Health assessment of Black-crowned Night-herons (Nycticorax nycticorax) of the New York Harbor estuary.

Blood samples from 145 Black-crowned Night-heron (Nycticorax nycticorax, BCNH) chicks (mean age 3 weeks) were taken from four island colonies (Goose (2004), Canarsie Pol (2005), Hoffman (2004 and 2005) and North Brother (2004 and 2005)) in New York Harbor in 2004 and 2005 to establish baseline health reference ranges for this species and to compare health indices of birds reared on different islands. Packed cell volume (PCV) and total solids (TS) did not differ among islands in either year. Herons raised on Hoffman Island in 2004 had lower white blood cell count (WBC), and higher activities of creatine phosphokinase (CPK), lactate dehydrogenase (LDH), aspartate amino transferase (AST), higher concentrations of potassium (K) and phosphorous (PHOS) and lower liver derived proteins (TP, prealbumin, albumin, alpha 1 globulins, alpha 2 globulins, beta globulins and gamma globulins) compared to herons from Goose and North Brother Islands. These changes suggest compromised health in chicks reared on Hoffman Island in 2004. On Hoffman in 2005, these biochemical analytes did not differ from concentrations and enzyme activities measured from birds on other islands. Although no single etiology can explain these extensive changes, it is likely that exposure to contaminants at foraging sites used by birds nesting on Hoffman and/or changes in prey availability and abundance causing birds to forage in different locations between years, led to differences measured in blood-based health indices. Avian health assessments coupled with foraging ecology serve as an excellent method for evaluating ecosystem health of the New York Harbor estuary system.