Abstract

Hematology and plasma biochemistry have proved to be useful as physiologic indicators in ecologic research, and for wildlife and conservation programs in natural populations of vertebrates. In avian populations, these parameters have been used for providing information on the physiologic state and adaptation of individuals to their habitat, changes in nutritional state, reproductive status, body condition, and health status. These acquire a serious importance when threatened avian populations are affected by the emergence of infectious diseases. The wetlands of the Ramsar Nature Sanctuary “Carlos Anwandter” (number 6CL001) on the Cruces River, in Valdivia (39°34–49´S; 33°02–18´W), southern Chile, support 119 avian species, mainly waterfowl. The sanctuary contains the largest known breeding colony of black-necked swans (BNS) on its southern zone distribution. Since March 2004, the BNS populations have been affected by a drastic reduction of the common waterweed Egeria densa (“luchecillo”), their main food. According to a study, this reduction was related to water pollution due to recent pulp mill industrial activity upstream of the Cruces River, with three effects on BNS population: (1) a drastic decline in population abundance (from 6,000 to 250 individuals), (2) deaths of >300 individuals with nonspecific clinical signs, and (3) a complete absence of reproductive activity.¹

With the aim of evaluating health status, we captured 165 BNS from 2003 to 2005 in two sampling periods: (1) a priori environmental episode period (before the initiation of the pulp mill activity): 46 animals were tested between June and September 2003; and (2) a posteriori environmental episode period (after initiation of the pulp mill activity): 119 animals were tested between September 2004 and March 2005. Blood was collected from the medial metatarsal or the superficial ulnar veins.

Eleven hematologic variables, nine biochemical values, serologic tests for Newcastle disease (NCD), Mycoplasma gallisepticum, and bacterial cultures for Salmonella sp. were determined during the first period. Six biochemical values, antibody response to NCD, adenovirus type 1 (AdV-1), and avian pox virus (APV), and Aspergillus flavus were added to the testing during the second period. Seventy-seven samples were evaluated serologically. Additionally, necropsies were performed on two adult BNS that died within 18 h of captivity.

Hematologic and biochemical parameters were similar (p>0.05) between males and females during the first period. Samples from the second period revealed a normocytic, normochromic, nonregenerative anemia; leukopenia; decreases in the body mass (body weight without effect on total length), triglycerides, and uric acid; and an increase in β-hydroxybutyrate levels. The methodologies, and serologic and culture results are presented in Table 1.

Table 1. Agents and serologic test results of tests applied, during both
periods, to black-necked swans at the Nature Sanctuary in Valdivia, Chile

The BNS were most likely immune suppressed due to a weight decline following a decrease in their food source. This is the first report of positive serologies for NCD, AdV-1, and A. flavus in wild black-necked swans. This monitoring study is evidence of variations in flock health a priori and a posteriori to the drastic reduction of Egeria densa due to environmental contamination.

Literature Cited

1.  CONAMA. 2005. Reporte Final: “Estudio sobre origen de mortalidades y disminución poblacional de aves acuáticas en el santuario de la naturaleza Carlos Anwandter, en la provincia de Valdivia.” Acuerdo número 1210-1203/2004-12-14. Dirección Regional Conama Xª Region de Los Lagos—Universidad Austral de Chile, Valdivia, Chile. (available online: www.conama.cl/portal/1255/article-31832.html) (VIN editor: This link was not accessible as of 1-22-21). Final Report: “Study about the origin of mortalities and population reduction of waterbirds in the Nature Sanctuary Carlos Anwandter, at the Valdivia Province.” Complementary Agreement Number 1210-1203/2004-12-14. National Environmental Agency (CONAMA)—Austral University of Chile.