Variable effect of playback of chickadee mobbing calls on detection probability of boreal forest birds

Modification of the point count survey method to include playback of songbird mobbing calls in an attempt to increase detection probabilities has met with mixed success. We compared detection probabilities for boreal forest songbirds using traditional point count methods and counts using broadcasts of the mobbing calls of Black‐capped Chickadees (Poecile atricapillus) in an attempt to increase detection probability. We conducted 594 point counts during the 2010 breeding season in Newfoundland, Canada. Each point count consisted of an 8‐min silent observation period followed by an 8‐min broadcast of Black‐capped Chickadee mobbing calls. Occupancy model results showed that response to playback broadcast varied across species, with detection probabilities higher for seven of 17 species during the silent portions of point counts and three species more likely to be detected during playback intervals. For all species, the number of visual detections increased during periods of playback and, averaged across species, individuals were >6 times more likely to be seen during the playback period than during the silent period. Differences in detection probability among observers were apparent during both silent and playback periods. We suggest that using playback of chickadee mobbing calls during point count surveys of common boreal forest songbird species may be most beneficial when visual detection is important. However, playback may also be useful for species‐specific surveys during periods when birds are less likely to be vocal or for studies of less common species with chronically low detection probabilities. A combined silent and playback approach could also be useful, although observer and species differences should be accounted for if comparing data across species or studies.     

Optimizing surveys for marsh songbirds: does timing matter?

Analysis of data from point counts, a common method for monitoring bird population trends, has evolved to produce estimates of various population parameters (e.g., density, abundance, and occupancy) while simultaneously estimating detection probability. An important consideration when designing studies using point counts is to maximize detection probability while minimizing variation in detection probability both within and between counts. Our objectives were to estimate detection probabilities for three marsh songbirds, including Marsh Wrens (Cistothorus palustris), Swamp Sparrows (Melospiza georgiana), and Yellow‐headed Blackbirds (Xanthocephalus xanthocephalus), as a function of weather covariates and to evaluate temporal variability in detection probability of these three species. We conducted paired, unlimited radius, 10‐min point counts during consecutive morning and evening survey periods for our three focal species at 56 wetlands in Iowa from 20 April to 10 July 2010. Mean detection probabilities ranged from 0.272 (SE = 0.042) for Marsh Wrens to 0.365 (SE = 0.052) for Swamp Sparrows. Time of season was positively correlated with detection probability for Swamp Sparrows, but was negatively correlated with detection probability for Yellow‐headed Blackbirds, suggesting that detection probability increased during the breeding season for Swamp Sparrows and was highest early in the breeding season for Yellow‐headed Blackbirds. Understanding how detection probabilities of marsh songbirds vary throughout the breeding season allows targeted survey efforts that maximize detection probabilities for these species. Furthermore, consistent detection probabilities of marsh songbirds during morning and evening survey periods mean that investigators have more time to conduct surveys for these birds, allowing greater flexibility to increase spatial and temporal replication of surveys that could provide more precise estimates of desired population parameters.     

Making red squirrels more visible: the use of baited visual counts to monitor populations

Understanding changes in the distribution and abundance of the red squirrel Sciurus vulgaris in Europe, as a result of the spread of the introduced North American grey squirrel Sciurus carolinensis, is vital to planning and implementing red squirrel conservation measures. We studied the effectiveness of a variation on a common method of monitoring squirrels, standardised visual counts that made use of a diffuse baiting approach to increase their detectability. Significantly more sightings of squirrels occurred on baited than on unbaited visual transect lines in trials with the assistance of volunteers, and we recommend the use of baits in future studies.     

Forces structuring tree squirrel communities in landscapes fragmented by agriculture: species differences in perceptions of forest connectivity and carrying capacity

The North American red squirrel ( Tamiasciurus hudsonicus ) has expanded its range into the central hardwoods of the United States in conjunction with increasing forest fragmentation and declining gray squirrel ( Sciurus carolinensis ) populations. We used translocation experiments and patch occupancy data to test for interspecific differences in mobility and sensitivity to habitat loss and modification by agriculture. We released squirrels in fencerows to test the hypothesis that gray squirrels display inferior mobility relative to red and fox ( S. niger ) squirrels. Elapsed time to movement from fencerows for 76 individuals increased with distance to forest patches and harvesting of crops. Gray and red squirrels took longer to move from fencerows than fox squirrels, and gray squirrels were less successful at moving from fencerows than red and fox squirrels. Ecologically scaled landscape indices revealed the degree to which interspecific differences in mobility and individual area requirements accounted for the occurrence of these species across landscapes. Gray squirrel distribution was constrained both by individual area requirements and dispersal ability. Occurrence of red and fox squirrels was related to patch size but was unaffected by landscape connectivity.     

Effects of Rain on Palm Springs Ground Squirrel Occupancy in the Sonoran Desert

ABSTRACT Long-term monitoring programs must use informative yet cost-effective methods. Occupancy estimates that incorporate detection probabilities are used with increasing frequency to describe species status and make management recommendations. Estimating changes in the occupancy of points over time in response to management actions or environmental changes may be especially useful for management of the Palm Springs round-tailed ground squirrel (Spermophilus tereticaudus chlorus), a subspecies covered under the Coachella Valley Multiple Species Habitat Conservation Plan and Natural Community Conservation Plan. In 2002 and 2003, we estimated occupancy and detection probability of ground squirrels across lands modeled as ground squirrel habitat by the Scientific Advisory Committee for the Habitat Conservation Plan and tested a priori hypotheses about how occupancy varied among vegetation and substrate types. In the 2003 study, we asked whether these associations were affected by winter rains after the 2002 drought year. Occupancy in 2003 was estimated at 0.99 (SE = 0.01) in Western honey mesquite (Prosopis glandulosa) on dunes and hummocks, and occupancy of the remaining modeled habitat was best described by distance to mesquite, with the occupancy probability decreasing with increasing distance from mesquite on dunes or hummocks. The best-supported model in 2002 described the distribution of ground squirrels as a function of only vegetation and substrate type. However, the best-supported models in 2003 suggested that distance to mesquite was a component of the occupancy of non-mesquite vegetation. Mesquite seems to provide high-quality habitat that can support ground squirrels at high occupancy probabilities that may breed successfully every year. In contrast, other vegetation types provide low-quality habitat that can only support ground squirrels at low occupancy probabilities that may only breed occasionally. Mesquite could be an essential refugium during drought years, and the 4 best-supported models in 2003 suggest that restoration of mesquite beginning near currently occupied mesquite patches could be critical for maintaining ground squirrel populations on the preserves.     

Effects of point‐count duration on estimated detection probabilities and occupancy of breeding birds

Increasingly, point‐count data are used to estimate occupancy, the probability that a species is present at a given location; occupancy accounts for imperfect detection, the probability that a species is detected given that it is present. To our knowledge, effects of sampling duration on inferences from models of bird occupancy have not been evaluated. Our objective was to determine whether changing count duration from 5 to 8 min affected inferences about the occupancy of birds sampled in the Chesapeake Bay Lowlands (eastern United States) and the central and western Great Basin (western United States) in 2012 and 2013. We examined the proportion of species (two doves, one cuckoo, two swifts, five hummingbirds, 11 woodpeckers, and 122 passerines) for which estimates of detection probability were ≥ 0.3. For species with single‐season detection probabilities ≥ 0.3, we compared occupancy estimates derived from 5‐ and 8‐min counts. We also compared estimates for three species sampled annually for 5 yr in the central Great Basin. Detection probabilities based on both the 5‐ and 8‐min counts were ≥ 0.3 for 40% ± 3% of the species in an ecosystem. Extending the count duration from 5 to 8 min increased the detection probability to ≥ 0.3 for 5% ± 0.5% of the species. We found no difference in occupancy estimates that were based on 5‐ versus 8‐min counts for species sampled over two or five consecutive years. However, for 97% of species sampled over 2 yr, precision of occupancy estimates that were based on 8‐min counts averaged 12% ± 2% higher than those based on 5‐min counts. We suggest that it may be worthwhile to conduct a pilot season to determine the number of locations and surveys needed to achieve detection probabilities that are sufficiently high to estimate occupancy for species of interest.     

Patch occupancy by squirrels in fragmented deciduous forest: effects of behavior

We tested whether species-specific behavioral traits could explain patterns of habitat patch occupancy by five different squirrel species in Ontario, Canada: the northern and southern flying squirrel (Glaucomys sabrinus and Glaucomys volans), the North American red squirrel (Tamiasciurus hudsonicus), the eastern chipmunk (Tamias striatus), and the eastern gray squirrel (Sciurus carolinensis). Flying squirrel species exhibit group nesting in winter, which may put them at risk of extirpation in small patches with few individuals to contribute to group nests. Flying squirrels are also volant, potentially making non-treed matrix a barrier. Our surveys revealed that G. sabrinus was most likely to occur in large patches that were embedded in landscapes with low connectivity, and least likely to occur in small patches in highly connected landscapes. Conversely, G. volans was most likely to occur in large, well-connected patches and least likely to occur in small, unconnected patches. Patch occupancy by the cursorial squirrels was not strongly influenced by patch area or isolation. These findings reinforce previous studies suggesting that an understanding of species-specific traits such as behavior is an important consideration when interpreting habitat fragmentation effects.     

Teasing out biological effects and sampling artifacts when using occupancy rate in monitoring programs

ABSTRACT.   Recent declines in biodiversity stress the need for rigorous and reliable multispecies monitoring programs. A potential weakness of monitoring programs is a reliance on raw counts and the assumption either of complete detection or of constant detection probability for each species, regardless of the sampling situation. Until recently, these assumptions have largely remained untested and, therefore, to help insure accuracy, bird-monitoring programs have depended on standardization of counts and counts of longer duration. We tested the effectiveness of these strategies for providing unbiased occupancy rates using a method designed to accommodate situations where species detection probabilities are less than one and heterogeneous. We tested the effect of potential sources of heterogeneity in detection probability (vegetation structure, wind velocity, cloud cover, date, and time) on occupancy rate estimates of 13 bird species in southern France. We compared adjusted and raw occupancy rates for two sampling durations (10 and 20 min). Differences between raw and adjusted occupancy rates were low even for the shorter count duration, suggesting that standardized long counts should produce reliable estimates of occupancy rates even in the absence of correction by an appropriate method. This enhances the value of past monitoring programs where long standardized counts were used, but with designs that do not allow corrected estimates. However, we found that detection probability was heterogeneous for most species and that vegetation structure was an important source of heterogeneity. The possible effects of habitat on detection probability should be of special concern for long-term monitoring programs conducted in landscapes where habitats vary across time or space.     

Detection probability of Golden-winged Warblers during point counts with and without playback recordings

ABSTRACT Use of point‐count data to estimate population sizes of North American landbirds may be challenged by limitations on detection probability of particular species, thereby requiring correction factors to ensure accurate estimates. We estimated detection probability of Golden‐winged Warblers (Vermivora chrysoptera) during 3‐min point‐count surveys conducted both with and without use of playback recordings in a mixed shrubland‐forest habitat (clearcut area) and a 60‐m wide electric transmission line right‐of‐way (ROW) in central Pennsylvania from 20 May to 17 June 2002–2003. In addition, we assessed the value of playback with respect to response rates of warblers and distance within which warblers approached the observer. Without playback, detection probability was approximately 23% in the clearcut area and 61% in the ROW. Use of playback resulted in 7% and 19% net increases in probability at the clearcut area and the ROW, respectively; proportional increase was approximately 30% for both habitats. Warblers responded to playback 68% of the time, but response rate was greater within 100 m (72%) than beyond (53%). Most responses (85%) included approach of the warbler toward the observer, and most individuals approached within 10 m. We conclude that 3‐min point counts with playback do not yield detection probabilities sufficient to estimate population size of Golden‐winged Warblers without use of correction factors. Furthermore, detection probability in mixed shrubland‐forest habitats can be much lower than in linear habitats such as utility ROWs. Efforts to estimate population size of Golden‐winged Warblers from data of the North American Breeding Bird Survey should recognize that habitat structure has much influence on detection probability as it relates to distance at which an observer can hear (or see) warblers. Accordingly, we recommend that such efforts incorporate a maximum detection distance of 100–150 m in mixed shrubland‐forest habitats.     

A general approach of using hair-tubes to monitor the European red squirrel: A method applicable at regional and national scales

Monitoring constitutes a key element in the management and conservation of many mammal species. We describe a technique to obtain population indices for red squirrels (Sciurus vulgaris) using hair-tubes and compare these indices to population estimates obtained by live trapping. Data were collected in seven study areas in the Western and Central Alps in Italy and compared with data previously collected in 11 sites in northern England. The aim was to test if hair-tube census could be used to derive a general predictive model allowing accurate predictions of squirrel numbers in different years, habitats and geographic regions. We used model equations developed from the proportion of hair-tubes visited to predict densities obtained from live-trapping. Hair-tube data gathered in the Central Alps correctly predicted squirrel densities in the Western Alps. A combined data set pooling the sites of these two regions based on the first three years successfully predicted the two successive years. In addition, a combined model derived from areas monitored for five years had a high predictive value locally (89%) and internationally (73%) when applied to the English data set. We therefore believe that the predictive model developed in this study could be of general value and be used to monitor squirrel populations in European low density conifer habitats (0.1–0.5 squirrels/ha). The approach may also be suitable for many tree squirrel populations in North America and other arboreal rodents that occur at similar densities.     

The Mechanism of Replacement of Red Squirrels by Grey Squirrels: A Test of the Interference Competition Hypothesis

Introduced American grey squirrels have replaced native red squirrels in most of the range currently occupied in Britain and northern Italy. The mechanisms of the replacement are not yet fully understood. We restated the commonly cited Interference Competition Hypothesis (ICH) that grey squirrels interfere with the behaviour of red squirrels in three possible ways: 1. by direct aggressive interactions; 2. by interrupting red squirrel mating-chases; or 3. by forcing red squirrels to actively avoid areas intensively used by grey squirrels. We compared the activity pattern, behaviour and reproductive performance of red squirrels in two study areas in northern Italy, one with only red squirrels (control area C1), the other with both species (experimental area E1). The following predictions were tested: 1. the total time spent in both intraspecific and interspecific interactions by red squirrels increases in the experimental area; 2. most interspecific interactions are aggressive, with grey squirrels being the dominant species; 3. the proportion of breeding female red squirrels that are unsuccessful at weaning offspring increases in area E1; 4. grey squirrels take part and interfere with red squirrel mating-chases, and thereby decrease the reproductive output of red squirrel females; 5. the activity pattern of red squirrels in the mixed-species area is shifted with respect to that in the control area to the hours of the day during which grey squirrels show little activity; and 6. red squirrels will shift their home range (or at least their core-area) when grey squirrel densities increase to avoid interspecific core-area overlap. Our results supported only the first prediction of the ICH: they failed to support all the other predictions. Moreover, the increase in the percentage of active time red squirrels spent interacting with other squirrels in the experimental study area was very small (only 1–2 min/day). Red squirrels did not avoid the woodland patches most intensively used by grey squirrels and the interspecific core-area overlap was similar to red squirrel intraspecific core-area overlap. This suggested that red squirrels avoided spatial overlap with grey squirrels in a similar manner as with conspecifics and that an increase in grey squirrel numbers will augment the intensity of resource competition. We therefore conclude that our results do not lend support to the Interference Competition Hypothesis and that interference competition by grey squirrels cannot explain the large-scale replacement of red by grey squirrels that has occurred in Britain and in Piedmont.     

Contrasting seasonal dynamics in fleas of the Siberian flying squirrel (Pteromys volans) in Finland

Abstract.  1. The seasonal and spatial variation of the adult flea fauna (Siphonaptera) was examined in connection with live-trapping studies of the Siberian flying squirrel ( Pteromys volans ) in three study areas in southern Finland between 1997 and 2005.
2. The numerically dominant flea species of the Siberian flying squirrel were Tarsopsylla octodecimdentata octodecimdentata and Ceratophyllus (Monopsyllus) indages indages (Ceratophyllidae); the latter being a host specialist of the Siberian flying squirrel. Tarsopsylla octodecimdentata , which also commonly occurs on the red squirrel ( Sciurus vulgaris ), infected a large proportion of the host population throughout the winter, whereas C. indages occurred predominantly during the summer and autumn, being practically the only flea species in nests during the flying squirrels' breeding season and on juveniles still inhabiting their natal nest.
3. The use of nest boxes by flying squirrels did not have any positive effects on flea populations, but it may have had a negative impact on T.   octodecimdentata .
4. The potentially vulnerable C.   i.   indages is a predictable, widespread component in the flea fauna of the Siberian flying squirrel at various spatial scales, and it is likely to occur in most of the permanent flying squirrel populations in Finland.     

Genetic Structure of the French Red Squirrel Populations: Implication for Conservation

The decline of the red squirrel (Sciurus vulgaris) in several European countries due to the introduction of the American grey squirrel (S. carolinensis) and the predicted arrival of the grey squirrel in France in the near future has lead to the development of a preventative conservation project in this country. In this study, we conducted an extensive survey of mitochondrial DNA variation in French red squirrels using a fragment of the mitochondrial D-loop and we compared the results with previously published data from other European populations. Our main aims were: (1) to determine whether genetically differentiated populations, which could represent prioritized units for conservation purposes, were present in France and (2) to determine whether the French population, which is currently largely undisturbed, could provide information on the postglacial recolonization history of the species. We found that French D-loop haplotypes show almost no tendency to cluster by geographic origin, be it region or country, suggesting that French red squirrels have not been isolated from other populations during an evolutionarily significant period and that they do not constitute an Evolutionary Significant Unit. The French red squirrels showed strong signals of population expansion, the opposite to what is observed in most other European populations, making them of particular interest to study the postglacial expansion history of the species.     

Comparison of survey methods for monitoring Clark's Nutcrackers and predicting dispersal of whitebark pine seeds

ABSTRACT Clark's Nutcrackers (Nucifraga columbiana) disperse seeds of whitebark pines (Pinus albicaulis) in western North America by their scatter‐hoarding behavior. Because of declines in whitebark pine, resource managers are seeking an effective means of monitoring nutcracker population trends and the probability of seed dispersal by nutcrackers. We tested the reliability of four survey techniques (standard point counts, playback point counts, line transects, and Breeding Bird Survey routes) for estimating population size by conducting surveys at sites where a portion of the nutcracker population was marked with radio transmitters. The efficacy of distance sampling, based on detection rates from our unadjusted surveys, was also assessed. We conducted counts of whitebark pine cones within stands and related the probability of seed dispersal within stands to cone production and nutcracker abundance. We conducted 70 h of surveys for Clark's Nutcrackers at eight sites from July through November in 2007 and 2009 and estimated cone densities at six of these sites. Detection rates for all survey techniques were low and variable and we detected an average of 5.6 nutcrackers per 30 min of survey time. We also found no difference in detection rates among survey types, although significantly more nutcrackers were detected during surveys conducted during the peak of whitebark pine cone harvest (P < 0.0001). Nutcracker abundance was not correlated with cone density (P= 0.29) and we observed nutcrackers pouching seeds at all sites. Thus, cone density did not provide reliable information on whether seed dispersal was likely to occur. We suggest that alternate methods be considered for monitoring populations and assessing seed dispersal probability because we did not reliably detect nutcrackers using conventional survey techniques and because nutcracker abundance was not correlated with cone density.     

The anatomy of a range expansion: changes in cranial morphology and rates of energy extraction for North American red squirrels from different latitudes

Species with expanding ranges provide unique opportunities to examine environmentally induced adaptations in ecological traits and anatomical characteristics. Since the late 1800s, the North American red squirrel (Tamiasciurus hudsonicus) has expanded its range into the central hardwoods of the United States in conjunction with increasing agricultural fragmentation. We examined whether red squirrels from the central hardwoods (west‐central Indiana, USA) displayed differences in foraging behaviors and morphology relative to red squirrels from conifer‐dominated environments (upper peninsula of Michigan, USA), a biome in which red squirrels evolved. Specifically, we measured rates of energy extraction, variation in cranial morphology, and diet preference between red squirrels from both regions. In addition, we compared foraging behaviors of red squirrels from the central hardwoods to those of a competitor that coevolved with nut‐producing trees, the gray squirrel (Sciurus carolinensis). Red squirrels from Indiana and Michigan differed significantly in the efficiency with which they used food items, with individuals from each region extracting calories at a more rapid rate for items that were common in their region. The enhanced efficiency of southern red squirrels feeding on black walnuts (Juglans nigra) was correlated with geographic differences in cranial morphology; skulls of southern squirrels were larger, with longer jaws and higher metrics associated with greater mandibular force than northern squirrels. Contrary to our expectations, red squirrels from Indiana and Michigan did not differ qualitatively in preferences for food items, suggesting that diet choice may be governed by perishability of food items rather than by rates of energy extraction. Gray squirrels were more efficient than Indiana red squirrels in using all food items, and differed only slightly from red squirrels with regard to preference for food items. Measures of efficiency of resource use, after accounting for species‐specific metabolic requirements, suggest that red squirrels are unlikely to compensate ecologically for declining gray squirrel populations in fragmented portions of the central hardwoods, with potentially adverse effects for forest regeneration and succession. Our results demonstrate that invading species can display significant flexibility in adapting to new environments, but they may not be flexible enough to exploit resources in a manner comparable to native species.     

Poxviral Disease in Red Squirrels Sciurus vulgaris in the UK: Spatial and Temporal Trends of an Emerging Threat

The squirrel poxvirus (SQPV) is the probable mediator of apparent competition between the introduced invading gray squirrel (Sciurus carolinensis) and the red squirrel (Sciurus vulgaris) in the UK, and modeling studies have shown that this viral disease has had a significant impact on the decline of the red squirrel in the UK. However, given our limited understanding of the epidemiology of the disease, and more generally the effects of invasive species on parasite ecology, there is a need to investigate the transmission dynamics and the relative pathogenicity of the virus between species. We aimed to increase our knowledge of these processes through an empirical study in which we: (i) used pathological signs and transmission electron microscopy (TEM) to diagnose SQPV disease in red squirrels found dead during scanning surveillance between 1993 and 2005; (ii) detected antibody to SQPV using an enzyme-linked immunosorbent assay (ELISA) in the same animals; and (iii) mapped cases of the disease, and the gray squirrel distribution, using a geographical information system. We analyzed the distribution of cases of SQPV disease according to woodland type, a measure of squirrel density. SQPV disease occurred only in areas of England also inhabited by seropositive gray squirrels, and as the geographical range of gray squirrels expanded, SQPV disease occurred in these new gray squirrel habitats, supporting a role for the gray squirrel as a reservoir host of the virus. There was a delay between the establishment of invading gray squirrels and cases of the disease in red squirrels which implies gray squirrels must reach a threshold number or density before the virus is transmitted to red squirrels. The spatial and temporal trend in SQPV disease outbreaks suggested that SQPV disease will have a significant effect on Scottish populations of red squirrels within 25 years. The even spread of cases of disease across months suggested a direct rather than vector-borne transmission route is more likely. Eight juvenile and sub-adult free-living red squirrels apparently survived exposure to SQPV by mounting an immune response, the first evidence of immunity to SQPV in free-living red squirrels, which possibly suggests a changing host-parasite relationship and that the use of a vaccine may be an effective management tool to protect remnant red squirrel populations.     

Effects of experimental playbacks on availability for detection during point counts

Point counts are the most commonly used technique for surveying passerines during the breeding season. Several methods for estimating probabilities of detection during point count surveys have been developed. These methods have focused primarily on accounting for the influence of environmental factors (e.g., weather and noise) on detectability, however, the probability that birds are available for detection (e.g., sings or moves) during point counts has received less attention. We used sequential point counts to determine the effect of playback of the mobbing calls of Black‐capped Chickadees (Poecile atricapillus) and the flight calls of Red‐tailed Hawks (Buteo jamaicensis) on availability for detection (e.g., singing or moving) during point‐count surveys. We conducted 180 point counts over a 2‐yr period in central – east central Minnesota to evaluate the possible effect of playbacks on observed density, overall species richness, minute of first detection, and distance of first detection. We also used removal models to quantify the magnitude of changes in detectability and direction of response to playbacks for 10 focal species. Playback of the mobbing calls of Black‐capped Chickadees increased observed density and decreased the average distance of detection and time of first detection, whereas playback of the flight calls of a Red‐tailed Hawk resulted in a decrease in observed density and species richness, and an increased time of first detection. Playback treatment was a covariate in all best performing models for the 10 species analyzed, but the magnitude and direction of response to playbacks were species specific. The importance of playback type in detectability models indicates that the calls of heterospecifics can influence species availability for detection. As such, researchers using playback methods should seek to quantify species‐specific responses in detection probability and consider how component detection probabilities could influence survey outcomes.     

Predator‐Associated Vocalizations in North American Red Squirrels (Tamiasciurus hudsonicus): To Whom are Alarm Calls Addressed and How do They Function?

Alarm vocalizations produced by prey species encountering predators can serve a variety of functions. North American red squirrels are a small-bodied mammal popularly known for producing loud, conspicuous alarm calls, but functional accounts of calling in this species are few and contradictory. We conducted research over a 3-yr period on a sample of 47 marked red squirrels in the foothills of the Canadian Rockies. We recorded the production of alarm calls during encounters with natural predators and in a series of simulated predator experiments. We tested for variation in call production patterns consistent with three traditional hypotheses concerning the conspecific warning functions of alarm calling: namely that they serve as warnings to kin, to potential mates, or to territorial neighbors with which callers have an established relationship. Patterns of calling did not provide clear support for any of these hypothesized functions. We consider several possible qualifications to our results. We also consider the possibility that conspicuous calls given by red squirrels during encounters with predators are directed at the predators themselves and function to announce their detection and possibly deter them. This possibility is consistent with additional life-history features of red squirrels including that they are a relatively solitary and territorial, food-hoarding species that produces the same conspicuous vocalizations in response to other squirrels intruding on their territory to steal cones. An important corollary of this account is that red squirrel alarm calls probably do not entail referentially specific messages about different types of predator, as proposed previously.     

European red squirrel population dynamics driven by squirrelpox at a gray squirrel invasion interface

Infectious disease introduced by non‐native species is increasingly cited as a facilitator of native population declines, but direct evidence may be lacking due to inadequate population and disease prevalence data surrounding an outbreak. Previous indirect evidence and theoretical models support squirrelpox virus (SQPV) as being potentially involved in the decline of red squirrels (Sciurus vulgaris) following the introduction of the non‐native gray squirrel (Sciurus carolinensis) to the United Kingdom. The red squirrel is a major UK conservation concern and understanding its continuing decline is important for any attempt to mitigate the decline. The red squirrel–gray squirrel system is also exemplary of the interplay between infectious disease (apparent competition) and direct competition in driving the replacement of a native by an invasive species. Time series data from Merseyside are presented on squirrel abundance and squirrelpox disease (SQPx) incidence, to determine the effect of the pathogen and the non‐native species on the native red squirrel populations. Analysis indicates that SQPx in red squirrels has a significant negative impact on squirrel densities and their population growth rate (PGR). There is little evidence for a direct gray squirrel impact; only gray squirrel presence (but not density) proved to influence red squirrel density, but not red squirrel PGR. The dynamics of red SQPx cases are largely determined by previous red SQPx cases, although previous infection of local gray squirrels also feature, and thus, SQPV‐infected gray squirrels are identified as potentially initiating outbreaks of SQPx in red squirrels. Retrospective serology indicates that approximately 8% of red squirrels exposed to SQPV may survive infection during an epidemic. This study further highlights the UK red squirrel – gray squirrel system as a classic example of a native species population decline strongly facilitated by infectious disease introduced by a non‐native species. It is therefore paramount that disease prevention and control measures are integral in attempts to conserve red squirrels in the United Kingdom.     

A grey future for Europe: Sciurus carolinensis is replacing native red squirrels in Italy

Introduced mammals can cause extinction of native species due to replacement competition, disease, predation or hybridization. We studied the colonization of Piedmont (NW-Italy) by American grey squirrel (Sciurus carolinensis) and its effect on the native red squirrel (Sciurus vulgaris). Presence/absence data (2 × 2 km²), of both species were (re)constructed using questionnaires, literature, existing databases, unpublished information, and direct monitoring with hair-tubes. In 1970 red squirrels were still widespread and greys were restricted to forests near the introduction site. By 1990, grey squirrels had increased their range to 220 km², which coincided with the disappearance of native squirrels from 33 squares inside this range. The invasive species continued its spread occupying an area of 2,016 km² in 2010; within this area red squirrels went extinct in 88 squares. Overall, from 1970 to 2010 red squirrel went extinct in 62 % of 2 × 2 km² (ca. 1,689 km²), and were replaced by grey squirrels. The spread of the alien species was slow in the first 20 years, but doubled in the successive two decades. Nevertheless spread was slower than in Ireland and England. Grey squirrel adapt to climate and habitats in both North and South Europe, causing extinction of the native red squirrel. A EU LIFE co-funded project with the aim to control the grey squirrel in North Italy and recent trade-restrictions and trade-ban are a first step in reducing the risk of grey squirrels invading other countries, but their effectiveness will have to be evaluated.