Variation In Time Budgets Research Articles

Population level behavioural responses to variation in habitat quality across multiple locations in a fragmented landscape

Population level behavioural responses to variation in habitat quality across multiple locations in a fragmented landscape

Why time‐limited individuals can make populations more vulnerable to disturbance

Individual variation in disturbance vulnerability (i.e. the likelihood that disturbance negatively affects an individual's fitness) can affect how disturbance impacts animal populations, as even at low disturbance levels some individuals could be severely affected and die. Individual variation in vulnerability can arise due to different responses to disturbance. We propose a new hypothesis that even when individuals respond similarly to disturbance, time‐limited individuals are more at risk that their condition deteriorates since they have limited ability to extend their foraging time to compensate for disturbance. We investigate this ‘time‐limitation hypothesis' both empirically and mathematically by studying how individuals that differ in their average foraging time (presumably due to differences in foraging efficiency) are affected by disturbance. We used tracking data of 22 wintering Eurasian oystercatchers Haematopus ostralegus to compare time budgets between disturbed and undisturbed tidal periods. In three tidal periods with severe disturbance by transport airplanes, more than a third of the variation in additional flight time and foraging time loss was explained by individual differences. Inefficient individuals that foraged longer in undisturbed tidal periods experienced higher costs in disturbed tidal periods, since they lost more foraging time. We next used an analytical energy balance model to study how time‐limited individuals differed in their maximum disturbance thresholds. Both our theoretical model and empirical study suggest that inefficient individuals in a time‐limited environment may be unable to increase their foraging time to compensate for the effects of disturbance. Consequently, the magnitude of individual variation in time budgets strongly determines what proportion of the population is at risk that their condition deteriorates due to disturbance. Our hypothesis implies that, when assessing disturbance effects on a population, it is not only important to consider individual variation in disturbance responses, but also variation in time budgets that determine the consequences of disturbance.

The Influence of Leaf Consumption on Time Allocation in Black Howler Monkeys (Alouatta pigra)

The analysis of factors that determine variation in time budgets is important to understand the interactions between environment, behaviour and fitness. We tested the hypothesis that changes in the dietary patterns of black howler monkeys (Alouatta pigra) caused by a decrease in the availability of preferred foods are a main determinant of variation in time budgets. We predicted that individuals would trade off travel time for resting time (i.e., minimize energy expenditure) as the diet included more leaves. We conducted our study in the Mexican state of Campeche between 2005 and 2008, where we studied the behaviour of 28 adult males and 32 adult females belonging to 14 different groups for a total of 3,747.2 focal sampling hours. Study groups lived in forest fragments with variation in habitat quality. Individuals showed different rest:travel trade-offs in response to leaf consumption according to the quality of the forest fragments they lived in. Individuals that lived in high-quality fragments increased resting time under more folivorous regimes, whereas those living in low-quality fragments increased travel time. Our results suggest that howler monkeys living in low-quality fragments spend more time foraging to compensate for the low quality of the available resources.

Migrating Montagu's harriers frequently interrupt daily flights in both Europe and Africa

Time budgets are a powerful but hitherto seldom used way to study how migrants organise their bi‐annual travels. We studied daily time budgets of travelling Montagu's harriers Circus pygargus, based on GPS tracking data, in which we were particularly interested in how time budgets differ between regions and seasons, and are affected by wind. We found that Montagu's harriers used a relatively broad daily time window for travelling by starting daily travels just after sunrise and ending daily travels just before sunset. Occasionally, flights were extended into the night. Montagu's harriers frequently interrupted their daily flights for on average 1.5 h d–1. These interruptions occurred in all regions and seasons. The tracking data during interruptions suggested two different behaviours: in 41% of all interruptions the birds were moving (presumed foraging,) and in 32% they were stationary (presumed resting; the remaining interruptions could not be classified). The interruptions for foraging indicate that Montagu's harriers have a fly‐and‐forage migration strategy (i.e. combine travelling and foraging on the same day), but the interruptions for resting illustrate that their travels comprise of more than fly‐and‐forage behaviour alone. The large number of interruptions for foraging in the Sahara Desert indicates that this region is less hostile for a migrating raptor than presumed previously. Importantly, harriers spent more time on interruptions for resting on days with stronger headwinds, suggesting that interruptions for resting serve a function of waiting for more favourable weather conditions. Daily variation in time budgets was largely explained by wind; harriers flew more hours per day, and interrupted their flights fewer hours per day, on days they experienced stronger tailwinds. In contrast, time budgets were similar between regions and seasons, suggesting that wind rather than landscape and season shape travel routines of Montagu's harriers.

An investigation into genetic and phenotypic variation in time budgets and yield of dairy cows

Time budgets (TB) of lactating Holstein cows in a freestall loose housing system were recorded twice in early and late lactation to study genetic and phenotypic variation in TB. Time budget traits were recorded using focal animal scanning at 10-min intervals for full 24-h sessions. The study included 243 first-lactation cows, with 389 TB records in early lactation (50 to 123d in milk) and 403 records in late lactation (152 to 248d in milk). Milk was recorded at 3-wk intervals during the same periods, and yield was expressed as energy-corrected milk. Time budget traits were analyzed with mixed linear models to obtain estimates of genetic variation (heritability) and permanent animal variance (repeatability). Correlations between TB traits and energy-corrected milk yield were estimated at the individual cow level. In early lactation, the cows spent, on average, 5.0h eating and 1.8h at feed gates without eating while they were still locked in the gates. Cows lay down for 10.4h and stood in stalls for 3.2h. The cows also spent 2.8h standing in aisles, but only 0.5h in the milking area. In late lactation, cows spent 1h more lying, but less time standing in stalls and less time eating and at the feed gates. Time budget traits were moderately repeatable although highly consistent across lactation stages. Estimates of heritability were moderate for eating time (0.20) but almost zero for lying time. Correlations showed that cows with higher yield spent more time eating and less time lying. As there is a trade-off between lying time and eating time, lying time approached lower limits for cows with highest yields. It is suggested that time is viewed as an important but restricted resource that cows may be short of while trying to maintain high yields.

Seasonal variation in time budgets and milk yield for Jersey, Friesland and crossbred cows raised in a pasture-based system

The time budgets and daily milk yield of Jersey and Friesland cows and their crosses were compared in a pasture-based system by recording the time spent grazing, drinking, lying, standing and walking in four seasons of the year (cool-dry, hot-dry, hot-wet and post-rainy). Observations were made from 0800 to 1400 hours on seven cows per breed. Seven observers monitored the cows at 10-min intervals for 6 h using stop watches. Time spent standing was higher (P < 0.05) for Friesland compared to Jersey cows and the crossbred cows during the hot-wet season. Time spent walking differed among the three genotypes with the Jersey spending more time (P < 0.05) in both hot-wet and cool-dry seasons. No differences were noted on time spent lying down (P > 0.05) across the genotypes in the hot-wet season. In the cool-dry season, differences in time spent grazing (P < 0.05) were noted with the Jersey cows spending more time. The Friesland and the crossbred spent more time lying down (P < 0.05) than the Jersey cows in the cool-dry season. No time differences were noted for time spent standing (P > 0.05) in the same season. The Jersey cows spent the longest time walking (P < 0.05) during the cool-dry period. There were seasonal differences in time spent in all activities (P < 0.05). Time spent on grazing was longest in post-rainy season and lowest in hot-wet season. Differences were observed in the time spent lying down (P < 0.05). The longest period was observed in the hot-dry season and lowest in the hot-wet season. Daily milk yield varied (P < 0.05) with breed with the Friesland and Jersey producing higher yields than the crosses. The highest amount was produced in hot-dry and the least in hot-wet season. Milk yield and lying down were positively correlated (P < 0.05) in Jersey and Friesland cows. Standing was negatively correlated with milk yield (P < 0.05) in both Friesland and Jersey cows. No significant relationship was observed for the crossbred cows. It was concluded that the genotypes show different levels of sensitivity to seasons and that a relationship exists between milk yield and time budgets.

Effects of lactation on the time‐budgets and foraging patterns of female black howlers (Alouatta pigra)

Lactation is an energy demanding phase in the reproductive cycle of female mammals. For this reason, several studies have assessed the effects of lactation on female behavior. In this study we examine the influence of lactation on the time-budgets and foraging patterns of female black howlers (Alouatta pigra) in Campeche, Mexico. We observed 32 adult females and 35 infants belonging to 14 groups of black howlers for a total of 2,224 focal hours. We found that lactating females spent more time being inactive and feeding from fruits than nonlactating females. In addition, during the first two-thirds of lactation females were more active (i.e., rested less, fed more, devoted more time to social activities, and moved more) and foraged more intensively (i.e., ranged over larger distances, used more feeding trees and feeding species, and consumed more leaves) than females in the last third of lactation. Lactation seems to force black howler females to reduce activity and to maximize the intake of high-quality foods, with inactivity being the highest during late lactation, when females probably face the cumulative effects of nursing older infants and of a new pregnancy. Early lactation is probably the most energetically demanding stage of lactation for black howler females. This study demonstrates that despite being energetically constrained by a highly folivorous diet, reproductive state affects several dimensions of the behavior of black howler females. Therefore, variation in time-budgets and foraging strategies of howlers has been probably underestimated by previous research that has not considered physiological differences among individuals.

Between breed genetic variation for welfare-related behavioural traits in domestic fowl

Feather pecking (FP) resulting in feather loss and cannibalism (C) is an important welfare problem in domestic fowl ( Gallus gallus domesticus). Behavioural hypotheses to explain this behaviour have generally been proposed on the basis of within breed experiments or by comparing two lines. We examined these hypotheses by utilising a multi-breed experimental design to estimate the between breed genetic variation for feather pecking and cannibalism, behavioural time budgets and measures of fear, sociality and coping strategy. There was extensive between breed (genetic) variation in feather pecking, cannibalism and general pecking behaviour. There was no evidence for between breed genetic variation in time budgets; that for fear and coping strategy was slight whereas some measures of sociality were moderately high. Between breed genetic correlations between behavioural traits and feather score, skin score and mortality were low and those between sociality and skin lesions and culling were labile. We conclude that there is a strong genetic basis for damaging feather pecking and cannibalism and that these behaviours are not strongly related genetically to other behavioural traits.

Influence of growth rate retardation on time budgets and energetics of Arctic Tern Sterna paradisaea and Common Tern S. hirundo chicks

Time budgets of free‐living chicks of Arctic Terns Sterna paradisaea and Common Terns S. hirundo throughout development are presented with special reference to changes in time allocation when growth rate varies. Chicks of both species were inactive most of the time observed (87%). Time allocated to the different behaviours changed during development and was generally better correlated with body mass than age. Slower growing nestlings were brooded more and allocated more time to quiescence and less time to locomotion, preening, begging and attacking (the latter two significant only for the Arctic Tern). The energetic implications of variation in time budgets with age and growth rate were considered. Parental brooding resulted in an average energy saving of nearly 40% of an individual nestling's thermoregulatory costs. Whereas thermoregulatory costs remained nearly unchanged in Arctic Tern chicks, these were negatively correlated with growth rate in Common Terns. Tentatively, we estimated a 30% reduction in a nestling's total energy requirement for a 50% reduction in average growth rate for both species.

Interspecific variation in time budgets among sympatric dabbling ducks

The effect of some of the ecological differences among Swedish dabbling ducks, population densities and sex ratios on the proportion of time allocated to foraging was studied during the breeding season 1986 and 1987. Time budget data were collected at southern Gotland, Sweden, and correlation analyses were done with ecological differences determined from the literature and from observations. Increasing male bias in the sex ratios increased the amount of time spent vigilant early in the breeding season for both sexes in April 1987 and for males in May 1987, and also increased the amount of movements of males in April 1987 and of females in May 1986, but decreased movements of males in June 1986. The amount of time spent vigilant did also decrease with increasing male bias for females in June 1986. The proportion of time spent foraging by females in May 1986, but also in May 1987 and June 1986, decreased as the male bias increased. In early breeding season (April), the proportion of time devoted to aggressions (for males) and movements (for females) were positively correlated with the population densities. This did not, however, lead to decreased foraging time. In late season (July) the foraging time was positively correlated with population densities, indicating intraspecific exploitative competition for prey. Migration distance and degree of carnivory did not influence amount of time allocated to foraging. In conclusion, it was shown that sex ratios and population densities did influence time allocation among dabbling ducks during some parts of the breeding season.

Environmental influences on mountain gorilla time budgets.

Data on the time budgets of mountain gorillas (Gorilla gorilla beringei) were collected during field studies in the Virunga Volcanoes region of Rwanda and Zaire. Focal sampling was used to determine the proportion of time that individuals of different age/sex classes spent in several mutually exclusive activity states. The gorillas spent the majority of daylight hours feeding; most of the rest of the day was devoted to resting, with little time spent moving or engaged in social activity. The time budget varied among the different subhabitats used by the gorillas, and the gorillas satisfied subsistence needs more quickly when in areas where food was more abundant and/or of better nutritional quality. Silverbacks spent more time feeding than all other age/sex classes, but age/sex class differences were not great. All age/sex classes responded to variability in habitat quality in similar fashion. Unlike the case for many other primates, there was no significant seasonal variation in time budgets. There was a direct relationship between group size and time spent feeding, although variation in relation to group size was lower than that in relation to variation in habitat quality. These results are consistent with the relationship of feeding time to body size in primates. They are also consistent, with other evidence that social foraging entails a cost to gorilla females, but that this cost is low in comparison to those faced by many other primates. Permanent association with males apparently offers little ecological disadvantage to females, who are likely to be more than compensated by mutualistic benefits.