DOI: 10.5061/dryad.3j9kd51kc
title: Temporal and spatial variation in sex-specific abundance of the avian vampire fly (Philornis downsi)

description: Understanding the range and behaviour of an invasive species is critical
 to identify key habitat areas to focus control efforts. Patterns of range
 use in parasites can differ temporally, across life stages and between
 sexes. The invasive avian vampire fly, Philornis downsi, spends the larval
 stage of its life within bird nests, feeding on developing nestlings and
 causing high levels of mortality and deformation. However, little is known
 of the ecology and behaviour of the non-parasitic adult fly life stage.
 Here, we document sex-specific temporal and spatial patterns of abundance
 of adult avian vampire flies during a single Darwin’s finch breeding
 season. We analyse fly trapping data collected across 7 weeks in
 the highlands (N = 405 flies) and lowlands (N = 12 flies) of Floreana
 Island (Galápagos). Lowland catches occurred later in the season, which
 supports the hypothesis that flies may migrate from the food-rich
 highlands to the food-poor lowlands once host breeding has commenced. Fly
 abundance was not correlated with host nesting density (oviposition site)
 but was correlated with distance to the agricultural zone (feeding site).
 We consistently caught more males closer to the agricultural zone and more
 females further away from the agricultural zone. These sex differences
 suggest that males may be defending or lekking at feeding sites in the
 agricultural zone for mating. This temporal and sex-specific habitat use
 of the avian vampire fly is relevant for developing targeted control
 methods and provides insight into the behavioural ecology of this
 introduced parasite on the Galápagos Archipelago.
description: Adult vampire flies were collected using baited McPhail traps
 hung in trees (Causton et al. 2019; Lincango and Causton 2009). Traps were
 baited with 150 mL of liquid lure composed of 600-g ripe Hawaiian papaya,
 75-g sugar, and 4 L of water, blended and fermented in the sun 3 days
 prior to use. Trapping occurred in the highland and lowland site. At each
 site, traps were placed within four study plots, each containing 12 traps
 separated by 50 m in a three by four trap lattice (Fig. 1). In addition,
 four traps were placed in two more study plots along a single transect
 each separated by 50 m (N = 32 traps per site, total N = 62 traps; Fig.
 1). Traps were placed alternatively at 4 and 7 m high to capture potential
 sex ratio differences of flight height found previously by Kleindorfer et
 al. (2016). Bait lure was replaced and all specimens collected every 5
 days. This was repeated nine times from January 19th to March 5th for a
 total of 563 trapping events. Collected flies were stored in 70% ethanol,
 identified, and sexed under a stereomicroscope following morphology
 described in Kleindorfer et al. (2016).<br> Distance of each trap to
 the agricultural zone boundary was calculated using coordinate data. The
 host nesting density, i.e. the number of active Darwin’s finch nests per
 200 m × 100 m study plot, was collected from our long-term nest monitoring
 protocol (see Kleindorfer et al. 2014), which occurred concurrently with
 trapping. Search effort for active nests within study plots was equal
 across highland and lowland sites. The host species monitored were the
 small ground finch (Geospiza fuliginosa), cactus finch (Geospiza
 scandens), small tree finch (Camarhynchus parvulus), medium tree finch (C.
 pauper), and the hybrid tree finch (C. parvulus × C. pauper as well as
 introgressed individuals). Each monitored host nest that was with eggs
 (incubation phase) or nestlings (feeding phase) within each study plot
 (100 m × 200 m) during each trapping period (5 days) was counted as an
 active nest, giving a nesting density of Darwin’s finch nests per plot for
 each trapping event.