Size Determinants in Territories With Inflexible Boundaries: Manipulation Experiments on White-Winged Trumpeters’ Territories

Abstract

We investigated determinants of territory size in White-winged Trumpeters (Psophia leucoptera), frugivorous, cooperatively breeding birds that defend large, permanent, all-purpose territories in lowland Amazonian rain forest. During a 7-mo period, we measured changes in food density at a site in Manu National Park, Peru, and conducted full-day focal samples on individuals that allowed us to record daily food intake of territorial birds. We used data from laboratory analyses on energy content of fruit species eaten by trumpeters to calculate a phenology of energy content for food available on territories of focal groups, and to calculate daily energy intake of focal trumpeters. Additionally, we used lab measurements of basal metabolic rate of trumpeters to estimate daily energy requirements of wild trumpeters.Both census and focal sample data suggested that food availability on trumpeter territories varied widely, sometimes greatly exceeding and sometimes falling short of the amount that we calculated was necessary to meet average daily energy requirements of groups. To determine whether trumpeter territory size was related to food density, we conducted fruit removals. Every day, we removed an amount of fruit from the territory that was equivalent to the amount of fruit ingested daily by the focal group during a control period preceding the removal experiment. We conducted removal experiments during periods when food density on territories appeared to be abundant and also when food abundance appeared to be low. Trumpeter food consumption did not change when fruit was removed during periods of resource abundance; however, when experimental removals were conducted during periods of food scarcity, the total energy value of food consumed decreased significantly. These results suggest that food abundance on trumpeter territories sometimes exceeds and sometimes is close to or below the amount needed to meet energy needs of the groups. Based on our data, we propose that territory size of White-winged Trumpeter groups reflects some minimum size needed to provide the group with a baseline level of food intake during seasonal periods of decreased food abundance.

A field study investigating effects of landmarks on territory size and shape

“…Clearly defined boundaries can allow residents to determine easily when another individual has intruded and can reduce time spent defending against neighbours [13]. Although landmarks could lower defensive costs, adjusting territory boundaries may be costeffective only when territories are not contiguous [16,17], as in this study, or when individuals are not highly territorial [18,19]. A strong response to landmarks may be most likely in species defending territories in simple, homogeneous habitats, such as the fish we observed in this study.…”

Response of frugivorous primates to changes in fruit supply in a northern Amazonian forest

“…Overall, fruiting pattern is spatially synchronous across the eastern part of the island showing two distinct annual fruiting peaks (Moskovits, 1985). As in other tropical forests, the study site regularly experiences periods of absolute scarcity of fruits (Mendes Pontes, 2000), when insufficient fruit may be available to fulfill the metabolic needs of frugivores (Sherman and Eason, 1998;Terborgh, 1986).…”

“…In general, changes in local distribution of primates in response to changes in fruit density during HFS (with exception for Alouatta macconnelli) were not detected. This may indicate that fruit supply during this period is likely to meet (or even exceeds) frugivore needs (Sherman and Eason, 1998). During HFS, a number of abundant and important fruits can be found everywhere throughout the eastern part of MES (Milliken and Ratter, 1998).…”

“…Fruit supplies in seasonal forests are subjected to marked spatiotemporal variation, being unevenly distributed compared to other potential foods such as leaves or arthropods Stone, 2007). Tropical seasonal forests have relatively long fruit shortages, leading frugivores to face potential energetic deficits, what ultimately drive important responses in their ecology and physiology (Goldizen et al, 1988;Knott, 1998;Ramos Pereira et al, 2010;Sherman and Eason, 1998;Vogel et al, 2012).…”

Assessing the Effects of Logging Activities on Avian Richness and Diversity in Different Aged Post-Harvested Hill Dipterocarp Tropical Rainforest of Malaysia

“…Food resources distribution may regulate population of bird species (Wright et al, 1999;Johnson and Sherry, 2001) and fruit abundance influences the species composition and foraging behaviour of fruit eating birds (Moegenburg and Levey, 2003). For example; fruit eating birds always concentrated where fruit occurs abundantly because their diet consists of more than 50% fruits (Kinnard et al, 1996;Sherman and Eason, 1998;Malizia, 2001;Renton, 2001).…”