Strong circumstantial evidence for ethanol toxicosis in Cedar Waxwings (Bombycilla cedrorum)
Several flocks of Cedar Waxwings (Bombycilla cedrorum) were found dead after colliding with solid objects such as picture windows, plexiglass, and fences. Necropsy examination revealed that all birds had engorged themselves with over-ripe berries of the Brazilian Pepper Tree (Schinus terebinthifolius) and had hemorrhages in the breast muscles and the coelomic cavity due to hepatic rupture. Microscopic examination of tissues revealed no underlying pathological conditions. Ethanol was detected at levels of 260–1,000 ppm in the intestinal contents and liver, respectively. The cause of death in these birds was trauma that resulted from colliding with hard objects when flying under the influence of ethanol.
KeywordsBombycilla cedrorumCedar WaxwingEthanolSchinus terebinthifoliusToxicosis
Ethanol-Vergiftung beim Zedernseidenschwanz (Bombycilla cedrorum)
Gruppen von Zedernseidenschwänzen wurden nach Zusammenstößen mit festen Objekten wie Panoramafenstern, Plexiglas und Zäunen tot aufgefunden. Die Untersuchung der Körper ergab, dass sich die Vögel an überreifen Beeren des brasilianischen Pfefferbaums (Schinus terebinthifolius) überfressen hatten und aufgrund von Rissen im Leberparenchyms starke Blutungen im Bereich des Brustmuskels und der Leibeshöhle aufwiesen. Die Gewebe-Mikroskopie zeigte keine tiefer gehenden Ursachen; aber im Verdauungstrakt wie auch in der Leber konnte Ethanol in Konzentrationen von 260 bis 1,000 ppm nachgewiesen werden. Die Todesursache war bei diesen Vögeln ein Trauma, das sie höchstwahrscheinlich als Ursache von Zusammenstößen mit harten Gegenständen unter einer Ethanolvergiftung davontrugen.
Flying accidents have been reported in birds associated with various poisoning such as road salt (Töpfer 2010) and ingestion of fermented fruits (Fitzgerald et al. 1990; Stephen and Walley 2000; Töpfer 2010; USGS National Wildlife Health Center 2010). This report describes the gross and microscopic and toxicological findings from 21 to 90 Cedar Waxwings (Bombycilla cedrorum) that were submitted for necropsy after death caused by flying into stationary hard objects.
Summary of Cedar Waxwings (Bombycilla cedrorum) die-off in Southern California during 2005 through 2007
No. of Cedar Waxwings
San Pedro, LA County, CA., nearby School
Liver rupture, intracoelomic hemorrhages
West Lake Village, LA County, CA; Residential
Liver rupture, internal hemorrhages; berries from a California Pepper Tree (Schinus molle) in crop, gizzard
Santa Clarita, LA County, CA; residential property
Liver rupture, intracoelomic hemorrhages; berries from a California Pepper Tree (Schinus molle) in pharynx, crop, gizzard
Newhall, LA County, CA; residential property
Liver rupture, intracoelomic hemorrhages; berries from a California Pepper Tree (Schinus molle) in pharynx, crop, and gizzard
Newhall, LA County, CA; residential property
Liver rupture, intracoelomic hemorrhages; berries from Brazilian Pepper Tree (Schinus terebinthifolius) in pharynx, crop, and gizzard; ethanol was detected in intestinal content (0.026 %, 260 ppm) and liver (0.1 %, 1,000 ppm)
Valencia, LA County, CA; residential property
Liver rupture, intracoelomic hemorrhages
Full necropsies including bacteriology, toxicology, histopathology, and RT-PCR for avian influenza and Newcastle disease were performed on 13 of the 21 carcasses and gross observation (cursory examination without further laboratory tests) was carried out on the other eight carcasses. Several of the dead birds had numerous berries and seeds in their mouths, crops, proventriculi, and gizzards prompting the submission of clippings from a recently planted pepper tree including bark, leaves, and berries for toxicological analysis.
Samples of liver, spleen, kidney, lung, heart, stomach, small and large intestines, pancreas, and half of the brain were fixed in neutral buffered formalin overnight, embedded in paraffin wax, sectioned at 4 μm, and stained with haematoxylin and eosin. A section of liver and intestinal pools were collected for routine aerobic and Salmonella culture. Brains were submitted to the CAHFS toxicology laboratory for cholinesterase activity, and livers and kidneys for heavy metal screening.
Livers, gastrointestinal pools, and plant clippings from the pepper tree were submitted to the Pacific Toxicology laboratories (Chatsworth, CA, USA) for ethanol analysis. For the ethanol testing, samples were prepared by homogenization with 18 mΩ water from a Barnstead NANOpure Infinity® water purification system (Thermo Fisher Scientific, Waltham, MA, USA) and filtered into autosampler vials. Ethanol was quantified by gas chromatography with flame ionization detection (GC-FID), with n-propanol as an internal standard. Samples were kept refrigerated before analysis. As an extra quality control step, we added 10 % EtOH to one sample in the autosampler vial prior to analysis. The quantitation of ethanol in the spiked sample was measured to be 13.8 % ethanol.
At necropsy, all carcasses were in excellent nutritional condition. All birds had focal to extensive acute hemorrhages of pectoral musculature, oropharyngeal and intracoelomic hemorrhage, and hepatic rupture. No other abnormalities were noted in the gross examination.
In the histological examination, we found the lungs to be markedly congested with patchy atelectasis and widespread hemorrhage of bronchi and parabronchi. Ruptured liver sections had acute hemorrhages along the torn borders. There were mild pre-existing lesions in most liver sections characterized by multifocal small, discrete and random foci of lymphocytes, plasma cells, and macrophages.
Skeletal muscle sections showed foci of pronounced acute hemorrhages accompanied by acute myofiber degeneration and necrosis. No other significant histological abnormalities were observed in other examined tissues. Toxicologic heavy metal screening of livers revealed acceptable non-toxic concentrations. The measured brain cholinesterase activity was within an acceptable range for this species of bird. The berries were identified by the University of California, Davis herbarium, as Schinus terebinthifolius (Anacardiaceae, cashew family) commonly known as the Brazilian Pepper Tree. The Brazilian Pepper Tree fruit (drupes) grow in clusters and as they ripen turn bright red (MacDonald et al. 2008). Then, the red skin dries to become a pink papery shell surrounding the seed. The Brazilian Pepper Tree is an invasive plant introduced as an ornamental (Center for Aquatic and Invasive Plants, University of Florida 2010). Birds are one of its primary mechanisms for seed dispersal (Shetty et al. 2011; MacDonald et al. 2008).
No bacterial pathogens were isolated from livers and intestinal contents by aerobic and Salmonella culture. Cloacal swabs from these birds were tested for avian influenza and exotic Newcastle disease by RRT-PCR with negative results.
There were mixed fungal growths on the bark. Cultures of berries had a low to a high Cladosporium sp. count.
A significant finding in our study is the detection of 1,000 ppm ethanol in the liver of one of nine birds, 260 ppm in two of six pools of intestinal contents, and 700 ppm from the out-of-state submission of one of two gastrointestinal pools analyzed. Ethanol was not detected in eight livers, in six pools of crop, and six pools of gizzard contents. In our study, the primary cause of death in the 21 birds necropsied was hepatic rupture and severe internal hemorrhage from blunt trauma.
Cedar Waxwings are an important avian frugivores of North America, more frugivorous than American Robins (Turdus migratorius) (Witmer 1996), and “intensive foragers” (Avery et al. 1993; del Hoyo et al. 2005; Cornell University Lab of Ornithology 2011). These birds can swallow berries whole (Cornell University Lab of Ornithology 2011) and consume roughly two meals of fruit “in a single foraging trip” due to their distensible esophagus (Levey and Duke 1992).
The annual diet of Cedar Waxwings constitutes about 84 % fruit, and reaches up to 100 % during the months of October to April, while flowers account for 44 % of their diet in May when fruit is scarce (del Hoyo et al. 2005).
Cedar Waxwings are occasionally found dead after having flown against fixed objects during the night-time (del Hoyo et al. 2005). This was not the case in our study, since the Cedar Waxwings were seen flying in flocks during the daylight hours and colliding with hard objects. Although ethanol was detected in the liver of just one of the nine birds and two of the three intestinal pools, based on the absence of other etiological conditions, ethanol intoxication was suspected as the cause of the disorientation and collision with blunt objects. We speculate that this was also the case for the 69 untested birds since all 90 shared the same environment with accessibility to the berries of the Brazilian Pepper Tree. The source of ethanol was the fermented berries from the Brazilian Pepper Tree.
A toxic agent, ethanol, has been extensively studied. By far the most common natural source of ethanol is fermentation of fruit sugars by yeasts (Levey 2004). However, very little information has been reported on natural ethanol intoxication in birds (Stephen and Walley 2000), although the effects of orally administered ethanol have been studied in various animals such as turkeys, pigeons, chickens, and bats (Prinzinger and Hakim 1996; Bashir and Javed 2005; Wiens et al. 2008; Orbach et al. 2010; Sanchez et al. 2010).
The Cedar Waxwing is the smallest (15–18 cm) of the three species of the family Bombycillidae; the Bohemian Waxwing (Bombycilla garrulus) is the largest (23 cm) and the Japanese Waxwing (B. japonica) is slightly smaller than the Boehemian Waxwing. The Bohemian Waxwing has a relatively large liver and the adaptation to eating large amount of berries (Pulliainen et al. 1981); it is also assumed the other two Waxwings have relatively large livers.
The Cedar Waxwing consumes a large quantity of berries daily and its short intestines will facilitate the easily digested food to travel rapidly through the digestive tracts; furthermore, having a large liver (4.9 % of the total body mass) as a detoxification organ is an adaptation, as toxins are more often present in fruits than in buds or animal matter (Pulliainen et al. 1981). In a feeding trial of Bohemian Waxwings, blood ethanol levels were found to be as high as 20 and 50 ppm, and it was suggested that these levels are so low that they cannot be assumed to have any influence upon the bird’s flying ability and behavior (Eriksson and Nummi 1983). However, Cedar Waxwings used in the study were much larger (mean body mass, 60 g) than in our report (mean 34.5 g; range 32.0–37.0 g; n = 7). Alcohol dehydrogenase (ADH) activity is high in fruit eaters and low in seed-eating birds (Eriksson and Nummi 1983; Prinzinger and Hakim 1996; Bashir and Javed 2005; Wiens et al. 2008; Orbach et al. 2010; Sanchez et al. 2010).
Prinzinger and Hakim (1996) reported that the combination of the high ADH activity and the low concentration of alcohol normally found in fermented fruits and berries means that birds have no problem in coping with alcohol. Others have estimated that, if the Waxwing ate 30 g of rowan berries in 1 h, the alcohol content in the water phase of the bird would be 0.5 %, in spite of its alcohol elimination. This high ethanol concentration might be expected to affect the bird’s ability to fly (Eriksson and Nummi 1983). The ethanol content in the liver and intestinal contents of the Cedar Waxwings in our study are similar to a previous report of suspected ethanol toxicosis in the same species (Fitzgerald et al. 1990).
By eliminating other possible underlying causes of trauma in the Cedar Waxwings in this report, and based on the strong circumstantial evidence, we conclude that, indeed, when fruit and berry ethanol content is high there are significant consequences when consumed by birds.