DOI: 10.5061/dryad.8gtht76rj
title: Occupancy model for Rattus spp. in high and low human human refuse supplementation conditions

description: Globally, the genus Rattus is one of the most influential exotic species
 due to its high rates of competitive exclusion and large dietary breadth.
 However, the specific foraging strategies of urban and urban-adjacent
 populations remain largely unknown. We examined Rattus spp. dependency on
 human food supplementation in a peri-urban population. Through a natural
 experiment made possible by the COVID-19 shelter in place order in Santa
 Cruz California, USA, we measured changes in activity between invasive
 rats and native rodents with and without human supplementation. We
 measured invasive rat presence in normal (pre-COVID) conditions near
 dining halls and similar waste sources, and again under COVID lockdown
 conditions where all sources of human supplementation were removed. We
 found a decrease in Rattus presence after the removal of human refuse (p
 &lt; 0.001), while native small mammal presence remained unchanged.
 These results have strong conservation implications, as they suggest that
 proper waste management is an effective, targeted, and less-invasive form
 of population control over conventional forms of poison. 
description: All fieldwork was conducted from November 23, 2019, to February
 14, 2021 in two trapping periods. Trapping in Period 1 (November 2019 –
 March 2020) served as a control for <em>Rattus </em>presence
 under normal (pre-COVID) conditions and lasted for 14 weeks. Trapping
 during Period 2 (October 2020 – February 2021) took place during the
 shelter in place order and was conducted at the same sites as Trapping
 Period 1. Trapping Period 2 lasted for 14 weeks, and served as our
 experimental treatment approximately one year later during the COVID
 lockdown when human supplementation was absent. To test our hypothesis
 that invasive rats are dependent on human supplementation, the first site
 in each trapping transect originated at a semi-exposed source of human
 refuse (dining hall dumpster, compost pile, etc.). We placed each
 sequential site in a direction away from the initial refuse source, and
 towards natural habitat. To reduce the probability of capturing the same
 individual, each transect contained three sites spaced 75 m apart each,
 for a total transect length of 150 m (N = 15 sites) (Oca et al. 2017). We
 used camera traps (Bushnell Trophy Cam; Bushnell Corp., Overland Park, KS,
 USA) that were left on-site for four consecutive nights to document
 <em>Rattus </em>presence (N = 60 trap nights per trapping
 period). We programmed the cameras to capture three images every 30
 seconds once movement was detected. Each site was baited with 30 grams of
 sunflower seeds (<em>Helianthus annuus</em>). All sites were
 originally open to the public (vehicles not allowed) but were closed from
 March 31, 2020 to September 2, 2020. To test the
 influence of habitat on <em>Rattus </em>presence and to
 account for errors in camera trap detection, we used occupancy modeling in
 the unmarked package in R (Fiske 2011). We binary-coded invasive
 <em>Rattus </em>presence or absence with a 1 or a 0,
 respectively, and indexed habitat composition at each site as a covariate
 (1 = mixed redwood, 2 = mixed oak, 3 = meadow) (Fiske 2011).  We treated
 each individual night as a survey trial, which yielded four repeated
 surveys at each site. Finally, we back-transformed our detection and
 occupancy estimates and fitted 95% confidence intervals. To test the
 influence of habitat on <em>Rattus</em> presence, we created
 three models: one with variable occupancy, one with variable detection,
 and one with both variable occupancy and variable detection as a function
 of habitat.