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Communication

Is Winter Feeder Visitation by Songbirds Risk-Dependent? An Experimental Study

by
Brygida Manikowska-Ślepowrońska
* and
Krzysztof Ślepowroński
Department of Vertebrate Ecology and Zoology, Faculty of Biology, University of Gdańsk, ul. Wita Stwosza 59, 80-308 Gdańsk, Poland
*
Author to whom correspondence should be addressed.
Birds 2025, 6(3), 45; https://doi.org/10.3390/birds6030045 (registering DOI)
Submission received: 10 July 2025 / Revised: 14 August 2025 / Accepted: 14 August 2025 / Published: 17 August 2025
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Simple Summary

Winter bird feeders provide high-energy food for birds when natural food resources are limited. Since winter feeders are visited by many bird species, they also attract domesticated and wild predators. In this experimental study, we investigated the reactions of eight passerines visiting a winter feeder to the presence of a predator or a food competitor. Behavioral response was measured by the number of visits and duration of foraging. In our study, we included age and sex of the most numerous species noted during the experiment—the Great Tit. The presence of food competitors and the risk of predation significantly deterred birds from feeding at the winter feeder. Therefore, if birds chose to forage at the feeder throughout the study, their foraging time remained consistent regardless of whether the feeder was unmodified, competitors were present, or there was a risk of predation.

Abstract

Winter bird feeders provide high-energy food for birds when natural food resources are in short supply. We performed an experimental study including two treatments and a control to investigate the reactions of eight passerine species visiting a winter feeder to the presence of a predator or a food competitor, measured by the number of visits and foraging time. We included in analyses the age and sex of the most numerous species, the Great Tit (Parus major). Our results showed that the number of feeder visits per 30 min differed significantly among species, treatments (predator, competitor, or control), and time intervals of time elapsed from the start of the treatment. The presence of food competitors and predation risk significantly deterred the birds from feeding at the feeder. The number of visits to the feeder by Great Tits was significantly affected by age (more frequent visits by immatures), sex (more frequent visits by males), treatment (less frequent visits by immatures during predation risk and by adults during both experiments), and the time elapsed since the start of the experiment (more frequent visits by adult females during the first eight time intervals after the start of the experiment). Surprisingly, the duration of the foraging visits to the feeder was significantly influenced by species (lower for all tit species compared to the other visiting species) and the time elapsed since the start of the treatment (shorter foraging duration during the first nine time intervals for Hawfinch (Coccothraustes coccothraustes), European Greenfinch (Chloris chloris) and European Robin (Erithacus rubecula)), but not by the treatment itself. This suggests that the decision to use the feeder is risk-dependent, but when birds choose to forage, their foraging time is risk-independent.

1. Introduction

Winter bird feeders can provide high-energy food for birds when natural food resources are in short supply [1,2]. The energy demands of birds in winter are high, and this season is considered as critical for the survival of many avian species, e.g., [1,3,4]. Food supplementation during winter may influence birds considerably by improving nutritional condition, increasing fat loads, increasing winter survival rates, improving condition, and affecting the phenology of the following breeding season [5,6,7,8,9]. However, winter feeding has specific effects on overall energy management strategies in some species [10]. The regular excess amounts of high-energy food may affect the excess fat load reserves of birds [10,11,12]. This can cause them to take off slowly from the feeder, for example, when faced with a predator, which affects their apparent survival rate [10,11]. During winter in the temperate zone, ambient temperatures reach seasonal negative peaks. Also, avian foraging time is constrained by short day lengths. These factors generally result in increased foraging activity throughout the day until it sharply declines as sunset approaches [13,14].
Winter feeders are visited by many birds, which makes them attractive to both domesticated and wild predators, potentially impacting passerines’ winter survival [1,15,16]. For this reason, such foraging sites may make visiting birds more vulnerable to predation [15,17]. Thus, the ability to recognize and avoid predators enables birds to survive in the natural environment [18]. The animals used the risky feeding site only if the potential additional energy gains outweighed the fitness costs of the additional predation risk [19]. The presence of predators may modify the use of foraging sites in winter, e.g., [20]. The proximity of the predator does not determine the rate of predation risk itself due to the various feeding specializations and hunting techniques of different predator species [21]. Some passerines, such as the Great Tit (Parus major), categorize predators according to the perceived danger [22], and even respond adequately to predation risk by changing their fat reserve levels [23].
Foraging at the winter feeder may also be associated with increased inter- and intra-specific food competition. For many competitors, intake rates may decrease either due to interference or exploitation competition [24]. Competition is expected to be the strongest among individuals of the same species, as conspecifics have the most similar foraging demands [25].
Crowding at winter feeders provides an excellent opportunity to conduct experiments examining how birds respond to predators or/and food competitors [26]. While previous studies have described the reactions of passerines to aerial predators at feeders, e.g., [26,27,28], few have investigated these responses in relation to the age and/or sex of foraging individuals. To address this knowledge gap, we conducted a series of behavioral experiments. Specifically, we investigated how passerines visiting a winter feeder responded to the presence of a predator and a food competitor, as measured by the number of visits and foraging time. For the most numerous species, the Great Tit, we also considered age and sex, which could be reliably determined through visual identification. We expected that (1) the presence of a predator (a picture of the Long-eared Owl (Asio otus)) at the feeder would deter passerines from visiting the feeder or reduce considerably their numbers and visit duration; (2) the presence of a large food competitor (a stuffed Eurasian Collared Dove (Streptopelia decaocto)) at the feeder would result in less frequent and shorter visits compared to the control group without the presence of a large-sized competitor monopolizing food sources; (3) with the progress of the experiment, the birds visiting the feeder would get used to the predator’s picture or the food competitor’s dummy and would visit the feeder more frequently, spending more time per visit. Birds often avoid bird models for several hours but soon start to recognize that a decoy is not a real threat [29].
In the case of expectations (1) and (2), we also predicted some inter- and intra-specific differences in the reaction. Given that large- and medium-sized passerines usually initiate and win agonistic interactions with smaller species [30], we expected differences in the reaction at the inter-specific level. At the intra-specific level, we expected age-, sex-, and personality-related differences in the reaction. Older individuals, being more experienced, are better at avoiding danger than younger ones [31,32]. Immature passerines forage more intensively than adults in their natural habitat during winter [33]. Males may be more aggressive than females due to their higher testosterone levels [34,35,36]. Bold individuals may approach unfamiliar objects more quickly than shy ones [35,36,37,38]. Furthermore, males often discover new food sources, such as novel bird feeders, first [39].

2. Materials and Methods

2.1. Study Site and Experimental Design

We conducted the study at a winter bird feeder in a garden situated in the suburban village of Otomin, near Gdańsk (Poland; 54.32 N, 18.51 E), during winter 2012/2013. The feeder (45 × 45 × 30 cm; set 2 m above the ground) was supplied with unhusked sunflower (Helianthus sp.) seeds (the most preferred passerine food in feeders in both urban and rural habitats in Poland [40]), every morning, starting from late October until the end of March. Food was available at the feeder daily during day hours (it was cleaned after sunset).
We recorded the presence of birds and their behavior using a surveillance camera (SET1ch_KAM1 color HD camera, producent: Protel, Poland) during two experimental sessions and one control. Recordings were performed between sunrise and sunset (i.e., 9 h between 7:00 and 15:00 each day) in quite similar weather conditions. Other studies have shown that temperature does not significantly affect birds’ reactions to discovering winter feeders [34,41,42]. The camera was set up in a fixed position facing the feeder.
We conducted an experimental study including two treatments and a control:
Experiment 1: Predation risk (hereafter PREDAT): The feeder was supplied with food (sunflower seeds); the backside of the feeder was covered with cardboard and a photograph of the potential predator, the Long-eared Owl, was attached to it (the size of the photo reflects the size of its head size); the other sides of the feeder were not modified (Figure 1A). Many passerines visiting the feeder including tits (Paridae) and the Hawfinch (Coccothraustes coccothraustes) contribute considerably to the diet of wintering Long-eared Owls in Poland [43]; moreover, owls are the most serious predators for tits during the twilight period [44]. Birds, e.g., pigeons, are able to identify real objects (e.g., other birds) on photographs [45]. Date: 20 February 2013; recording duration: 9 h; mean daily air temperature: −3.2 °C (at Gdańsk-Rębiechowo, located 7 km from the study area [46]).
Experiment 2: Food competition with risk of resource monopolization (hereafter COMPET): The feeder was supplied with food (sunflower seeds); the stuffed Eurasian Collared Dove was placed inside the feeder (the chosen species is a common passerine competitor in winter feeders [26]); the other sides of the feeder were not modified (Figure 1B). Date: 22 February 2013; recording duration: 9 h; mean daily air temperature: −4.6 °C (at Gdańsk-Rębiechowo, located 7 km from the study area [46]).
Control: The feeder was supplied with food (sunflower seeds) (hereafter CONTR). No feeder sides were modified (Figure 1C). Date: 19 December 2012; recording duration: 9 h; mean daily air temperature: −1.7 °C (at Gdańsk-Rębiechowo, located 7 km from the study area, [46]).

2.2. Analysis of Recorded Material

During the analysis of the recorded material, we noted the species, age, and sex (if visual identification was possible) of the visiting birds, as well as the duration of their visits and the number of visits per 30 min time interval from 7:00 to 15:00 (N = 16 time intervals). The sex of two species, i.e., European Greenfinch (Chloris chloris) and Hawfinch, was identified based on morphological features [47]. The sex and age of the most numerous species, the Great Tit, were identified based on morphological features and/or color ring combinations coding the bird sex and age. This information was obtained during the capture and ringing of 130 individuals in the same place two months before the experiments began. The captured birds were marked with round metal leg rings with a unique number. Additionally, color-coded plastic rings (four different color codes for sex and age groups) were added to the other leg. As Marsh Tit (Poecile palustris) and Willow Tit (Poecile montanus) were indistinguishable on recordings, we considered them as one category, ‘Poecile Tit’ (after [22]).

2.3. Statistical Analysis

In analyses of video recordings from the PREDAT, COMPET, and CONTROL treatments, we included the eight most frequently visiting species (Great Tit, Eurasian Blue Tit (Cyanistes caeruleus), Poecile Tit, European Robin (Erithacus rubecula), Coal Tit (Periparus ater), Common Blackbird (Turdus merula), Hawfinch, and European Greenfinch) recorded during all treatments.
We were unable to distinguish between the individuals due to the approach we used. However, the impact of presumable pseudoreplication was insignificant when we incorporated species (individual ID) as a random factor in analyses based on our datasets (Wald Test; X2 = 0.30; df = 1; p = 0.58). Similarly, the temporal effect was insignificant (considered time intervals) (Wald Test; X2 = 0.82; df = 1; p = 0.37).
To identify and create a visual representation of factors significantly affecting the number of visits per 30 min, we used generalized linear model trees with Poisson distribution (GLM trees) [48], with the following factorial predictors: treatment (PREDAT, COMPET, and CONTR), species (8 levels—Great Tit, Eurasian Blue Tit, Poecile Tit, Coal Tit, European Robin, Hawfinch, European Greenfinch, and Common Blackbird), and time elapsed from the start of the treatment (16 consecutive 30 min time intervals between 7:00 and 15:00). In the case of the Great Tit, we also performed a regression tree that included two additional factorial predictors, age (immature, adult) and sex (female, male). If a particular species was not observed during the assigned time interval, we assigned a 0 value.
We performed a general linear model tree (LM tree) [49] to examine and create a visual representation of the effect of species, treatment (PREDAT, COMPET, and CONTR), and time elapsed from the start of the treatment on the duration of foraging visits to the feeder. The data on the duration of foraging visits were normalized using log transformation.
In the GLM/LM tree approach, the response variable is split into groups based on one or more predictors or splitting variables (fixed effects), in order to minimize differences within groups while maximizing differences between or among the groups. Regression trees can use combinations of categorical and/or numerical explanatory variables. Regression trees identify successive critical values of the predictors, splitting the response variable in a dichotomous hierarchical manner [50]. We performed regression tree analysis in the partykit package [51] in R software ver. 4.1.3 [52].

3. Results

In total, during 27 recorded hours, 1266 visits of individuals from 13 species were recorded, but those obviously included many pseudoreplications (repeated visits of the same individual) (Table 1).

3.1. Number of Visits per 30 Min

The number of feeder visits per 30 min differed significantly among species, treatments, and time intervals of time elapsed from the start of the treatment (Figure 2). The first split for Node 1 indicated that the number of visits differed significantly between the Great Tit (Node 2; mean ± SD: 12.63 ± 10.42) and other visiting species (Eurasian Blue Tit, Coal Tit, Poecile Tit, Hawfinch, European Greenfinch, European Robin, and Common Blackbird; Node 7; 1.79 ± 3.06). The next split (Node 2) showed that the number of Great Tit visits to the feeder was significantly higher during COMPET and CONTR (Node 3; 17.84 ± 8.79) compared to PREDAT (Node 6; 2.19 ± 2.54). In the first group (Node 3), the number of visits was significantly lower during COMPET (Node 4; 13.06 ± 5.21) compared to CONTR (Node 5; 22.63 ± 9.16). In the case of the remaining species (Node 7), the number of visits to the feeder was significantly lower during COMPET and PREDAT (Node 11; 0.98 ± 1.46), compared to CONTR (Node 8; 3.39 ± 4.48), with Eurasian Blue Tit, Coal Tit, European Greenfinch, and Poecile Tit (Node 9; 5.11 ± 5.01) visiting the feeder significantly more frequently than Hawfinch, Common Blackbird, and European Robin (Node 10; 1.10 ± 2.09). European Greenfinch, Hawfinch, and European Robin (Node 17) were characterized by a lower number of visits after the fourth time interval (i.e., between 9:00 and 14:59; Node 18; 0.29 ± 0.54) compared to the first four time intervals (i.e., between 7:00 and 9:00; Node 19; 0.92 ± 1.14) during COMPET and PREDAT. The COMPET and PREDAT group (Node 11) was divided into two groups with different species. In the first group, consisting of Eurasian Blue Tit, Coal Tit, Poecile Tit and Common Blackbird the number of the feeder visits was significantly higher during COMPET (1.81 ± 1.88) compared to PREDAT (0.95 ± 1.39). In the case of COMPET experiment (Node 13), the number of visits to the feeder was lower during the first thirteen time intervals after the start of the treatment (i.e., between 7:00 and 14:29; Node 17; 1.63 ± 1.60) than during the last time interval (i.e., between 14:30 and 14:59; Node 15; 4.5 ± 3.70) (Figure 2).
The number of visits to the feeder by the Great Tit per 30 min was significantly influenced by sex, age, treatment, and the time elapsed since the start of the treatment (Figure 3). The first split for Node 1 showed that the number of visits differed significantly between age groups of the Great Tit, with a higher number of visits by immatures compared to adults. The next split (Node 2) showed that the number of visits to the feeder by immatures was significantly lower during PREDAT (Node 8; mean ± SD: 0.33 ± 0.64) compared to COMPET and CONTR (2.61 ± 2.63). A further split (Node 3) revealed that the number of visits to the feeder by females (1.25 ± 1.24) during COMPET and CONTR was significantly lower compared to males (3.97 ± 2.95). In the COMPET and CONTR groups, immature males (Node 4; 1.25 ± 1.24) visited the feeder less frequently than during COMPET (Node 6; 2.63 ± 1.89) and CONTR (Node 7; 5.31 ± 3.24). In the adult group (Node 9), females visited the feeder less frequently (0.14 ± 0.31) than males did (1.35 ± 1.31). Adult females visited the feeder more frequently during CONTR (Node 11; 0.31 ± 0.48) compared to COMPET and PREDAT. Adult females visited the feeder significantly more frequently during the first eight time intervals after the start of the experiment (i.e., between 7:00 and 11:29; Node 13; 0.14 ± 0.53) compared to the following six time intervals (between 11:30 and 14:29; Node 14; 0.06 ± 0.24) during COMPET and PREDAT. Adult males during PREDAT (Node 17; 0.56 ± 0.89) visited the feeder less frequently compared to COMPET and CONTR (Node 16; 1.75 ± 1.32) (Figure 3).

3.2. Foraging Duration

The duration of foraging visits differed between species and time elapsed from the start of the treatment (Figure 4), but not between treatments. The first split (Node 1) divided foraging duration into the tit group (i.e., Eurasian Blue Tit, Coal Tit, Poecile Tit, and Great Tit) and the four remaining species group (i.e., Common Blackbird, Hawfinch, European Greenfinch, and European Robin). Foraging time at the feeder for all tit species was significantly lower (Node 2; mean ± SD: 4.18 ± 7.64 sec) compared to the other visiting species. The next split (Node 3) showed that the foraging time at the feeder of the Common Blackbird (Node 4; 168.33 ± 119.83 sec) was significantly longer than that of Hawfinch, European Greenfinch, and European Robin (43.31 ± 50.39 sec). The Hawfinch, European Greenfinch, and European Robin group (Node 5) was characterized by a significantly shorter foraging duration during the first nine time intervals after the start of the experiment (i.e., between 7:00 and 11:59; Node 6; 41.63 ± 55.62 sec) than during the last seven time intervals (i.e., between 12:00 and 14:59; Node 7; 47.0 ± 36.71 sec) (Figure 4).

4. Discussion

Our experimental study revealed that the number of bird visits to the winter feeder was species- and risk-dependent. As we expected, the number of visits to the feeder for all species was significantly higher during the treatment without any modifications (CONTR) compared to remaining treatments. This suggests that the lower attendance of passerines at the feeder with applied modifications compared to the unmodified feeder might be a result of fear. Similar reactions, reflected in changes in the number of birds visiting the feeder when exposed to stuffed predators, harmless birds, or non-threatening objects, have been reported in tits and other passerines during experiments at the winter feeder [22,26,42,53,54,55]. All recorded tit species and a Common Blackbird visited the feeder during the PREDAT treatment (with predation risk without limited escape route) significantly less frequently compared to the remaining treatments. This may be due to the fact that predation is a stronger selective agent than competition, affecting the winter mortality of small birds [56,57,58]. Therefore, they reacted most strongly with fear when facing the predator. It has been documented that many passerines, including tits, can distinguish between different species of predators, as well as between different genera of owls [21]. Thus, as we expected, they limited the number of visits to the feeder in the presence of danger. Also, other studies have reported that the presence of a stuffed Eurasian Sparrowhawk (Accipiter nisus) or Great Horned Owl (Bubo virginianus) at the winter feeder resulted in passerines avoiding visiting the feeder [22,53,54]. The number of visits to the feeder by Hawfinch, European Greenfinch, and European Robin was similar during the COMPET (presence of the food competitor with risk of resource monopolization) and PREDAT treatments. Also, individuals visited the feeder more frequently during the first four time intervals (i.e., between 7:00 and 9:00). Adult female Great Tits visited the feeder more frequently during the first eight time intervals after the experiment began, compared to the remaining intervals during the COMPET and PREDAT treatments. Great Tits visit feeders often and regularly in large numbers [59], usually arriving earlier than other bird species [39].
In midwinter, when the days are the shortest and the energetic requirements for self-maintenance are at their highest, small passerines follow a characteristic pattern of daily foraging intensity, with generally heavy feeding in the morning, light feeding during the middle part of the day, and usually moderate foraging before the afternoon, e.g., [60,61], until feeding declines sharply as sunset approaches [13,14]. Heavy foraging during the first hours of the day at high latitudes is necessary due to overnight starvation, especially in the case of individuals with low social status [14,62,63]. Young individuals with a lower social rank are often forced to start their foraging activities in feeding sites earlier than older, dominant individuals, because older individuals have larger reserves and thus they can avoid foraging during dawn and dusk periods [63]. Small passerines have to replenish their reserves every day to survive the next long and cold winter nights [14,62]. Even if it puts them at risk of being killed by a predator, they should not delay building up their reserves until the late afternoon [14]. Thus, birds foraging at the feeder, where predation risk is present, face a trade-off between the risk of death from starvation and predation. It may affect daily patterns of energy load gathering just like artificial lights in urban areas. Some passerine species extend their activity period even by few hours utilizing artificial light during the winter [64]. In addition, Hawfinch and European Greenfinch are species with relatively large body sizes and strong bills. They usually initiate agonistic interactions and win them, when confronting other smaller passerine species [30]. Therefore, it cannot be excluded that they are capable of behaving more boldly towards a competitor for food.
Also, the presence of a competitor for food resources resulted in a significantly lower number of visits to the feeder in all species. This contrasts with the results of other studies on tits, in which the presence of neither thrush nor pigeon dummies affected the number of visits to the feeder [26]. In our study, after a low number of visits in the first hours after the start of the COMPET treatment, Coal Tit, Eurasian Blue Tit, Poecile Tit, and Common Blackbird started to visit the feeder more frequently during the last time interval before sunset. Birds often avoid artificial models of predators or non-threatening objects for several hours but soon recognize that a decoy is not a real threat [29,54]. It is possible that some birds visited the feeder multiple times during the day or that they were forming the same flocks. Considering this possibility, perhaps they observed the feeder during the day with the stuffed competitor and recognized that it was not a threat, finally foraging more readily, especially as dusk approached. They may have been more eager to forage at that time, as many birds forage more intensively before sunset, e.g., [60]. Also, it cannot be excluded that they may have become habituated.
As we expected, we found that in the case of the Great Tit, the number of visits to the feeder was also influenced by sex and age. Regardless of treatment, immatures paid more visits than adults, which is a consequence of the proportion of both age categories in winter feeders [65,66]. Also, Great Tits of a higher social rank are less active than subordinate immature individuals during the day [66]. All immatures, regardless of sex, and adult males were characterized by a significantly lower frequency of visits to the feeder during the PREDAT treatment compared to the other treatments. The response of adult females to the PREDAT and COMPET treatments was similar, whereas they visited the feeder significantly more frequently during the CONTROL treatment. Adult females may have avoided the risks associated with food competition and predation because they are reportedly the least dependent on food supplementation within the four sex and age groups of this species during winter [67]. In addition, male Great Tits are bolder and generally take greater risks than females [21,39,68]. We found no significant differences in the number of visits to the feeder of immature females during the COMPET and CONTROL treatments. We recorded a similar pattern in adult males. An inferior social status of immature females may have influenced their foraging frequency at the feeder during the COMPET treatment. They may have taken advantage of the absence of the tit age and sex groups with a higher social status (males and adults; [33]) as dominant individuals have been shown to have priority access to the feeder over subordinates [69,70]. Inferior female immatures, which are the smallest and weakest, must visit the feeders more frequently to forage [65,67], prioritizing the need to accumulate fat over the risk of competition for food with a stuffed pigeon. In general, adults should be more experienced and better at avoiding dangers [32], so they should be able to recognize predators, e.g., [22,28,53]. For example, they did not respond to a food competitor such as a pigeon by reducing the number of visits to the feeder.
In contrast to our expectations and results on the number of visits, time spent by birds at the feeder was not risk-dependent, i.e., not treatment-dependent. We found that the duration of foraging visits to the feeder was influenced significantly by species and time elapsed from the start of the treatment. Our results contrast with those from the study on the response of tits to the presence of predators, such as Eurasian Sparrowhawk and Kestrel (Falco tinnunculus), at the feeder [26]. Tvardíková and Fuchs (2012; [26]) reported that in the presence of a predator, the tits that took the risk of arriving stayed at the feeder site for longer, although they often did not feed [26]. Also, many passerines perceived the potential risk from predators and spent more time foraging at the safe feeder, i.e., with a close refuge available to escape from predators [71]. Our results may differ from those findings, due to the small sample size, the lack of treatment replication, and the possibility of pseudoreplication.
Foraging duration in our studies was species-dependent. Hawfinch, European Greenfinch, and European Robin foraged significantly longer during the last seven time intervals than during the first nine time intervals after the start of the experiment. This result mirrors their daily foraging pattern, with more frequent but shorter visits in the morning and fewer but longer visits in the afternoon, dedicated to replenishing their energy requirements to survive the following night. One should remember that the lack of an effect of treatment on foraging duration may be affected by the fact that we only recorded duration during the birds visits, and the number of visits was very low for most of the studied species in the first intervals after the treatment started. Thus, we were only able to collect a larger sample size for the particular treatments when the birds had become accustomed to the predator image and the stuffed competitor.

5. Conclusions

To conclude, we found that the decision to use the feeder was risk-dependent, whereas the time spent foraging was risk-independent. We also found that the response of the birds to the experimental treatment depended on the species, the time elapsed from the beginning of the experiment, and the individual’s age and sex (in the Great Tit). Our study, despite being based only on singular experiments, provides insight into the species-, sex-, and age- dependent reactions of birds to threats at the winter feeder. We are aware of the limitations of this study, especially the lack of repetition of experiments and the fact that this short-term study (a small variety of external conditions were included in analyses) took place in a single location. The captured tits were marked with color-coded plastic rings (four different color codes for sex and age groups) added on the bird’s leg. Although this marking system enabled us to determine the sex and age of the birds in the recordings, unfortunately, it did not allow for the birds to be accurately identified as particular individuals. It should also be remembered that there are limitations to the study, such as pseudoreplication (repeated visits by the same individual), which cannot be eliminated in natural conditions using this level of bird marking and following this methodology approach. Also worth mentioning is that we used different types of dummies in the threat experiments (a stuffed specimen and a picture), which could have had a different impact on the birds visiting the feeder. It is also important to remember that, if any species has a hoarding habit, this aspect may have an impact on the visitation rate at the winter feeder. We do believe that none of the surveyed species exhibit such a strong habit. To fully study reactions at bird feeders, including those of predators and competitors, it is necessary to repeat experiments multiple times in multiple sites with varying environmental and weather conditions. Nevertheless, this work presents an alternative method of data analysis robust to typical regression problems such as overfitting, collinearity, and bias with regard to the types of explanatory variables used [51,72] and allowing results to be presented in a visually clear form. Also, our study reports findings regarding local population levels, and we did not aim to show the variability of behavioral responses at the species level. Studies like this provide a good basis for investigating the trade-offs between self-maintenance and the risk of predation or competition faced by small passerines when searching for food in the temperate zone during winter. Further studies performed under various environmental conditions (e.g., at different ambient temperatures) and including repetitions of experiments are needed to fully comprehend the mechanisms that regulate the risk of particular behaviors. This type of research can be hindered by the presence of both wild and domesticated predators. Our garden feeder was free from predators such as feral cats (Felis domesticus) and red squirrels (Sciurus vulgaris). We did not observe any visits by the Sparrowhawk or the Pygmy Owl (Glaucidium passerinum) (not present in this area) in the recordings. However, when planning this type of research, researchers should be aware that such disturbances may occur.

Author Contributions

Conceptualization, methodology, software, formal analysis, investigation writing—original draft preparation, visualization, and project administration: B.M.-Ś.; resources, data curation, and writing—review and editing: B.M.-Ś. and K.Ś. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Birds were captured following the Polish Law, i.e., under ringing permission. The need for ethical approval for this study was exempted by the Ministry of Science and Higher Education National Ethics Committee for Animal Experiments.

Acknowledgments

We are thankful to Laura Gładun for help with the video analyses. We are grateful to Karolina Cieślińska (certified C1 English user) for the preparation of Figure 1, all invaluable suggestions, and English language improvements.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Experimental settings at the winter feeder supplied with sunflower seeds: (A) predation risk (a picture of the Long-eared Owl (Asio otus)), (B) food competition with risk of resource monopolization (a stuffed European Collared Dove (Streptopelia decaocto)), and (C) control (without any modifications).
Figure 1. Experimental settings at the winter feeder supplied with sunflower seeds: (A) predation risk (a picture of the Long-eared Owl (Asio otus)), (B) food competition with risk of resource monopolization (a stuffed European Collared Dove (Streptopelia decaocto)), and (C) control (without any modifications).
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Figure 2. GLM tree model characterizing the number of birds visiting the winter feeder per 30 min for eight species of birds [Great Tit, Eurasian Blue Tit (Blue Tit), Coal Tit, Poecile Tit, European Robin (Robin), Common Blackbird (Blackbird), Hawfinch, and European Greenfinch (Greenfinch)] with species, treatment [predation risk (PREDAT), risk of resource monopolization (COMPET), and control (CONTR)], and time elapsed form the start of the treatment as initial explanatory variables. Encircled variables have the strongest association to the response variable. The p values listed at each encircled node represent the test of independence between the listed variables (species, treatment, and time elapsed from the start of the treatment) and the response variable (number of visits per 30 min). Terminal nodes indicate which variable levels characterize the number of visits per 30 min (boxplots), and n indicates the number of individuals corresponding to specific species or treatment levels. Boxplots show the median (band inside the box), the first (25%) and third (75%) quartile (box), the lowest and the highest values within 1.5 interquartile range (whiskers), and outliers (circles).
Figure 2. GLM tree model characterizing the number of birds visiting the winter feeder per 30 min for eight species of birds [Great Tit, Eurasian Blue Tit (Blue Tit), Coal Tit, Poecile Tit, European Robin (Robin), Common Blackbird (Blackbird), Hawfinch, and European Greenfinch (Greenfinch)] with species, treatment [predation risk (PREDAT), risk of resource monopolization (COMPET), and control (CONTR)], and time elapsed form the start of the treatment as initial explanatory variables. Encircled variables have the strongest association to the response variable. The p values listed at each encircled node represent the test of independence between the listed variables (species, treatment, and time elapsed from the start of the treatment) and the response variable (number of visits per 30 min). Terminal nodes indicate which variable levels characterize the number of visits per 30 min (boxplots), and n indicates the number of individuals corresponding to specific species or treatment levels. Boxplots show the median (band inside the box), the first (25%) and third (75%) quartile (box), the lowest and the highest values within 1.5 interquartile range (whiskers), and outliers (circles).
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Figure 3. GLM tree model characterizing the number of Great Tit visits at the winter feeder per 30 min for immature and adult males and females of this species, treatments [predation risk (PREDAT), risk of resource monopolization (COMPET), and control (CONTR)] and time elapsed from the start of the treatment as initial explanatory variables. Encircled variables have the strongest association to the response variable. The p values listed at each encircled node represent the test of independence between the listed variables (sex, age, treatment, and time elapsed from the start of the treatment). Terminal nodes indicate which variable levels characterize the number of visits per 30 min (boxplots), and n indicates the number of individuals corresponding to sex, age, treatment, or time elapsed from the start of the treatment levels. Boxplots show the median (band inside the box), the first (25%) and third (75%) quartile (box), the lowest and the highest values within 1.5 interquartile range (whiskers), and outliers (circles).
Figure 3. GLM tree model characterizing the number of Great Tit visits at the winter feeder per 30 min for immature and adult males and females of this species, treatments [predation risk (PREDAT), risk of resource monopolization (COMPET), and control (CONTR)] and time elapsed from the start of the treatment as initial explanatory variables. Encircled variables have the strongest association to the response variable. The p values listed at each encircled node represent the test of independence between the listed variables (sex, age, treatment, and time elapsed from the start of the treatment). Terminal nodes indicate which variable levels characterize the number of visits per 30 min (boxplots), and n indicates the number of individuals corresponding to sex, age, treatment, or time elapsed from the start of the treatment levels. Boxplots show the median (band inside the box), the first (25%) and third (75%) quartile (box), the lowest and the highest values within 1.5 interquartile range (whiskers), and outliers (circles).
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Figure 4. LM tree model characterizing the duration of foraging visits to the winter feeder for eight species of birds (Eurasian Blue Tit, Coal Tit, Great Tit, Poecile Tit, Common Blackbird, European Greenfinch, Hawfinch, and European Robin) and time elapsed from the start of the treatment as initial explanatory variables. Encircled variables have the strongest association to the response variable. The p values listed at each encircled node represent the test of independence between the listed variables (species and time elapsed from the start of the treatment). Terminal nodes indicate which variable levels characterize the duration of foraging visits (boxplots) at the winter feeder, and n indicates the number of individuals corresponding to species or elapsed time levels. Boxplots show the median (band inside the box), the first (25%) and third (75%) quartile (box), the lowest and the highest values within 1.5 interquartile range (whiskers), and outliers (circles). All of the dichotomies are statistically significant.
Figure 4. LM tree model characterizing the duration of foraging visits to the winter feeder for eight species of birds (Eurasian Blue Tit, Coal Tit, Great Tit, Poecile Tit, Common Blackbird, European Greenfinch, Hawfinch, and European Robin) and time elapsed from the start of the treatment as initial explanatory variables. Encircled variables have the strongest association to the response variable. The p values listed at each encircled node represent the test of independence between the listed variables (species and time elapsed from the start of the treatment). Terminal nodes indicate which variable levels characterize the duration of foraging visits (boxplots) at the winter feeder, and n indicates the number of individuals corresponding to species or elapsed time levels. Boxplots show the median (band inside the box), the first (25%) and third (75%) quartile (box), the lowest and the highest values within 1.5 interquartile range (whiskers), and outliers (circles). All of the dichotomies are statistically significant.
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Table 1. Bird species and the number and frequency of individuals recorded at the winter feeder during each treatment and in total.
Table 1. Bird species and the number and frequency of individuals recorded at the winter feeder during each treatment and in total.
SpeciesPREDAT
[N; %]		COMPET
[N; %]		CONTROL
[N; %]		Total
[N; %]
Great Tit (Parus major) *35; 25.74209; 60.40344; 43.88588; 46.45
Crested Tit (Lophophanes cristatus)--13; 1.6613; 1.03
Eurasian Siskin (Spinus spinus)13; 9.563; 0.87-16; 1.26
European Greenfinch (Chloris chloris) *5; 3.683; 0.8776; 9.6984; 6.64
Hawfinch (Coccothraustes coccothraustes) *6; 4.412; 0.5821; 2.6829; 2.29
Blackbird (Turdus merula) *7; 5.1522; 6.364; 0.5133; 2.61
Eurasian Tree Sparrow (Passer montanus)--24; 3.0624; 1.90
Eurasian Blue Tit (Cyanistes caeruleus) *26; 19.1245; 13.01113; 14.41184; 14.53
European Robin (Erithacus rubecula) *11; 8.0910; 2.8925; 3.1946; 3.63
Coal Tit (Periparus ater) *9; 6.6229; 8.3859; 7.5397; 7.66
Eurasian Jay (Garrulus glandarius)1; 0.742; 0.5810; 1.2813; 1.03
Yellowhammer (Emberiza citrinella)4; 2.941; 0.2921; 2.6826; 2.05
Poecile Tit (Poecile palustris and P. montanus) *19; 13.9720; 5.7874; 9.44113; 8.93
Total1363467841266
* Species included in analyses.
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Manikowska-Ślepowrońska, B.; Ślepowroński, K. Is Winter Feeder Visitation by Songbirds Risk-Dependent? An Experimental Study. Birds 2025, 6, 45. https://doi.org/10.3390/birds6030045

AMA Style

Manikowska-Ślepowrońska B, Ślepowroński K. Is Winter Feeder Visitation by Songbirds Risk-Dependent? An Experimental Study. Birds. 2025; 6(3):45. https://doi.org/10.3390/birds6030045

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Manikowska-Ślepowrońska, Brygida, and Krzysztof Ślepowroński. 2025. "Is Winter Feeder Visitation by Songbirds Risk-Dependent? An Experimental Study" Birds 6, no. 3: 45. https://doi.org/10.3390/birds6030045

APA Style

Manikowska-Ślepowrońska, B., & Ślepowroński, K. (2025). Is Winter Feeder Visitation by Songbirds Risk-Dependent? An Experimental Study. Birds, 6(3), 45. https://doi.org/10.3390/birds6030045

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