Table 4.

Calculations for estimates of the percent of American White Pelican chicks that were infected by WNV and survived to fledge from the breeding colonies at Chase Lake, North Dakota (2006–2007), Bitter Lake, South Dakota (2006–2008), and Medicine Lake, Montana (2006)

Year and study area	Late breeding season mortality rate (%)*	Chicks surviving late breeding season	Chicks with antibodies at fledging (%)	Cumulative incidence of WNV in chicks (dead + chicks with antibodies)	Of chicks before outbreak, chicks infected by WNV that survived to fledge†
2006
Chase Lake	10	90	18 (20)	10 + 18 = 28	18/28 = 64%
Bitter Lake	14	86	43 (50)	14 + 43 = 57	43/57 = 75%
Medicine Lake	8	92	20 (22)	8 + 20 = 28	20/28 = 71%
2007‡
Chase Lake	30	70	45 (64)	30 + 45 = 75	45/75 = 60%
Bitter Lake	25	75	56 (74)	25 + 56 = 81	56/81 = 69%
2008‡
Chase Lake§	8
Bitter Lake	13	87	38 (44)	13 + 38 = 51	38/51 = 75%

For these calculations, we assume a beginning population of 100 chicks in mid-July, which is just before the start of WNV infections in each colony.

^*Mortality rates of American White Pelican chicks during late breeding season (mid-July to fledging).

^†Nearly all late-breeding season mortality can be attributed to WNV.² Before the 2002 arrival of WNV in the region, reported late-breeding season mortality rate was < 4%.²

^‡The percent of chicks with WNV neutralizing antibodies was not measured at Medicine Lake in 2007–2008.

^§Sample size too small for meaningful calculation.