DOI: 10.5061/dryad.cfxpnvx9r
title: Optimal prey for red fox cubs – an example of dual optimizing foraging strategy in foxes from a dynamic wetland habitat

description: The red fox (Vulpes vulpes) is the most abundant mesopredator in the
 Central-European region. Detailed knowledge about their feeding behavior
 is important both from ecological and wildlife management reasons. Food
 choices of foxes are poorly predictable in high-biodiversity marshlands.
 The main aim of our study was to sample parallel the main food-type
 abundances in the study area and analyze the diet of fox cubs and
 cohabiting adults across three years during the period of maternal
 dependence of the cubs. According to the optimal foraging theory, we
 predicted that the cubs’ diet would show higher energy content, would be
 more varied, and the individual prey species fed to the young would be
 larger. We analyzed the composition of adult fox and cub fecal samples
 collected separately around dens in a marshland of western Hungary, May
 2014, 2017 and 2020, when the abundance values of main food sources
 differed. Rodents and waterfowl dominated the diet, but their relative
 occurrence in the samples showed yearly variations. We found that vixens
 follow a dual optimizing foraging strategy regarding their provisioning of
 the cubs and their own diet. Adult foxes optimized their diet according to
 the actual yearly abundances of their main food sources. Additionally,
 they preferred prey items that can be consumed at the site of capture
 (large carrion and small individual prey items). Cubs on the other hand
 were provisioned with optimal high-energy food, even if those in question
 became less abundant in that year. Vixens mostly fed to their young either
 larger rodents and waterfowl, or multiple small rodents at a time – these
 types of prey are both optimal for transportation as a single load.
 Providing optimal prey at an early age in a changing environment may
 contribute to the ecological success of the red fox.
description: For the assessment of the diet composition and feeding habits of
 the red fox, we collected 265 intact scat (fecal) samples in three years
 (Table 1), Y1 (year 1 – 2014), Y2 (year 2 – 2017), Y3 (year 3 – 2020).
 Scat samples of cubs and an additional 14 partly consumed prey remains
 were collected in the surroundings of inhabited dens with actual ongoing
 cub-rearing, within a distance of 3–5 m from one den with cubs per
 year. We prepared and analyzed the fecal samples by
 means of a standard procedure (Jędrzejewska & Jędrzejewski, 1998).
 Samples were soaked in water, washed through a sieve (0.5 mm mesh) and
 dried. All prey remains were separated, and using a microscope, all
 feather, bone, teeth, hair, fish scales and seed remains were identified
 to the lowest possible taxonomic level by using key features (detailed by
 Lanszki et al., 2020) and our vertebrate, invertebrate and plant reference
 collections. Besides their identification, we also collected prey
 frequency data from the individual fecal samples. Small mammals have paired bone structures (e.g.,
 lower jaws, femurs) that allow an assessment of the minimum number of
 individuals in a scat through the pairing of left and right-sided
 bones. Based on the
 processing, we detected a minimum of one individual per sample for each
 prey taxon.