Correlates of lake use by breeding common scoters in Scotland

1. Many populations of sea‐ducks, which typically winter at sea but breed on fresh water, are declining. Numbers of common scoters Melanitta nigra (L.) breeding in Scotland halved between 1995 and 2007, despite most breeding sites having special conservation status. To identify potential conservation measures, a 3‐year study was conducted, investigating correlates of lake use by scoters. 2. At 26 scoter breeding lakes, food abundance (macroinvertebrates) and foraging habitats (substrates, water depth) were measured, and their associations with scoter lake use explored using multi‐model inference. Correlates of macroinvertebrate abundance (water quality, fish abundance) were also investigated. 3. Averaged over 3 years (2009–2011), these lakes held 26.7 (SE 6.3) females, around half the Scottish breeding population. Scoters occurred more often at lakes having abundant large‐bodied invertebrates and extensive shallow water. Lakes where the average weight of the largest invertebrate in each sample exceeded 4 mg had 9.2 times (females) or 27 times (broods) more scoter records than other lakes. Lakes where water depths (10 m from the shore) averaged less than 1.3 m had 2.5 times (females) or 12 times (broods) more scoter records than other lakes. 4. The abundance of large‐bodied invertebrates was greater where small fish species (mostly three‐spined sticklebacks Gasterosteus aculeatus) were more common and brown trout Salmo trutta were scarcer. 5. Results suggest two approaches to scoter conservation. At lakes used for hydro‐electricity generation, water level regimes that provide extensive shallow water should be tested to see if these benefit scoters. At lakes used for trout fishing, trout reduction by increased angling should be trialled, to see if this increases large‐invertebrate abundance and scoter use. Copyright © 2015 John Wiley & Sons, Ltd.     

Variations in the dietary cation–anion difference and the acid–base balance of dairy cows on a pasture-based diet in south-eastern Australia

The variation in the dietary cation–anion difference (DCAD) and the urinary pH of dairy cows was examined over the year 1996–97 in Victoria, south-eastern Australia. Mineral concentrations in the pasture and dairy cow milk production were also examined. Three farmlets (A, B and C) under different feeding and management systems were used for the purpose of the study. Feeding management was based on grazed grass with stocking rates of 1·4, 2·5 and 4·7 cows ha^–1 for farmlets A, B and C respectively. Cows on farmlets B and C received more supplementary feed than those on the A farmlet.
The urine of the cows in each herd was sampled for pH twice monthly, after morning milking. A sample of the feed on offer the previous day was collected and analysed for crude protein, in vitro dry-matter digestibility and macrominerals. Milk yields were recorded on the same day as urine sampling and weather data for the previous day were also collected.
Pasture cation–anion difference was not greatly influenced by stocking rate or associated management practices, although mineral concentrations in pasture did vary. Urine pH was unaffected by changes in climate, management strategies (e.g. stocking rate), season and stage of lactation. Moreover, urine pH was also unaffected by changes in DCAD until the DCAD declined below approximately +15 mequiv. 100 g^–1 for two consecutive sampling periods.
It is concluded that when this threshold for DCAD (+15 mequiv. 100 g^–1) is breached, even in late lactation, a decrease in urine pH occurs. In south-eastern Australia, the DCAD offered to non-lactating cows in the last 2 weeks of pregnancy, in spring-calving herds, on a pasture-based diet is nearly always above that regarded as optimum in other feeding systems.