Monitoring Wildlife Using Camera Traps: Effect of Bait Type in Pine Plantations and Natural Hardwood Stands

Abstract

Camera traps across from cages baited with either sardines or suet were installed in forests on the campus of Ferrum College in Virginia, USA, during the Fall and Spring seasons over two years. The objective of this study was to determine the vertebrate wildlife abundance and species composition in natural hardwood forests with mixed pine species compared to pine plantations. We found that the forest type and bait preference differed among the species by season. The relative abundance of natural foods and the need for winter thermal cover may explain the capture success in this study.

1. Introduction

Camera traps are motion-triggered devices that are useful and cost-effective for short- and long-term passive monitoring of wildlife and allow for estimates of species detection, relative population abundance, and activity patterns [1,2]. The placement of camera traps is important for camera captures, and includes choosing the correct habitat for the target species, locating traps along travel corridors and log features, and the season of wildlife activity [3,4].

Using baits or lures could increase the capture efficiency of animals, but could also include bias, especially for estimates of the population size [5]. Studies have shown that different types of baits have varying success in attracting wildlife to camera traps. For example, [2] Randler [2] found that different baits, such as tuna and mustelid mix, affected the detection and the number of images taken by camera traps. Ferreira-Rodríguez and Pombal [6] tested four attractants (chicken, canned sardines, peanut butter, and cat urine) and found that fish and meat baits had the best performance.

The forest type may also influence wildlife habitat use and camera traps may allow for the quantification of species habitat use to inform natural history studies and management [7]. Deciduous (hardwood) forests typically have a better habitat structure for wildlife than pine plantations for many species [8]. Deciduous forests typically also offer more food resources, particularly hard mast provided by tree species such as oaks (Quercus), hickories (Carya), and beech (Fagus) [9]. These are important food resources for species such as White-tailed Deer (Odocoileus virginianus), White-footed Mice (Peromyscus leucopus) and Gray Squirrels (Sciurus carolinensis), among others.

Pine plantations provide pine seeds, which are food sources for some species, but because they are monocultures, they offer less structure and food diversity for wildlife. There is a lack of comparative studies in the literature comparing natural hardwood forests and pine plantations using camera traps and whether the type of bait may influence the captures of wildlife in these forest types.

In this study, we used baited camera traps to determine wildlife use of pine plantations compared to natural mixed deciduous–pine forests at multiple sites at a property in southwestern Virginia over four sampling periods from 2022 to 2024. During the last two sampling periods, we also compared habitat use with cages baited with two different types of bait (canned sardines and suet cakes).

2. Materials and Methods

The study was conducted at four sites on the campus of Ferrum College in Franklin County, Virginia, USA, during the Fall and Spring seasons from 2002 to 2024. At each site, we placed two camera traps in stands dominated by deciduous forest with some pine trees (hereafter referred to as “hardwood”) stands and also an adjoining pine plantation (hereafter referred to as “pine”) stands. Hardwood stands were mature (>80 years old) mixed pine–hardwood forests with the canopy dominated by Oak (Quercus spp.), Red Maple (Acer rubrum), Tuliptree (Liriodendron tulipifera), and White Pine (Pinus strobus) tree species. All hardwood stands were selectively logged approximately 30 years ago. Pine stands were either Loblolly Pine (Pinus taeda) stands approximately 60 years old or White Pine stands approximately 30 years old. We selected sampling sites in different parts of the Ferrum College campus where there were adjacent hardwood and pine stands.

All camera traps in this study were STC-PC12 V2 Stealth cameras (Stealth Cam, LLC, Irving, TX, USA). They were mounted on trees using a strap at a height of 1.5 m. Across from the camera traps at the same height and at a distance of 5–10 m were 12 × 12 cm metal cages affixed to a tree with elastic cords that contained either a partially opened can of sardines in soybean oil or a high-energy suet cake (C&S products Inc., Fort Dodge, IA, USA) (Figure 1 and Figure 2). Suet cakes are typically used for attracting songbirds, but can also attract mammals. Traps were set to take two photos with a delay time of 30 s between camera captures. We recorded one capture of an animal once per photo session. Repeated captures that appeared to be same animal were not counted unless there was a 30 min delay in a photo capture. We did not differentiate between animals upon appearance and acknowledge that captures may include repeated captures of the same animal even if they included the 30 min new capture counting delay. In some cases, captures included more than one animal of the same species. In this case, all animals were counted.

We installed camera traps during two seasons (Fall and Spring) in adjoining hardwood and pine stands in two sampling periods: 2022–2023 and 2023–2024. Fall sampling occurred between August and November and Spring sampling occurred between February and April. In both Fall and Spring sampling seasons, we sampled two different pairs of pine and hardwood stands with camera sampling periods in each stand lasting 14 days. Cameras were checked for battery status and photos were downloaded every 7 days. We also replaced bait each 7 days.

In the 2022–2023 sampling period, we only baited traps with canned sardines, but in the 2023–2024 sampling period, we baited one trap with sardines and the other with suet. To reduce the possibility of attracting wildlife to both traps in the same location, we separated traps with different bait types by at least 20 m.

Because we did not uniformly trap all bait types, forest types, and seasons, we mostly used descriptive statistics in this paper for overall results that were summed over all camera traps per forest type and bait. We also used chi-square contingency tests for the various treatments for overall captures and individual species where there appeared to be a possible statistically significant differences between forest types or bait types.

3. Results

Comparing only the habitat use of pine and hardwood stands during the first year of the study, we recorded six identifiable species in the hardwood stands and only three identifiable species in the pine stands in the Fall of 2022 (

Table 1. Total camera photos of wildlife species in the Fall of 2022 in deciduous forests (hardwood) and pine plantations. Photos were considered unique if an individual animal of a species was photographed at least 30 min later than the first photo.

Fall 2022	Forest Type
Species	Hardwood	Pine Plantation
Black Bear (Ursus americanus)	5	0
Gray Squirrel (Sciurus carolinensis)	1	0
House Cat (Felis catus)	1	0
Raccoon (Procyon lotor)	16	15
Southern Flying Squirrel (Glaucomys volans)	3	6
Virginia Opossum (Didelphis virginiana)	1	0
White-tailed Deer (Odocoileus virginianus)	45	2
Unidentified	5	2
TOTAL	77	25

). There were more than 3× the number of captures in the hardwood stands (p < 0.001), mainly due to a very large number of captures of White-tailed Deer (Odocoileus virginianus) (p < 0.001). We captured five photos of Black Bear (Ursus americanus) in the hardwood stands and none in the pine stands. There were numerous captures of Raccoon (Procyon lotor) in both forest types. Only Southern Flying Squirrel (Glaucomys volans) had more camera captures in the pine plantations than hardwood forests.

In the Spring of 2023, there were seven identifiable species of wildlife with camera captures in hardwood stands and five in pine plantations (

Table 2. Total camera photos of wildlife species in the Spring of 2023 in deciduous forests (hardwood) and pine plantations. Photos were considered unique if an individual animal of a species was photographed at least 30 min later than the first photo.

Spring 2023	Forest Type
Species	Hardwood	Pine Plantation
Gray Squirrel (Sciurus carolinensis)	15	16
Pileated Woodpecker (Dryocopus pileatus)	1	0
Raccoon (Procyon lotor)	5	27
Southern Flying Squirrel (Glaucomys volans)	13	2
Virginia Opossum (Didelphis virginiana)	8	10
White-footed Mouse (Peromyscus leucopus)	2	0
White-tailed Deer (Odocoileus virginianus)	3	12
Unidentified	2	2
TOTAL	49	69

). Summed over all the species, there were nearly 1.5× more camera captures of wildlife in the pine plantations than the hardwood forests, but this difference was not significant (p = 0.19). This trend was mostly due to a larger number of captures of Raccoon (p = 0.003) and White-tailed Deer (p = 0.09) in the pine plantations compared to hardwood forests. Unlike in the Fall season, there was a larger number of captures of Southern Flying Squirrel in the hardwood forests (p = 0.03).

Unlike in the Fall of 2023, there were more species captures in the pine plantations (7) than in the hardwood forests (3) (

Table 3. Total camera photos of wildlife species in the Fall of 2023 in deciduous forests (hardwood) and pine plantations with contrasting bait types (sardines and suet). Photos were considered unique if an individual animal of a species was photographed at least 30-min later than the first photo.

Fall 2023	Forest Type
	Hardwood		Pine Plantation
Species	Sardines	Suet	Sardines	Suet
Black Bear (Ursus americanus)	0	0	2	1
Gray Squirrel (Sciurus carolinensis)	3	0	1	1
Gray Fox (Urocyon cinereoargenteus)	0	0	0	1
Raccoon (Procyon lotor)	10	12	17	20
Tufted Titmouse (Baeolophus bicolor)	0	0	0	1
Virginia Opossum (Didelphis virginiana)	0	0	0	2
White-tailed Deer (Odocoileus virginianus)	2	8	5	16
Unidentified	0	0	2	0
TOTAL	15	20	27	42

). The number of captures was also higher in the pine plantations, mainly due to a larger number of White-tailed Deer and Raccoons (p = 0.09). Only Gray Squirrel (Sciurus carolinensis) had higher captures in the hardwood stands. Although not statistically significant, captures were higher for the cameras baited with suet than those with sardines, particularly for White-tailed Deer and Raccoons. Only Gray Squirrel and Black Bear had higher captures for the cameras baited with sardines. Gray Fox (Urocyon cinereoargenteus), Virginia Opossum (Didelphis virginiana), and Tufted Titmouse (Baeolophus bicolor) were only captured at sites baited with suet.

In the Spring of 2024, there were 11 species captured in the pine plantations and only 6 species in the hardwood stands (

Table 4. Total camera photos of wildlife species in the Spring of 2024 in deciduous forests (hardwood) and pine plantations with contrasting bait types (sardines and suet). Photos were considered unique if an individual animal of a species was photographed at least 30 min later than the first photo.

Spring 2024	Forest Type
	Hardwood		Pine Plantation
Species	Sardines	Suet	Sardines	Suet
American Crow (Corvus brachyrhynchos)	2	0	0	0
Coyote (Canis latrans)	0	0	1	0
Gray Squirrel (Sciurus carolinensis)	0	0	3	1
Gray Fox (Urocyon cinereoargenteus)	0	0	1	0
Hairy Woodpecker (Leuconotopicus villosus)	0	2	0	0
Hermit Thrush (Catharus guttatus)	0	0	0	2
Raccoon (Procyon lotor)	4	7	29	18
Southern Flying Squirrel (Glaucomys volans)	2	0	4	0
Tufted Titmouse (Baeolophus bicolor)	0	0	0	4
Virginia Opossum (Didelphis virginiana)	0	5	13	6
White-breasted Nuthatch (Sitta carolinensis)	0	0	0	2
White-footed Mouse (Peromyscus leucopus)	0	0	0	3
White-tailed Deer (Odocoileus virginianus)	10	3	1	2
Unidentified	0	0	0	1
TOTAL	18	17	52	39

). There were larger numbers of captures of species in pine stands than in the hardwood stands (p < 0.001), particularly for pine stand cameras baited with sardines, driven mostly by captures of Raccoons (p < 0.001) and Opossums (p = 0.03). Songbirds, in general, were only captured at the sites baited with suet, most of these in pine plantations. In the hardwood stands, there was an equal number of captures for the cameras baited with sardines and suet. White-tailed Deer had more captures in the hardwood stands (p = 0.05).

4. Discussion

The number of captures among species differed by season and bait type (bait was only used in the second year of sampling). The most common species captured were White-tailed Deer and Raccoons, and to a lesser extent Virginia Opossums, Gray Squirrels, and Southern Flying Squirrels.

White-tailed Deer are very abundant in the area and the photos of this species varied greatly between seasons. As herbivores, they were unlikely attracted to the bait, but perhaps were captured more due to other factors, such as the hard mast availability or winter thermal cover [9,10]. The large number of captures of White-tailed Deer in the hardwood stands in the Fall of 2022 may be due to an abundance of acorn nuts (Quercus hard mast) in that season during that year. Interestingly, deer captures were much lower in the following Spring and following Fall and tended to be higher in the pine plantations. Then, they were captured more frequently in the hardwood stands in the Spring of 2024.

Raccoons were commonly captured in all years and seasons, but in the Fall seasons, they were equally abundant in the hardwood and pine plantations. The camera captures indicated a strong preference, however, for the pine plantations in the Spring seasons. Raccoons are opportunistic omnivores [11], but perhaps were more attracted to bait during the Spring seasons when there was the most food scarcity and their preference for pine stands may also have been related to the greater thermal winter cover provided there. They were particularly attracted to the sardines compared to the suet in the second year, perhaps because they often locate food by olfactory sensing [11]. Virginia Opossums are also opportunist omnivores [11] and their captures showed a similar trend to those of Raccoons.

The two squirrel species captured in this study included the Eastern Gray Squirrel and the Southern Flying Squirrel. Gray Squirrels are diurnal and Flying Squirrels are nocturnal. Both rely heavily on hard masts, particularly in the Fall, but also rely on acorns in the Winter and Spring by scatter-hoarding or caching food [11]. Their captures indicate a general preference for hardwood stands, but Southern Flying Squirrels also were more abundant in some seasons in the pine plantations, contrary to a previous live capture study in the forests at these sites [6].

Black Bears were only captured on camera in the Fall, which was expected because this species feeds heavily in the Fall and hibernates in Virginia from November to April. The few captures indicated a preference for the hardwood stands in the Fall of 2022 and for the pine plantations in the fall of 2023.

Few bird species were captured during the first year, when only sardines were used as bait. The camera captures of songbirds, although not in large numbers, became more numerous at the suet-baited cameras in year 2. All of the captures occurred in the Spring of 2024 in the pine plantations, which could be explained by the food scarcity at that time of year and the need for more thermal cover provided by the pine plantations [12].

One surprising result of this study was the larger number of wildlife photos recorded in the pine plantations compared to the hardwood forests. Hardwood forests tend to have more food and habitat structure for wildlife [8,9]. It should be noted, however, that most of the species in this study have relatively large home ranges and their occurrence in pine plantations in close proximity to hardwood stands may not be unexpected, particularly in spring, when there is more thermal cover in pine plantations.

5. Conclusions

Like other studies, this study indicates the usefulness of camera trapping for detecting and monitoring wildlife species and determining their habitat preferences. It also showed that the type of bait provided in front of the camera traps can attract different species of wildlife and may vary in capture success during different seasons. The relative abundance of habitat structure and natural foods during certain seasons may also play a strong role in camera capture success.