Nomadism and seasonal range expansion in a large frugivorous bird

Abstract

Studies on the ranging behaviour of birds often suggest that ranges vary seasonally with larger ranges in the non‐breeding compared to the breeding season. However, due to limitations in tracking methods very little is known about the underlying processes driving seasonal differences in ranging behaviour, especially in fragmented, heterogeneous landscapes. Such knowledge is particularly important if movements deliver essential ecosystem functions such as seed dispersal. We contrasted the daily ranging behaviour between the breeding and non‐breeding season of a frugivorous bird and demonstrate how larger seasonal ranges in the non‐breeding season emerge through switching from a stationary home range behaviour to nomadism. We tracked movements of 29 male trumpeter hornbills Bycanistes bucinator across a fragmented landscape of eastern South Africa during different breeding and non‐breeding seasons using high temporal resolution GPS data‐loggers. Birds in the breeding seasons showed a typical, stationary home range pattern. In the non‐breeding seasons birds, rather than expanding their stationary daily ranges, switched to nomadic movements that were characterized by shifts of the general location of daily ranges to a different area every couple of days. We also found that during the breeding seasons hornbills were mostly located in large continuous forests; birds in the non‐breeding seasons frequently used forest patches within the agricultural landscape and residential areas. These seasonal differences in the movement behaviour of trumpeter hornbills may have important consequences for seed dispersal of plant species. Our findings show how seasonal range expansion of frugivorous birds may be driven by fundamental behavioural changes that have important consequences for ecosystem processes.

Scale‐Dependent Spatial Match between Fruits and Fruit‐eating Birds during the Breeding Season in Yungas Andean Forests

“…The high mobility of birds allows them to track fruits over large land tracts, such as landscapes or regions, but the establishment of territories and the care of the offspring must confine frugivore movements to areas close to the nest (Lenz et al . ). Most studies reporting bird–fruit adjustments at large spatial scales assessed non‐breeding temperate birds, either during migration (Mudrzynski & Norment , Wolfe et al .…”

“…Breeding birds typically have stationary home ranges, while non‐breeding birds can modify the location of their daily ranges, even without changing the range size (Mueller & Fagan , Lenz et al . ). At small spatial scales, birds revisit predictable food sources within their territories, and may even memorize the spatial location of feeding sites and use this knowledge in their foraging decisions (Henderson et al .…”

“…Migratory birds can exploit heterogeneous spatial patterns of food supply during migration, and in wintering areas can distribute themselves in response to variation in food availability (Loiselle & Blake 1991, Johnson & Sherry 2001, Teller ıa et al 2014, Wolfe et al 2014. During the breeding period, foraging movements of parent birds are expected to be more constrained than at other times of their life cycle (Côrtes & Uriarte 2013, Slagsvold et al 2013, Lenz et al 2015. Breeding birds typically have stationary home ranges, while non-breeding birds can modify the location of their daily ranges, even without changing the range size (Mueller & Fagan 2008, Lenz et al 2015.…”

“…During the breeding period, foraging movements of parent birds are expected to be more constrained than at other times of their life cycle (Côrtes & Uriarte 2013, Slagsvold et al 2013, Lenz et al 2015. Breeding birds typically have stationary home ranges, while non-breeding birds can modify the location of their daily ranges, even without changing the range size (Mueller & Fagan 2008, Lenz et al 2015. At small spatial scales, birds revisit predictable food sources within their territories, and may even memorize the spatial location of feeding sites and use this knowledge in their foraging decisions (Henderson et al 2006, Salwiczek et al 2010).…”

“…We assessed this relationship at two spatial scales, one at a local (<1 km 2 ), fine-grained (tens of meters) extent, and the other at the landscape level (<100 km 2 ), with a spatial resolution on the order of a hectare. We conducted the study during the peak of the breeding season, when most birds are likely central-place foragers constrained to explore resource abundance in the surroundings of the nest (Orians & Pearson 1979, Lenz et al 2015. On average, fruit-eating species have a breeding season shorter than 2 months, during which the females invest two-thirds of the daylight hours in nest attentiveness during incubation and both adults feed and care for nestlings, with high nestling feeding rates close to ten visits per hour (Auer et al 2007).…”