Organochlorine residues in guano of long-fingered bats (Myotis capaccinii) from Lake Maggiore (NW Italy)

The long-fingered bat Myotis capaccinii is one of the most endangered Mediterranean bats. At present, only two maternity colonies of the species are known in Northern Italy, roosting at Lake Maggiore (at Isola Bella) and at Lake of Lecco. Even if it is possible that some further colonies occur, ignored due to the lack of surveying, the paucity of records reflects a condition of true rarity and highlights the conservation interest of the two colonies. At Isola Bella, M. capaccinii occurs within a mixed-species colony (together with M. myotis, M. blythii and M. daubentonii), constituting approximately the 75-85% of the roosting bats. Colony size, monitored during the last 14 years by annual counts (total number of individuals, excluding juveniles) varied in the range of 477-859 individuals. Demographic trend over the same period resulted negative (rs=-0.78; p<0.01). This trend cannot be related to direct disturbance, as the roost is inaccessible without permission and equipment. Some negative factors that could affect the colony (restoration works; artificial lighting illuminating the entrance of the roost) were avoided by caution measures (renovations were carried out while the bats were absent and without altering the characteristics of the roost; lighting system was removed). Nevertheless, other causes cannot be excluded: bats may suffer from disturbance during winter months (elsewhere, since only few individuals hibernate at Isola Bella), because of predation from wild or domestic animals (cats represent the most common potential predators in the area), diseases, and degradation and loss of their foraging habitat. According to literature, calm water bodies are the preferred foraging habitats for M. capaccinii; prey, caught in flight and by trawling/gaffing, are mainly represented by adults, pupae and larvae of Diptera Chironomidae and other aquatic insects; the contribute of small fish to diet can also be important. Lake Maggiore represents a large foraging area for the individuals of the colony, which can be observed chasing close to the water surface after their emergence from the roost. Thus, the water quality of the lake, through its effects on aquatic prey, may play a role in the local conservation of the species. Lake Maggiore has a well-documented history of contamination byDDTand its relatives of around 50 years, due to the discharges of a production plant into the Toce river, one of the main inlets of the lake. Although the synthesis of DDT ended in 1996, the recovery of the lake has been delayed sinceDDTs are particularly persistent and therefore still present within the lake basin, in particular in biota and sediments. Bats are particularly vulnerable to these and similar organochlorine (OC) compounds, which have been recognized as one of the severe causes of the dramatic declines in bat populations occurred in the 50s-70s. We hypothesized that long-fingered bats of Isola Bella may accumulate OCs from their prey and partially excrete them in urine and feces. Previous works on other bat species have demonstrated a positive correlation between the levels of OCs in guano and those present in bat carcasses from the same colonies: chemical analysis of guano may therefore serve as an indirect and nondestructive technique to detect exposure and accumulated contaminant loads occurring in bats. We analyzed three guano samples, collected beneath the colony of Isola Bella in March, May and June of 2011. Data revealed the presence of parental DDT compound (pp'DDT), confirming the presence of some hot spot DDT sources in the area. Among DDTs, p,p´-DDE was by far the most dominant metabolite, with concentrations ranging from 85.79 to 181.20 ng g-1, followed by pp´DDD and pp- DDT, which ranged between 0.97-2.36 ng g-1 d.w. PCBs, of unknown and probably diffuse sources, were also present, reaching the concentration of 212,59 ng g-1. Since the recorded OC levels are not negligible, in order to go deeper into the possible causes of the colony decrease, a monitoring program concerning the contamination seems necessary