Sex‐specific prey partitioning in breeding piscivorous birds examined via a novel, noninvasive approach

Abstract

Piscivorous birds frequently display sex‐specific differences in their hunting and feeding behavior, which lead to diverging impacts on prey populations. Cormorants (Phalacrocoracidae), for example, were previously studied to examine dietary differences between the sexes and males were found to consume larger fish in coastal areas during autumn and winter. However, information on prey partitioning during breeding and generally on sex‐specific foraging in inland waters is missing. Here, we assess sex‐specific prey choice of Great Cormorants (Phalacrocorax carbo) during two subsequent breeding seasons in the Central European Alpine foreland, an area characterized by numerous stagnant and flowing waters in close proximity to each other. We developed a unique, noninvasive approach and applied it to regurgitated pellets: molecular cormorant sexing combined with molecular fish identification and fish‐length regression analysis performed on prey hard parts. Altogether, 364 pellets delivered information on both, bird sex, and consumed prey. The sexes differed significantly in their overall prey composition, even though Perca fluviatilis, Rutilus rutilus, and Coregonus spp. represented the main food source for both. Albeit prey composition did not indicate the use of different water bodies by the sexes, male diet was characterized by higher prey diversity within a pellet and the consumption of larger fish. The current findings show that female and male cormorants to some extent target the available prey spectrum at different levels. Finally, the comprehensive and noninvasive approach has great potential for application in studies of other piscivorous bird species.

High‐resolution multi‐marker DNA metabarcoding reveals sexual dietary differentiation in a bird with minor dimorphism

“…Sexual partitioning of food resources is known to occur in many animal species, but the extent and ecological significance of this phenomenon are still poorly understood (Ruckstuhl & Neuhaus, 2006). In birds, differences in diet indicative of resource differentiation have mostly been studied in birds with considerable sexual dimorphism in body size (Bravo, Ponce, Bautista, & Alonso, 2016; Catry, Alves, Gill, Gunnarsson, & Granadeiro, 2012; Donals et al., 2007; Gonzalez‐Solis, Croxall, & Wood, 2000; Thalinger, Oehm, Zeisler, Vorhauser, & Traugott, 2018) or in bill size or shape (Smith, 1990; Summers, Smith, Nicoll, & Atkinson, 1990; Temeles, Mazzotta, & Williamson, 2017; Temeles & Roberts, 1993). As a consequence, intraspecific dietary differentiation in birds has been largely attributed to morphological differences, with more sexually dimorphic species expected to show higher resource differentiation (Alarcón et al., 2017; Fonteneau, Paillisson, & Marion, 2009; Lewis et al., 2005; Phillips, McGill, Dawson, & Bearhop, 2011; Selander, 1966).…”

Endpoint PCR coupled with capillary electrophoresis (celPCR) provides sensitive and quantitative measures of environmental DNA in singleplex and multiplex reactions

“…In dPCR, this separates positive from negative droplets [10,56], whereas the lowest fluorescence signal distinctly different from background noise needs to be specified for both qPCR [22] and capillary electrophoresis [17]. The detection threshold of ≥ 0.08 RFU employed for both singleplex and multiplex celPCRs enabled the clear distinction of successful amplification from background fluorescence and was chosen based on previously used thresholds (0.07 and 0.1 RFU [27,57]) and after reviewing background signals in PCR and extraction negative controls. In dPCR, we chose to set a conservative threshold right below the cloud of positive droplets [56], therefore the amplitude of the threshold varied depending on the length of the target fragment.…”

Fish as predators and prey: DNA‐based assessment of their role in food webs

“…Hence faeces have been analysed to track consumption of fish (Granquist et al ., 2018; Hong et al ., 2019; Jarman et al ., 2013; Sommer et al ., 2019) and their diet (Corse et al ., 2010; Guillerault et al ., 2017). Additionally, pellets produced by piscivorous birds that regurgitate indigestible prey remains proofed as suitable source of trophic information (Oehm et al ., 2017; Thalinger et al ., 2018). Likewise, lost food items or dropped prey remains can provide valuable information on a diet.…”

“…(2019) show that %FOO overestimates the importance of rare prey items in metabarcoding studies, leading to potential pitfalls for analyses on bioenergetics and niche partitioning. Therefore, research addressing the foraging ecology of fish and piscivores beyond prey diversity tends to employ a mixture of molecular and morphological methods to obtain a holistic picture of feeding ecology (Alonso et al ., 2014; Thalinger et al ., 2018; Thomas et al ., 2017). On the other hand, Baker et al .…”

“…(2014) for a summary of the nomenclature used to describe this point). Moreover, such feeding experiments allow the impact of various factors to be investigated separately, as, for example, consumer and prey identity, meal size, diet composition or ambient temperature (Albaina et al ., 2010; Thalinger et al ., 2018; Thomas et al ., 2014) (see also Figure 3). First, consumer‐related variables such as species identity and life stage can play an important role (Greenstone et al ., 2010; Sint et al ., 2018).…”