Foraging Substrate Research Articles

Sex-related Differences in Habitat Use in Wintering American Kestrels

AbstractWe investigated sex-related differences in habitat use in wintering American Kestrels (Falco sparverius) at two scales: within a 10 m radius and within a 100 m radius of perch sites. Female kestrels used areas containing a higher percentage of short vegetation (<0.25 m high) suitable for foraging than did males at both scales (100 m radius females 80%, males 69%; 10 m radius females 80%, males 73%). At both scales, females had more pasture (a high-quality foraging substrate) available than did males; areas within a 100 m radius of male perch sites contained more woodlot than did female perch sites. Logistic regression models indicated greater overlap between male and female habitat use on a 10 m radius scale than on a 100 m radius scale, suggesting that males may preferentially select smaller areas devoid of woody vegetation relative to what is available within 100 m radius of perch sites. Our results suggest that males may be constrained to winter in areas with lower overall foraging opportunities and possibly higher predation risk than areas used by females. Our work supports the hypothesis that males and female kestrels prefer open areas as wintering habitat.

Foraging Substrate and Escape Substrate: Patch Use by Three Species of Gerbils

The three Negev Desert gerbils, Gerbillus pyramidum (greater Egyptian sand gerbil), Gerbillus allenbyi (Allenby's gerbil), and Gerbillus dasyurus (Wagner's gerbil), show strong patterns of habitat selection along a gradient, from sandy to loessal to rocky habitats, respectively. Within a habitat, a gerbil must be able to harvest seeds and escape predators. To test for the habitat-specific processes governing habitat partitioning by gerbil species, we investigated the roles of escape substrate and foraging substrate in affecting patch use. In an aviary, we manipulated predatory risk using artificial illumination and the presence of Barn Owls (Tyto alba). We manipulated escape substrate and foraging substrate by creating habitat and food patches of sand, rock (a mix of sand and small rocks), and loess substrate. In response to owls, all three gerbil species foraged less and increased their giving-up densities (GUDs) in food patches. In response to foraging substrate, all three species had their lowest GUDs on sand, and their highest GUDs on loess. Gerbillus dasyurus responded less intensively to owls when loess comprised the foraging substrate. Also, each species depended more on its “home” foraging substrate than did the others for the total amount of seeds harvested. Gerbillus pyramidum in particular harvested a greater proportion from sand than did G. dasyurus. Escape substrate had no direct effects on patch use. However, G. dasyurus exhibited a foraging substrate × escape substrate interaction, as the rocky escape substrate enhanced its use of the rocky foraging substrate. Our experiments show that foraging substrate contributes to habitat use by G. allenbyi and G. pyramidum, and that both foraging substrate and escape substrate contribute to habitat use by G. dasyurus.

Sex-related Differences in Habitat Use in Wintering American Kestrels

Abstract We investigated sex-related differences in habitat use in wintering American Kestrels (Falco sparverius) at two scales: within a 10 m radius and within a 100 m radius of perch sites. Female kestrels used areas containing a higher percentage of short vegetation (<0.25 m high) suitable for foraging than did males at both scales (100 m radius females 80%, males 69%; 10 m radius females 80%, males 73%). At both scales, females had more pasture (a high-quality foraging substrate) available than did males; areas within a 100 m radius of male perch sites contained more woodlot than did female perch sites. Logistic regression models indicated greater overlap between male and female habitat use on a 10 m radius scale than on a 100 m radius scale, suggesting that males may preferentially select smaller areas devoid of woody vegetation relative to what is available within 100 m radius of perch sites. Our results suggest that males may be constrained to winter in areas with lower overall foraging opportuniti...

Legislative methods for specifying stocking density and consequences for the welfare of finishing pigs

EU Council Directive 91/630/EEC specifies a banded system of increasing space allowance for finishing pigs, which imposes a degree of inflexibility on housing management. The study presented in this paper investigated whether there are measurable differences in welfare when pigs are kept at the minimum stocking densities described by the bands of the regulations (B), compared to those calculated using an equation (E) relating space allowance and live weight; Area (m 2)=0.030×Live weight 0.67 (kg). Furthermore, the study compared different floor types [fully slatted (F), solid without straw (N) or solid with straw bedding (S)] at these stocking densities. Eighteen groups of 12 pigs were allocated to this 2×3 factorial experiment, between 29 and 110 kg live weight. Data were collected on a range of welfare parameters. No effects of the space allowance treatments or interactive effects between space allowance and floor type were found. S pigs showed higher levels of manipulative behaviours than N pigs (47 vs. 57% of time spent active, N vs. S; P<0.01), with S pigs manipulating straw approximately 45% of active time. Observed skin damage was less in N pigs compared to S pigs, but this may have been confounded by their pens being more soiled (59 vs. 77% clean floor area, N vs. S; P<0.001). Post slaughter assessments did not show differences between treatments. It was concluded that straw provision may provide welfare benefits in terms of pen cleanliness and its properties as a foraging substrate. The results indicated that the equation method of specifying minimum space requirements, which offers practical advantages compared with the banded method, provides a similar degree of welfare. This conclusion may help to form the basis for future European welfare legislation.

The influence of dietary fibre and the provision of straw on the development of stereotypic behaviour in food restricted pregnant sows

The inability of sows to appropriately express feeding motivation has been identified as one of the major contributory factors in the development of stereotypic behaviour. It has been proposed that the development of these repetitive behaviours may be mitigated either by reducing feeding motivation, for example by feeding sows bulky diets which increase gut fill, or by providing sows with a foraging substrate. Forty-eight nulliparous sows were used in a 2×2 factorial design comparing the interactive effects of a high fibre diet and the provision of straw on the behaviour of food restricted pregnant sows. Sows were fed the same daily weight of iso-energetic conventional (C) or high fibre (H; containing 600 g of unmolassed sugar beet pulp per kg of food) diets during gestation and were housed in pens with straw (S) or without straw (N). Behaviour was recorded by direct observation and video during their second gestation. Levels of chain and bar-directed behaviour were highest in the hour immediately following food presentation. Although no difference was found in activity levels or levels of chain and bar manipulation between dietary treatments, sows fed the high fibre diet spent less time manipulating straw (C vs. H; 46.3 vs. 37.0%, P<0.05) than sows fed the conventional diet, after adjustment for the time spent feeding (C vs. H; 20.0 vs. 29.4%, P<0.001). In addition, increasing dietary fibre tended to reduce the level of manipulation of substrates other than straw, but only in the final hour of observation. This suggests that fermentation of sugar beet pulp may play a role in maintaining levels of satiety later in the day, when the satiety levels of conventionally fed sows are starting to decline. The provision of straw significantly reduced levels of chains and bar manipulation (S vs. N; 14.4 vs. 35.3%, P<0.01), and levels of non-manipulative oral behaviour (S vs. N; 0.4 vs. 3.8%, P<0.05). Although the daily provision of fresh straw may provide a reliable way of reducing pen component manipulation and the development of stereotypic behaviour, it is unclear to what extent welfare is improved by exchanging excessive pen component manipulation with the excessive manipulation of straw.

Levels of aggression in floor fed sows: effects of straw bedding and high fibre diets

In competitive feeding systems in which sows are group rather than individually fed, aggression can arise as sows compete for limited supplies of food (Csermely and Wood-Gush, 1990). Aggression may also occur as a result of sows’ motivation to feed remaining unsatisfied due to restricted access to food (Buré, 1991). Feeding sows a high fibre diet which will rapidly increase gastric distention (Brouns et al., 1997) may reduce both the motivation to compete for food and aggression associated with sustained feeding motivation. Sows provided with straw bedding may use straw as a foraging substrate with which to express their foraging behaviour. The aim of this experiment was to investigate the interactive effects of a high fibre diet and straw bedding on levels of aggression in floor fed sows.

Levels of aggression in floor fed sows: effects of straw bedding and high fibre diets

In competitive feeding systems in which sows are group rather than individually fed, aggression can arise as sows compete for limited supplies of food (Csermely and Wood-Gush, 1990). Aggression may also occur as a result of sows’ motivation to feed remaining unsatisfied due to restricted access to food (Buré, 1991). Feeding sows a high fibre diet which will rapidly increase gastric distention (Brouns et al., 1997) may reduce both the motivation to compete for food and aggression associated with sustained feeding motivation. Sows provided with straw bedding may use straw as a foraging substrate with which to express their foraging behaviour. The aim of this experiment was to investigate the interactive effects of a high fibre diet and straw bedding on levels of aggression in floor fed sows.

Comparison of bovine rumen liquor and bovine faeces as sources of micro-organisms for the in vitro gas production technique for assessing silages of maize and maize plant fractions

A previous study (Mauricio et al., 1998) with 12 forage substrates (straw, hay and dried grasses) showed a high correlation between rumen liquor and faeces for total gas production and in vitro organic matter digestibility (OMD). However parameters estimated using faecal inoculum were generally lower man when using rumen liquor. To confirm this observation, a second study was conducted using maize silage and silages made from maize plant fractions.

Comparison of bovine rumen liquor and bovine faeces as sources of micro-organisms for thein vitrogas production technique for assessing silages of maize and maize plant fractions

A previous study (Mauricioet al., 1998) with 12 forage substrates (straw, hay and dried grasses) showed a high correlation between rumen liquor and faeces for total gas production andin vitroorganic matter digestibility (OMD). However parameters estimated using faecal inoculum were generally lower man when using rumen liquor. To confirm this observation, a second study was conducted using maize silage and silages made from maize plant fractions.

Feather pecking in domestic chicks: its relation to dustbathing and foraging

Feather pecking is a serious problem in poultry housing, as it may lead to feather damage, injuries and even mortality. We tested predictions of the two prevalent hypotheses claiming that feather pecking is related to dustbathing and foraging, respectively. Forty-two groups of 30 laying hen chicks,Gallus gallus domesticuswere reared in pens with a slatted floor. Access to sand as a dustbathing substrate and straw as a foraging substrate was varied between groups. The rate of feather pecking was measured in early development up to week 7. The provision of a sand area did not prevent the chicks from developing high rates of feather pecking that caused injuries. Chicks that had access to sand from day 10 showed higher rates of feather pecking than chicks that had access to sand from day 1. The provision of straw to chicks that had developed high rates of feather pecking led to a decrease in this behaviour. Chicks that could use both sand and straw from day 1 on did not show high rates of feather pecking, and no injuries were observed in these groups. There was no significant difference in dustbathing activity between housing conditions characterized by high or low rates of feather pecking. On the other hand, foraging activity was inversely related to the rate of feather pecking, and the occurrence of feather pecking could be delayed from week 4 to week 7 by postponing procedures that led to changes in foraging behaviour. In conclusion, the results show that the presence of an appropriate substrate for dustbathing does not prevent domestic chicks from developing feather pecking. On the other hand, housing conditions that promote foraging behaviour are effective in reducing and preventing feather pecking.

The effect of high fibre diet and the provision of straw as a foraging substrate on the development of stereotypic behaviour in group housed sows

Food restriction appears to be a contributory factor in the development of stereotypic behaviour in sows. The sustained feeding motivation following the ingestion of a small meal of concentrated food results in high levels of foraging in the post-prandial period. In the absence of a suitable foraging substrate to facilitate the expression of complex behaviours, foraging may be channelled into a limited number of highly repetitive behavioural sequences (Lawrence and Terlouw 1993). High fibre diets may mitigate the development of such behaviours (Brouns, Edwards and English 1994) by providing increased gut fill in the post-prandial period, thereby reducing foraging motivation and consequently the need for a foraging substrate. The aim of this study was to examine the interactive effects of a high fibre diet and the provision of straw on levels of stereotypic behaviour in sows.

Provision of straw as a foraging substrate reduces the development of excessive chain and bar manipulation in food restricted sows

Pregnant sows fed at commercial levels remain highly food motivated for most of the day. The inability to express this behaviour appropriately may, under certain conditions, result in the development of abnormal oral activities such as stereotypic chain and bar manipulation. Ninety-six gilts, all between 1 and 3 weeks post service, were entered into a 2 × 2 factorial design comparing food level (low, 1.8 kg/23 MJ day −1 (L); high, 3.2 kg/40 MJ day −1 (H)) and the provision of a foraging substrate (S, straw; N, no straw). The gilts were loose housed in groups of six with individual stalls. A 70 cm chain loop was attached to the front of each stall. The sows were fed at 09:00 h, during which time S sows received straw (approximately 1.5 kg per sow). Behaviour was recorded over the first two parities, by time sampling for the 2 and 6 h after the start of feeding and over 24 h using video recordings. Activity levels were highest just after feeding, with L sows being more active than H sows (L vs. H, 79% vs. 49% for the second hour after the start of feeding, F 1,12 = 41.5, P < 0.001). Most of the postprandial activity consisted of manipulating substrates. In LN sows, particularly in Parity 2, this behaviour was mainly directed towards chains and bars, resulting in levels three to four times higher than in other groups (26%, 7%, 4% and 4% for the second hour after feeding for LN, LS, HN and HS respectively; Tukey's HSD, P < 0.05). LS sows directed their foraging behaviour mainly towards the straw. It is concluded that in food-restricted pregnant sows, abnormally high levels of chain and bar manipulation can be prevented by providing straw which apparently acts as a foraging substrate.

Foraging Efficiencies of Competing Rodents: Why Do Gerbils Exhibit Shared-Preference Habitat Selection?

Two coexisting gerbil species, Gerbillus allenbyi (26 g) andG. pyramidum (40 g), exhibit shared-preference optimal habitat selection. In a mosaic of stabilized sands and semistabilized dunes, both species primarily prefer the semistabilized-dune habitat. We hypothesized that foraging benefit, due to the lower amount of loess in the semistabilized dunes, is the underlying cause for this preference. We tested this by measuring foraging efficiencies (giving-up density of seeds) in both manipulated foraging substrates (sand and loess) and natural habitats (semistabilized dunes, stabilized sands, and loess plateau). We also compared harvest rates on sand and loess. We used the loess substrate and loess plateau habitat to exaggerate the effect of loess on the gerbils' foraging behavior. Regarding foraging substrate, gerbils had significantly higher foraging efficiencies on sand in the field. They also had significantly higher harvest rates on sand in the laboratory. Regarding habitats, both species were more efficient in semistabilized dunes than in stabilized sands or loess plateau. Additional results suggested that the area surrounding a foraging patch had an important role in predator avoidance. We concluded that the semistabilized-dune habitat allowed gerbils to forage more efficiently in a patch, because it is easier to dig for seeds in the sandy substrate found there, and because gerbils enjoyed lower predatory risk traveling to and from the seed patch. The results supported the hypothesis that foraging benefit is the basis of the shared-preference habitat selection of the gerbil species

Effects of Substrate on Foraging Decisions by a Namib Desert Gerbil

We investigated the role of foraging and escape substrates on foraging decisions of a Namib Desert gerbil, Gerbillurus tytonis (Rodentia), in the field. We used the giving-up density technique, which uses artificial seed trays to assess foraging decisions. We tested whether the foraging decisions made in the trays were an artifact of prior knowledge of a food source by comparing giving-up densities in trays that were randomly placed in different parts each night with that in trays that remained in fixed position throughout the experiment. There was no significant difference in giving-up densities between these two treatments, which suggests that prior knowledge of food location does not affect foraging decisions. We examined the preferences of gerbils for the different substrates using seed trays. The gerbils showed significant differences among habitats in the amount of seed taken and between new-moon and full-moon nights. They removed more seeds where the difference between the size of the seeds and the size of the sand substrate was large. This finding is congruent with the hypothesis that tactile discriminatory ability affects the foraging behavior of these rodents. Although these rodents alter their foraging behavior in response to predation risk, there was no significant difference in the amount of seeds taken in habitats differing only in the degree of compaction of escape substrates.

On the Selection of Tree Species by Acanthizidae in Open-forest Near Sydney, New South Wales

SummarySelection between tree species as foraging substrates by four species of Acanthizidae was studied in an open eucalypt forest near Sydney, New South Wales. Weebills Smicrornis brevirostris, Striated and Little Thornbills Acanthiza lineata and A. nana foraged more often than expected on the foliage of Narrow-leaved Ironbark Eucalyptus crebra than on that of Grey Box E. moluccana. By contrast Gerygone olivacea used the two trees in about the same proportion as the amount of foliage of each species. Weebills and Striated Thornbills selected Narrow-leaved Ironbark foliage as a foraging substrate more often than Little Thornbills in winter but not in spring. Little Thornbills foraged on Narrow-leaved Ironbark foliage more often in spring than in winter. The selection of eucalypt foliage as a foraging substrate is correlated with the abundances and kinds of invertebrates found on the two tree species. Invertebrates were generally more abundant on the foliage of Narrow-leaved Ironbark than on that of Grey Box in both winter and spring. Lerp-forming psyllid insects, however, were more abundant per leaf on Grey Box than Narrow-leaved Ironbark in winter, but not in spring. Grey Box leaves are larger than those of Narrow-leaved Ironbark and when the abundances of psyllids were corrected for leaf area (i.e. as numbers/cm2), the difference between Grey Box and Narrow-leaved Ironbark in winter was not significant. However, in spring the numbers of psyllids/cm2 on Narrow-leaved Ironbark foliage was greater than on Grey Box foliage. The differences in invertebrate abundances account for some of the differences in the use of the two eucalypts as foraging substrates, but variability in invertebrate abundances between leaves and individual trees, as well as differences in foliage morphology, may also have been important.

Degradation and utilization of forage hemicellulose by rumen bacteria, singly in coculture or added sequentially

Procedures for sequential addition experiments were developed to study the mechanisms involved in the synergistic and inhibitory interactions observed in forage hemicellulose digestion by rumen bacterial cocultures. One organism was allowed to ferment a forage substrate, the culture tube was sterilized and then inoculated with a second organism. No differences were found in the extent of degradation or utilization between fermentations sterilized by oxidation or heat, and based on ease of handling, heat was used in all subsequent experiments. Studies were conducted with Fibrobacter succinogenes A3c, Ruminococcus flavefaciens B34b and Prevotella ruminicola H2b, singly and in all possible combinations. Results from the sequential addition studies substantiated earlier suggestions that the increase observed in hemicellulose utilization results from initial solubilization of the hemicellulose from the forage by the non-utilizer and subsequent utilization of subsequent utilization of this solubilized polysaccharide by the utilizing, but non-degrading organism.

The effect of feeding regime and the provision of a foraging substrate on the development of behaviours in group-housed sows

The effect of feeding regime and the provision of a foraging substrate on the development of behaviours in group-housed sows

Some Determinants of Dispersal by Crab Spiderlings

Dispersal of young from their natal sites may be determined by their numbers or by availability of hunting sites, possible correlates of maternal hunting success and habitat selection. To test these alternatives, I observed the dispersal (ballooning on silken threads, moving on threads among vegetation, walking) of second—instar crab spiders Misumena vitia (Thomisidae) from nests and experimental releases that differed in number of spiderlings and proximity to hunting sites. The probability of ballooning by young crab spiders did not differ with size of clutch, individual size, or egg size; however, substrate had a strong effect. Spiderlings often ballooned within minutes from nests not near hunting sites, but usually remained much longer, up to several days, on excellent foraging substrates, typically goldenrod (Solidago spp.) flowers. Spiderlings released on both goldenrod in bud and asters (Aster sp.) in bud left quickly, often ballooning directly from them. Spiderlings from nests within 1 m of flowering goldenrods usually moved to these flowers, ones several metres away seldom moved to them. The choice of nest sites by the spiderlings' mothers thus indirectly affected the spiderlings' dispersal behavior. The lack of a significant correlation between maternal clutch size and spiderling dispersal means that dispersal does not change maternal fitness differences originally resulting from differential success in foraging (reported elsewhere).

A Field Test of Risk‐Sensitive Foraging in Black‐Capped Chickadees (Parus Atricapillus)

The combination of a nonlinear functional relationship between energy intake and fitness, along with stochasticity in foraging success, has led to the development of risk—sensitive foraging models. These models are significant because they can lead to predictions different from those of the traditional deterministic models based upon a premise of simple energy intake rate maximization. The risk—sensitive foraging models suggest that the energy state of the forager could affect its sensitivity to the variance in foraging success associated with a particular strategy. Empirical tests conducted on several species of small, captive animals have generally supported the risk—sensitivity models; however, no experiments on free—living animals had been done. I conducted the first field test of a risk—sensitive foraging model. The test was conducted on Black—capped Chickadees (Parus atricapillus), using an experimental feeder that mimicked their natural foraging substrate and allowed me to manipulate the expected value and the variances of prey. I estimated chickadee daily energy expenditure and their rate of food intake and determined them to be on a positive energy budget while using the feeder. The birds were given a choice of two prey types with equal expected values but different variances. Consistent with a risk—sensitive foraging model, the chickadees showed a clear, significant preference for the lower variance prey. Analysis of the foraging rates of the birds revealed no significant difference related to prey type other than the difference in variance. The results suggest the importance of the incorporation of environmental stochasticity into models of animal foraging.

Foraging Segregation of Australian Warblers (Acanthizidae) in Open Forest near Sydney, New South Wales

Nine species of Australian warblers (Acanthizidae) occur together in open eucalypt forests near Sydney, New South Wales. The ecological segregation of six of these species, which foraged primarily in shrub and tree vegetation and are similar sized (5-8 g), was studied during 1984. Seasonal data were obtained for five species; Weebill Smicromis brevirostris, White-throated Warbler or Gerygone Gerygone olivacea, Striated Thornbill Acanthiza lineata, Little Thornbill A. nana and Buff-rumped Thornbill A. reguloides. The sixth species, Brown Thornbill A. pusilla, was uncommon and seasonal comparisons were not possible. As has been reported for similar species associations in the northern hemisphere, the species studied differed in prey attack behaviour, foraging heights, use of plant species and selection of foraging substrates. There were significant seasonal differences in the use of foraging resources. For example, bark was more important as a foraging substrate in autumn and winter than in spring and summer. A. reguloides foraged more on the ground outside the breeding season than when nesting. The increased abundance of flying insects during summer correlated with an increased use of hawking and snatching as prey attack behaviours by all species. Despite their differences, species broadly overlapped in their use of resources and had similar niche breadths. Overlaps in the use of resources were greatest during spring, when prey resources were probably most abundant, and least in autumn when prey decreased in abundance. The forest in which the study was conducted was dominated by two species of eucalypts. Birds selected between these species but used the same foraging behaviours in each. Despite the selection between eucalypt species, the limited array of plant species had little effect on species richness. Comparison of niche breadths for the same species at other sites where there were different numbers of co-existing species suggests that niche breadth and overlap may be primarily determined by the availability of resources (e.g. substrates, plant species) and not by competitive interactions between the species themselves.