The taphonomic impact of scavenger guilds in peri‐urban and rural regions of central and southern Alberta. Part I – Identification of forensically relevant vertebrate scavengers

As a body decomposes in an outdoor environment, numerous taphonomic agents can act on the process of human decomposition. It is important to understand the impact of these agents as they can vary the rate of soft and hard tissue loss which may alter postmortem interval estimations. One taphonomic factor which has not been extensively investigated in many regions of the world, including Canada, are vertebrate scavengers. The current study aimed to identify scavenger guilds in the peri‐urban and rural regions of two major cities in Alberta (Calgary and Edmonton) where human remains are frequently located. Vertebrate scavenger activity was recorded continuously using cellular and noncellular trail cameras. Images were analyzed to determine how the scavenging profiles (i.e., scavenger species, arrival time, and feeding behavior) impacted the loss of soft and hard tissue. We identified a range of mammalian and avian scavengers and found that coyote and black‐billed magpie were the predominant scavengers recorded at the Edmonton peri‐urban and rural sites, and the Calgary peri‐urban sites. In contrast, when a site was within bear territory such as the Calgary rural sites, black and grizzly bears were the predominant scavengers. At all sites, the large mammalian scavengers were responsible for most soft tissue loss and subsequent hard tissue dispersal. None of the scavengers demonstrated a clear preference for open versus closed sites. This taphonomic information is important to consider when searching for human remains at these locations or in other North American regions with comparable scavenger guilds.

scavengers.The current study aimed to identify scavenger guilds in the peri-urban and rural regions of two major cities in Alberta (Calgary and Edmonton) where human remains are frequently located.Vertebrate scavenger activity was recorded continuously using cellular and noncellular trail cameras.Images were analyzed to determine how the scavenging profiles (i.e., scavenger species, arrival time, and feeding behavior) impacted the loss of soft and hard tissue.We identified a range of mammalian and avian scavengers and found that coyote and black-billed magpie were the predominant scavengers recorded at the Edmonton peri-urban and rural sites, and the Calgary peri-urban sites.In contrast, when a site was within bear territory such as the Calgary rural sites, black and grizzly bears were the predominant scavengers.At all sites, the large mammalian scavengers were responsible for most soft tissue loss and subsequent hard tissue dispersal.None of the scavengers demonstrated a clear preference for open versus closed sites.This taphonomic information is important to consider when searching for human remains at these locations or in other North American regions with comparable scavenger guilds.

K E Y W O R D S
decomposition, forensic taphonomy, porcine analogues, skeletal dispersal, soft tissue loss, vertebrate scavenging

Highlights
• Large mammalian scavengers accelerate soft and hard tissue loss in Alberta, Canada.
• Avian and mammalian scavengers showed no preference for open versus closed sites.
• Remains were dispersed by mammalian scavengers only.

| INTRODUC TI ON
In a forensic investigation, the search and recovery of human remains is a challenging task as there are numerous taphonomic agents that can act on the remains, particularly when located in an outdoor environment.Within the realm of forensic taphonomy, many factors have been investigated to better understand the taphonomic impact of the environment [1][2][3][4], season [5][6][7][8], soil [8][9][10], and species present in the deposition ecosystem [11][12][13][14][15][16] on the human decomposition process.The latter encompasses both invertebrate and vertebrate species, some of which will feed on human remains.While there has been significant research to investigate region-specific invertebrate activity in the field of forensic entomology [17][18][19], there have been fewer studies that focus on region-specific vertebrate activity, particularly in Canada where the current study was conducted.
Vertebrate scavenging activity is heavily influenced by climatic and ecological factors, including resource availability, competition, and the dietary requirements of obligate and facultative scavengers [14,16,20].Obligate scavengers rely solely on scavenging for survival whereas facultative scavengers will scavenge if the opportunity arises without being solely dependent on this feeding behavior [21].When scavengers are present in an environment, it can result in the accelerated loss of soft tissue, disarticulation, and subsequent dispersal of hard tissue from human remains [12,15,22].The rate and degree to which this occurs is highly dependent on the scavenger guild (i.e.groups of species) in the deposition location [14,23].An understanding of scavenger guilds, their feeding behavior, and impacts on human decomposition can therefore enhance the recovery of scattered remains, the interpretation of ante-mortem versus post-mortem artifacts, and the estimation of time since death in medico-legal criminal investigations [12,24,25].
In North America, regional vertebrate scavenging has been observed or studied in numerous locations including Tennessee [26,27], Oklahoma [28], Illinois [29], Texas [12,30,31], Florida [13], Colorado [32,33], and Hawaii [34].The majority of these locations represent southern states of the USA which have notably distinct ecosystems and scavenger guilds compared to the northern states of the USA [22,35] and Canada.To date, only four studies have been published for unique regions of Canada: central Alberta [36], southern Ontario [37], northern Ontario [38], and Quebec [39].
As vertebrate species ranges differ spatially and temporally across Canada, the current study was conducted to add to the knowledge base of forensically relevant scavenger guilds in populated regions of Canada.
This study was designed in conjunction with the Calgary and Edmonton Police Canine Units to provide new information to human remains detection (HRD) dog handlers that could assist with their searches for human remains.The aim was to identify the scavenger guilds in the vicinity of these two major cities in Alberta where human remains are frequently located [40,41] and identify how the scavenging profiles (i.e., scavenger species, arrival time, and feeding behavior) impact the loss of soft and hard tissue.Urban centers are known to contain different fauna to rural areas [42], and urban fauna behaves differently to rural fauna [43,44].To this end, we studied both peri-urban and rural locations, as well as open and closed habitats, in and around Calgary and Edmonton over a two-year period.
To reduce the number of variables, the studies were conducted in the same season (summer) of 2021 and 2022 to assess inter-year variability.At the completion of all trials, a search was conducted to determine the degree of dispersal by each scavenger guild (data to be published in a forthcoming manuscript).

| Experimental locations and specimens
The study comprised 16 trials in which pig carcasses were placed in a natural environment and monitored for scavenging activity.The study was conducted during the summer months across a two-year period (2021 and 2022) to investigate inter-year variability for this season.Two major cities of Alberta (Calgary and Edmonton) were chosen based on the frequency of which the police partners are asked to search for scavenged human remains.At each location, two sites were chosen to represent a peri-urban environment and a rural environment, to determine any patterns of urban proximity with scavenging activity.At each site, the impact of habitat was investigated by placing one carcass in an open site (less than 10% canopy cover above the remains) and one carcass in a closed site (more than 50% canopy cover above the remains), as in previous Canadian scavenging studies [38,39].
The locations within Calgary and Edmonton were changed between the 2021 and 2022 trials to investigate comparable periurban and rural regions in proximity to each city, but also to avoid learned behavior from local scavengers of the initial trials.Table 1 outlines the site locations for each year of the trial including the habitat, trial length, and temperature range.Although a prior study suggested that pigs are not accurate models of human decomposition for associated scavenging studies [27], in the current study they were deemed necessary to investigate the local scavenger guilds for the province of Alberta.Presently, Canada only has one human decomposition facility, located in the province of Quebec, with a different climate and scavenger guilds [39] to the region of interest in this study.For each trial, a pig carcass (Sus scrofa domesticus, Suidae), weighing 200-250 lbs each, was used as an analog for an average human body weight.Pig carcasses were purchased from local farmers as excess food stock and thus did not require animal ethics approval through the lead organization at the time (Université du Québec à Trois-Rivières).All subjects were killed the morning of collection using a penetrating captive bolt as recommended in the Alberta Humane Handling Guidelines for Pigs: Standards for the Care of Compromised and Unfit Animals [45].All carcasses were transported in individual body bags to prevent oviposition during transport and carcasses were deposited on the same day for each site.All trials commenced during the month of August which represents the summer season in North America.

| Observations and recordings
For the 2021 trials, one Spypoint Link-Micro-LTE cellular trail camera (Spypoint) and one Spypoint Force-11D noncellular trail camera (Spypoint) were installed on a nearby tree to continuously monitor the scavenging activity on and around each pig carcass.Each carcass was anchored to a nearby tree using wire cable wrapped around the torso.The wire cable was found to have minimal influence on the scavenging and dispersal process in prior studies by the authors [38] and was used to prevent immediate loss of the carcass by large mammal scavengers dragging the carcass out of view of the cameras.For the 2022 trials, a Browning Recon Force Elite HP4 trail camera (Trail Cam Quebec) was added as a third camera to each site to capture video recordings in addition to the still images of the other two cameras.This experimental design limited the need to conduct regular visits to the site, thus reducing human scent and disturbance which may have impacted the presence of certain scavengers at the site.
All trail cameras captured color images/video during the day and infrared images/video during the night.The initial two trail cameras were set to capture a single photo following the detection of motion, with a 1-min delay before subsequent images were taken.If scavenging was seen to be constant and extensive (using the remote images), the delay would sometimes be extended to reduce the impact on data storage and battery life.The video trail camera was set to capture a 20-s recording following the detection of motion, with a 5-min delay before subsequent recordings were taken.These settings were adapted from prior studies [38,39] and found to be suitable for the purposes of capturing optimal data, while balancing the requirements of SD card storage and battery life.Ambient temperature data was collected hourly at each site using an ONSET HOBO® Pendant data logger (UA-002-64), which allowed determination of the minimum, maximum, and average temperatures for each trial (see Table 1).
The Spypoint Link-Micro-LTE cellular trail cameras were monitored remotely using the Spypoint app until the remains had been completely scavenged or had been removed from the deposition site and dispersed.This was deemed the conclusion of the trial, at which time the researchers returned to the sites to recover the equipment, download data and conduct a search for the remains (data relating to TA B L E 1 Trial data (urban proximity, habitat, trial length and temperatures) for scavenging studies conducted in Calgary and Edmonton in 2021 and 2022.dispersal and recovery of remains will be published in a forthcoming manuscript).

| Data collection and analysis
Following retrieval of the cameras, data were downloaded and the images input into Timelapse2 Image Analyser (V2.3.0.5), opensource software used for image analysis, and available through the University of Calgary (https:// saul.cpsc.ucalg ary.ca/ timel apse/ ).The following information was compiled from the images: date of event, time of day, species identified at the carcass, number of individuals, whether the species fed on the remains, diurnal period, carcass feeding location (i.e., head, abdomen, rear, or combination of more than one location), whether the carcass was moved, and the approximate percent of the carcass remaining.Decomposition stages were not estimated for this study due to rapid desiccation of the remains at all sites and the difficulty of scoring decomposition when regions of the carcass are being consumed by vertebrate and invertebrate scavengers.The data was then imported into R software [46] for processing and analysis of temporal scavenging profiles.A new feeding event was recorded when a gap in photo sequence did not correspond to the camera delay, or when the scavenger moved away from the carcass (or left the field of view) before returning later.

| Environmental data
The Calgary trials commenced on August 4, 2021, and August 12, 2022, while the Edmonton trials commenced on August 11, 2021, and August 24, 2022.All trials were deemed to have commenced in the summer and were considered to be "complete" by fall (see Table 1), in that the carcasses remained in view of the cameras until

| Scavenger guilds by habitat type
For each location (Calgary, Edmonton) and site (peri-urban, rural), Overall, coyote were mostly observed to feed either on their own or in pairs (mean of 1.1 individuals per feeding event, with a maximum of 5) for all locations, whereas black-billed magpies were observed to feed on their own or in groups (mean of 1.7 individuals per event with a maximum of 12) throughout the study.magpies and coyote were the only scavengers common to all locations.Black bear was only observed scavenging at the Calgary sites; however, it should be noted that black bear were observed at the Edmonton rural sites but did not scavenge (even when visiting with cubs).Striped skunks were observed to scavenge at three of the four locations, although it should again be noted that they were also observed at the fourth location (Edmonton rural) but did not scavenge.The presence of grizzly bear at the Calgary rural site only and turkey vulture at the Edmonton rural site only is consistent with being at the edge of their respective ranges.Small mammals such as ermine, fisher, and red fox are present at both locations but were not observed to scavenge as frequently as larger mammals and birds.

| Scavenger feeding behavior by location and urban proximity
The avian scavengers (black-billed magpies and turkey vulture) were the only diurnal scavengers.All other scavengers were typically crepuscular or nocturnal but some (like coyote and bears) would feed at anytime during the day or night.Grizzly bear, black bear, and coyote were typically the first scavengers to arrive after carcass placement and demonstrated longer feeding event durations (Figure 7).Black-billed magpies and smaller mammals tended to arrive later in the trials after other scavengers had already commenced feeding and demonstrated shorter feeding event durations (Figure 7).Note, in Figure 7 the mean feeding event for red fox is higher than coyote due to the smaller number of events recorded.and reported in a forthcoming manuscript) is believed to have resulted from coyotes, foxes, and semi-wild dogs as they were observed at the deposition sites on the cameras.However, their activity could not be confirmed as the carcasses were already out of frame by that time.

| Carcass depletion due to scavenging
At the Calgary rural sites in the 2022 trial, carcass depletion did not occur as rapidly, even with intensive black bear scavenging.
Carcasses commenced decomposition with significant invertebrate scavenging; however, black and grizzly bears were observed to feed on the carcasses at the deposition sites during this time.Vertebrate scavenging occurred for a period of approximately 8 weeks before the majority of soft tissue was lost and some hard tissue dispersal had occurred.The most likely agents of dispersal based on imagery were bears and coyotes.
The Edmonton peri-urban sites in the 2021 trial were comparable to the equivalent sites in Calgary in that the carcasses were predominantly depleted due to invertebrate scavenging, prior to vertebrate scavenging occurring.At the time, the first scavenger appeared (coyote), approximately 22 days after commencement, the carcasses were already desiccated with some bone exposure.
Feeding by coyotes typically occurred at the deposition site in pairs or in families of up to five members, accelerating soft tissue loss.
Black-billed magpies only contributed to minimal soft tissue loss and no movement.Vertebrate scavenging occurred for a period of 6 weeks until complete carcass depletion and removal of the skeletal remains from the camera view (by coyotes).
At the Edmonton peri-urban sites in the 2022 trial, vertebrate scavenging occurred in conjunction with invertebrate scavenging.
Black-billed magpies consumed larvae and some soft tissue.The In the 2022 Edmonton rural trial, vertebrate scavenging occurred in conjunction with invertebrate scavenging.Soft and hard tissue loss was predominantly the result of coyote scavenging, either alone or in pairs and complete carcass depletion and dispersal occurred within 6-8 weeks.Black-billed magpies had minimal and no impact on soft tissue loss and hard tissue dispersal, respectively.

| DISCUSS ION
This study aimed to identify the scavenger guilds of two major cities in Alberta where human remains are commonly located by police HRD dog handlers and search and rescue teams.The secondary aim was to determine variability of these scavenger guilds based on urban proximity (peri-urban vs. rural) and habitat (open vs. closed).
The tertiary aim was to identify how the scavenging profiles impact the loss of soft and hard tissue.All studies were conducted during the summer months which allowed for inter-year comparison but meant that seasonal impact was not investigated.

| Scavenger guilds by location and urban proximity
When comparing the two cities, there are several similarities and differences that can be observed in the scavenger guilds.Regardless of the year of study, the Calgary peri-urban, Edmonton peri-urban, and Edmonton rural scavenger guilds were dominated by a mammalian scavenger (coyote) and an avian scavenger (black-billed magpie).Although the black-billed magpies often fed in groups and for extended periods of time during the day, their impact in terms of soft tissue removal was minimal.As a result, the majority of soft tissue loss and hard tissue dispersal was predominantly the result of coyote scavenging at these locations, either as a sole scavenger or in families of up to five coyotes feeding at once.A prior study has reported that group size in urban areas is typically five to six adults, although coyotes can often travel and hunt alone or in loose pairs [47].In addition to being predators, they are also opportunistic scavengers, taking advantage of available food resources [48].In urban and periurban areas of Alberta, coyote populations have increased with indications of modified behavior around humans, which aligns with their presence as the most common mammalian scavenger in these areas [48].This information can be helpful in predicting the most likely scavenger for human remains discovered in periurban regions of Calgary and Edmonton.While no prior studies have been reported for the Calgary region specifically, a study conducted in Edmonton city in 2002 and 2004 also reported evidence of coyote and black-billed magpie scavenging which is consistent with our findings [36].
It is interesting to note that at our locations, invertebrate scavenging occurred extensively prior to vertebrate scavenging commencing.This phenomenon has been previously reported by the authors in a study conducted in Quebec [39] and may be the reason for the timidity of coyotes (the first scavenger to arrive) approaching decomposed remains.In the video imagery, coyotes were observed to regularly approach the remains with caution, investigate, and attempt to drag the remains but without feeding for many days/ nights before commencing their scavenging behavior.Similar canid behavior has been reported by Young et al. [24] for red fox scavenging deer remains, noting behaviors such as sniffing or licking the remains, quick bite and release, and jumping back from the remains, all of which we observed for coyotes in this study.Coyotes have a highly organized social system and will defend their territory from other coyotes; however, this timidity may have been the result of scent marking by other large mammals (e.g., bears), even when they did not scavenge [21].As a result, loss of soft tissue and hard tissue typically took longer in the summer Alberta studies compared to scavenging by coyotes in prior summer Ontario studies [38].This provides an interesting observation of the differences in scavenging behavior between the same species across Canada and acts as a caution towards applying universal predictors of scavenging behavior based on species type alone.
In contrast, the predominant scavengers at the Calgary rural sites were grizzly and black bears.Coyote and black-billed magpies also scavenged in the 2022 trials and there was evidence of their activity (not recorded with imagery) in the 2021 trial; however, observed at the latter site but did not feed on the carcass.Black bears are opportunistic foragers with their preferred food source consisting of berries, nuts, grasses, and tree sap during summer [11,50].However, their diet can vary by season and may incorporate a percentage of animals and insects when needed [50].
When black bears were identified as scavengers, they approached and fed on the remains relatively quickly after carcass placement.
Carson et al. [11] report that bears scavenge for more prolonged periods than what is documented for smaller vertebrates, which is consistent with our findings (see Figure 7).As one of the most common large carnivores in Canada, it is logical that they also represent one of the two most prevalent scavengers in this study in terms of the removal of soft and hard tissue (coyote being the other).This information can inform forensic investigations by suggesting the most likely scavenger for human remains discovered in bear territories.However, their disappearance due to hibernation for certain months of the year must be considered, along with the other scavengers (e.g., coyote) that will fill this gap, representing multiple scavengers on a single body.It should also be considered that the presence of a large carnivore in a region does not necessarily make it a scavenger of human remains.
The presence of a sole turkey vulture at the Edmonton rural site in 2021 was unexpected at this location since it is at the northern edge of the vulture's breeding range and they are typically not observed in Calgary or Edmonton.However, it fed minimally and had little impact on the overall loss of soft tissue so would not be considered a high impact scavenger within the Edmonton guild.This is a particularly relevant finding since vultures are often thought to be primary scavengers and were reported to be such in an Ontario study conducted by the authors [38].Other small mammals scavenged infrequently and while they can all be deemed as potential scavengers for both Calgary and Edmonton, there were no trends observed for their presence at certain locations based on urban proximity.

| Scavenger guilds by habitat type
It was originally hypothesized that habitat type-whether the site had a majority tree canopy (closed) or not (open), would affect the first scavengers to arrive at the carcass.The assumption was that a lack of tree canopy would allow for avian scavengers to more readily locate the carcass through sight or scent.However, with the exception of a sole turkey vulture which may have used scent to locate the carcass [13], the only avian scavengers recorded at all sites were the black-billed magpies which readily accessed the carcasses in both habitat types.Studies conducted in Central Florida [13] and the Lowveld of South Africa [25] also found that canopy density had no impact on when pig carcasses were scavenged by avian species.Similarly, the coyote which was the first mammalian scavenger to arrive at three of the four locations in our study did not seem to show a preference for habitat type, although it should be noted that coyotes would generally attempt to move the carcass from the deposition site.While Grubb and Ellis [20] reported that coyotes in their study preferred open or forest edge sites, they also noted that coyotes would often drag the carcasses from the original deposition site.Furthermore, Indra et al. [16] report that canids will move scavenged body parts from the initial deposition site to scavenge without competition, to feed offspring in a den, or to cache food for later consumption.All other large (grizzly and black bear) and small (ermine, red fox, fisher, and striped skunk) mammals in our study showed no preference for one habitat type over the other.

| Scavenger arrival and feeding behavior by location and urban proximity
The avian scavengers (black-billed magpie and turkey vulture) were the only diurnal scavengers to visit the carcass which is consistent with previous reports [20,38,51] noting that they can search more efficiently and scavenge uncontested areas of a carcass more prevalently during daylight hours.The small mammalian scavengers were predominantly crepuscular or nocturnal.Large mammalian scavengers fed throughout the day and night.Coyotes showed a slight preference for crepuscular and nocturnal feeding [20], whereas grizzly and black bears showed no preference and would often actively scavenge during the day and within hours of each other.With the exception of the Calgary rural 2021 trial where a sole grizzly bear rapidly consumed the remains, the other study locations typically took between 6 and 10 weeks for carcass depletion whereby the majority of soft tissue had been consumed and the hard tissue disarticulated and dispersed from the original deposition site.This is an interesting observation given the presence of large mammals in the scavenger guilds and the anecdotal belief that their presence leads to rapid (e.g., hours or days) scavenging and dispersal of remains.It should be noted that this finding may be due to the fact that the studies were all conducted during the summer months when maximum temperatures reached between 30 and 40°C.Due to higher temperatures, low humidity, and extensive invertebrate scavenging, most of the carcasses rapidly desiccated and may have been less appealing to the scavengers present at the location [15].However, coyotes, black-billed magpies, and other small mammals were observed to feed on desiccated soft tissue at these locations.A summer study conducted in Ontario, Canada, in 2020 demonstrated very rapid carcass depletion of between 2 and 9 days with comparable daily high temperatures [38].A study using human remains in Tennessee, USA, also reports rapid carcass depletion in summer in 45 days [27].Both Ontario and Tennessee typically have higher levels of humidity during the summer months which may have meant that the carcass did not desiccate as rapidly and therefore was more appealing to scavengers during the study timeframe.

| Limitations of the study and future work
One of the challenges of this study was locating land that represented typical locations in which human remains would be discovered.Due to the length of each study and requirement for the land to be minimally used by humans, we used private or restricted-access property with known wildlife.This meant that at some locations, the distance between carcass placement was only several hundred metres due to land availability.This sometimes resulted in the same scavenger locating different carcasses at the site (in both the open and closed habitats) which may have affected their scavenging behavior.The principle of "scavenger swamping" has been reported in ecological studies [42,52,53,54,55] and can also be problematic in forensic studies such as the current and previous ones [38,39].In our previous study, we recommended a distance of ~1 km between sites to minimize the impact of cross-scavenging [38]; however, the current study has demonstrated that the distance is dependent on the type of scavengers present.During the Calgary rural trial in 2021, the same grizzly bear located both carcasses (open and closed habitat) that were placed more than 2 km apart.This suggests that the distance between experimental carcasses in a forensic context should increase when mammals with large territorial ranges are likely present in the region.
For the same reason, multiple carcasses were not used at each site in the study even though the use of replicates would improve statistical validity [56].The presence of multiple carcasses would ultimately change the feeding behavior of scavengers by dispersing their presence and the feeding duration at a carcass across multiple food resources.As this represents an unrealistic scenario in a forensic context, single carcasses were deemed more representative of the conditions we were trying to recreate involving a single human body.While this may be considered a limitation of the study, the repetition of the study at comparable locations across 2021 and 2022 provides some repeatable data on the scavenger guilds for Calgary and Edmonton.Future repeat studies at these locations will ideally help to increase the robustness of this data for statistical analyses.
Due to logistical and resource constraints, the studies were only conducted during the North American summer (studies commenced in August) with the scavenging period extending into the fall (ending in October).Hence, the scavenger guilds reported only represent the animals present at these locations during warmer months.They do not incorporate scavenger variation that can result in other seasons due to hibernation, diapause, or migration [37,38].Prior studies by the authors suggest that carcass depletion can take longer during the fall and winter months in Canada [37][38][39].It is recommended that the current studies be conducted in other seasons at the same locations to better understand how the scavenger guilds vary and the resulting impact on soft and hard tissue loss.In particular, the Calgary rural sites would demonstrate distinctly difference scavenger guilds resulting from the absence of black and grizzly bears due to hibernation.This is important to consider given the fact that human remains can be deposited at any time of the year in Alberta (although is more challenging during winter months when considerable snow accumulation has occurred).

| CON CLUS ION
Our study has identified the scavenger guilds for Calgary and Edmonton during the summer months of 2021 and 2022.Although we did not intend to compare variability between locations, it is notable that three of the four sites (Calgary peri-urban, Edmonton peri-urban, and Edmonton rural) consistently identified coyote and black-billed magpie as the most prevalent scavengers during the study period.Urban proximity did not impact the scavenger guild at the Edmonton locations but did impact scavenger diversity between the peri-urban and rural sites at the Calgary location, where the rural site was surrounded by a matrix of natural areas and permitted access to more wary scavenger species.The habitat type, specifically whether the carcass was placed in an open or closed environment, did not appear to impact the scavenger guilds and arrival of first scavengers (avian or mammalian) to the carcasses.Generally, we observed a consistency in scavenger guilds across the years for each site, with the exception of the sole grizzly bear in the Calgary rural trial in 2021.Time for decomposition and dispersal of remains in Alberta was longer than Ontario locations that reported different scavenger guilds (even when corrected for season).These findings present important information about the likely scavengers in two densely-populated regions of Alberta and their feeding behavior.
Related findings on dispersal patterns of remains will be published in a forthcoming manuscript.The results offer new and relevant information to organizations tasked with searching for human remains, especially remains that may have been scavenged and scattered from the original deposition site in an Albertan landscape.

ACK N OWLED G M ENTS
We would like to thank the following people for assistance with experimental set-up and data collection: Murray Burke, Dennis Dalziel, Chris Dilschneider, Gabe Graham, Jason Macgregor, Clay Scoulding, and Ian Vernon.

CO N FLI C T O F I NTER E S T S TATEM ENT
No potential conflict of interest is reported by the authors.

R E FE R E N C E S
The vegetation in the study location was broadly similar across the sites.Canopy tree species were mostly deciduous (e.g., trembling aspen Populus tremuloides and balsam poplar Populus balsamifera) with scattered white spruce (Picea glauca).The understory comprised willows (Salix spp.; in wetter sites), wild rose (Rosa spp.), and saskatoon serviceberry (Amelanchier alnifolia) with the herbaceous layer tending to be dominated by native and exotic grasses.In the open sites, the canopy species were sparse or absent.Within each site, the distance between open and closed habitatsranged from approximately 200 m to 2 km depending on land availability.The sites were chosen as they represented typical terrain in these areas where the HRD dog handlers had previously searched for human remains.Each site was chosen by the handler(s) for that region.All sites are classified as Dfb (continental subarctic climate) by the Köppen-Geiger climate classification.
most soft tissue had been scavenged and hard tissue was dispersed from the deposition site.Since the studies spanned both summer and fall months, the overall temperatures had broad minimum and maximum ranges as follows: −1.8 to 39.6°C (Calgary 2021); −8.1 to 42.2°C (Edmonton 2021); −5.7 to 36.5°C (Calgary 2022); and 0.9 to 39.2°C (Edmonton 2022).

Figure 1 F I G U R E 1
Figure 1 provides an overview of the species that were observed to scavenge at each location, categorized by urban proximity and year of study.At the Calgary peri-urban sites, coyote (Canis latrans, Canidae) and black-billed magpie (Pica hudsonia, Aves)

3 . 4 |
habitat types were investigated-one open canopy and one closed canopy.It was thought that habitat type may impact the prevalence of avian versus mammalian access even though a recent study in eastern North America (Ontario, Canada) did not support this hypothesis[38].Comparing the data for all locations revealed no preference for avian scavengers since magpies (as the predominant avian scavenger) arrived around the same time at open and closed sites in both the 2021 and 2022 trials (Figure2).F I G U R E 2 Scavenger guilds for Calgary and Edmonton categorized by habitat type (closed vs. open) and year of study.Mammalian scavengers also showed no preference with coyote, grizzly bear, black bear, red fox, and striped skunk observed scavenging at both open and closed sites.For other scavengers that were only observed in one habitat type, this was more likely the result of their infrequent scavenging than a preference for, or accessibility to, a particular habitat.It should be noted that for the open and closed sites that were in close proximity to each other (e.g., less than 500 m apart), it is possible that the same scavengers were accessing both sites.This was more likely at the peri-urban sites than the rural sites due to land availability.Regardless, no scavenging species appeared to show a preference for the open versus closed site and thus all subsequent data interpretation combined the habitats for each location and site.Scavenger arrival and feeding behavior by location Scavenging behavior at each location based on urban proximity and year of study is shown in Figure 3. Specifically, it highlights the first scavengers to arrive at the carcass for each trial, the time since placement of the carcass when each scavenger type arrived, the time of day of scavenging (diurnal, crepuscular, and nocturnal), and duration of activity.At the Calgary peri-urban sites in the 2021 trial, the coyote was the first mammal scavenger to arrive and the black-billed magpies the first and only avian scavengers to arrive.Both species arrived approximately 25 days after carcass placement and were the predominant scavengers throughout the trial.Coyote were predominantly nocturnal scavengers, although were observed to feed occasionally during the day, while the black-billed magpies were only diurnal scavengers.The red fox appeared later in the trial (approximately 40 days after carcass placement) solely as an infrequent nocturnal scavenger.In contrast at the Calgary periurban sites in the 2022 trial, a sole ermine was the first scavenger to arrive 20 h after carcass placement, followed over the next few weeks by a coyote, two black bears, and a striped skunk.All species were observed at various times of the day and night and scavenged infrequently.The predominant scavenging resulted from black-billed magpies that arrived approximately 30 days after carcass placement and fed frequently for the remainder of the trial.While black-billed magpies represented the most prevalent scavenger, they removed minimal soft tissue during feeding, and it was subsequent feeding of coyote, black bear, red fox, and striped skunk that resulted in the majority of soft tissue loss and hard tissue dispersal.Black-billed magpies were the only diurnal scavengers, whereas all other species were either crepuscular or nocturnal scavengers in the 2022 trial.At the Calgary rural sites in the 2021 trial, a large grizzly bear (Figure 4) arrived within 8 h of carcass placement and fed consistently throughout the day and night for a period of approximately 30 h on one carcass.Once it had consumed the carcass and dragged it from view of the camera, it located the other carcass soon after and continued to feed in the same manner.These sites were deemed too F I G U R E 3 Scavenger guilds for Calgary and Edmonton categorized by urban proximity and year of study, demonstrating scavenger arrival, time of day and duration of feeding.dangerous to enter to move the cameras to observe additional scavenger behavior.As a result, no additional scavenging activity could be documented, although additional scavenging (likely canid) was observed during the search for the remains several weeks later.The Calgary rural site in the 2022 trial showed a more diverse and potentially more accurate representation of the scavenger guild for this location.Black bear and grizzly bear were the first scavengers to arrive, approximately 3 and 4 days after carcass placement, respectively.Black bears fed consistently for a large proportion of the trial with at least nine different individuals confirmed (one "cinnamon" bear, a larger black bear, a sow black bear with two cubs, and a sow black bear with three cubs including one "blonde" cub).While they did not feed together, other than the sows and respective cubs, they did feed within hours of each other demonstrating overlap in their territory.Their feeding activity occurred predominantly during daylight hours which can range from 05:30 to 22:00 during summer in Alberta.Coyote and striped skunk were infrequently observed as nocturnal scavengers.Black-billed magpies only arrived toward the end of the trial (approximately 50 days after carcass placement) as diurnal scavengers and fed consistently in groups until the end of the trial.The Edmonton trials showed much greater consistency in scavenger guilds and behavior based on urban proximity and year.The predominant scavengers in both the 2021 and 2022 trials for the peri-urban sites were coyote and magpies.In the 2021 trial, the coyote would typically arrive first (approximately 12 days after carcass placement) with black-billed magpies arriving later in the trial (approximately 30 days after carcass placement).Coyotes were observed to feed in families of up to five individuals predominantly at night (Figure 5), while black-billed magpies would feed alone or in groups as diurnal scavengers.In the 2022 trial, the first scavenger to arrive was again the coyote (approximately 3 days after carcass placement), which typically fed alone or in pairs while black-billed magpies appeared later in the trial (approximately 14 days after carcass placement).While coyotes fed throughout the day, they were most active as nocturnal scavengers, whereas black-billed magpies were only active during daylight hours.At the Edmonton rural site in the 2021 trial, a sole turkey vulture was the first scavenger to arrive after 7 days but fed infrequently as a diurnal scavenger with minimal soft tissue loss.Striped skunk and fisher were also observed infrequently in this trial.Coyotes represented the most prevalent scavengers in the 2021 and 2022 Edmonton rural trials, with black-billed magpies appearing around the same time as coyotes in the 2021 trial (>40 days after carcass placement).In the 2022 trial, coyotes appeared much earlier (approximately 4 days after carcass placement), though magpies appeared at around the same time as in 2021 (approximately 40 days after carcass placement).Similar to the peri-urban sites, coyote was more frequently observed feeding at night, while the black-billed magpies only fed during daylight hours.

Figure 6 F I G U R E 5 F I G U R E 6
Figure 6 separates the species type by location and urban proximity to show trends relating to scavenger behavior.Black-billed from the deposition site by coyotes with some displacement by foxes.Scavenging and dispersal occurred predominantly by coyotes for a period of 6-7 weeks before carcass depletion and dispersal resulted and the trials were ended.A similar trend was observed at the Calgary peri-urban sites in the 2022 trial, with the majority of soft tissue depletion resulting from invertebrate scavenging, prior to vertebrate scavenging.By the time mammalian scavenging commenced by bears and coyotes (approximately 14 days after carcass placement), the carcasses were already desiccated with some bone exposure.Bears tended to feed at the deposition site, while coyotes would attempt to move the carcasses or parts thereof.Black-billed magpies consumed larvae and small amounts of soft tissue but did not move F I G U R E 7 Mean feeding event duration for all scavengers recorded at the Calgary and Edmonton locations.the remains.Scavenging continued through the summer and fall months by bears, coyotes, skunks, and foxes, but complete carcass depletion and dispersal did not occur by the time of the first snowfall in October 2022.At the Calgary rural sites in the 2021 trial, carcass depletion occurred rapidly due to a sole grizzly bear.Although the open and closed sites were approximately 2 km apart, it is believed that the same grizzly bear was responsible for scavenging at both sites.Carcass depletion and removal from camera view occurred within 1.5 days of carcass placement at the closed site and within 4 days of carcass placement at the open site.At both sites, the grizzly did not move the carcasses far from the deposition sites.Subsequent dispersal of the skeletal elements (identified during the searches

TA B L E 2 8 • 5 • 4 •
Scavenging behavior by species type for studies conducted in Calgary and Edmonton in 2021 and 2022. in soft tissue or using orifices to access internal organs • Minimal consumption of soft tissue • No movement of intact carcass • No movement of disarticulated elements Black-billed magpie Individual to groups of Consume insect larvae along with soft tissue • Despite feeding in groups, minimal impact on soft tissue loss • No movement of intact carcass • No movement of disarticulated elements Skunk Individual • Tear and consume small amounts of soft tissue • Consume insect larvae along with soft tissue • Rarely observed scavenging • No movement of intact carcass • Minimal movement of disarticulated elements Fisher Individual • Tear and consume small amounts of soft tissue • Rarely observed scavenging • No movement of intact carcass • Minimal movement of disarticulated elements Ermine Individual • Tear and consume small amounts of soft tissue • Rarely observed scavenging • No movement of intact carcass • Minimal movement of disarticulated elements Fox Individual • Cautious approach to carcass, particularly when other carnivores' scent was present • Tear and consume small amounts of soft tissue • Removal of disarticulated elements over distances less than large canids Coyote Individuals to family groups of Cautious approach to carcass, particularly when other carnivores' scent was present • Tear and consume large amounts soft tissue • Consume soft tissue during fresh, decomposed and desiccated stages • Often scent marked carcass and territory • Attempt to drag intact carcass from deposition site • Removal of disarticulated elements over large distances Black bear Individual to family groups of Tear and consume large amounts of soft tissue, often laying down to feed • Consume insect larvae along with soft tissue • Consume soft tissue during fresh, decomposed and desiccated stages • Often scent marked carcass and territory • Move entire carcass from deposition site but only minimally (e.g.metres) • Removal of disarticulated elements over distances less than large canids Grizzly bear Individual • Tear and consume large amounts of soft tissue for hours at a time, often laying down to feed • Consume soft tissue during fresh and decomposed stages • Move entire carcass from deposition site but only minimally (e.g.metres) • Removal of disarticulated elements over distances less than large canids majority of soft tissue loss and all hard tissue loss resulted from coyotes scavenging alone or in pairs, with complete carcass depletion and dispersal occurring within approximately 8 weeks.The Edmonton rural sites in the 2021 trial were also predominantly depleted due to invertebrate scavenging prior to intensive vertebrate scavenging occurring.Although a turkey vulture arrived during the early stages of decomposition and black-billed magpies scavenged throughout the study, they had minimal impact on soft tissue loss.By the time that coyote scavenging commenced, approximately 40 days after deposition, the carcasses were already desiccated with some bone exposure.Soft and hard tissue loss resulted predominantly from a sole coyote scavenging and complete carcass depletion occurred in approximately 8-10 weeks of carcass placement.
feeding was considerably reduced compared to the other sites, which was likely due to presence of bears in the area.A recent study confirmed this behavior noting that when there is a carcass, bears will deter coyotes from scavenging due to their size and the predator/prey hierarchy [57].Grizzly bears were only observed at the Calgary rural sites since their range does not extend to the peri-urban regions of Calgary or the city or rural regions of Edmonton.Typically, grizzly bears are only found in the foothills, mountains, and boreal regions of Alberta as they are more sensitive to high density of roads and human disturbance (especially motorized recreation)[49].Notably, the Calgary rural site was located within a landscape matrix of low human disturbance, whereas the three other locations were located within a broader matrix of urban and/or agricultural use.While black bears were only recorded scavenging at the Calgary sites, their range extends to the peri-urban regions of Calgary and the Edmonton rural site in 2021.A sow and cubs were

FU N D I
N G I N FO R M ATI O N The Canada 150 Research Chair in Forensic Thanatology [C150-2017-12] and the Natural Sciences and Engineering Research Council of Canada [RGPIN/6098/2019] supported this research.

Table 2
provides a summary of the typical scavenging behavior and carcass movement observed by the species identified across all trials.At the Calgary peri-urban sites in the 2021 trial, the carcasses were considerably depleted due to invertebrate scavengers, prior to vertebrate scavengers arriving.The first mammalian scavenger (coyote) appeared 22 days after carcass placement by which time the carcasses were desiccated with some bone exposure.Black-billed magpies appeared around the same time and consumed larvae as well as small amounts of soft tissue.Carcasses were readily moved