Food consumption and faecal deposition of plant nutrients by black swans (Cygnus atratusLatham) in a shallow New Zealand lake

✍ Scribed by S. F. Mitchell; R. T. Wass

• Publisher: Springer
• Year: 1995
• Tongue: English
• Weight: 775 KB
• Volume: 306
• Category: Article
• ISSN: 1573-5141
• DOI: 10.1007/bf00017690

✦ Synopsis

Deposition of faeces by black swans (Cygnus atratus Latham) feeding on benthic algae in a shallow New Zealand lake was determined by collection of faeces from the lake bottom and from the shore . The two methods showed good agreement after adjustment for the weight loss on immersion . The mean daily faecal output per swan was 52 g dry weight . The nitrogen content of the faeces averaged 2 .3% of dry weight, and was dominated by soluble organic nitrogen (59% of total N) . Phosphorus averaged 0 .44% of dry weight, with 66% of it being particulate, and 30% soluble reactive phosphorus . Although faecal inputs of total phosphorus were sufficient to generate concentrations of 15-30 mg m -3 , the faecal contributions of both N and P were only a minor component of the fluctuations observed in the lake, and were also small in relation to the total nutrient pool in the water and benthic algae . Waterfowl faeces appear to have low ratios of N to P, which will favour dominance of the phytoplankton by cyanobacteria in lakes where the faecal component of nutrient loads is large . The few data available suggest that the nitrogen content of waterfowl faeces is largely independent of that in their food . Food consumption, calculated by using cellulose as an indigestible faecal marker, was 104 g dry weight swan -' d -', a figure that appears low in relation to those for other swan species . Even the highest published figure for food intake by a swan is only about one half of the corresponding average metabolically-adjusted figures for geese, and we caution against the uncritical use of bioenergetic models for determining rates of food consumption and defaecation .