A parasite reduction conservation intervention does not improve fledging success or most condition metrics for Purple Martins

Abstract

Eastern Purple Martins (Progne subis subis) have an unusually close relationship with humans, as they nest exclusively in man-made nest boxes. Current conservation policy directly promotes further interaction with this species by advocating regular replacement of nest materials during the nestling phase to reduce ectoparasite load and increase nestling fitness. We conducted the first test of the efficacy of this recommendation and found that it was partially effective in reducing parasite abundance, but had no effect on nestling fledging success, body mass, leukocyte count, or triglyceride or uric acid concentration. We found a small but significant increase in nestling hematocrit associated with nest material replacement, implying that parasites may induce nestling anemia. Contrary to our expectations, we also found elevated heterophil/lymphocyte ratios in nestlings with replacements, possibly indicating elevated physiological stress associated with nest replacements. Based on our results, we do not recommend nest material replacements to combat routine parasite infestations.

Impacts of purple martin landlord stewardship activities on nest box occupancy

“…We chose 2017–19 as our 3‐year study period as a balance between providing enough time for each landlord's efforts to impact martin occupancy (B. Woelk, Camrose Wildlife Stewardship Society, personal communication) and avoiding too much time to pass before nest boxes are transferred to a different landlord with different stewardship practices. Williams et al (2020) used a similar 3‐year period to investigate the effects of martin nest replacement. In the event that a different landlord became responsible for a martin nest box, we used occupancy data only for the years during which the most recent landlord managed the nest box.…”

“…Future research should incorporate more robust measures of martin nesting success, such as the numbers, weights, and other physiological characteristics of eggs, nestlings, and fledglings (Brown 1978, Williams et al 2020.…”

“…Such calcium supplementation increases the number of eggs laid and young hatched (Rush and Hill 2006). Even though most martin guidebooks recommend that nest sites be cleaned annually in order to remove parasites and moldy nest material (Stokes et al 1997), studies have shown that martins prefer houses that have not been cleaned since the previous occupancy (Jackson and Tate 1974) and that changing nest material does not reduce parasite infections (Williams et al 2020).…”

“…Today, the proper design, location, and habitat of martin nest boxes is critical in attracting nesting martins (Davis and Brown 1999, Eads 2001, Doughty and Fergus 2002, Bridge et al 2016, Anderson and Hvenegaard 2021). However, at a broad scale, habitat suitability is not related to martin fecundity (Williams et al 2020). Martin landlord stewardship practices are important to nesting success, as supported by considerable anecdotal and some scientific evidence (e.g., Bailey and Bonter 2017, Raleigh et al 2019).…”

“…Parasites, such as blowfly larvae ( Protocalliphora hirundo ) that feed on the blood of martin nestlings, can have detrimental effects on the fledging success of nestling birds (Merino and Potti 1995, Hurtrez‐Boussès et al 1997), so landlords attempt to limit the negative effects by replacing nests and removing blowfly larvae from nestlings (Hill 1994). However, nest replacement had no effect on fledging success (Williams et al 2020).…”