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The dynamics of the meteorological variables and of the monthly and daytime bird number and parasite prevalence and load in individuals of Junco phaeonotus in Loma Alta, Nevado de Toluca, Mexico
Study area In Nevado de Toluca the vegetation is dominated by pine forest and mixed forests (pine-fir, fir-oak and pine-oak) (Villers Ruiz et al., 1998). However, in Ejido Loma Alta, the predominant tree is fir Abies religiosa (Kunth Schltdl. et Cham.). We carried out the study in Ejido Loma Alta, Municipality of Zinacantepec, State of Mexico, approximately 40 km away from the capital city. The open area was devoted mainly to farmland (sheep, horse) and cropland (potatoes, oats). Hereafter, we will designate both habitat types as “farmland”.
Sampling period During the years 2017-2018 we recorded bird morphometric data and fat score in the same zones. We compared these between habitats. For parasite sampling together with the study of morphological traits we carried out bird sampling from August 2018 through July 2019. The closest days within the same month encompassed the same fieldwork event. Fieldwork was conducted from 7:00 a.m. through 19:00 p.m. per day, over two days.
Bird sampling We identified the sampling zones according to the vegetation cover and land use. At each habitat, we set five 12m x 2.5m mist nets (produced by Ecotone, Poland) at sampling points where we previously had observed activity of individuals of J. phaeonotus: in the forest, at least 40 m away from the forest edge, and in the farmland, at least 60 m away from the forest edge. During the years 2017-2018 we recorded bird morphometric data and fat score in the same zones. We compared these between habitats. For parasite sampling together with the study of morphological traits we carried out bird sampling from August 2018 through July 2019. The closest days within the same month encompassed the same fieldwork event. Fieldwork was conducted from 7:00 a.m. through 19:00 p.m. per day, over two days. Throughout the year we use the Central Standard Time (CST; UTC/GMT -5 hours) observed in Mexico City from the first Sunday of April through the las Sunday of October, in each fieldwork event, we fulfilled 24 hours of sampling.
Each net was checked once each hour. During events that could endanger birds’ life, we closed the nets and compensated the lost sampling hours the next day, after finishing the regular sampling. Each bird was released from net, put into a fabric bag, and brought to the banding station, where it was ringed with a unique code. Fat score, bird’s age, wing, tail, and tarsus length [mm] were measured, following Busse and Meissner (2000). We used a simple age class estimation system: juvenile – birds that still bore their fledgling plumage after hatchling, immature – non-reproductive birds with their first plumage after fledgling plumage, before their first alternate moult, adult – reproductive individuals that either had passed through or were in their first alternate plumage, and undefined age (J, I, A, and L, respectively) (Busse and Meissner, 2000). To test if birds spend more of their time in a particular habitat, we compared the number of birds recaptured in a given habitat, and the number of birds recaptured in both habitats, with the expected equal number of birds in both recapture classes, using the 𝛘2 test for goodness of fit (Sokal and Rohlf, 1995).
Faecal parasites’ sampling Immediately after defecation, we removed the faeces from the holding bag and isolated them in Eppendorf tubes with 2% potassium dichromate solution (K2Cr2O7) (Duszynski and Wilber, 1997). We transported them to the laboratory of Population and Community Ecology of the Autonomous University of the State of Mexico, Toluca, and we kept then in Petri dishes at room temperature (approx. 20-23 ° C) for 8 or 10 days, for sporulation of most of the cells to occur. After sporulation, we placed the samples in a refrigerator at 4-7°C until analysed. Afterwards, we centrifuged the samples (5 min at 1,500 rpm [= 225 g]). We used the Sheather's modified sugar flotation solution (Duszynski and Wilber, 1997) to separate the oocysts. We observed the samples in the Laboratory of Molecular Biology, Faculty of Agronomy, UAEMex, to determine the presence of oocysts in each of the samples, using an optical microscope with 4X, 10X, 40X and 100X objectives. We counted the oocysts of all the positive samples and photographed them with a camera included in the microscope using the Image Driving Boft Ware program. We assessed parasite prevalence (number of faecal samples with parasites/total number of samples), parasite load (number of parasites per sample), maximum number of parasites in a sample, per day, hour or month), and the dispersion of the parasite load (difference between a particular load and the average parasite load).
Analysis To test the effect of meteorological variables on parasite load, prevalence and number of birds captured we first fitted three GLM using the mentioned variables as response. The explicative variables were meteorological factors mentioned in the previous section. For parasite load and number of birds we used the negative binomial error distribution, and for prevalence, the binomial error distribution. We included all the variables in the GLM models. Then, using the stepAIC function in the MASS package (Venables and Ripley, 2002), we performed a backward selection of the most important variables. This function automatically selects the best terms in the model: it begins with the full model (all environmental variables) and sequentially removes and recombines variables to select a set that minimizes the Akaike information criterion (AIC) of the final model. We checked the model’s goodness of fit by plotting standardized residuals against fitted values and by normal QQ-plots, and for multicollinearity in each component model by calculating the variance inflation factor (VIF) for each predictor. VIF > 10 indicating a possible collinearity did not occur in our data. We used these reduced models into the structural equation model analysis (SEM) in PiecewiseSEM package (Lefcheck, 2016). We created the visualization of the SEM models in CorelDRAW (Corel Corporation, 2020). We drew in this data set the relationship between the average per month per hour dynamics of the meteorological variable and put on the same figure the daytime dynamics of the number of birds and of the parasite prevalence per month (FigMonthlyBirdNo,Meteo&Prevalen) or per hour (FigHourlyBirdNo,Meteo&Prevale). For these relationships we obtained regression functions by adjusting models of polynomial functions of different degrees. We drew the monthly and the daytime dynamics of the number of birds and of the parasite prevalence (data placed in "AverCoccidiaEstimatorsPerMonth" and "AverCoccidiaEstimatorsPerHour").
Data type
We obtained the meteorological data for each sampling day and hour, for the Raíces locality (3531 m asl), Nevado de Toluca, from Meteoblue weather database (Meteoblue, 2021). This locality is located approx. 0.5 km in a straight line from the study site. We used the following variables: mean, maximum and minimum temperature per day per month [ºC], total precipitation [mm], relative humidity [%], total cloud cover [%], high cloud cover [%], medium cloud cover [%],
total column cloud ice [mm], total column cloud water [mm], connective available potential energy (CAPE) [Jkg-1], sunshine duration [min], shortwave radiation [W m-2], longwave radiation [W m-2], UV radiation [W m-2], direct shortwave radiation [W m-2], diffuse shortwave radiation [W m-2], mean sea level pressure [hPa], evapotranspiration [mm], potential evapotranspiration [mm], FAO reference evapotranspiration [mm], soil temperature 0-7 cm down [ºC], soil moisture 0-7 cm down [m3m-3] and soil moisture available to plant [fraction]. The raw data for the meteorological varaibles are stored on the MeteoDataLomaAlta2018-2019. We used the other datasheets to obtained the per hour (averaged per month) and the per month (averaged per hour) means. The original data of the dynamics of the number of birds and of the parasite prevalence are placed in "AverCoccidiaEstimatorsPerMonth" and "AverCoccidiaEstimatorsPerHour" Financed by the grant 4333/2017/CI from Universidad Autónoma del Estado de México, to Mariusz Krzysztof Janczur
