The potential of seed‐eating birds to spread viable seeds of weeds and other undesirable plants

The potential for seed‐eating birds to spread viable seeds was investigated using captive‐feeding trials to determine seed preference, passage time through the gut, and viability of passed seeds for bronzewing pigeons (Phaps chalcoptera), peaceful doves (Geopelia striata), crested pigeons (Ocyphaps lophotes), Senegal doves (Streptopelia senegalensis), zebra finches (Taeniopygia guttata), black ducks (Anas superciliosa) and wood ducks (Chenonetta jubata). Test seeds were bladder clover (Trifolium spumosum), crimson clover (Trifolium incarnatum), gorse (Ulex europaeus), canola (Brassica napus) and red panicum (Setaria italica). Their consumption was compared with that of commercial seed mixes. Although all test seeds were recognizable foods, their consumption usually decreased in the presence of other foods, except for canola, where consumption rates were maintained. Hard‐seeded bladder clover was the only species where viable seeds were passed by obligate seedeaters. In contrast, viable seeds of canola and gorse were passed by seed‐eating omnivorous/herbivorous ducks, although the germination of passed seeds (42%) was reduced significantly compared with that of untreated control seed (67%). Field validation with wild, urban bronzewings and Australian magpies (Gymnorhina tibicen) offered canola and commercial seed yielded similar outcomes, with a range of viable seeds recovered from magpie soft pellets. Mean seed passage time in captive birds ranged from 0.5 to 4.3 h for all test seeds and commercial seed mixes, suggesting that these bird species may potentially disperse seed over moderate distances. Despite the low probability of individual birds spreading viable seed, the high number of birds feeding in the wild suggests that the potential for granivorous and seed‐eating omnivorous birds to disperse viable seeds cannot be discounted, particularly if exozoochorous dispersal is also considered.     

Estimating red deer Cervus elaphus populations: an analysis of variation and cost-effectiveness of counting methods

• 1 Different counting methods are currently used to estimate red deer populations in the open range in Scotland, but there are few data available to compare variation in estimates, or relative cost‐effectiveness.
• 2 While it is impossible to determine the accuracy of counts (as real numbers are unknown), variation within and between different methods can be measured by repeat counts of the same area within as short a period as possible.
• 3 This study aimed to quantify the variation observed from repeat counts using each of four methods (ground, helicopter, infrared helicopter and dung‐counting methods) at one of three study sites in late winters 2003, 2004 and 2005. Additional data from digital camera images of groups from counts in other areas of Scotland were also used to assess the accuracy of visual counts.
• 4 Coefficients of variation (CVs) within any method of between 5% and 16% were recorded, consistent with previous comparisons for red deer open range counts in Scotland. CVs were lowest for ground and helicopter counts. The infrequency of optimal conditions was likely to limit the applicability of infrared counts in Scotland.
• 5 In terms of cost‐effectiveness, helicopter counting was the least labour‐intensive, with costs of other techniques depending on the availability of existing manpower as an overhead cost.
• 6 It is concluded that helicopter counts are most likely to minimize errors while maximizing cost‐efficiency. Accuracy can be improved by the use of digital photography for counting larger deer groups. Estimates are likely to be improved further by increasing the frequency of counts and using the same methods, counters and routes for repeat counts.

     

Long-term changes in breeding phenology at two seabird colonies in the western North Sea

There is compelling evidence that the breeding phenology of many species has changed substantially in recent decades. However, taxonomic and spatial variation in the direction and rate of change is still not well understood. We explored these issues by analysing a dataset containing information on first egg dates of 10 species of seabird at two major breeding colonies (86 km apart) in the western North Sea over a period of 35 years. Within a species, timing of breeding was positively correlated between the two colonies, suggesting that factors affecting the phenology of these species operated at a regional rather than a colony scale. Comparison of time trends among the species revealed contrasting patterns, with some showing no systematic change, others becoming earlier and others later. The clearest species groupings appeared to be among the terns with arrival and/or first egg dates becoming earlier in Arctic Terns Sterna paradisaea , Common Terns Sterna hirundo and Sandwich Terns Sterna sandvicensis , and among the auks (Common Guillemot Uria aalge , Razorbill Alca torda and Atlantic Puffin Fratercula arctica ) and Black-legged Kittiwake Rissa tridactyla where the trend was in the opposite direction towards later breeding. This general trend towards later breeding in the latter group of species contrasts with correlational evidence from many other organisms indicating that breeding phenology is advancing in response to climate change.     

Disease spread of non-specialised fungal pathogens from inoculated point sources in intraspecific mixed stands of cereal cultivars

Spread of Septoria nodorum from inoculated point sources was examined in pure stands and mixtures of two spring wheat cultivars Kolibri and Maris Butler. Gradients in disease were observed soon after inoculation; the presence of the more resistant cultivar (Maris Butler) in the mixtures retarded the outward spread of disease compared with the susceptible pure stand (Kolibri). Regression analysis suggested that gradients in incidence were influenced by nearness to the source whereas gradients in severity were not. Spread of disease was also examined in pure stands and mixtures for the host/pathogen combinations, winter wheat (cvs Maris Huntsman and Maris Ranger)/S. nodorum and winter barley (cvs Maris Otter and Hoppel)/Rhynchosporium secalis. In contrast to the spring wheat experiment, no gradients were observed; explanations for the uniform distribution of disease were (a) extensive spread prior to the period of assessment, (b) no physical barrier to dispersal due to the juvenile growth stage of the crop and (c) exhaustion of the point-source.     

The roles of grass leaf litter in streams draining tussock grassland in New Zealand: retention, food supply and substrate stabilization

1. We investigated the roles of grass litter in streams that drain upland New Zealand tussock grassland, paying particular attention to the ways in which grass leaves differed in their characteristics from much more intensively studied tree leaves. 2. The instantaneous retention rates of tussock grass leaves (Chionochloa rigida) on the bed of a second-order stream (0.157–0.515 m^?1) were significantly higher than those of the elliptical leaves of lemonwood trees (Pittosporum eugenioides; 0.068–0.180 m^?1). 3. Instantaneous retention rates of grass leaves in two third-order streams were very low. At high discharge, leaf retention rate was greater in Timber Creek (0.0040 m^?1), a braided, gravel bed stream, than in the adjacent Kye Burn (0.0010m^?1), with its well-defined channel and large, stable substrate particles. At baseflow, retention rates were similar in the two streams (0.0053–0.0064 m^?1 for Timber Creek; 0.0047–0.0058m^?1 for Kye Burn). Nevertheless, total coarse particulate organic matter (mainly derived from tussock litter) was present at lower densities in Timber Creek than Kye Bum, reflecting the instability of the bed of the former and its tendency to spread over a wide area at high discharge. 4. The results of a colonization tray experiment, in which substrate was mixed with tussock leaves, nylon ribbon or nothing, indicate that tussock leaves do not play an important role as microhabitat or food in the two third-order streams. This may reflect the poor food quality of grass litter, and/or the relatively low availability and predictability of its supply. 5. An in situ experiment revealed that tussock leaves play a role, analogous to that reported for certain seagrasses, in stabilizing substrate and reducing sediment transport, apparently by reducing bed roughness and therefore the force of friction on the bed.     

Epidemics of Phymatotrichum root rot (Phymatotrichum omnivorum) in cotton: environmental correlates of final incidence and forecasting criteria

Epidemics of Phymatotrichum root rot (PRR), caused by Phymatotrichum omnivorum, in cotton were monitored in field plots at the Blackland Research Center, Temple, Texas during the years 1969–1982. In most years disease incidence, assessed at periodic intervals during the growing season, increased smoothly and levelled off at values in the range 0–04-0-99 (proportion of plants killed). During two years there were marked increases in PRR late in the growing season. Increments in PRR were associated with preceding increments in precipitation but only when the latter were large. The final incidence of PRR late in August was directly related (in all but one of the 14 years) to cumulative precipitation in the range 36–100 cm, and inversely related (in all 14 years) to air temperatures greater than 34 ^oC. Regression was used to relate final PRR incidence to derived weather variates but the equations obtained did not provide a realistic basis for forecasting: the best predictive variates included cumulative precipitation up to mid-August. A threshold criterion given by P/T > 1·45, where P was cumulative precipitation (cm) from 1 January and T was the mean maximum temperature (°C) during the preceding 10 days, was derived. This criterion satisfactorily grouped years with high (>0·;50) and low (<0–50) incidences of PRR. In those years where a forecast of high incidence was made, the criterion was satisfied prior to the first appearance of PRR (mid-June); where a forecast of low incidence was made, the criterion was not satisfied until late August. The forecasting criterion was evaluated at three sites in the Blacklands region in 1983, at two in 1984, and at Temple only in 1985. In 1983 and 1984, final PRR incidences of less than 0–50 were forecast and observed; in 1985, cumulative annual precipitation exceeded 50 cm by early June, the threshold criterion was satisfied prior to the first observation of symptoms, and PRR incidence was 0–80 late in August.