Dynamic table-visiting behavior of birds at outdoor restaurants and cafés
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Received: 6 November 2020 | Revised: 5 February 2021 | Accepted: 9 February 2021 DOI: 10.1111/eth.13145 RESEARCH ARTICLE Dynamic table-visiting behavior of birds at outdoor restaurants and cafés Paul D. Haemig1,2 | Sara Sjöstedt de Luna3 | Henrick Blank1 1 Nature Division, Government of Jönköping Province, Jönköping, Sweden Abstract 2 Department of Natural Sciences, Linneaus Fear of humans and its effect on animal behavior is increasingly being recognized as University, Kalmar, Sweden an important structuring force in ecological landscapes, with consequences for eco- 3 Department of Mathematics and Mathematical Statistics, Umeå University, logical interactions and communities. When aggressive, physically dominant species Umeå, Sweden are displaced by anthropogenic disturbance, physically weaker species exploit com- Correspondence petitor and predator downtimes to forage in previously risky places. Birds feeding at Sara Sjöstedt de Luna, Department of outdoor restaurants and cafés in association with humans are exposed to fluctuating Mathematics and Mathematical Statistics, Umeå University, Umeå, Sweden. levels of perceived danger caused by frequently changing densities of human diners. Email: sara.sjostedt.de.luna@umu.se Consequently, birds must make decisions about which dining tables to visit based on Editor: Christian Rutz trade-offs between foraging gain and perceived danger from avian competitors and humans. We tested the hypothesis that interspecific differences in response to per- ceived danger, combined with varying densities of human diners, dynamically alter which bird species predominates at dining tables. We found that house sparrows (Passer domesticus) tolerated higher human diner-densities than larger-sized, more physically dominant Eurasian jackdaws (Coloeus monedula). Sparrows were usually the first birds to visit diner-occupied tables and spent more time there than jack- daws. However, at diner-abandoned tables, this pattern changed: During low diner- densities at surrounding tables, jackdaws were usually the predominant species in first visits and minutes spent visiting, while at high diner-densities sparrows usually predominated. Moreover, along a gradient of increasing human diner-density, spar- rows gradually replaced jackdaws as the predominant species in first visits and time at abandoned tables. However, at diner-occupied tables, once a sparrow chose which table to visit, factors other than diner-density influenced its choice of where to for- age there (table-top or ground). To our knowledge, our research is the first scientific study of table-visiting behavior by birds at outdoor restaurants and cafés, and the first to reveal interspecific differences in table-visiting behavior by birds there. KEYWORDS anthropogenic disturbance, behavior and ecosystem services, feeding associations, human ecology, temporal interactions, urban ecology This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made. © 2021 The Authors. Ethology published by Wiley-VCH GmbH. Ethology. 2021;00:1–12. wileyonlinelibrary.com/journal/eth | 1
2 | HAEMIG et al. 1 | I NTRO D U C TI O N TA B L E 1 An updated list of wild bird species observed visiting outdoor restaurants and cafés in Sweden. In order to qualify for this list, a bird species had to (1) be seen visiting the outdoor Anthropogenic disturbance is increasingly being documented serving area of a genuine restaurant or café while human diners as a pervasive phenomenon influencing the behavior and ecol- were present, and (2) be observed there eating (or taking away) ogy of many kinds of animals (Cayuela et al., 2020; Firebaugh food or food remains served to human diners. The sixteen species & Haynes, 2016; Li et al., 2016; Tambling et al., 2015; Turner listed below belong to six monophyletic phylogenetic clades: A et al., 2019; Wilson et al., 2020). One mechanism, increased fear of (Passeridae, Motacillidae, Fringillidae), B (Paridae), C (Corvidae), D (Columbidae), E (Anatidae), L (Laridae). Data come from Table 2 of humans by wildlife, impacts a multitude of different species, directly Haemig et al. (2015) and from new, unpublished observations made and indirectly, in many different ecological communities and land- by the first author scapes (e.g., Berger, 2007; Clinchy et al., 2016; Leighton et al., 2010; Magle et al., 2014; Miller & Schmitz, 2019; Rösner et al., 2014). Monophylogenetic Bird Species (Scientific Name, Swedish Name) Clade Consequently, wild animals foraging close to humans must make de- cisions based on trade-offs involving food gain and perceived danger House Sparrow (Passer domesticus, Gråsparv) A from humans (Dwinnell et al., 2019; Kohl et al., 2018; Lodberg-Holm Eurasian Tree Sparrow (Passer montanus, A et al., 2019). Pilfink) Species vary in how threatening they perceive humans to be, and White Wagtail (Motacilla alba, Sädesärla) A this is reflected in the different changes they make to their foraging Common Chaffinch (Fringilla coelebs, Bofink) A activity (Mendes et al., 2020; Nickel et al., 2020; Suraci et al., 2019). Great Tit (Parus major, Talgoxe) B At anthropogenic food sources, species compositions and compet- Eurasian Jackdaw (Coloeus monedula, Kaja) C itive interactions are often altered (Francis et al., 2018; Galbraith Common Magpie (Pica pica, Skata) C et al., 2015); however, we lack precise information on the influence Hooded Crow (Corvus cornix, Kråka) C of perceived danger from humans on foraging decisions by different Rook (Corvus frugilegus, Råka) C species there. Rock Dove (Columba livia, Stadsduva) D In Sweden, sixteen bird species are known to visit outdoor Mallard (Anas platyrhynchos, Gräsand) E serving areas of restaurants and cafés and feed in association with Mew Gull (Larus canus, Fiskmås) L human diners (Table 1, Appendix 1). In contrast, over 90 Swedish Black-headed Gull (Larus ridibundus, L bird species visit bird feeders (BirdLife Sverige, 2020, see also Skrattmås) Elgmork, 2002, 2011 for year-round censuses in nearby Norway). Herring Gull (Larus argentatus, Gråtrut) L Remarkably, some of the most frequent avian visitors to bird feeders Lesser Black-backed Gull (Larus fuscus, L in Sweden have never been recorded as visitors to restaurants and Silltrut) cafés, even though they frequently forage within sight of these din- Great Black-backed Gull (Larus marinus, L ing establishments (e.g., blue tit Cyanistes caeruleus, European green- Havstrut) finch Chloris chloris, Eurasian nuthatch Sitta europaea, yellowhammer Emberiza citinella, Eurasian bullfinch Pyrrhula pyrrhula, marsh tit Poecile palustris, common blackbird Turdus merula, European robin of the dynamics and functioning of this familiar and apparently Erithacus rubecula, great-spotted woodpecker Dendrocopos major, cosmopolitan feeding association with humans remain unknown. common starling Sturnus vulgaris, hawfinch Coccothraustes cocco- To help remedy this deficiency, we conducted field studies on the thraustes, fieldfare Turdus pilaris). Thus, while casual observers may table-visiting behavior of Eurasian jackdaws (Coloeus monedula) and think of restaurants and cafés as anthropogenic food sources eco- house sparrows (Passer domesticus) in the outdoor serving areas of logically similar to bird feeders, this view may be naïve and simplistic. restaurants and cafés in Sweden. We chose these two species be- Restaurants and cafés differ from bird feeders and other an- cause, in urban areas of Sweden, they are the most common birds thropogenic food sources in that they are the sites of simultaneous seen visiting restaurants and cafés, often occurring together at the human-bird feeding associations, that is, places where both humans same dining establishments (Haemig et al., 2015). and birds congregate to eat the same foods in close proximity to The two species differ significantly in morphology, hab- each other. Just how old these human-bird feeding associations are its, and evolutionary history (Fjeldså, 2013, Haemig et al., 2015; is unknown. In Africa, Asia, and South America, wild birds have been Madge, 2009; Summers-Smith, 2009). Eurasian jackdaws average observed feeding in association with at least sixteen different gen- 6.8 times larger in biomass than house sparrows (Madge, 2009; era of non-human primates, so at least some of the human-bird feed- Summers-Smith, 2009), and frequently chase the latter away from ing associations that we see today at restaurants and cafés might be dining tables and food remains. Yet, jackdaws act more wary and very ancient (Haemig et al., 2015). afraid of humans and certain novel objects than do house sparrows To our knowledge, no scientific studies have ever been made of (Greggor et al., 2016; Moller & Tryjanowski, 2014), so their bully-bird table-visiting behavior by birds at outdoor restaurants and cafés, nor niche at restaurants and cafés could conceivably be restricted by their responses to anthropogenic disturbance there, so key aspects their own wariness. Despite these differences, both bird species are
HAEMIG et al. | 3 opportunistic generalists in diet, with wide overlap in the types and called the focal-t able. During every minute, he recorded how many sizes of food that they eat (Madge, 2009; Summers-Smith, 2009). birds of each species visited the focal-t able and which parts of that At restaurants and cafés, they generally eat the same foods and vie table they visited: table-top, chairs or benches, ground underneath. with each other for food scraps of all sizes (unpublished field obser- He also recorded how many human diners sat at the focal-t able, and vations of the first author). how many sat at all tables immediately adjacent to the focal-t able. Although both jackdaws and sparrows associate with humans at He included in these numbers any restaurant employees present. restaurants to obtain food, they also perceive humans as a danger Each sampling session continued for as long as the human diners and frequently flee from them. In this report, we document for the occupied the focal-t able, and for up to 15 min after they left, not first time significant differences between Eurasian jackdaws and counting minutes when restaurant personnel visited the abandoned house sparrows in table-visiting behavior and test a hypothesis that table. Upon completing one sampling period, a new sampling pe- interspecific differences in response to perceived risk, combined riod began as soon as one or more new diners entered the outdoor with varying densities of human diners, dynamically alter which bird serving area and sat down at a vacant table. Many sampling sessions species predominates at tables. According to the hypothesis, varying were conducted at each restaurant or café, and every dining place densities of human diners in outdoor serving areas create varying usually required a period of several days or weeks to complete. levels of danger that are perceived differently by jackdaws and spar- Sampling sessions conducted per day ranged from zero to eleven. rows, resulting in frequent alteration in which bird species appears Some days yielded no data because either birds and/or human din- at a dining table. ers failed to appear in the outdoor serving areas, for example during strong winds or rain. The visits of diners with pet dogs also caused many temporary terminations and lost hours of sampling (see below). 2 | M E TH O DS Saturday afternoons at outdoor cafés frequently resulted in only one or two sampling sessions because diners did not work that day and 2.1 | Study sites could spend hours chatting before they left the focal-t ables. Total data collection at each dining establishment was not stopped until Field research was conducted in the outdoor serving areas of 21 res- data from a wide range of human diner-densities at two spatial scales taurants and cafés, in the following twenty cities, districts and towns (defined in the next paragraph) were collected: (Small scale: 0.15– of Sweden: Säffle, Stenungsund, Varberg, Örebro, Kumla, Alingsås, 0.67 to 0.8–3.1 diners/m2, median = 0.4–1.7 diners/m2; Large scale: Karlsborg, Hjo, Skövde, Mariestad, Vårgårda, Skara, Vänersborg, 0–18.7–56.7 diners/100 m2, median = 0–29.4 diners/100 m2). It was Lidköping vid Vänern, Norrahammar, Jönköping, Huskvarna, Gränna, impossible to standardize the highest diner-density point for the Eksjö, Vimmerby. All restaurants and cafés were located in urban en- restaurants and cafés because dining establishments varied greatly vironments; however, they differed greatly from each other in size, in the size and spacing of their tables, resulting in diner-density dif- number of tables, the presence or absence of trees and bushes, and ferences even if all tables were fully occupied. numerous other parameters. The only common element uniting all At the end of each day's research, the first author used a tape the 21 was an urban setting and the presence of both house spar- to measure a small-scale area (the focal-t able) and a large-scale area rows and jackdaws visiting tables where human diners ate. Like most (the focal-t able plus all adjacent tables and the spaces between them) urban vertebrates, house sparrows and jackdaws are habitat gener- for all focal-t ables. Together with the minute-by-minute counts of alists (Ducatez et al., 2018). the number of human diners and restaurant employees present, Pilot studies began in 2015 and continued into 2016. By that these area data were later used to calculate human diner-density at time, the first author could see from preliminary results at aban- both spatial scales for each minute that birds visited the focal-t ables. doned tables that the predominant bird species often varied, pos- Human diner-density in the small-scale area was expressed as diners sibly due to fluctuating densities of human diners. He consequently per m2, while that of the large-scale area was expressed as diners designed a new research protocol (described below) to test this per 100 meters squared. Because no two human diners are identical, hypothesis. Sampling using the new research protocol began in the diner-density can be viewed as a measure of the total average influ- summer of 2016 and continued until the spring of 2020, whenever ence of diner presence on foraging birds. time and weather permitted. After the field research was finished, the data for every min- ute of each sampling period was examined to determine which bird species was first to visit each newly occupied focal-t able and each 2.2 | Experimental design recently abandoned focal-t able (hereafter called simply an “aban- doned focal-t able”) during every sampling session. In addition, the At lunchtime, in the outdoor serving area of each restaurant or café, presence of each bird species at focal-t ables was calculated and ex- the first author chose a location to sit with a clear view of as many pressed in bird-minutes, where each visit by an individual bird to the dining tables as possible. To begin a sampling session, he started a focal-t able during a minute was assigned a value of one bird-minute. stopwatch as soon as a new diner, or group of diners, entered the For example, if three individual birds of the same species visited the outdoor serving area and sat down to eat at a vacant table, hereafter focal-t able during a single minute, the species was assigned a value
4 | HAEMIG et al. of three bird-minutes for that minute. If a single individual bird vis- geographic area of Sweden. To make certain that, our data of first ited a focal-t able for three minutes, it was also assigned a value of visits to focal-t ables did not bias our results in terms of self-selection three bird-minutes (Haemig et al., 2015). Note that our bird-minute (Webster & Rutz, 2020), we also recorded the total number of bird- data do not reveal the length of individual bird visits, but rather the minutes spent at focal-t ables by each bird species. total presence of a bird species over time at the focal-t ables. For ex- ample, if the minute-by-minute data show that for two consecutive minutes a single sparrow was present at the focal-t able, this fact can 2.3 | Statistical analyses mean either that an individual sparrow was present for two minutes, or that two sparrows were present, one visiting only during the first To test if there was a significant difference between bird species minute, and the other visiting only during the second minute. in first visits to diner-occupied versus abandoned focal-t ables, we The human diner-density at both spatial scales for every minute first computed the proportion of the occupied focal-t ables where that a bird was present at the focal-t ables was calculated using the house sparrow was the first visitor (and not jackdaw) for each of the area data and the minute-by-minute censuses. First-visit data were n = 21 restaurants/cafés, and the corresponding proportions for the also used to calculate the number and frequency of house sparrow abandoned focal-t ables. Then a two-sided one-sample (paired) t test visits to the table-tops of diner-occupied focal-t ables along a gra- was performed on the (21) differences in proportions of first visits to dient of human diner-density. First-visit and bird-minute data for focal-t ables by house sparrows between occupied and abandoned abandoned focal-t ables was also placed along a gradient of human focal-t ables (Appendix 2, column 8), testing our null hypothesis of diner-density for examination. no difference (µ = 0.000). The same test was applied to column 8 We had hoped to be able to also study the effect of other bird in Appendix 3 to determine if the difference in proportion of bird- species (Table 1) on the table-visiting behavior of jackdaws and minutes by house sparrows (and consequently jackdaws) at occupied house sparrows. However, at the restaurants and cafés sampled versus abandoned focal-t ables was significantly different from zero. in this study, visits by other bird species were too few and infre- We also compared how the two bird species responded to a quent to supply enough data for statistical analysis. In addition, wide range of values of a single, greatly fluctuating biotic factor: examination of our minute-by-minute records for the rare visits by The density of human diners in an area comprising the abandoned these other species provided no evidence that such visits affected focal-t able, all adjacent dining tables, and the spaces between them. the basic patterns of predominance that we found. Although birds Using the focal-t able as our basic unit, we categorized each of the like the Common Magpie (Pica pica), Hooded Crow (Corvus cornix), 229 abandoned focal-t ables according to human diner-density and and Herring Gull (Larus argentatus), are larger-sized and physically the bird species making the first visit. To test if the distribution along able to dominate the smaller birds we studied, they acted more wary the gradient of human diner-density with respect to first visits at and afraid of humans than even the jackdaw, and usually visited the abandoned focal-t ables was the same for house sparrows and jack- focal-t ables only sporadically – and then only at the lowest human daws, we first performed a chi-square test for independence on the diner-densities. Their greater wariness of humans and infrequent, data for these two species in Table 2. To reduce the possibility of isolated visits consequently meant that they had no significant im- error, we lumped the data in the last two columns of Table 2, and the pact on predominance patterns of house sparrows and jackdaws chi-square test was thus applied to a 2 × 4 table with 3 degrees of at the restaurants and cafés we studied. However, because ours is freedom. To further investigate the relation between diner-density the first study of table-visiting behavior by birds at restaurants and versus bird species we fitted a logistic regression model to the aban- cafés, we would not rule out the possibility that these other bird doned focal-t able data points. The model takes into account poten- species might have significant impacts at other dining places. tial dependence between focal-t ables from the same restaurant. In Sweden, dogs are permitted to accompany human diners in The response variable was 1 if house sparrow was the first visitor the outdoor serving areas of restaurants and cafés, and to remain at to the abandoned focal-t able, and 0 if jackdaw was first visitor. The their tables. Because dogs are predators, they can sometimes influ- explanatory variables were Restaurant (random factor, intercept) ence bird behavior. However, we found their exact effects difficult and Human diner-density (100 m2) as a linear covariate. The logistic to measure because dogs do not normally visit restaurants or cafés regression models the log odds ratio by unless accompanied by human diners. Hence, when dogs come to a ( ) p restaurant the number of both human diners and dogs increases, and log = + Restauranti + Diner − density (1) 1−p when dogs leave the number of both dogs and human diners also de- creases, confounding the influence of dogs and humans. To reduce the possibility of dogs biasing the results of our research, we did not where p denotes the probability of house sparrow being the first visitor use any data gathered when dogs were present at focal-t ables or at to an abandoned focal-table. Using this model, we tested if there was tables adjacent to them. a significant (linear) trend in the log odds ratio, along the gradient of To ensure that our results were truly representative of the nor- diner-density, that is, if was significantly different from zero. mal behavior of the bird species that we studied, we conducted our The logistic regression model (1) was also used to test if diner- fieldwork over six field seasons and in numerous cities over a wide density was correlated with the house sparrow choice of foraging
HAEMIG et al. | 5 site at diner-occupied focal-t ables (table-top or ground underneath). Here the response variable was 1 if the first visit by house sparrows to a diner-occupied focal-t able was on the table-top, and 0 if on the ground. The logistic regression models were fitted to the N aban- doned focal-t able data points, using the lme4-package in the soft- ware program R (Bates et al., 2015; R Core Team, 2020). 3 | R E S U LT S 3.1 | First visits by birds to focal-tables At all 21 restaurants and cafés, the house sparrow was usually the first bird species to visit diner-o ccupied focal-t ables (Figure 1, Appendix 2). In contrast, at 17 of 21 restaurants and cafés, the Eurasian jackdaw was usually the first bird species to visit aban- doned focal-t ables (Figure 1, Appendix 2). Reflecting the complete reversal of predominance between these two bird species at occu- F I G U R E 2 Boxplots of the proportions of focal-t ables where pied versus abandoned focal-t ables, the average difference in pro- the total number of bird-minutes by house sparrow were larger portion of first visits by house sparrows to occupied focal-t ables than those by jackdaw. The left boxplot illustrates the computed versus abandoned tables was 0.669, significantly different from proportions for the 21 restaurants at abandoned tables and the zero (Appendix 2, two-sided t-test, df = 20, n = 21, t-value = 14.45, right boxplot the 21 proportions at occupied tables. Data from Appendix 3 p-value < 0.001). at abandoned focal-t ables more bird-minutes than house sparrows 3.2 | Total bird presence at focal-tables at a majority (13) of the restaurants and cafés (Figure 2, Appendix 3). Reflecting the complete reversal of predominance between these At all 21 restaurants and cafés, the house sparrow was usually pre- two bird species at occupied versus abandoned focal-t ables, the av- sent at occupied focal-t ables more bird-minutes than the Eurasian erage difference in proportion of bird-minutes by house sparrows jackdaw (Figure 2, Appendix 3). In contrast, the jackdaw was present at occupied focal-t ables versus abandoned tables was 0.550, sig- nificantly different from zero (Appendix 3, two-sided t test, df = 20, n = 21, t-value = 12.22, p-value < 0.001). 3.3 | Bird visits to abandoned focal-tables along a gradient of increasing human diner-density First visits to abandoned focal-t ables by the two bird species were distributed significantly different along the human diner-density gra- dient (Table 2, Chi-square Test for Independence [df = 3, N = 229] χ 2 = 27.93, p = 0.00001). When diners were entirely absent from the area comprising the abandoned focal-t able, adjacent tables, and the spaces between them, diner-density equaled zero diners per 100 m2. At this time, the Eurasian jackdaw was most often the bird species making first-visits to abandoned focal-t ables (Table 2). As diner- density increased, the proportion of tables with jackdaws making first visits gradually declined, but still predominated, up to a density of approximately 20 diners per 100m2; where there was a reversal of predominant species and house sparrows thereafter made most first F I G U R E 1 Boxplots of the proportions of focal-t ables where visits to abandoned focal-t ables. The pattern for house sparrows the first visit was made by a house sparrow (instead of jackdaw). was opposite that of jackdaws. The lowest proportion of first vis- The left boxplot illustrates the computed proportions for the 21 restaurants at abandoned tables and the right boxplot the 21 its occurred at zero diners per 100m2, and then gradually increased proportions at occupied tables. Data from Appendix 2 along the gradient of human diner-density (Table 2).
6 | HAEMIG et al. TA B L E 2 Distribution of first visits by bird species to focal-t ables abandoned by human diners along a gradient of increasing human diner-density in an area that includes the focal-t able, all neighboring tables, and the spaces between. Shown are the total numbers of abandoned focal-t ables where each bird species made the first visit when diner-densities were at the levels indicated at the top of each column. In parentheses are the number of restaurants and cafés where the majority of first visits to focal-t ables were made by each bird species at the diner-densities indicated at the top of each column. The last two rows show the proportion of the total number of abandoned focal-t ables in each column where the house sparrow was the first visitor, and the corresponding odds ratio Human diner-density (diners per 100 m2) 0 0.01–10.00 10.01–20.00 20.01–3 0.00 Over 30.00 Eurasian Jackdaw 61 (18) 57 (16) 27 (11) 8 (3) 1 (1) House Sparrow 13 (1) 22 (4) 20 (6) 16 (9) 4 (2) Proportion of House 0.176 (0.053) 0.278 (0.200) 0.426 (0.353) 0.667 (0.750) 0.800 (0.667) Sparrow, p Odds Ratio, p/(1-p) 0.214 (0.056) 0.385 (0.250) 0.742 (0.546) 2.000 (3.000) 4.000 (2.000) TA B L E 3 Three estimated logistic Estimate Std. Error z-value p-value regression models with explanatory (a) First visit to abandoned focal-t ables made by house sparrows (versus jackdaws), N = 229 variables being diner-density (per m2 or Intercept −1.6963 0.3128 −5.424 5.83 × 10 −8 per 100 m2) and restaurant (intercept, random effect). The response variable Diner-density per 100 0.0909 0.0196 4.645 3.41 × 10 −6 is 0/1 corresponding to if: a) first visit to m2 abandoned focal-t able is made by house Restaurant 0.816 (std.dev.) sparrow (1) or jackdaw (0), b) first visit (b) Table-top (versus ground) visits to diner-occupied focal-t ables made by house sparrows, to diner-occupied table made by house N = 181 sparrow is on the table-top (1) or on the Intercept −1.9592 0.5466 −3.585 0.000338 ground (0). Estimated coefficients, their standard errors, z-values and p-values are Small-scale diner- −0.3153 0.5715 −0.552 0.5812 given as well as the standard deviation for density per m2 the random factor restaurant Restaurant 0.738 (std.dev.) Intercept −1.8306 0.4729 −3.871 0.000109 Large-scale diner- −0.0277 0.0267 −1.039 0.2987 density per 100 m2 Restaurant 0.750 (std.dev.) Logistic regression modeling found a significant positive linear choice of table-top or ground by analyzing the frequency of first vis- trend in the log odds ratio with increasing diner-density (̂ = 0.0196, its by house sparrows to table-tops of diner-occupied focal-t ables at p-value < 0.001, Table 3a, Figure 3) and the odds ratio increased by different diner-densities. At both spatial scales, no statistically sig- ( ) approximately 2% e ≈ 1.02 when diner-density increased by one nificant correlation was found (Table 3b). ̂ unit. Similar distribution patterns along the gradient can be seen if we look at which species has the majority of first visits to aban- 4 | D I S CU S S I O N doned focal-t ables at each restaurant or café (data in parentheses in Table 2), and also at total bird-minutes spent visiting abandoned Variation in the distribution of food and interspecific aggression in- focal-t ables (Table 4). In the latter case, the change from jackdaw fluences how animals use their environment (Haemig, 1996, 1999; to house sparrow predominance seems to occur at a lower diner- Kuijper et al., 2015; Gallager et al., 2017; Gaynor et al., 2019; Zanette density of approximately 10 diners per 100m2 (Table 4). and Clinchy, 2019). These factors fluctuate in time, as well as space, creating fluid, dynamic situations where localities can change quickly from being safe to dangerous, and vice-versa (Courbin et al., 2019; 3.4 | Table-top visits to diner-occupied focal-tables Kohl et al., 2018; Palmer et al., 2017; Smith et al., 2019; Swanson by house sparrows et al., 2016; Zeller et al., 2019). Birds often respond to increased inter- specific aggression by decreasing frequency of visits and time spent A house sparrow visiting a diner-occupied table must choose where at risky sites, and will even switch foraging sites to escape aggression to forage: the table-top or the ground (substrate) under the table and (Haemig, 1996). Anthropogenic disturbance, including the fear that chairs. We investigated if diner-density was correlated with sparrow humans cause in many wildlife species, adds still more complexity to
HAEMIG et al. | 7 F I G U R E 3 Odds ratios (left panel) and log odds ratios (right panel) versus various levels of human diner-density per 100 m2. The odds ratios are computed from the proportion of the total number of abandoned focal-t ables (in each category of human diner-density) where the house sparrow was the first visitor. Data from Table 2, last row TA B L E 4 Distribution of bird presence at focal-t ables (N = 229) We found evidence consistent with the hypothesis that interspe- abandoned by human diners along a gradient of increasing cific differences in avian response to perceived danger, combined human diner-density in an area that includes the focal-t able, all with fluctuating densities of human diners, dynamically alter which neighboring tables and the spaces between. Shown are the total bird species predominates at dining tables, that is, which species number of bird-minutes spent by each species at abandoned focal-t ables when diner-densities at neighboring tables were at the usually visits tables first or spends most time (bird-minutes) there. levels indicated at the top of each column. The last row shows the House sparrows were usually the first birds to visit focal-t ables oc- proportion of the total number of abandoned focal-t ables in each cupied by human diners and usually spent more bird-minutes there column where the house sparrow had more bird-minutes than the than Eurasian jackdaws (Tables 2 and 3). The fact that sparrows usu- jackdaw for the corresponding human diner-density ally exceeded jackdaws in both of these measures of predominance Human diner-density (diners per 100 m2) confirmed our initial impressions that sparrows were more tolerant of risk from humans than jackdaws. 0.01– 10.01– 20.01– Over 0 10.00 20.00 30.00 30.00 However, at focal-t ables abandoned by human diners, this pat- tern changed dramatically. There, Eurasian jackdaws were usually Eurasian Jackdaw 481 344 136 34 1 the first visitors to the focal-t ables and usually spent more bird- House Sparrow 193 238 139 79 68 minutes there than house sparrows (Figures 2 & 3, Appendices 2 & House Sparrow 0.286 0.409 0.505 0.699 0.986 3), showing that they predominated at abandoned focal-t ables. Proportion We hypothesized that human diner-density in the area occu- pied by the focal-t able and all immediately adjacent tables (plus the total information that an animal must use to decide when and the spaces between them), combined with interspecific differences where to forage, and many studies show that wildlife may perceive in avian response to danger, was responsible for the dramatically even benign or friendly humans as a danger and avoid them (e.g., different results between occupied and abandoned tables as well Berger, 2007; Clinchy et al., 2016; Dwinnell et al., 2019; Leighton as the greater variation in results seen with abandoned tables. To et al., 2010; Lodberg-Holm et al., 2019; Magle et al., 2014; Mendes test this idea, we arranged our results of first visits to abandoned et al., 2020; Miller & Schmitz, 2019; Rösner et al., 2014; Suraci focal-t ables along a gradient of human diner-density, according to et al., 2019). the diner-density recorded at the precise minute when the table- In the present study, we discovered evidence suggesting that visit occurred. Our analysis found that as diner-density increased anthropogenic disturbance caused by humans dining at restaurants (Table 2), house sparrows gradually replaced jackdaws as the pre- and cafés affected the birds associating with them in more ways than dominant species at abandoned focal-t ables. Jackdaws were usually by humans simply leaving food scraps for the birds to eat. Our re- the first visitors to abandoned focal-t ables when diner-density was search documented both direct and indirect human impacts on the zero. As diner-density increased, the proportion of abandoned focal- behavioral ecology of the birds, some negative and some positive. tables where jackdaws were the first visitor generally decreased. At
8 | HAEMIG et al. larger human diner-density (around 20 diners per 100m2 or more), reducing risk. Alternatively, the larger brain size of the jackdaw may there was a reversal in which bird species predominated, with most result in more cautious approach to feeding in association with hu- abandoned focal-t ables recording house sparrows as the first visitor mans (Møller & Erritzøe, 2014; Sayol et al., 2020). In addition, many (Table 2). Looking at the distribution of bird presence (measured in bird taxa differ from each other in degree of attraction to novelty or bird-minutes) at abandoned focal-t ables along the gradient of human avoidance of it, and these differences also affect foraging choices diner-density, we found a similar pattern of gradual replacement of (Crane et al., 2020; Greggor et al., 2016; Haemig, 1989). jackdaws by house sparrows (Table 4). For example, Greggor et al. (2016) studied bird behavior in We interpreted the results of our study to mean that the per- England and found that corvids were more fearful of novel objects ception by jackdaws of more hazardous risk at focal-t ables in areas than other songbirds. Our similar discovery that jackdaws were of higher human diner-d ensity, and consequently the jackdaws’ more fearful of humans than house sparrows at restaurants and avoidance of them, created fine-s caled, spatio-temporal foraging cafés could indicate that behavior in both contexts reflects the same refuges for house sparrows to exploit. Specifically, these refuges inherent trait (boldness). While elucidating the exact causes of this were (a) focal-t ables occupied by human diners, and (b) abandoned difference is beyond the scope of the present paper, we urge fu- focal-t ables with adjacent dining tables having high human diner- ture researchers to consider the possibility that the reasons could density. Often these spatio-temporal refuges existed for only min- be based, at least in part, on different evolutionary histories and utes, but their summed length of time was substantial and created strategies, and also on different lengths of time with which the two an open, dynamic niche for the more diner-tolerant house spar- species have had feeding associations with humans, fossil hominids, rows to exploit, free from harassment, displacement, and klep- and/or other prehistoric animals. In an earlier paper, we showed that toparasitism by jackdaws. This seems especially true when one the house sparrow and certain of its relatives in monophyletic Clade considers the fact that busy restaurants usually have many dining A (Passer montanus, Motacilla alba, Fringilla coelebs) are together the tables in their outdoor serving areas, with human diners coming most frequent avian visitors to restaurants and cafés in rural areas and going by the minute. of Sweden—which humans have inhabited far longer than urban Our field notes of bird behavior during data collection support areas (Haemig et al., 2015). Clade A has now split into at least three these interpretations. For example, the first author frequently saw families (Passeridae, Motacillidae, Fringillidae), suggesting that an jackdaws avoiding diner-occupied tables, even when jackdaws were ancient, common ancestor before the split might have participated physically closer to them than house sparrows when the diners ar- in feeding associations with fossil hominids and/or other prehistoric rived. At abandoned focal-t ables, he observed jackdaws physically animals before switching to modern hominids. If true, it could mean displacing house sparrows, and even chasing sparrows away from that ancestors of the house sparrow formed close feeding associa- the focal-t ables when they approached too close to them. In nine tions with hominids, and/or other relevant taxa, long before the an- instances, he recorded jackdaws stealing first-visits from house cestors of the jackdaw. And if so, the house sparrow line could have sparrows this way. Yet, he also recorded eleven instances of jack- had more time to evolve behavioral and evolutionary adaptations for daws losing first-visits to house sparrows when diners or restau- feeding in intimate association with hominids, resulting in it today rant personal walked near an abandoned focal-t able, scaring away showing less fear of humans than the jackdaw. an approaching jackdaw. The results for bird-minutes were similar: To our knowledge, our research is the first scientific study of Sparrows lost at least 18 bird-minutes when jackdaws drove them table-visiting behavior by birds at outdoor restaurants and cafés. away from abandoned focal-t ables, yet the sparrows gained at least The results we obtained are consistent with the hypothesis that we 22 bird-minutes when jackdaws there fled approaching humans and tested and suggest that human diners cause a spatial and temporal the sparrows responded by visiting the focal-t ables. Thus, anthro- redistribution of bird species that enhances coexistence of the two pogenic disturbance resulted in sparrows regaining approximately bird species. Our study is also the first to show interspecific differ- the same number of first-visits and bird-minutes that they lost to ences in table-visiting behavior by birds, and the first to specifically jackdaw aggression. identify human diner-density as a key ecological factor correlated House sparrows that visited diner-occupied focal-t ables usually with which bird species appears and predominates at dining tables. foraged there in the absence of jackdaws. Data from these tables Because human diners, house sparrows, and corvids are cos- show no correlation of diner-density with house sparrow choice of mopolitan in distribution, we believe it possible that our findings foraging site (table-top versus ground under table and chairs). We, could have application in predicting bird behavior and distribution therefore, hypothesize that once a sparrow decided which diner- at restaurants and cafés in many parts of the world. This would occupied focal-t able to visit, some other unmeasured factor, such be important because it could enable more humane and ethical as food quality and availability, was more important to the sparrows treatment of birds at restaurants and cafés, as well as increase than diner-density in influencing their decision to forage on the enjoyment of dining experiences there for both humans and birds. table-top or ground. And in doing that, it would also contribute to preserving and nur- Why do sparrows and jackdaws differ in their tolerance of human turing traditional feeding associations between birds and humans diners? There could be many explanations. For example, the smaller that possibly have been a part of human ecology since antiquity size of the sparrow could give it greater agility than the jackdaw, (Haemig et al., 2015).
HAEMIG et al. | 9 We studied jackdaws and house sparrows that foraged at the Dwinnell, S. P. H., Sawyer, H., Randall, J. E., Beck, J. L., Forbey, J. S., Fralick, G. L., & Monteith, K. L. (2019). Where to forage when afraid: Does same restaurants and cafés. We, therefore, limited our sampling perceived risk impair use of the foodscape? Ecological Applications, only to dining establishments where both of these bird species were 29, e01972. https://doi.org/10.1002/eap.1972 present. However, in our previous study (Haemig et al., 2015), we Elg, M. (2006). Landskapen i våra hjärtan. Liber. also discovered restaurants and cafés where only one species (jack- Elgmork, K. (2002). Seasonal variation of birds on a feeding site in a sub- urban area near Oslo, Norway. Fauna Norvegica, 22, 1–8. daw or house sparrow) fed in association with human diners. The Elgmork, K. (2011). Dynamics of garden birds at a feeding station in a present study, therefore, has a built-in bias and we caution readers suburban area near Oslo, Norway, 2000–2008. Ornis Svecica, 21, not to make assumptions about jackdaw and sparrow behavior at 179–189. “monospecific” dining establishments until birds there can be stud- Firebaugh, A., & Haynes, K. J. (2016). Experimental tests of light- ied and the results compared to our results. pollution impacts on nocturnal insect courtship and disper- sal. Oecologia, 182, 1203–1211. https://doi.org/10.1007/s0044 2-016-3723-1 AC K N OW L E D G E M E N T S Francis, M. L., Plummer, K. E., Lythgoe, B. A., Macallan, C., Currie, T. We thank the many managers and personnel at the restaurants and E., & Blount, J. D. (2018). Effects of supplementary feeding on in- cafés who allowed us to conduct this study. We are also grateful to terspecific dominance hierarchies in garden birds. 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HAEMIG et al. | 11 APPENDIX 1 Correction: All Fisher's Exact Tests in Haemig et al., (2015) were two-t ailed (two-sided) tests and should have stated this fact. In Table 4 of Haemig et al., (2015), pp. 10–11, six of the eight Fisher's Exact Tests were correctly labeled as two-t ailed, but the labeling for the two remain- ing Fisher's Exact Tests (“Eurasian Jackdaw versus White Wagtail” and “Clade B versus Clade C”) was accidently deleted by malfunctioning software. Both these latter tests should state that they were two-t ailed. APPENDIX 2 Number of first visits to focal-t ables by house sparrows (Passer domesticus) and jackdaws (Coloeus monedula) in the outdoor serving areas of each of the restaurants and cafés (n = 21). Each row represents a single restaurant or café. The city (or district) and landscape province of each restaurant or café are listed, as well as the number of first visits by each bird species and the proportions calculated from them. The final col- umn (8) was used for the (paired) t test. The final row shows the sums for columns 3,4,5,6, and the means and standard deviations for columns 2, 7, and 8. For more information on landscape provinces see Elg (2006). Occupied tables Abandoned tables Proportion of Proportion of first visits to first visits to abandoned occupied focal- focal-tables Column City or District tables made by House House made by house 2 minus (Landscape Province) house sparrows Sparrow Jackdaw Sparrow Jackdaw sparrows Column 7 Säffle (Värmland) 1.000 5 0 1 5 0.167 0.833 Stenungsund (Bohuslän) 1.000 8 0 5 3 0.625 0.375 Varberg (Halland) 0.923 12 1 13 4 0.765 0.158 Örebro (Närke) 1.000 12 0 0 11 0.000 1.000 Kumla (Närke) 1.000 6 0 3 11 0.214 0.786 Alingsås A (Västergötland) 0.909 10 1 4 8 0.333 0.576 Alingsås B (Västergötland) 0.833 5 1 0 8 0.000 0.833 Karlsborg (Västergötland) 1.000 18 0 4 7 0.364 0.636 Skövde (Västergötland) 1.000 12 0 5 7 0.417 0.583 Mariestad (Västergötland) 0.875 7 1 0 9 0.000 0.875 Hjo (Västergötland) 1.000 8 0 3 9 0.250 0.750 Vårgårda (Västergötland) 1.000 8 0 9 5 0.643 0.357 Skara (Västergötland) 1.000 6 0 2 7 0.222 0.778 Vänersborg 1.000 5 0 3 8 0.273 0.727 (Västergötland) Lidköping (Västergötland) 0.917 11 1 3 5 0.375 0.542 Norrahammar (Småland) 1.000 7 0 2 10 0.167 0.833 Jönköping (Småland) 1.000 10 0 4 10 0.286 0.714 Huskvarna (Småland) 1.000 11 0 1 8 0.111 0.889 Gränna (Småland) 0.900 9 1 5 7 0.417 0.483 Eksjö (Småland) 1.000 7 0 6 5 0.545 0.455 Vimmerby (Småland) 1.000 8 0 2 7 0.222 0.778 Totals (means, standard (0.969, s = 0.05) 185 6 75 154 (0.300, s = 0.21) (0.66, deviations) s = 0.21)
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