The Effects of Group Size and Reproductive Status on Vigilance in Captive Callithrix jacchus

Abstract

Previous work on mammals and birds has often demonstrated a negative relationship between group size and individual vigilance. However, this relationship has received only weak support in nonhuman primates. This result may be due to the failure to distinguish different forms of vigilance such as antipredatory vigilance and social monitoring. Here, we tested the effects of group size, reproductive status (breeding vs. nonbreeding), and sex on antipredatory vigilance and social monitoring in captive common marmosets (Callithrix jacchus). Behavioral observations using one-zero sampling were conducted on adult members of three captive groups of small, medium, and large size. Data were analyzed using a series of general linear models (GLMs) analyses of covariance (ANCOVAs). We found an overall negative group size effect on antipredatory vigilance and that breeders, especially breeding males, were significantly more vigilant than nonbreeders. Conversely, we found that social monitoring increased with group size. Unlike the results for antipredatory vigilance, neither breeders and nonbreeders nor males and females differed in their amounts of social monitoring. However, the effect of group size appeared to differ for nonbreeding males compared to all other adults. Our results generally support the idea that individuals in larger groups are safer with breeding males likely playing a prominent role in protection from predation. The increase in social monitoring may be related to increased reproductive competition with the presence of adult offspring, but future studies need to clarify the target of social monitoring in both breeders and nonbreeders. Overall, the study underlines the importance of distinguishing different forms of vigilance and other factors as they may confound the effects of group size on antipredatory vigilance.

What have we been looking at? A call for consistency in studies of primate vigilance

“…Mothers with dependent infants more vigilant than those with independent young or females without infants Boinski et al (2003), Treves (1999c), Treves et al (2003) No difference found between adult females with or without infants Treves (1998) All adult individuals increased vigilance after birth of infants Treves et al (2001) Vigilance increased when infant-carrying Steenbeek et al (1999), Stojan-Dolar & Heymann (2010) Age Vigilance increases with age in both sexes Boinski et al (2003), Busia et al (2016), de Ruiter (1986, Fragaszy (1990), Gosselin-Ildari & Koenig (2012) Vigilance decreased with age in both sexes Watson et al (2015) No age-related effects Caine & Marra (1988) Activity Vigilance higher during resting and traveling van Schaik & van Noordwijk (1989) Vigilance higher during resting Cowlishaw (1998), Gaynor & Cords (2012), Stojan-Dolar & Heymann (2010), Suzuki & Sigiura (2011) Vigilance lower during grooming than resting or feeding Cords (1995) Routine vigilance higher during feeding Teichroeb & Sicotte (2012) No difference between feeding or resting Macintosh & Sicotte (2009), Teichroeb & Sicotte (2012 Vigilance higher during foraging than resting Kutsukake (2006) Isbell & Young (1993), Kazahari & Agetsuma (2010) f , Hill & Cowlishaw (2002) h Subgroup size Vigilance lower with larger subgroup sizes but only in boundary areas Busia et al (2016) No effect of daily party size Kutsukake (2006) Group composition…”

“…Treves et al (2003) highlighted that the greatest increase in vigilance was found when immatures were conspicuous; however, allogrooming has been shown to reduce maternal vigilance towards infants in several species (Kutsukake, 2006(Kutsukake, , 2007Maestripieri, 1993;Treves, 1999c). Finally, GosselinIldari & Koenig (2012) reported that "antipredatory" vigilance was higher for breeding than non-breeding individuals, whilst "social monitoring" was mostly unaffected by breeding status.…”

“…Nevertheless, a negative group-size effect was present when S. mystax formed mixed species groups with saddleback tamarins (Saguinus fuscicollis), although this effect was only apparent during resting behaviors. When GosselinIldari and Koenig (2012) defined "antipredatory vigilance" and "social monitoring" as separate behaviors, they subsequently detected a negative group-size effect on "antipredatory vigilance" in common marmosets (Callithrix jacchus). Similarly, when vigilance of this species was categorized as either "induced" or "routine", the frequency of "induced vigilance" (scans longer than 1 s) increased with group size (Teichroeb & Sicotte, 2012).…”

“…When "social monitoring" has been recorded as a distinct behavior, varied results have emerged with Gosselin-ildari and Koenig (2012) reporting social monitoring to increase with group size, whilst Kazahari and Agetsuma (2010) found social monitoring frequency was higher in small feeding groups of Japanese macaques. The subject of gaze may also be important.…”

“…16 Baldellou & Henzi (1992), Boinski et al (2003), Caine (1987), Campos & Fedigan (2014), Cowlishaw (1998) Total number of studies utilizing one-zero sampling 7 Bshary & No€ e (1997), Fragaszy (1990), Gosselin-Ildari & Koenig (2012), Koenig (1998), Steenbeek et al (1999), Suzuki & Sigiura (2011), Tsingalia & Rowell (1984 a Utilized instantaneous scan sampling and continuous focal sampling.…”