Environmental variability and population dynamics: do European and North American ducks play by the same rules?

Density dependence, population regulation, and variability in population size are fundamental population processes, the manifestation and interrelationships of which are affected by environmental variability. However, there are surprisingly few empirical studies that distinguish the effect of environmental variability from the effects of population processes. We took advantage of a unique system, in which populations of the same duck species or close ecological counterparts live in highly variable (north American prairies) and in stable (north European lakes) environments, to distinguish the relative contributions of environmental variability (measured as between-year fluctuations in wetland numbers) and intraspecific interactions (density dependence) in driving population dynamics. We tested whether populations living in stable environments (in northern Europe) were more strongly governed by density dependence than populations living in variable environments (in North America). We also addressed whether relative population dynamical responses to environmental variability versus density corresponded to differences in life history strategies between dabbling (relatively "fast species" and governed by environmental variability) and diving (relatively "slow species" and governed by density) ducks. As expected, the variance component of population fluctuations caused by changes in breeding environments was greater in North America than in Europe. Contrary to expectations, however, populations in more stable environments were not less variable nor clearly more strongly density dependent than populations in highly variable environments. Also, contrary to expectations, populations of diving ducks were neither more stable nor stronger density dependent than populations of dabbling ducks, and the effect of environmental variability on population dynamics was greater in diving than in dabbling ducks. In general, irrespective of continent and species life history, environmental variability contributed more to variation in species abundances than did density. Our findings underscore the need for more studies on populations of the same species in different environments to verify the generality of current explanations about population dynamics and its association with species life history.Peer reviewe

Vigilance in a Cooperatively Breeding Primate

Collective vigilance is considered a major advantage of group living in animals. We investigated vigilance behavior in wild mustached tamarins (Saguinus mystax), small, arboreal, cooperatively breeding New World primates that form stable mixed-species groups with saddleback tamarins (Saguinus fuscicollis). We aimed 1) to investigate whether vigilance patterns change according to individual activity and 2) to examine whether there is a social component of vigilance in their cooperative and nonaggressive society. We studied 11 factors that may influence vigilance and used this data to interpret the possible functions of vigilance. We observed 44 individuals in 3 mixed-species and 2 single-species groups of 2 populations that differed in population density and home range sizes. Vigilance changed greatly when individuals were engaged in different activities and individual vigilance was affected by different sets of factors depending on the activity. As vigilance decreased in proximity of conspecifics and heterospecifics when feeding, and in larger mixed-species groups when resting, we conclude that the predominant function of vigilance in mustached tamarins is predator related. However, the absence of the group size effect in very large single-species groups suggests that it may also function to maintain group cohesion. In the population with higher density and smaller home ranges individuals also increased their vigilance in home range overlap areas. We found no evidence that mustached tamarins monitor group mates to avoid food stealing or aggression. The effect of heterospecifics on individual vigilance suggests that collective vigilance might have been an important incentive in the evolution of tamarin mixed-species groups

The effect of climate change on avian offspring production: A global meta-analysis

Climate change affects timing of reproduction in many bird species, but few studies have investigated its influence on annual reproductive output. Here, we assess changes in the annual production of young by female breeders in 201 populations of 104 bird species (N = 745,962 clutches) covering all continents between 1970 and 2019. Overall, average offspring production has declined in recent decades, but considerable differences were found among species and populations. A total of 56.7% of populations showed a declining trend in offspring production (significant in 17.4%), whereas 43.3% exhibited an increase (significant in 10.4%). The results show that climatic changes affect offspring production through compounded effects on ecological and life history traits of species. Migratory and larger-bodied species experienced reduced offspring production with increasing temperatures during the chick-rearing period, whereas smaller-bodied, sedentary species tended to produce more offspring. Likewise, multi-brooded species showed increased breeding success with increasing temperatures, whereas rising temperatures were unrelated to repro- ductive success in single-brooded species. Our study suggests that rapid declines in size of bird populations reported by many studies from different parts of the world are driven only to a small degree by changes in the production of young

Feeding consequences of the dominance status in Great Tit Parus major groups

The feeding consequences of the dominance status in Great Tits feeding on sunflower seeds at artificial feeders were studied. Behavioural and morphometrie correlates of feeding success and dominance status were examined. Analyses with colour-ringed Great Tits revealed marked individual differences in feeding success. Individuals with a high feeding success had a high dominance status, wide breast stripe plumage, and short seedhandling and waiting time. Breast stripe width best explained the variation in individual feedingsuccess. Watching and avoidance, as indicated by long handling andwaitingtimes, decreased the feeding success of subordinate Great Tits . An analysis confined to birds less than one year old indicated that males succeeded better than females. Ahigh dominance status was associated with a wide breast stripe, and breast stripe plumage presumably signalled an individual's dominance status in the groups . This status signalling system, however, did not operate when only first-year males were considered

Population estimates and the timing of waterfowl censuses

The effect of the timing of waterfowl censuses on the estimates ofbreeding population sizes of different species was studied in southeast Finland from 1991 to 1994. Lakes used only for breeding and a local stop-over lake that was used for staging during spring migration were analysed separately . Also, the effect ofthe break-up of ice cover on the order of lake occupation by breeding pairs was studied. A standard waterfowl census was made four times in May at an interval of approximately seven days in each year . In general, the timing of waterfowl censuses within the three-week period considered did not cause serious biases in population estimates, though differences between species and between lake types were observed. The timing of the break-up of the ice cover was critical in the build-up of local breeding populations. However, pairs of many species, especially the Mallard, Teal, and Common Goldeneye occupied breeding lakes even when the lake still was considerably covered by ice. Acomparison of recommended census times between earlier studies and this study suggests that in some species censuses could be started much earlier than previously recommende