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Higher rates of non-breeding territory occupancy of urban compared with rural Masked Lapwings Vanellus miles on Phillip Island, Victoria.

Introduction

A key feature of anthropogenic modification of environments is the creation of extensive areas dedicated to food production, spatially separated from areas dedicated to providing housing. This creates gradients within landscapes between 'rural' areas and urbanised (henceforth 'urban') areas (McDonnell and Pickett 1990). In some places, clear demarcation is evident between rural and urban areas, especially where urbanisation is ongoing (McDonnell and Pickett 1990). Masked Lapwings Vanellus miles inhabit both urban and rural areas on Phillip Island, southern Victoria, Australia (Cardilini et al. 2013). The high population evident in urban areas on the island is likely to be related to invasive predator eradication (Craig Bester, pers. comm., 1 May 2018). Since 2006 an intensive Red Fox Vulpes vulpes eradication program has been implemented. In 2017 Phillip Island was declared fox-free and no sign (prints, scats, remote camera or tracker dog detections or confirmed sightings) of a fox had been detected in the two years preceding the declaration. Indeed, before fox eradication lapwing remains were prominent at some fox dens on the island (Peter Dann, unpubl. data, 12 December 2018).

In southern Australia, lapwings breed in winter (Chambers et al. 2008), and (at least on Phillip Island) urban birds realise enhanced maternal condition, parental defence and reproductive success compared with those in ex-urban areas (Cardilini et al. 2013). Within urban areas, yards of holiday houses with extensive grass and an abundance of food are preferred (Roche et al. 2016a). Some birds, particularly passerines, exhibit higher-intensity territorial defence, and greater tolerance of humans and novel stimuli, in urban compared with ex-urban areas (Evans et al. 2010; Fokidis et al. 2011; Lowry et al. 2011; Scales et al. 2011). This may result from habituation or local selection for shy versus bold genotypes (van Dongen et al. 2015). Lapwings are more aggressive to humans in urban environments (Cardilini et al. 2013) and carefully adjust parental defence to the threat of humans approaching nests (e.g. whether or not the human is using a lawn mower; Lees et al. 2013).

Most research on urbanisation in birds reports the negative effects of urban environments on them, and no study known to us examines breeding territorial occupancy outside the breeding period. In general, occupancy of shorebird breeding territories outside the breeding period is poorly studied, though some shorebirds are known to visit their territories during the non-breeding season (Weston and Elgar 2005). Holding territories outside a breeding season may serve to defend the territory and its resources, or to attract mates (Turpie 1995; Lanctot et al. 2000). The benefits of living on urban versus rural territories for lapwings are emerging, but it is unknown whether 1) territories are multiple use, in the sense they are maintained during the non-breeding period, and 2) whether occupancy varies between habitats. Here we surveyed a marked population of lapwings to index the occupancy of the species on its breeding territories during the non-breeding season. We surmised that occupancy may be lower on rural territories because of a restriction in food supply (inferred from the poorer female condition in rural areas; Cardilini et al. 2013). Territory occupancy outside breeding may indicate higher quality territories, and might serve to avoid costs associated with territory establishment. In a review of 22 studies of territory occupancy in 17 species, Sergio and Newton (2003) found occupancy always deviated from a random pattern in species in which it was tested and was always correlated with productivity and/or with some other measure of territory quality. Our survey is the most comprehensive available to date for this species and locality and this also enabled us to report the minimum population size of lapwings on Phillip Island.

Methods

Phillip Island (38[degrees] 289 32" S, 145[degrees] 129 12" E) hosts a large population of lapwings, and consists of a matrix of urban and rural areas (see Cardilini et al. 2013). In 2010, adults were captured on their (geolocated) nest using a larger variant of a walk-in trap, which incorporated a door for extraction of the captured bird (see Tan et al. 2015). Each adult was fitted with a unique alpha-alpha engraved leg flag which enabled subsequent identification (Australian Bird and Bat Banding Schemes [ABBBS] authority 1763/4; Deakin University Animal Ethics, B02/2012; Government permit, 10005298). Young were captured by hand and were banded, but not flagged (only birds of flying age were flagged). This, plus many follow-up sightings, enabled us to clearly locate nesting locations and the extent of breeding territories, including for the breeding season preceding our count (see below) as lapwings generally maintain a pair bond and the same territory between seasons (Michael A Weston, unpubl. data, 1 October 2018). Eggs and chicks were aged using the approaches outlined in Cardilini et al. (2013). We calculated laying and hatching dates from this data to illustrate the relevant breeding period (the incubation phase lasts c. 30 days and brood-rearing phase extends for c. 35 days after hatching).

On 16 and 17 March 2011, AC and MW surveyed every publicly accessible road on Phillip Island and counted every lapwing encountered, noting age, location, and flag status (and identification, if applicable). We drove slowly, stopping frequently, and surveying all areas with binoculars. Territories where birds had been flagged were comprehensively searched. The weather was fine and still, and no road was counted twice. Our survey took place during the non-breeding period (Fig. 1), and we were able to compare the position of each marked bird from its nest site during the preceding breeding season, and determine if it was present within its breeding territory (i.e. the area in which it was seen while breeding in the previous breeding season).

Results

We counted 1104 lapwings on Phillip Island. The minimum urban population was 536 (for 21 we were unable to determine flag or band) and we counted 568 birds in rural or beach areas (75 of which we were unable to determine flag or band). We found 21 flagged birds (7 in rural areas, 14 in urban areas). Flagged birds were always seen with at least one and never more than four other birds (consistent with the idea that these were family groups). Banded offspring (fully grown) were seen with flagged adults on two occasions, suggesting at least some family groups stay together for a time after the breeding season. Birds were not seen in the urban, higher elevation areas of Wimbledon Heights and Smiths Beach.

Birds that maintained territory were usually within one hundred metres of their 2010 nest site (n = 67 sightings; Fig. 2). A General Linear Mixed Model examining distance from nest (logged), featuring bird identity as a random effect, and breeding versus non-breeding season and habitat as fixed effects, revealed a significant interaction between habitat and season ([F.sub.1,51.252] = 6.439, p = 0.014). Birds in rural areas occurred further from their nest sites during the non-breeding period compared with urban birds (Fig. 2).

We found 41% of urban territories were occupied (14 out of 34 birds flagged in 2010), compared with 22% of rural territories (6 out of 27 birds flagged in 2010). This difference was statistically significant at a = 0.10 (Fishers Exact Test, p = 0.098, one-sided) and would likely become more so with further replication. Of the seven flagged birds that we saw in rural habitats, all but one had remained on its previous territory. Six of the seven rural birds sighted on-territory during the non-breeding season had territories on rural land that was directly next to urban habitat, i.e. within tens of metres. Only one rural bird maintained a territory that was not close to urban habitat. However, this bird's habitat was on the well-kept grounds of the Phillip Island airport. We did not find any birds maintaining territory on rural land that was distant (> 1 km) from urban or human-maintained habitats, nor did we find any rural breeding birds in urban areas.

Discussion

Our findings stem from a single (but intense, systematic and comprehensive) survey during a single non-breeding period, but suggest that, at least during this non-breeding period, our index of territory occupancy was higher in urban territories. This finding is consistent with our predictions, based on lower food availability in rural territories. Urban areas on Phillip Island may have a more consistent and diverse food supply associated with regular garden maintenance and watering, and experience fewer natural predators (Cardilini et al. 2013, Roche et al. 2016a). This contention that rural territories have fewer prey resources needs to be explicitly tested by directly measuring food resources. However, indexing the food of lapwings is difficult, as pitfall trapping does not reflect the items in lapwing diet (Roche et al. 2016b). For lapwings, measuring earthworm abundance and availability will be required.

Several alternative explanations for our results apply. The first is that the more extensive rural habitat on the island allows rural birds to move further than urban birds and still inhabit equivalent habitat. We think this is unlikely because of the scale of urban areas and options to move out from urban territories. We have observed many non-breeding flocks during both breeding and non-breeding seasons in both urban and rural areas, including on rooftops in urban areas (Michael A Weston, unpubl. data, 1 October 2018). Lapwing territory densities could be higher in urban areas (unmeasured, and difficult to measure due to the fine-scale matrix of private property), and so more competition for territories may exist there, encouraging territory fidelity. This possibility also warrants investigation.

Another possible explanation for our findings is that rural lapwings, with reduced female body condition and a greater array of natural predators (Cardilini et al. 2013), may experience lower inter-seasonal survival. We do not have sufficient data to model survival of lapwing adults, but we have observations of flagged adults being taken by predators such as Swamp Harrier Circus approximans in rural areas (L Renwick, pers. comm., 11 September 2013). Finally, detectability of lapwings may differ between urban and rural environments. However, we experienced higher detectability in rural rather than urban locations (Michael A Weston, pers. obs., 1 October 2018), suggesting that this cannot explain our results.

Some studies show advantages to urban populations of birds (Isaksson et al. 2018), although the mechanisms through which this occurs are varied and likely not fully elucidated. In our simple, one-off survey, the case for rural territories being potentially 'suboptimal' in relation to urban territories, is strengthened by illustrating another dimension in which urban and rural lapwings differ. Poor food supplies on rural territories may also explain other documented differences: reduced female condition, less vigorous parental defence, and poorer reproductive success for rural birds (Cardilini et al. 2013). Two features of our study system may differ from other ecosystems, and explain these apparent advantages to urban-dwelling lapwings. Firstly, the absence of introduced foxes as a predator on the island, which themselves are highly urbanised in the region (Marks and Bloomfield 1999), may remove this potential disadvantage of living in urban areas. Secondly, the presence of infrequently used residential properties in the urban matrix (e.g. holiday homes) means that the effects of human disturbance, which are prevalent in most urban environments, can be avoided (Roche et al. 2016a).

Acknowledgements

Write-up was facilitated by the Beach Ecology and Conservation Hub (Venus Bay) and bands were provided by the Australian Bird and Bat Banding Schemes (ABBBS; 1763). Work was conducted under ethical clearances (A64/2009, B02/2012, B08/2015, B01/2018), government permits (10005298, 10006205, 1007554, 10008619) and ABBBS Colour Marking Authority and project approval (1763/2). Thanks to Laura X Tan and Kevin Bartram for artwork.

References

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Received 11 October 2018; accepted 21 March 2019

Adam PA Cardilini (1), Daniel Lees (1), Peter Dann (2) and Michael A Weston (1,3)

(1) Deakin University, Geelong, Australia. School of Life and Environmental Sciences, Centre for Integrative Ecology, Faculty of Science, Engineering and the Built Environment (Burwood Campus), 221 Burwood Highway, Burwood, Victoria 3125, Australia. (2) Phillip Island Nature Parks, Cowes, Phillip Island. (3) Corresponding author: mweston@deakin.edu.au
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Article Details
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Title Annotation:Contribution
Author:Cardilini, Adam P.A.; Lees, Daniel; Dann, Peter; Weston, Michael A.
Publication:The Victorian Naturalist
Article Type:Report
Geographic Code:8AUVI
Date:Jun 1, 2019
Words:2509
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