  551   631  470    111   135   188  189  156   -314  *
Brown Pelican      5    5     1    4      0     0     0    0    0     -4  *
Black Brant       71   75   206  117    264   318   365  306  313   +196  *
dabblers @@     5165 5079  3382 4542   3028  2895  2403 2909 2809  -1733  *
Canvasback         8    0     0    3    395   349   637  528  477   +474  *
scaup sp.        530  698   445  558    507   196   524  257  371   -187  NS
scoter sp.       269  201   161  210    108   120   246  128  151    -59  NS
Common Golden.     0    0     0    0     10     5     9    6    8     +8  *
Bufflehead       207   83   171  154    137   172   174  129  153     -1  NS
Red-br. Mergans.   7    6     3    5     14     9    12    4   10     +5  NS
Ruddy Duck        30   11    21   21    115    63   194   61  108    +87  *
American Coot    559  574   447  527     21    20    27   27   24   -503  *

TOTAL           7154 7345  5524 6674   4755  4349  4824 4580 4627  -2047  *
@ Red-throated and Pacific Loons.
@@ 90% or more of the dabbling ducks were American Wigeon; there were also some Mallards, Northern Pintails, Gadwall, and Eurasian Wigeon.

FIGURE 1. The lower part of Yaquina Estuary, Oregon. Bunker C oil extended from the wreck of the freighter on the ocean side of the north jetty upstream to Coquille Point. The Marine Science Center dock is where tide heights were measured. Cross-hatching indicates the area censused for waterbirds.

map of lower Yaquina Estuary and the Blue Magpie on the ocean side of the North Jetty

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