Table 1 Overview of 31 studies to date examining the ecology, behavior and genetics of the Darwin’s finch Philornis downsi host-parasite system since the first discovery of P. downsi larvae in Darwin’s finch nests on Santa Cruz Island, Galápagos Archipelago, in 1997. Shown are data for 1) Number of finch host species or species name when singular, 2) Island, 3) Year study undertaken, 4) Sample size of nests (including number of control versus experimental [Exp.] nests), 5) P. downsi prevalence, 6) Mean number and range of P. downsi (in unmanipulated nests), 7) Percentage of in-nest mortality of nestlings in unmanipulated nests, 8) Effects on host, 9) Additional comments, 10) Type of study (Ecology, Genetics, Behavior), 11) Experimental study (E) versus Observational study (O), 12) Reference
1) Host species | 2) Island | 3) Year of study | 4) Sample size | 5) P. downsi prevalence | 6) Mean number of P. downsi per nest (range) | 7) In-nest mortality (%) | 8) Effects on host | 9) Comments | 10) Type of Study | 11) Exp. (E) versus Obs. (O) study | 12) Reference |
|---|---|---|---|---|---|---|---|---|---|---|---|
9 species | Santa Cruz | 1998 | 63 | 97 % | N/A | First study to describe P. downsi in bird nests on Santa Cruz Island | Ecology | O | Fessl, Couri, Tebbich 2001 [29] | ||
12 species | Santa Cruz | 1998–2000 | 177 | 97 % | 15.7 ± 7.4–49.8 ± 31.2 (0–182) | 27 % | Number of larvae increased with nestling age; P. downsi not found in nests during incubation | Intensity compared for nestling age <8 days vs. >8d; species differed in intensity | Ecology | O | Fessl, Tebbich 2002 [28] |
3 Darwin’s finch species | Santa Cruz | 2000, 2004, 2005 | 63 | 100 % | −32.4–95.2 % | Damage to nestling nasal cavities; calculated 18–55 % overnight blood loss in nestlings due to parasitism | Identify two stage life cycle of P. downsi with 1st instar within nestling nares and 2nd and 3rd instar feeding externally | Ecology | O | Fessl, Sinclair, Kleindorfer 2006 [42] | |
2 Darwin’s finch species | Santa Cruz | 2000, 2004 | 27 | 100 % | 18.4 ± 2.4–23.2 ± 4.2 | 66 % | Parasitized nestlings had 61 % lower survival, 56 % lower body mass, 28 % lower hemoglobin concentration | 11 nests prayed with 1 % permethrim (~1 P. downsi left per nest; range 0–5 larvae) | Ecology | E | Fessl, Kleindorfer, Tebbich 2006 [41] |
Darwin’s finches | All islands | P. downsi given highest risk ranking for invasive species that negatively impact endemic fauna | 23 % (around 463 species) of Galapagos invertebrate species are introduced of which 6 are confirmed to be highly invasive and harmful to endemic species | Ecology | Causton, Peck, Sinclair, Roque-Albelo, Hodgson, Landry 2006 [26] | ||||||
Small ground finch | Santa Cruz, Floreana, Isabela | 2004 | 24 | 92 % | 23 ± 6 (0–90) | 2 % lower hemoglobin concentration per additional larva | Effect of clutch size on P. downsi number per nestling | Ecology | O | Dudaniec, Kleindorfer, Fessl 2006 [44] | |
6 Darwin’s finch species | Santa Cruz | 1998–2005 | 131 | 100 % | 30.2 ± 4–66.8 ± 7.6 | 55 % | Positive association between P. downsi intensity and rainfall (eight year study); same intensity across habitats on Santa Cruz | Species differences in intensity | Ecology | O | Dudaniec, Fessl, Kleindorfer 2007 [33] |
Darwin’s finches | 13 islands | 1998–2005 | 515 | 27.0 (1–182) | P. downsi was found on 11 of 13 islands sampled (absent from flat arid islands); more parasites in highland nests on elevated islands | Lowland nests on elevated islands had more P. downsi than lowland nests on flat islands | Ecology | O | Wiedenfeld, Jiménez, Fessl, Kleindorfer, Valarezo 2007 [39] | ||
5 Darwin’s finch species | Santa Cruz, Floreana, Isabela | 2004–2006 | 64 | 100 % | High gene flow between islands; some genetic differentiation of P. downsi on Floreana; evidence for genetic bottleneck | Sequenced CO1 mitochondrial gene fragments | Genetics, Ecology | O | Dudaniec, Gardner, Donnellan, Kleindorfer 2008 [40] | ||
Medium ground finch | Santa Cruz | 2004–2006 | 63 | 64–98 % | (0–200) | 16–37 % | Number of P. downsi per nestling (but not per nest) predicted survival; no effect of P. downsi on nestling size | Nests earlier in the breeding season had more P. downsi per nest | Ecology | O | Huber 2008 [34] |
Small ground finch | Santa Cruz | 2008 | 623 | 36.3 % of adult birds had malformed beaks with enlarged naris (likely caused by P. downsi during the nestling phase) | Ecology | O | Galligan, Kleindorfer 2009 [48] | ||||
5 Darwin’s finch species | Santa Cruz | 2000–2004 | 43 | 100 % | 23.0 ± 3–57.0 ± 4 | Larger finches built larger nests; within species, larger nests had more P. downsi | Behavior | O | Kleindorfer, Dudaniec 2009 [90] | ||
Small ground finch | Floreana | 2004–2006 | 39 | 94 % | 8.0 ± 1.6–39.3 ± 4.6 (0–78) | 3–33.4 % | Arid lowland nests had 80 % fewer P. downsi and 91 % lower in-nest mortality than highland nests | Ecology | O | O’Connor, Dudaniec, Kleindorfer 2010 [89] | |
Medium ground finch | Santa Cruz, Daphne Major | 2008 | 67 | More Philornis-specific antibodies in females than males, and more during the nesting period | No P. downsi found on Daphne Major | Ecology, Behavior | O | Huber, Owen, Koop, King, Grant, Grant, Clayton 2010 [46] | |||
3 Darwin’s finch species | Santa Cruz, Floreana | 2008 | 11 | 89 % | 27.1 ± 8.5 (0–74) | 79.2 % | Multiple P. downsi entries into the nest during incubation and feeding; nestlings stood on top of each other presumably to avoid larvae; adults preened nestling nares and nest base; nestling consumed larva | In-nest video; altered time budgets and behavior in heavily parasitized nests; adults removed dead nestling from nest | Behavior, Ecology | O | O’Connor, Robertson, Kleindorfer 2010 [49] |
5 Darwin’s finch species | Santa Cruz, Floreana | 2004–2006 | 57 | 100 % | 30.8 ± 16.5 (5–65) | Genetic relatedness among P. downsi within nests was 57 % lower on Santa Cruz than on Floreana Island; between 1–6 different females laid their eggs per finch nest; each female mated with ~2 different males; each female laid ~5 eggs per finch nest with a maximum of 24 from one female | Genetics, Ecology, Behavior | O | Dudaniec, Gardner, Kleindorfer 2010 [117] | ||
Medium tree finch | Floreana | 2006, 2008 | 30 | 100 % | 43.1 ± 10.7–65.6 ± 8.5 (8–96) | 20–38 % total brood loss; 53 % of nests with partial or total brood loss | Parasite intensity did not predict fledging success; parasitized nestlings had grossly enlarged nares and tissue loss | Highest P. downsi intensity in critically endangered medium tree finch | Ecology | O | O’Connor, Sulloway, Robertson, Kleindorfer 2010 [38] |
Mangrove finch | Isabela | 2006–2009 | 15 | 100 | 40.8 ± 15.3 sd | 14 % | Less rat predation after rat control (30 % predation after control versus 54 % predation before); P. downsi explained 14 % nestling mortality | Before and after rat control | Ecology | O + E | Fessl, Young, Young, Rodríguez-Matamoros, Dvorak, Tebbich 2010 [63] |
Medium ground finch | Santa Cruz | 2008 | 48 | 90 % | 37.5 ± 4.9 | 96 % | Parasitized nestlings had ~30 % shorter primary feather length and 88 % lower fledging success | Nylon stocking placed over wire hoop as barrier to P. downsi; reduced parasite intensity to ~21 larvae per nest | Ecology, Behavior | E | Koop, Huber, Laverty, Clayton 2011 [63] |
Darwin’s finches | All islands | 2012-present | Summary of known P. downsi biology and impacts on endemic land birds | Launch of the P. downsi Action Plan | Ecology, Behavior, Genetics | Causton, Cunninghame, Tapia 2013 [72] | |||||
Medium ground finch | Santa Cruz | 2010 | 30 (15 control, 15 exp.) | 44.7 ± 6 (5–79) | No effect of P. downsi on attending female corticosterone level, body condition or hematocrit level | 15 nests sprayed with 1 % permethrin (~0 per nest) | E | Knutie, Koop, French, Clayton 2013 [102] | |||
Medium ground finch | Santa Cruz | 2010 | 43 (22 control,21 exp) | 100 % | 38.5 ± 5.1 | 100 % | Compared with fumigated nests, females at parasitized nests had more P. downsi-specific antibodies, spent 42 % less time brooding and 74 % more time standing erect in the nest | 14 females and 10 males from fumigated nests, 15 females and 10 males from parasitized nests | Behavior | E | Koop, Owen, Knutie, Aguilar, Clayton 2013 [47] |
Medium ground finch | Santa Cruz | 2009 | 13 (7 control, 6 exp.) | 83 % | 30.5 ± 7.5 | 86 % | No effect of rainfall on P. downsi intensity (two year study) | 6 nests sprayed with 1 % permethrin (zero P. downsi) | Ecology | E | Koop, Le Bohec, Clayton 2013 [88] |
Small ground finch | Floreana | 2010 | 14 (7 control, 7 exp.) | 100 % | 22.7 ± 3.9 (12–60) | 100 % | In-nest video; heavily parasitized nestlings had weak begging; parents only fed strongly begging nestlings | 7 nests sprayed with 1 % permethrin (zero P. downsi) | Behavior | E | O’Connor, Robertson, Kleindorfer 2014 [100] |
4 Darwin’s finch species | Floreana | 2004–2013 | 238 | 100 % | 27.5 ± 4.6 (2004) to 48.4 ± 6.5 (2013) | 50–90 % | Across the decade, P. downsi intensity increased (~28 to ~48), in-nest mortality increased (~50 to ~90 %), nestlings died younger (~11 to ~5 days after hatching); pupa size got 10 % smaller (~10 mm to ~9 mm) | Compared with other finches, small ground finch nests had more P. downsi pupae, which indicates higher fly reproductive success | Ecology | O | Kleindorfer, Peters, Custance, Dudaniec, O’Connor 2014 [37] |
3 Darwin’s tree finch species | Floreana | 2005, 2010 | 201 | 100 % | 25 ± 3–65 ± 18 | Hybrid finch nests had 50–79 % fewer P. downsi than medium tree finch (2005, 2010) | Contemporary hybridization in Darwin’s tree Finches; evidence for hybrid fitness | Behavior, Genetics, Ecology | O | Kleindorfer, O’Connor, Dudaniec, Myers, Robertson, Sulloway 2014 [7] | |
2 Darwin’s finch species | Santa Cruz | 2010, 2012 | 82 | 100 % | 25, 38 | 37–56 % | Extreme weather events and number of P. downsi influenced nesting success | Species differences in P. downsi intensity | Ecology | O | Cimadom, Ulloa, Meidl, Zöttl, Zöttl, Fessl, Nemeth, Dvorak, Cunninghame, Tebbich 2014 [36] |
4 Darwin’s finch species | Santa Cruz | 2013 | 37 (17 control, 20 exp.) plus 26 nests checked for treated cotton | 17 ± 3.9 | 46 % | Parasitized nests had 35 % lower fledging success | Permethrin-treated cotton from dispensers in 22 nests; 20 nests sprayed with 1 % permethrin (zero P. downsi) | Ecology | E | Knutie, McNew, Bartlow, Vargas, Clayton 2014 [70] | |
Small ground finch | Floreana | 2010 | 14 (8 control, 6 exp.) | 100 % | 24.2 ± 2.7 | Parasitized nestlings had larger relative (39 %) and absolute (3.3 mm) naris size compared with parasite-free nestlings (20.2 %, 1.6 mm) | 6 nests sprayed with 1 % permethrin (zero P. downsi); museum specimens had normal naris size suggesting post 1960s arrival of P. downsi | Ecology, Morphology | E | Kleindorfer, Sulloway 2016 [30] | |
3 Darwin’s finch species | Floreana | 2004–2014 | 582 | 100 % | 17.7 ± 3.3–87.8 ± 19.5 | Higher fly traps caught more female P. downsi; higher finch nests had more P. downsi | 28 McPhail traps placed at 1 m–7 m to test for fly sex ratio at different trapping heights | Behavior, Ecology | E | Kleindorfer, Peters, Hohl, Sulloway 2016 [71] | |
Medium ground finch, mockingbird | Santa Cruz | 2012, 2013 | 127 | P. downsi density (grams per nestling g) predicted finch but not mockingbird mortality; no P. downsi antibodies in nestlings; parasitized mockingbird but not finch nestlings begged more | 32 finch nests and 34 mockingbird nests prayed with 1 % permethrin | Behavior, Ecology | E | Knutie, Owen, McNew, Bartlow, Arriero, Herman, DiBlasi, Thompson, Koop, Clayton 2016 [105] |