Observations on feral hog ecology in south and southeast Brazil Marcelo Wallau1,3, Clarissa A. da Rosa2, Tiago dos Reis3, Carlos A. Wallau3, Nilson Molinos3 and La Hire Mendina Filho3

Feral hog population has been increasing significantly in

the past few years in Brazil (Fig. 1). Just recently, in 2013,

lethal control was authorized by the environmental agency

(IBAMA). Rio Grande do Sul state has the largest sheep

herd in Brazil and predation reports had grown exponential-

ly lately. Favorable environmental conditions and feed avail-

ability year-round may be enhancing reproductive capacity.

We collected data from reproductive characteristics of cap-

tured/harvested sows and modelled population growth

based on those parameters.

ulation of 10 adult sows. The population expansion poten-

tial, if no control is applied, and with good environmental

conditions is very large.

Preliminary results from research being conduced in

South and Southeast Brazil (A and B, respectively, in Fig.

1). In the South, data was collected by direct counts of the

number of fetus (>130 d) or unweaned piglets per sow.

Average of 7.5 ± 1.99 offspring per litter (N = 61; 7.62 ±

1.76 fetus per sow and 7 ± 2.86 piglets per sow).

Ranges of 4 to 14 fetus, and 3 to 12 piglets per sow.

No difference between the number of fetus per pregnant

sow and the number of unweaned piglets, what could indi-

cate a high survival rate.

Very distinct phenotypic groups observed indicate large

crossbreeding (Fig. 2)

Field observations indicate two farrowing seasons

(spring and fall).

Data from camera traps in the Southeastern region (B,

in Fig.1) identified an average of 2.3±1.6 piglets (n=55)

per sow. This difference between the two datasets could

be related to a longer invasion time and greater adapta-

tion of the population in the South, composed by appar-

ently larger and more hybridized animals (Fig. 2).

We built four, age-structured, deterministic population

growth models to compare different survival rates and lit-

ter sizes. Juveniles were considered apt to reproduce in

the first year (F1), with litter size 1/2 of adults, and adults

reproduce until the maximum age of 3 yo (Fig. 3).

Model A: 2 litters of 7.5 piglets per year, juvenile and

adult survival rate of 0.33 and 0.5, respectively.

Model B: 1.2 litters of 5.6 piglets per year, same survi-

cal as A.

Model C: same as A, but juvenile survival rate of 0.15

Model D: same as A, but juvenile and adult survival

rates of 0.46 and 0.7, respectively

Figure 2: Sounder in South (A) and Southeastern (B) Brazil.

P3 1 2 3 P1 P2

F2 F3 F1

Figure 3: life cycle of feral hogs. Fi, age-specific fertility; P age-

specific probability of survival.

Model A Model B Model C Model D

P1 0.33 0.33 0.15 0.46

P2, P3 0.5 0.5 0.5 0.7

F1 0.62 0.46 0.28 0.87

F2, F3 3.75 1.68 3.75 5.25

λ 1.67 1.22 1.14 2.34

s(P1) 1.68 1.13 2.47 1.68

e(P1) 0.33 0.3 0.32 0.33

Both sensitivity (s) and elasticity (e) were larger for P1

for all models (Table 1). Juvenile survival appears to have

the largest impact on the increase of λ, and should be one

of the focus of population control (Biber and Ruf 2005).

Asymptotic population growth rate (λ) was larger for Mod-

el D, indicating a higher colonization potential with in-

creased reproductive and survival rates. Figure 4 shows

the behavior of all models over 9 years, with a initial pop-

Table 1: survival and fecundity parameters for feral hog population

growth models A, B and C, and respective sensitivity, elasticity and

growth rate

Figure 5: Fetus of a pregnant feral sow (A). Note the variety on the skin pigmentation by the crossbreeding between domestic (D) and wild (W) hogs, probably from a domestic boar raised at the ranch nearby. Captured feral sow, hitched to a stake, raised “free-ranging” with sheep (B).

D W

A B

Adequate environmental conditions and large food avail-

ability seem to be increasing reproductive capacity of feral

hogs in South Brazil. We are facing a fast-increasing feral

hog population growth, and measures for control are not

being taken. While we discuss about “more adequate” reg-

ulations, e are losing the greatest ally, which is time.

1 Grazing Ecology Research Group, Federal University of Rio Grande do Sul, RS, Brazil 2 Mammals Ecology and Conservation Laboratory, Federal University of Lavras, MG, Brazil

3 Javali no Pampa Team, RS, Brazil

Figure 4: Deterministic population growth projection, using both models

A, B, C and D, over 9 years, with starting population of 10 adult sows.

Laws and regulations for feral hog control are very com-plicated, time consuming and expensive (See Rosa et al, this conference).

Cultural issues with domestic pigs raised free-ranging (Fig.5).

Lack of knowledge on efficient techniques on feral hog control.

Disinterest of the majority public agencies on the subject and lack of support to farmers.

References Bieber, C., and T. Ruf. 2005. Population dynamics in wild boar Sus scrofa: Ecology, elasticity of growth rate and implications for the management of pulsed resource consu-mers. J. Appl. Ecol. 42(6):1203–1213

Pedrosa, F., R. Salerno, F.V.B. Padilha, and M. Galetti. 2015. Current distribution of in-vasive feral pigs in Brazil: economic impacts and ecological uncertainty. Braz J Nat Con-serv. 13:84-87.

Introduction

Data on Reproductive Biology

Modelling

Main Challenges

Conclusions

Figure 1: Expansion of feral hog population in Brazil from 1989 to 2015

(Pedrosa et al. 2015)

A

B

LECOM