Temporal and spatial variation in sex-specific abundance of the avian vampire fly (Philornis downsi)

Abstract

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.

Genetics reveals shifts in reproductive behaviour of the invasive bird parasite Philornis downsi collected from Darwin’s finch nests

“…N e was highest in 2006 and 2014 (but values for 2008 could not be obtained for the 10% missingness dataset), and lowest in 2020. Notably, this temporal decrease matches a decrease in mean in-nest P. downsi intensities (Common et al 2021) and daily catch rates of adult P. downsi across the sampling years (2014: 0.35 ± 0.03; Kleindorfer et al unpublished data;2020: 0.28 ± 0.02;Common et al 2022). The estimated values for effective population size were significantly smaller than expected, given the widespread distribution and high in-nest intensity of P. downsi.…”

“…Bait lure was replaced, and specimens were collected every seven days, for a total of seven trapping events. In 2020, 32 traps were placed every 50 m in a 200 m × 100 m lattice in two study plots, and along two 200 m transects in two separate plots (Common et al 2022). Traps were hung at four and seven metres high, to capture both male and female P. downsi, as previous research found a difference in capture height between the sexes .…”

Nesting Success and Nesting Height in the Critically Endangered Medium Tree Finch (Camarhynchus pauper)

“…El Niño lowers marine productivity, and also has strong effects on terrestrial ecosystems [40] by changing rainfall patterns and plant productivity, and thus, exerting bottom-up effects on food webs including predator-prey interactions [41]. Parasite abundance is furthermore heavily influenced by precipitation [42,43] and a recent study on Floreana Island identified rainfall, proximity to human population and fruiting trees as the most important factors determining avian vampire fly abundance [44].…”

Galápagos yellow warblers differ in behavioural plasticity in response to traffic noise depending on proximity to road

“…We conducted the experiment in the lowlands and highlands on Santa Cruz Island and Floreana Island. All study areas have previously been part of long-term annual nesting monitoring of Darwin’s finch breeding biology monitored by our research group since 2000 (Common et al, 2022; Kleindorfer et al, 2021). Santa Cruz highland study plots were located in the Los Gemelos area (–0.625982, –90.384829), and the lowland study plots in the El Barranco area (0.739068, –90.301467).…”