Small Mammal Predators Research Articles

Predator–induced synchrony in population oscillations of coexisting small mammal species

Comprehensive analyses of long-term (1977-2003) small-mammal abundance data from western Finland showed that populations of Microtus voles (field voles M. agrestis and sibling voles M. rossiaemeridionalis) voles, bank (Clethrionomys glareolus) and common shrews (Sorex araneus) fluctuated synchronously in 3 year population cycles. Time-series analyses indicated that interspecific synchrony is influenced strongly by density-dependent processes. Synchrony among Microtus and bank voles appeared additionally to be influenced by density-independent processes. To test whether interspecific synchronization through density-dependent processes is caused by predation, we experimentally reduced the densities of the main predators of small mammals in four large agricultural areas, and compared small mammal abundances in these to those in four control areas (2.5-3 km(2)) through a 3 year small-mammal population cycle. Predator reduction increased densities of the main prey species, Microtus voles, in all phases of the population cycle, while bank voles, the most important alternative prey of predators, responded positively only in the low and the increase phase. Manipulation also increased the autumn densities of water voles (Arvicola terrestris) in the increase phase of the cycle. No treatment effects were detected for common shrews or mice. Our results are in accordance with the alternative prey hypothesis, by which predators successively reduce the densities of both main and alternative prey species after the peak phase of small-mammal population cycles, thus inducing a synchronous low phase.

Effects of a predator control experiment on Grey-winged Francolin (Scleroptila africanus) populations

One of the key findings of the Grey-winged Francolin Research Project conducted on the Stormberg Plateau, Eastern Cape Province, South Africa during 1988–1992 was that predation, particularly by small mammals on incubating female Greywinged Francolin Scleroptila africanus and their nests, was a major cause of mortality. To assess the response to this predation, small mammal predators were trapped intensively during the francolin breeding season in two 500ha plots, one on the farm Buffels Fontein and one on the farm Boschoff's Kraal. Trapping was not simultaneous on the two plots, but rather during 1992–1994 on Buffels Fontein and during 1995 and 1996 on Boschoff's Kraal. The Yellow Mongoose Cynictis penicillata was the most commonly trapped predator species (83%) in both plots. Grey-winged Francolin numbers during trapping in the plot at Buffels Fontein declined less during a drought than those in the untrapped control plot at Boschoff's Kraal. This suggests that the control of predators may buffer the negative effects of drought on Grey-winged Francolin reproductive success. However, the increases of populations in both plots during a period of higher-than-average rainfall indicate that Grey-winged Francolin can withstand predation during normal rainfall years.

Predators indirectly protect tundra plants by reducing herbivore abundance

The role of predators in controlling herbivores and indirectly affecting plant abundance is controversial, and some have argued that such trophic cascades are rare in terrestrial habitats. To examine the potential of trophic cascades in a shrubby tundra ecosystem, vole densities, plant damage and plant cover were examined in areas with and without small mammal predators. On islands without predators, vole densities and plant damage were upto five times higher compared with predator‐rich mainland habitats. As a consequence, the abundance of three out of five dwarf shrub species was substantially reduced on predator‐free islands, providing evidence for strong cascading effects in a rather large‐scale terrestrial system. Herbs on the other hand were not affected by the increased herbivory on islands. This suggests that the strength of trophic cascades also depends on the interaction between plant type and seasonality.

Small mammal abundance in Mediterranean post-fire habitats: a role for predators?

We studied patterns of small mammal abundance and species richness in post-fire habitats by sampling 33 plots (225 m 2 each) representing different stages of vegetation recovery after fire. Small mammal abundance was estimated by live trapping during early spring 1999 and vegetation structure was sampled by visual estimation at the same plots. Recently–burnt areas were characterised by shrubby and herbaceous vegetation with low structural variability, and unburnt areas were characterised by well developed forest cover with high structural complexity. Small mammal abundance and species richness decreased with time elapsed since the last fire (from 5 to at least 50 years), and these differences were associated to the decreasing cover of short shrubs as the post-fire succession of plant communities advanced. However, relationships between vegetation structure and small mammals differed among areas burned in different times, with weak or negative relationship in recently burnt areas and positive and stronger relationship in unburnt areas. Furthermore, the abundance of small mammals was larger than expected from vegetation structure in plots burned recently whereas the contrary pattern was found in unburned areas. We hypothesised that the pattern observed could be related to the responses of small mammal predators to changes in vegetation and landscape structure promoted by fire. Fire-related fragmentation could have promoted the isolation of forest predators (owls and carnivores) in unburned forest patches, a fact that could have produced a higher predation pressure for small mammals. Conversely, small mammal populations would have been enhanced in early post-fire stages by lower predator numbers combined with better predator protection in areas covered by resprouting woody vegetation.

The Effect of Supplemental Prey and Prescribed Fire on Success of Artificial Nests

Nest predation hinders recruitment of avian species and may be affected by availability of alternative prey and amount of nesting cover. Therefore, we evaluated effects of food abundance (i.e., supplemental prey) and time since prescribed fire on nest success of artificial ground nests. We monitored the fate of 759 artificial ground nests from June to July 2000. No interaction (P= 0.74) occurred between fire and supplemental prey treatments. Nest success in prey-supplemented plots (37.6%) did not differ (P= 0.70) from control plots (44.9%), and nest success in burned plots (41.8%) did not differ (P = 0.86) from nonburned plots (40.7%). Motion-sensitive cameras placed on feeders revealed that mesomammals accounted for >80% of visits to feeders, indicating that supplemental prey was detected and consumed by mesomammals. Nest predators differed as a function of food abundance, with combined avian and small-mammal predation being greater in prey-supplemented (46.5%) than in control (25.9%) plots. Nest predators also differed as a function of prescribed fire Avian predation of nests was greater in burned (13.7%) than nonburned (9.9%) plots. whereas small-mammal predation was greater in nonburned (30.9%) than in burned (15.1%) plots. Altering food and cover to manage nest success may result in compensatory predation. Further work to quantify the extent of compensatory predation is needed to fully understand trade-offs of various practices for managing nest predation.

Correcting observer effect bias in estimates of nesting success of a coastal bird, the White-fronted Plover Charadrius marginatus

Capsule A recently developed observer-effects model gives better estimates than the survival model. Aims To compare the performance of the traditional survival model with that of an observer-effects model in estimating nesting success. Methods We used survival data from 654 nests in a covariate-dependent extension of a maximum-likelihood estimator model to simultaneously estimate daily survival rate and observer effect on nesting success in four different sectors of a study site. Standard likelihood-ratio tests and Akaike's information criterion differences were used to compare model performances. Results A significant (negative) observer effect was detected in one of four sectors of the study area, and was probably attributable to small mammal predators. Despite significantly higher predation risk during the laying period, there was a significant positive observer effect during the laying period, contrasting with a weak negative effect during the incubation period, suggesting that an observer's tracks around unattended nests reduced predation risk. Likelihood-ratio tests indicated a significantly better fit using the observer effects model versus the Mayfield survival model in four of six scenarios. Conclusion The observer-effects model accounts for bias in estimates of nest survival rates, and is preferred over the survival model because the inclusion of observer effect as a variable does not over-parameterize the model.

An assessment of the potential influence of rainforest fragmentation on small terrestrial mammal predation in French Guiana

L’abondance et la richesse des principaux prédateurs de petits mammifères (serpents et carnivores) ont été estimées dans une forêt fragmentée suite à la mise en service du barrage de Petit-Saut (Guyane française). Les petits mammifères terrestres (Rongeurs et Marsupiaux) ont été capturés et leurs prédateurs recensés dans une zone de référence, sur deux îles (28 et 60 ha) et sur 33 îlots créés par l’inondation. Quatre espèces de félins et deux espèces de Mustélidés ont été observées de 1994 à 1996. Nous avons observé 121 serpents dont 72, appartenant à 13 espèces, étaient des prédateurs de petits mammifères. Les résultats montrent que les prédateurs de petits mammifères visitent régulièrement les îlots forestiers deux ans après leur isolement Le nombre de serpents a augmenté au cours de l’année qui a suivi l’inondation, puis a chuté à la fois en terme d’abondance et en terme de richesse spécifique, en particulier sur les îles et les îlots. Au cours de la même période, l’abondance des petits mammifères diminuait. Ces résultats, obtenus pendant et juste après la fragmentation forestière, suggèrent qu’une forte prédation sur les petits mammifères dans les îlots forestiers nouvellement formés, peut jouer un rôle important dans les variations de densité et les extinctions locales d’espèces-proies.

Nest‐site selection, egg pigmentation and clutch predation in the ground‐nesting Namaqua Sandgrouse Pterocles namaqua

Nest survival can, among a variety of factors, depend on nest-site complexity and concealment, and clutch crypsis. Nest-site selection by Namaqua Sandgrouse Pterocles namaqua was strongly non-random. Nests were sited within a local concentration of objects, most of them less than 15 cm high and concentrated within 30 cm of the nest centre. Nest-to-object orientation was random, indicating that the nest was sited close to objects neither for shade nor shelter from prevailing winds. A stepwise logistic regression analysis, using nine different object type, height and distance category totals as variables of nest-site complexity and concealment, found no effect of these variables on nest fate (survival vs mammal predation). A random-walk model simulating the foraging movements of a small mammal predator raised the possibility that the high level of nest predation suffered by Namaqua Sandgrouse was largely incidental (i.e. random). Namaqua Sandgrouse eggs were highly variable in appearance, but intra-clutch variability was less than that between clutches of different individuals. Intra-clutch diversity in pigment cover the number of wreathed eggs, the dominant pigment pattern, and the overall shade of the clutch (light/dark) did not affect clutch survival. However, clutches exhibiting diversity in background colout, pigment pattern or pigment intensity between eggs survived significantly better than clutches whose eggs were uniform for these variables suggesting there is some selection for clutch crypsis through visual diversity.

Studies of Ballooning and Resulting Patterns of Locally Contagious Distribution of the Bagworm Thyridopteryx ephemeraeformis (Haworth) (Lepidoptera: Psychidae)

A series of field studies was stimulated by the unexpected finding of a band of junipers (Juniperus virginiana) bearing heavy infestations of bagworms, the band running south-southwest to north-northeast through a woodlot (near Norman, OK) of otherwise lightly infested trees. Fidelity to wind direction was confirmed, and numbers of bagworms ballooning from 3.05 m to 36.58 m was measured, with Tanglefoot® traps mounted on metal fence posts. Ballooning numbers were satisfactorily described with a negative exponential model incorporating both gravitational and trap losses. No significant difference was found between ballooning distances achieved by larvae with and without early-stage bags. A study of infestation levels on ornamental junipers planted around houses on the north and south sides of east-west streets revealed both a strong front- vs. backyard difference, and a weaker but statistically significant side-of-street effect. Patterns reflecting short-range dispersal were found in a linear windbreak planting of northern white cedar (Thuja occidentalis), and in a 12 × 44 = 528-tree lattice of planted junipers (near Urbana, Illinois). A “bonfire” effect showing heaviest infestations in mid-lattice, and reduced infestations on the periphery (especially on the windward edge) was postulated and confirmed. Studies of the effect of increased “target” size of larger trees, and of the incidence of apparent bird and small mammal predation, are also reported.

Nest Predation on Woodland Songbirds: When Is Nest Predation Density Dependent?

Nest predation. if density dependent, may structure avian communities by selecting for nest-site characteristics that dilute the predators' perception of nest density (e.g., by increasing the number and types of potential nest sites) thereby reducing losses to predators. We tested for density dependent nest predation at a site dominated by predation from raccoons, Procyon lotor. and blue jays. Cyanocitta cristata. We used cohorts of 20 artificial ground nests placed on experimental grids at four densities (1.7, 7, 65, and 167 nests/ha). Predation was density dependent for one of two temporal replicates. In a second experiment, we tested for density dependent predation on both ground and shrub nests using more realistic nest densities (3.5 and 8.9 nests/ha) and excluding avian and small mammal predators by placing nylon screening over the nests. Predation was density dependent on artificial ground nests and density independent on shrub nests. Finally, we analyzed predation on natural shrub nests separating out avian (i.e., jays) and large mammalian predation based on disturbance to the depredated nest. In each of three years there was no evidence for density dependent predation. An outbreak of periodic cicadas in the first experiment and the maturation of a large mulberry crop during the second experiment demonstrated the importance of the distribution and abundance of alternative foods on the response of predators toward heterogeneity in nest abundance.

Different impact of pupal predation on populations of Epirrita autumnata (Lepidoptera; Geometridae) within and outside the outbreak range

1. We studied the effect of pupal predation on Epirrita autumnata populations within and outside the outbreak range, in northern and southern Finland, respectively. The purpose of the study was to evaluate the potential of pupal predation to contribute to the contrasting dynamics of northern and southern populations. In addition to overall pupal survival, we separately estimated the influence of small mammal and invertebrate predation. 2. Each summer for a period of 5 years, pupae inside their cocoons were buried in the ground. The pupae were re‐collected before the flight season and checked for damage. Direct and delayed density dependence of pupal survival was tested using the current and the previous year larval density indices, respectively. 3. Annual survival of pupae from both small mammal and invertebrate predation was lower in the south. Daily survival rates did not differ between the south and the north indicating that the difference in annual pupal survival is most likely due to the longer pupal period in the south. 4. In the south, pupal survival was negatively density dependent and resulted from small mammal predation. The results indicate that small mammals may prevent E. autumnata populations from reaching high densities in the south. 5. In the northern study area with a current outbreak, total pupal survival was density independent. Also small mammal predation was density independent, most likely due to predator satiation. Moreover, there was no difference in pupal survival between northern areas with and without a current outbreak. The results indicate that pupal predation was not a significant factor in termination of the outbreak, nor is it likely to contribute to the maintenance of the cyclic density fluctuations. 6. We conclude that low pupal survival and its density dependence are likely to contribute to stability of E. autumnata populations in southern Fennoscandia. On the contrary, shorter pupal period and the lack of density dependent pupal predation may make northern populations more prone to outbreaks. The potential regulating effect of pupal predation in southern populations is due to small mammals being able to respond to changes in E. autumnata densities.

Mortality of the white pine weevil associated with silvicultural practices in jack pine plantations

A synthesis of white pine weevil (Pissodes strobi Peck) mortality caused by predation (insects, birds, and mammalian predators), crowding of pupae, and abiotic factors, acting under different stand conditions given by the type of reforestation, depth of the duff, distance from woody debris, and presence of competing vegetation is presented, based on a four-year study conducted in northeastern Ontario. The type of reforestation (planted vs. aerial seeding) did not influence mortality to immature weevils in the leaders from either bird predation, insect predators and parasitoids or crowding of pupae, but 16% more weevils died during winter in a planted than in a seeded stand suggesting that there was an effect of site condition or small mammal predation on overwintering adults in the duff. Over all conditions, overwintering mortality averaged 76-92% with small mammal predation representing about 5-13%. Site conditions which augmented small mammal populations and predation, such as proximity to woody debris and presence of competing vegetation, had no effect on overwintering mortality of the weevils. The most important factor influencing overwintering mortality was likely the depth of duff where an inverse relationship was observed between mortality and depth. Forest managers should address conditions of duff depth and small mammal predation to increase the already significant overwintering mortality of adult weevils in young jack pine stands. Key words: Pissodes strobi, silvicultural treatments, planted and seeded stands, competing vegetation, duff layers, small mammal predation, overwintering mortality

A model for testing hypotheses of gypsy moth, Lymantria dispar L., population dynamics

A model for simulating long-term gypsy moth ( Lymantria dispar L.) population dynamics in North America has been developed. Simulated ecological processes include larval dispersal, foliage consumption on different host trees, reproduction, and mortality due to natural enemies (virus, 4 guilds of parasitoids, and 2 guilds of predators). Population dynamics in several forest stands can be simulated taking into account the migration of gypsy moth and its natural enemies. The model fits well to the following observations and data: (1) quasi-periodic outbreaks at approximately 10-year intervals, (2) life-tables in different outbreak phases, (3) increased parasitism in artificially augmented gypsy moth populations, and (4) phase plots of population dynamics. Simulated survival curves are intermediate between those reported by J.S. Elkinton et al. and by J.R. Gould et al. It is shown that low-density gypsy moth populations can be stabilized by immigration from high-density areas without any density-dependent local processes. The model supports the following hypotheses about gypsy moth population dynamics: (1) density fluctuations of small mammal predators is the most probable synchronization factor in gypsy moth populations; (2) the outbreak frequency depends on the proportion of susceptible tree species and the density of small mammal predators; (3) bacterial insecticide can be applied less frequently for gypsy moth control than can a chemical insecticide of the same killing power because the bacterial insecticide spares invertebrate natural enemies; (4) the success of gypsy moth eradication programs depends on the initial gypsy moth population density and on the type of functional response of predators. An alternative form of population bimodality hypothesis is suggested, according to which there are two types of gypsy moth population dynamics: eruptive in susceptible stands and stable in resistant stands.

Small mammal exclosures for studies of hypogeous fungi

Small mammal predation of hypogeous spo? rocarps (truffles) make estimates of truffle produc- tivity difficult. To develop effective small mammal ex? closures, four screen materials were tested over a 6-week period. Following the test, the selected mate? rial, aluminum window screen, was used on 1944 plots in a 2-year study. The failure of only five screens in this study indicates aluminum screen prevents most predation of hypogeous sporocarps.

Status of the golden jackal as an agricultural pest in Bangladesh: Joe E. Brooks, with M. Emdadul Haque and colleagues, discusses the jackal's role in the agroecosystem

The golden jackal is perceived by farmers in Bangladesh as a primary pest of agricultural crops and domestic livestock. Very few farmers take any actions to reduce jackal attack on crops or livestock other than guarding their fields at night during the ripening crop stages. Rarely have the role and importance of the jackal as a small mammal predator in the agroecosystem in Bangladesh been studied. Until studies are completed to clarify these issues, lethal methods of jackal management should not be attempted.

Direct and Indirect Consequences of Mink Presence in a Common Tern Colony

ABRAMS, P. A. 1982. Functional responses of optimal foragers. Am. Nat. 120:382-390. ANDERSON, D. W., AND J. J. HICKEY. 1970. Ecological data on egg and breeding characteristics of Brown Pelicans. Wilson Bull. 82(l): 14-28. BEEBE, F. L. 1960. The marine peregrines of the northwest Pacific Coast. Condor 62: 145-189. BENT, A. C. 1938. Life histories of North American birds of prey. Part 2. Orders Falconiformes and Strigiformes. Bull. U.S. Nat. Mus. 170. BROOKS, A. 1926. Notes on the status of the Peale Falcon. Condor 28:17-79. CRAIGHEAD, J.J., ANDF. C. CRAIGHEAD. 1969. Hawks, owls and wildlife. Dover Pub., New York. GREEN, C. DE B. 19 16. Note on the distribution and nesting habits of Falco peregrinus paeaiei, Ridgway. Ibis, Ser. 10, 4:473-476. HAMILTON, W. D. 197 1. The geometry of the selfish herd. J. Theoret. Biol. 3 1:295-3 11. HOLLINGS, C. S. 1959. The components of predation as revealed by a study of small mammal predation of the European pine sawfly. Can. Entomol. 9 1: 293-320. HOOGLAND, J. L., AND P. W. SHERMAN. 1976. Advantages and disadvantages of Bank Swallow (Riparia riparia) coloniality. Ecol. Monogr. 46:3358. KENWARD, R. E. 1978. Hawks and doves: attack success and selection in Goshawk flights at Woodpigeons. J. Anim. Ecol. 47:449460. OATEN, A., AND W. W. MURWCK. 1975. Functional response and stability in predator-prey systems. Am. Nat. 109:89-298. PORTER, R. D., AND M. A. JENKINS. 1988. Pollutants and eggshell thinning in peregrines and their prey in the Baja California region, p. 4 131122. In T. J. Cade, J. H. Enderson, C. G. Thelander and C. M. White [eds.], Peregrine Falcon populations, their management and recovery. The Peregrine Fund, Inc., Boise, ID. PORTER, R. D., M. A. JENKINS, M. N. K~RVEN, D. W. ANDERSON, ANO J. 0. KEITH. 1988. Status and Reproductive Performance of Marine Peregrines in Baja California and the Gulfof California, Mexico, p. 105-l 14, In T. J. Cade, J. H. Enderson, C. G. Thelander and C. M. White [eds.], Peregrine Falcon populations, their management and recovery. The Peregrine Fund, Inc., Boise, ID. PULL-, H. R. 1973. On the advantages of flocking. J. Theor. Biol. 38:419-422. RATCLIFFE, D. 1980. The Peregrine Falcon. Buteo Books, SD. VELARDE, E. 1989. Conducta y ecologia de la reproduccibn de la gaviota parda (Larus heermanni) en Isla Rasa, Baja California. Ph.D.diss. Universidad National Autonoma de Mexico, Mexico. VELARDE, E. 1992. Predation of Heennann’s Gull (Larus heermanni) chicks by Yellow-footed Gulls (Larus livens) in dense and scattered nesting sites. Colon. Waterbirds 15:8-l 3. VELARDE, E. MS. Comparative breeding biology of the Heermann’s Gull (Larus heermanni) in Isla Rasa, Gulf of California, Mexico. VELARDE, E., M. S. TORDESILLAS, R. ESQUIVEL, AND L. VIEYRA. MS. Use of seabirds as sampling agents of commercially important fish populations.

Tool-assisted predation on a squirrel by a female chimpanzee in the Mahale Mountains, Tanzania

A 12-year-old female chimpanzee (Pan troglodytes schweinfurthii) of M-Group in the Mahale Mountains National Park, Tanzania was seen to rouse, capture, and eat a squirrel hiding in the narrow hole of a tree. The kill was aided by the use of a sturdy tool modified from a branch of the same tree. This appears to be the first reported case for chimpanzees, or any other nonhuman primate, of tool-use that directly led to the capture of a mammalian prey species. This behavior is discussed in relation to possible factors contributing to the occurrence of tool-use in small mammal predation especially by females to exploit a low competition meat source.

The effects of harvest on arable wood mice Apodemus sylvaticus

The effects of cereal harvesting on the ecology of wood mice Apodemus sylvaticus were investigated at three arable study sites in Oxfordshire from 1987 to 1991 using both radio-tracking and live-trapping methodologies. The process of harvesting itself had little direct effect on the mice, but the removal of the cover afforded by the crop greatly increased predation pressure on the mice. After harvest, mice either emigrated from the arable ecosystem or reduced activity. Nevertheless, over half (17 of 32) of the mice radio-collared before harvest were taken by predators in the first week following harvest. Together with emigration, this produced an 80% decrease in the population. Post-harvest activities such as stubble burning subsequently further increased mortality. The dramatic increase in prey availability may benefit predators of small mammals in the cereal ecosystem such as tawny owls Strix aluco and weasels Mustela nivalis.

The Effects of Small Mammal Predators on Grassland Invertebrates, Investigated by Field Exclosure Experiment

The effects of small mammals on invertebrate prey populations in grassland were investigated by means of an exclosure experiment over a period of 2 yr. Using direct searches and suction sampling, numbers of invertebrates were compared in four experimental plots fenced to exclude small mammals and four control plots where they had free access. There was no evidence of differences in guild structure or species composition in either large or small invertebrates as a result of mammal predation, but numbers of large invertebrates were consistently and significantly smaller (by 22.7−64.8%) in the presence of mammals, due principally to the predatory effects of shrews

The seedling survivorship and growth of three Shorea species in a Malaysian tropical rain forest

ABSTRACTThere was fruiting of the dipterocarps of Pantai Aceh Forest Reserve, Penang, Peninsular Malaysia in September 1986. The opportunity was taken to investigate the establishment and seedling survival of Shorea curtisii, Shorea multiflora and Shorea pauciflora over the subsequent year. The germination and seedling survival of Shorea curtisii was compared between canopy gaps and forest understorey sites.Under the shaded conditions none of the species grew beyond the two leaf stage over their first year. Shorea multiflora seedlings suffered a 72% mortality, significantly lower than that of Shorea pauciflora (89%) and Shorea curtisii (93%). The major cause of mortality appeared to be drought, though Shorea curtisii was also prone to predation by small mammals.In a gap, Shorea curtisii seeds probably germinated less well but seedling survival (28% versus 7%) and growth was better than canopy-shaded conspecifics. Seedlings in gaps escaped small mammal predation.