key: cord-0285503-ajs73ojw
authors: Sebastianelli, Matteo; Savva, Georgios; Moysi, Michaella; Kirschel, Alexander N. G.
title: Tape lures swell bycatch on a Mediterranean island harbouring illegal bird trapping
date: 2020-03-15
journal: bioRxiv
DOI: 10.1101/2020.03.13.991034
sha: 57b4840ecf8d7907693749f070818ec7100866fd
doc_id: 285503
cord_uid: ajs73ojw

Mediterranean islands are critical for migrating birds, providing shelter and sustenance for millions of individuals each year. Humans have long exploited bird migration through hunting and illegal trapping. On the island of Cyprus, trapping birds during their migratory peak is considered a local tradition, but has long been against the law. Illegal bird trapping is a lucrative business, however, with trappers using tape lures that broadcast species’ vocalizations because it is expected to increase numbers of target species. Yet, by how much the use of song playback increases capture rates remains underappreciated. In particular, it is not known whether song playback of target species affects bycatch rates. Here, we show with the use of playback experiments that song playback is highly effective in luring birds towards trapping sites. We found that playback increases six to eight times the number of individuals of target species captured, but also significantly increases bycatch. Our findings thus show that in contrast to popular belief that tape lures are a selective trapping method, they also lead to increased captures of non-target species, which can include species of conservation concern.

playback is highly effective in luring birds towards trapping sites. We found that 23 playback increases six to eight times the number of individuals of target species 24 captured, but also significantly increases bycatch. Our findings thus show that in 25 contrast to popular belief that tape lures are a selective trapping method, they also lead 26 to increased captures of non-target species, which can include species of conservation 27 concern. 28 Background 29 Natural resources are globally threatened due to progressive overharvesting, with 30 animal diversity being particularly affected by its consequences. Birds are very sensitive 31 to anthropogenic impact, which has been a major cause of their decline [2, 3] . In addition 32 to indirect impacts on numbers caused by habitat loss and environmental toxification, 33 birds have also been impacted directly, by being targeted for food, the pet trade and 34 sport.

Every year, over two billion birds migrate along the Afro-Palearctic route and 36 concentrate in large numbers around the Mediterranean Basin, which is an important 37 biodiversity hotspot. Mediterranean islands are important stopover sites since they 38 provide trophic resources and shelter for migrant bird species. Humans and positioned about 100 m away from each other to reduce possible interference 94 between the experiment and control nets. Blackcap and Sardinian warbler stimuli were 95 alternately played in experimental sessions, where a session is an independent 96 experimental period where playback is played continuously for one hour at one of the 97 nets. In all cases, experimental sessions were paired, so that the experimental net in 98 session one was then the control in session two, and vice versa. 99

Illegal trappers are unlikely to use a large variety of stimuli for a given target 100 species, instead using a single stimulus they have found works well throughout. We 101 aimed to replicate the approach of trappers in using a small number of stimuli in our 102 experiments. We sourced from Xenocanto online repository (www.xeno-canto.org) two

We first conducted a t-test to determine whether there was an overall effect of 110 playbacks on the total number of captured birds. We then compared Poisson and 111 negative binomial generalized linear mixed models (GLMMs) implemented in R in the 112 lme4 package to investigate how playbacks influence the number of captured birds. 113

Given the slight overdispersion in our data, negative binomial GLMMs provided in all 114 cases the best fit according to the lowest corrected Akaike Information Criterion (AICc) 115 score calculated in the AICcmodavg package in R. 116

To assess whether playback attracted target species, we ran two models, one 117 with number of captured blackcaps and the other with number of Sardinian warblers as 118 dependent variables. In both models, we included as fixed factors the time, season, and 119 type of playback: a categorical variable with three levels: 1) no playback, 2) blackcap 120 playback and 3) Sardinian warbler playback. 121

To examine whether playback had an effect on non-target species, we specifically 122 tested the effect of playbacks on all species captured excluding individuals of the species 123 that emitted the given playback stimulus. Specifically, the effect of blackcap playback 124 was tested using as dependent variable the total number of captured birds excluding 125 blackcaps, whereas the effect of Sardinian warbler playback was tested using the total 126 number of trapped birds minus Sardinian warblers. We included time and type of 127 playback as fixed factors. We also included site as a random effect in all our models to 128 account for variation among sites. Models with the best fit (lowest AICc score) for each 129 set of GLMMs were validated by plotting residuals against predicted values and a qq- 

We caught significantly more birds (t-test: t=-4.82; p = <0.001) in experimental nets 134 (mean = 2.77, sd = 4.17), catching 333 birds of 31 species, than in controls (mean = 0.75, 135 sd = 1.39), where we trapped 90 birds belonging to 24 species (Fig. 1, Table S1 ). 136

Numbers of blackcaps were positively affected by both conspecific (GLMM: z = 8.33, p = 137 <0.001) and Sardinian warbler (z = 2.66, p = 0.007) playback, with more caught per 138 experiment in spring (z = 2.56, p = 0.01) compared to autumn (Table 1) . By contrast, 139

Sardinian warbler numbers caught were positively affected by conspecific playback (z = 140 5.60, p = <0.001) but not blackcap playback (z = 1.49, p = 0.133), while season also had 141 no effect on their capture rates (Table 1) . to escape competition for food, which has been shown in Sardinian warbler [47] . 234 However, we did not find that Sardinian warbler avoided blackcap experimental nets 235 more than controls. 236

In our study, we also show that other species responded positively to both 237 blackcap and Sardinian warbler playbacks. Related heterospecific birds such as Sylvia 238

warblers (e.g. S. curruca and S. melanothorax) responded to the calls, possibly because 239 of overlapping diet and habitat requirements [28] , thus contributing to the strong 240 positive response to both playbacks. Also, response to heterospecific vocalization might 241 be directly related to phylogenetic relatedness since they tend to share similar song 242 features, as demonstrated in other taxa [48] . Heterospecific responses of more distantly- 

Measuring and monitoring illegal use of 271 natural resources

Preliminary assessment of the scope and scale of illegal 274 killing and taking of birds in the Mediterranean

Key conservation issues for migratory 278 land-and waterbird species on the world's major flyways

Loss of functional 281 connectivity in migration networks induces population decline in migratory 282 birds

Decline of the North American avifauna

Eurasian Blackcap (Sylvia atricapilla)

Mechanisms and fitness effects of 396 interspecific information use between migrant and resident birds

Alarming features: Birds use specific 399 acoustic properties to identify heterospecific alarm calls

Impacts of passage migrant songbirds 402 on behaviour and habitat use of resident Sardinian Warblers Sylvia 403 melanocephala in Gibraltar. Ibis (Lond. 1859)

Response to interspecific vocalizations is affected by 406 degree of phylogenetic relatedness in Streptopelia doves