- University of Toronto
Summary
A three year study (1981 to 1983) was conducted to determine possible influences of wetland acidification on the reproduction and growth of the Eastern Kingbird (Tyrannus tyrannus). This species uses emergent aquatic insect prey to feed its nestlings. Egg characteristics and nestling growth were monitored for birds nesting in 26 lakes in the Killarney region near Sudbury, Ontario (pH range 4.27 to 6.26). The major percentage of variation in kingbird reproductive factors including clutch initiation, egg weight loss and tarso-metatarsus bone growth was explained by differences between siblings and among nests on a single lake. A smaller percentage of the variance in reproductive parameters was explained by the variation in water chemistry among lakes. Canonical correlation showed that sulfate, nitrate/nitrite, alkalinity, pH, and several metals (Fe, Mn, Al) accounted for a minor but significant variance in growth characteristics. These water chemistry parameters are influenced by lake acidification. The relationship observed between lake acidity and kingbird reproduction is therefore measurable but minor compared to the influence of genetic and inter-nest variables. The study showed no food limitation for the kingbird attributed to lake acidity.
Methodology
Twenty-six wetlands were surveyed for kingbird nests in May and early June of 1981, 1982 and 1983. Nests were found at 56 locations. Over 3 yr, 145 nests with 404 eggs were examined. Sixty-three nests were successful, producing 215 young (Table I).
Eggs were weighed and measured every four days to the nearest 0.01 g using a 5 g Pesola balance; length and width were measured to the nearest 0.05 mm using calipers. Nestlings were weighed and measured every four days until the birds fledged or disappeared and were presumed dead. Birds were weighed to the nearest 0.1 g using a 50 g Pesola balance. Wing chord length (distance between the upper wrist joint and first primary feather) of the right wing and tarso-metatarsus length (distance from the tarsal joint to the metatarsal joint) of the right leg were measured to the nearest 0.05 mm using calipers.
From these data egg volume, egg length-width ratio, egg water loss, growth rate of nestlings (i.e. weight increase), growth rate of tarso-metatarsus and growth rate of wings were calculated.
Rate of weight gain, rate of bone growth and rate of wing growth were calculated using Ricklefs' (1967) graphical technique. Logistic curves were used for calculations of weight and tarsus growth rate and Gompertz curves for wing chord growth rate calculations.
A limited number (n=18) of eggs were collected and frozen, for determinations of eggshell thickness and composition. Nine eggs were collected from the Killarney area (mean alkalinity 2.9 mg l-1) and, for comparative purposes, an additional nine were taken adjacent to wetlands remote from Sudbury on more buffered terrain. Seven of the latter were taken from the area of Lake Opinicon, 50 km north of Kingston, which is underlain by a mixture of granitic and marble bedrock (alkalinity 116 mq l-1). The two remaining were collected from near Long Point on Lake Erie which is underlain by limestone bedrock (alkalinity 209 mg l-1). In all cases eggs were taken from different nests. Eggshells were analyzed near the top (n=2), 0.75 cm from the top (n=4) and 2.0 cm from the top (n=4) for Na, Mg, AI, Si, P, S, K, Ca, Fe, Ba, Cr, Ni, Ag, Mn, Ti, Co, Hg, Zn, and Cs. Half-eggshells were coated with carbon and examined in a scanning electron microscope utilizing a static electron beam approximately 10 nm in diameter and an accelerating voltage of 15 KV for 60s under consistent lens conditions. The SEM was interfaced with a Traco Northern energy dispersive x-ray spectrometer and a TN2000 microanalyzer. Quantitative results were obtained with reference to polished plastic embedded mineral standards utilizing a least squares fitting routine with ZAF corrections. Eggshells were examined microscopically for differences in thickness.