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Birds at a Southern California beach: Seasonality, habitat use and disturbance by human activity

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Use of a Santa Barbara beach by people and birds varied in both time and space. There were 100 birds, 18 people and 2 dogs per kilometer. Bird density varied primarily with the season and tide while human activity varied most between weekend and weekday. Bird distributions along the beach were determined mainly by habitat type (particularly a lagoon and exposed rocky intertidal areas) For crows and western gulls, there was some evidence that access to urban refuse increased abundance. Interactions between birds and people often caused birds to move or fly away, particularly when people were within 20 m. During a short observation period, 10% of humans and 39% of dogs disturbed birds. More than 70% of birds flew when disturbed. Bird species varied in the frequency that they were disturbed, partially because a few bird species foraged on the upper beach where contact with people was less frequent. Most disturbances occurred low on the beach. Although disturbances caused birds to move away from humans, most displacement was short enough that variation in human activity did not alter large-scale patterns of beach use by the birds. Birds were less reactive to humans (but not dogs) when beach activity was low.
Content may be subject to copyright.
Biodiversity and Conservation 10: 1949–1962, 2001.
© 2001 Kluwer Academic Publishers. Printed in the Netherlands.
Birds at a Southern California beach: seasonality,
habitat use and disturbance by human activity
KEVIN D. LAFFERTY
United States Geological Survey, Western Ecological Research Center, Marine Science Institute,
University of California, Santa Barbara, CA 93106, USA (e-mail: lafferty@lifesci.ucsb.edu;
fax: +1-805-893-8062)
Received 18 July 2000; accepted in revised form 3 January 2001
Abstract. Use of a Santa Barbara beach by people and birds varied in both time and space. There were
100 birds, 18 people and 2 dogs per kilometer. Bird density varied primarily with the season and tide
while human activity varied most between weekend and weekday. Bird distributions along the beach were
determined mainly by habitat type (particularly a lagoon and exposed rocky intertidal areas). For crows
and western gulls, there was some evidence that access to urban refuse increased abundance. Interactions
between birds and people often caused birds to move or fly away, particularly when people were within
20 m. During a short observation period, 10% of humans and 39% of dogs disturbed birds. More than
70% of birds flew when disturbed. Bird species varied in the frequency that they were disturbed, partially
because a few bird species foraged on the upper beach where contact with people was less frequent. Most
disturbances occurred low on the beach. Although disturbances caused birds to move away from humans,
most displacement was short enough that variation in human activity did not alter large-scale patterns of
beach use by the birds. Birds were less reactive to humans (but not dogs) when beach activity was low.
Key words: beach, birds, disturbance, dogs, recreation, shorebirds
Introduction
About half of the shorebird species in North America are in decline, primarily due
to habitat destruction and degradation (Howe et al. 1989; Brown et al. 2000a). The
world’s growing coastal population continues to increase the encroachment of peo-
ple into shorebird habitat (Burger and Gochfeld 1991). A good example is Southern
California, where the climate and culture make beach recreation popular along the
Pacific Flyway. The resulting disturbance from humans and pets degrades habitat for
shorebirds because disturbance may reduce foraging efficiency and opportunities for
rest (Burger 1986; Brown et al. 2000b). Chronic, cumulative disturbance could, there-
fore, reduce shorebird reproduction and survivorship. In particular, short flights are en-
ergetically costly for small birds (Nudds and Bryant 2000) and shorebirds unsuccessful
in gaining necessary fat reserves have very low survival rates (Brown et al. 2000b).
To better understand how management actions might reduce disturbance, I in-
vestigated recreational activity and the responses of birds (primarily shorebirds) on
1950
a Southern California Beach. My research objectives were to determine: (1) factors
associated with bird and human use of the study site and (2) how disturbance varied
with bird species, human activity and the distance between the two. Based on similar
studies done with other species (Burger 1986), I expected that the effect of an activity
on birds would vary among activity types and that some bird species would be more
sensitive to disturbance than others (Burger and Gochfeld 1998).
People can disturb birds if they approach too closely or too quickly. In addition,
some dogs may actively chase birds for prolonged periods. The sensitivity of shore-
birds to dogs is illustrated by the observation that snowy plovers react at twice the
distance to dogs that they do to pedestrians (Fahy and Woodhouse 1995; Lafferty
2001). Perhaps this heightened reaction is because being chased conditions birds to
be wary of dogs or because birds instinctively view dogs as predators (Gabrielsen and
Smith 1995). Although they do not remove habitat or kill birds directly, disturbances
cause birds to suspend feeding and/or expend energy in flight, movement or vigilance.
Impacts to birds are most likely a result of cumulative effects on reproduction and
survivorship. Birds that forage slowly or ineffectively may not build the requisite fat
reserves that are especially important to stressed and depleted migrants who must rest
and feed to successfully resume their migratory journey (Puttick 1979).
Studies on piping plovers indicate that reproductive success is lower in areas with
high human disturbance because of reduced foraging efficiency and the depletion
of fat reserves (Burger 1986, 1991, 1994). In areas where people are absent, piping
plovers can spend 90% of their active time feeding compared with less than 50% in
areas where people are common (Burger 1994). Disturbance can also cause birds to
abandon habitat (Burger 1986). On the northeast coast of North America, gulls and
terns are least likely to be permanently displaced, ducks usually move a short dis-
tance while herons, egrets and shorebirds are most likely to be displaced the furthest
distance (Burger 1981). In Ventura County, for example, shorebird abundance is low
on beaches with high human use, presumably because disturbance causes birds to
seek more isolated locations (McCrary and Pierson 2000). Pet activity, in particular,
reduces shorebird abundance (Burger 1981; Klein 1993) and those birds that remain
must spend more energy on vigilance and escape at the expense of foraging and rest
(Pfister et al. 1992; Burger 1993; Burger 1994).
For this study, I observed shorebirds and human activity on the beach. In par-
ticular, I noted whether activity disturbed birds. Shorebirds were disturbed very fre-
quently. The effect of disturbance was influenced by the type of activity and varied
among bird species. Effects of disturbance on shorebird feeding and distribution were
difficult to determine.
Materials and methods
The study site (Figure 1) was a 2.85-km stretch of coastline that surrounds Coal Oil
Point between Ellwood Beach and the community of Isla Vista (Santa Barbara Coun-
1951
Figure 1. Map of the transect and study area.
ty, California). This area has a rich high-intertidal invertebrate assemblage, presum-
ably due to the large amount of drift algae deposited on the beach from offshore kelp
forests (Dugan et al. 2000), and attracts a diverse and abundant shorebird community.
The Southern Pacific Coast Regional Shorebird Plan considers Coal Oil Point an
important area for shorebirds (Page and Schuford 2000).
With an assistant, I conducted weekly shoreline surveys from January 1999 to
January 2000 along the beach between 10 A.M.and2P.M. The survey transect was
established to cover a recent (1999) US Fish and Wildlife Service designation of
western snowy plover critical habitat. I divided the study area into 11 sectors based
on landmarks, property boundaries and existing transects. We noted the weather and
tide conditions at the start of the survey and collected beach profile data at each sector.
For each sector, we counted the number of feeding and non-feeding birds (all species),
as well as other animals and humans using the beach. We only counted birds if they
interacted with the habitat. Usually, this meant that the bird was on the beach. We did
not count birds that flew over-head with the exception of raptors which we counted
if they were in clear view of the beach (due to their potential to disturb). We moved
rapidly enough so that the chance of double counting was low. Nonetheless, it was
possible to record people or birds in more than one transect or to miss them entirely.
1952
We also recorded disturbances that clearly caused birds to fly or move. We actively
avoided disturbing birds and when birds reacted to us we did not record the event as a
disturbance. Disturbance agents were classified according to type, behavior, distance
from bird(s) and location on the beach. Disturbed birds were classified according to
species, behavior prior to disturbance, number of birds and response. Survey dates
alternated between weekends and weekdays.
Depending on the comparison made, I analyzed data using Pearson’s or Spear-
man correlation coefficients, Fisher’s exact test, Kruskal–Wallis, Multivariate repeat-
ed measures analysis of covariance (ANCOVA) and χ22×2 contingency tables
when the data met the assumptions of the test employed. Counts were standardized
for sector length prior to analysis. All data were correlational so associations do not
necessarily imply causal relationships among variables.
Results
13 881 birds representing 57 species were counted during 48 surveys. Figure 2 lists
the species and shows the frequency and abundance of the most common species. Half
of the birds observed were feeding. The western snowy plover, a federally threatened
bird, was the most abundant species and represented 25% of the birds seen.
Bird abundances and density (Figure 2, Table 1) varied among seasons according
to migration patterns, but did not vary significantly from weekend to weekday. Bird
density also decreased marginally with tidal height and varied significantly, but incon-
sistently with temperature (Table 1). The density of birds varied significantly among
sectors along the transect (Figure 3, Table 1). The birds were attracted to areas with
exposed, rocky substrate (areas G–K, see Figures 1 and 3, had exposed rocks on some
days; at these sites, the relative abundance of birds was positively associated with the
percent of the beach profile that was exposed rock, r=0.61, n=231, P<0.01).
The proportion of rock substrate in these sectors was higher in the winter (due to sand
removal by winter storms) and at low tide. Snowy plovers were not seen in the five
sectors closest to the town of Isla Vista. Proximity to Isla Vista associated positively
with crow (r=0.82, n=10, P<0.05) and western gull abundance (r=0.71,
n=10, P<0.05). There were no indications that human activity reduced bird
abundance at the scale of a sector. For example, the relative abundance of birds in a
particular sector (i.e., the extent to which bird density deviated from the mean density
at that sector) was not negatively associated with the amount of human activity in a
sector (average r=0.09, n=10, P>0.05).
During the average observation period there were 51 people along the transect
(18 per kilometer). The average (and standard deviation) counts over the 48 dates
were 31.8 (29.8) people walking or jogging,18.9 (25.0) sitting, 4.8 (4.4) dogs and
0.2 (0.9) horses. Other potential disturbance agents included 7.6 (8.7) crows and 0.2
(0.5) raptors. People were evenly distributed throughout the transect except for a high
1953
Figure 2. Frequency and abundance of common bird species. Species abbreviations (from the English) as
per Klimkiewicz and Robbins (1978) listed below by feeding guild. Common shorebirds were: whimbrel
(WHIM), western snowy plover (SNPL), willet (WILL), sanderling (SAND), marbled godwit (MAGO),
semipalmated plover (SEPL), black-bellied plover (BBPL), western sandpiper (WESA), greater yellowlegs
(GRYE), American pipit (AMPI), least sandpiper (LESA), black turnstone (BLTU), long-billed curlew
(LOCU), killdeer (KILL), and dunlin (DUNL). Shorebirds seen but not plotted were: surfbird, spotted
sandpiper, ruddy turnstone, long-billed dowitcher, American avocet and wandering tattler. Common gulls
and terns were: western gull (WEGU), Heerman’s gull (HEEG), California gull (CAGU), ring-billed gull
(RBGU), royal tern (ROTE), mew gull (MEGU), and Bonaparte’s gull (BOGU). Gulls and terns seen but
not plotted were: least tern, Forster’s tern and Caspian tern. Common ‘Misc piscivores’ were: snowy egret
(SNEG), great egret (GREG), double-crested cormorant (DCCO). Misc. piscivores seen but not plotted
were: brown pelican, green heron, common merganser and great blue heron. Common land birds were:
American crow (AMCR), American pipit (AMPI), Say’s phoebe (SAPH), barn swallow (BASW), cliff
swallow (CLSW), American kestrel (AMKE), turkey vulture (TUVU). Land birds seen but not plotted
were: white-tailed kite, merlin, western kingbird, loggerhead shrike, European starling, white-crowned
sparrow, Cooper’s hawk, red-shouldered hawk, and violet green swallow. Waterfowl seen but not plotted
were: Canada goose and brant.
Table 1. Multivariate repeated measures analysis of bird density. Sectors,
not dates, were used as repeated measures since the same tide, temperature,
season and weekend designation affected all sectors within a given date.
Source Wilk’s λF df P
Sector 0.38 4.41 10, 27 0.0010
Season 0.11 2.89 30, 79 0.0001
Weekend 0.59 1.86 10, 27 0.0975
Season weekend 0.14 2.59 30, 79 0.0004
Temperature 0.37 4.65 10, 27 0.0007
Tide 0.55 2.20 10, 27 0.0505
1954
Figure 3. Beach width, substrate type and density of birds and humans along the transect.
density at a sunbathing area in the middle of the transect (F) and a low density at the
most eastern sector (K, east of the Camino Majorca Stairs) which was often narrow
or covered by water (Figure 3). Not surprisingly, human activity (Figure 4, Table 2)
was substantially higher on weekends.
Figure 4. Seasonal variation in beach use by humans and birds (includes all bird species). Sample size
included in bar or next to point. Weekend effect for birds removed for simplicity. Error bars indicate 95%
confidence intervals. Averages were based on a weekly 2.85 km beach transect. See Tables 1 and 2.
1955
Table 2. Multivariate repeated measures analysis of human
density. See Table 1.
Source Wilk’s λF df P
Sector 0.84 0.51 10, 27 0.8675
Season 0.47 0.78 30, 79 0.7796
Weekend 0.46 3.13 10, 27 0.0088
Season weekend 0.47 0.79 30, 79 0.7676
Temperature 0.82 0.59 10, 27 0.8014
Tide 0.88 0.94 10, 27 0.9427
During the 2–10 min we observed them, 10% the people disturbed an average of
10 birds each (of which about 7 flew). Joggers, which were less abundant than walk-
ers, had the same probability of disturbing birds but disturbed twice as many birds per
disturbing person (Table 3). Walkers, on the other hand, were more often in groups
so that there was, on average, no difference between the number of birds disturbed
by a walking event or a jogging event. People not moving along the beach were much
less likely to disturb birds and, when they did, they disturbed far fewer birds. Most
disturbances occurred when a disturber was within 20 m of a bird (Figure 5).
On average, there were 11 dogs to every 100 people, for an average density of
2 dogs per km. Due to the increased amount of human activity on the weekends, dog
abundance was more than twice as high on weekends (8) as on weekdays (3) (t-test,
P<0.005). Thirty-nine percent of dogs observed disturbed 22 birds each, 75% of
which flew (Table 4). Leashing reduced both the probability that a dog disturbed birds
(2 ×2χ2=5.1, Fisher’s exact test, (1 tailed) P=0.018) and the number of birds
per disturbance (Table 4). However, only 7% of pets were leashed. About 9% of dogs
chased birds during the brief observation period. Not surprisingly, dogs that chased
Table 3. Disturbance to shorebirds by people. Disturbance was defined as causing a bird to move or fly.
Activity corresponds to the total counts described as means in the Results. ‘% that disturb’ was based
on a 2–10 min observation period and was thus an underestimate of what a person disturbed during their
entire time on the beach. Disturbers were divided into walkers, joggers and bike riders. A disturbance
event could be caused by more than one disturber, e.g., two joggers, so data were divided accordingly.
‘Birds/disturbance’ was the number of birds disturbed per event. ‘Birds/disturber’ was the number of
birds disturbed per human that was involved in a disturbance. Standard deviations were not calculated
for the latter because of the difficulty in assigning disturbed birds to individuals in a group of disturbers.
Aircraft were present, but were not recorded. They did not cause disturbances in this study.
Walk Jog Still/Play Bike Total
Activity (n) 1524 907 – 2431
Disturbed (%) 16 0.4 10
No of events, No of disturbers 128, 201 109, 127 4, 7 8, 11 259, 346
No of disturbed birds 2272 3160 16 104 5552
Birds/disturbance (SD) 17.8 (27.3) 29.0 (63.8) 4 (5.3) 13 (4.8) 22 (46.7)
Birds disturbed/disturber 11.3 24.9 2.2 9.4 16
Disturbed birds that flew (%) 62 84 81 88 74
1956
Figure 5. Relative frequency distribution of distances between birds that were disturbed and the disturbing
agent. Each disturbance type sums to one. See Tables 3 and 4 for the relative abundance of the disturbance
agents.
birds were significantly more likely to disturb birds than were unleashed dogs that
did not chase birds (2 ×2χ2=41, P<0.0001). Although dogs that chased birds
disturbed a greater number of birds per event than unleashed dogs that did not chase,
this difference was not statistically significant.
There was substantial variation among bird species in the proportion of individ-
uals that were disturbed (Figure 6). Neither size of bird, guild (e.g., gull, shorebird,
piscivore), frequency of occurrence or density had an effect on the proportion of
individuals of a particular species that was disturbed (Multiple regression with all
P>0.05). A smaller proportion of land birds (10%) was disturbed than other birds
(59%) (n1=33 of the most common species, Mann–Whitney U=143, P=0.022).
Although a higher proportion of aquatic bird species that frequented the water’s edge
Table 4. Disturbance to shorebirds by dogs. See Table 3 for explanation. All chasing
dogs were unleashed but were not included in the unleashed totals.
Leashed Unleashed Chasing Total
Activity (total n, see Table 3) 18 221 25 264
Disturbed (%) 11 34 100 39
No. of events, No. of disturbers 2, 2 61, 75 25, 25 88, 102
No. of disturbed birds 11 1329 727 2229
Birds/disturbance (SD) 5.5 (6.3) 22.5 (40.9) 29.1 (38.8) 24.2 (39.2)
Birds/disturber 5.5 18.3 29.1 21.9
Disturbed birds that flew (%) 100 76 81 72
1957
Figure 6. Variation in disturbance among the most common aquatic birds. Data were pooled over all survey
dates. Bars are 95% confidence intervals around the percentage for the pooled data. Abbreviations as per
Figure 1.
were disturbed (78%) than aquatic birds that were more typically found on the dry
sand (19%), this was not significantly different, perhaps due to low sample size
(n2=26 of the most common aquatic species, Mann–Whitney U=29.5, P=0.08).
There was a non-random distribution of the locations (dry sand, moist sand, saturated
sand or rock, χ2=6032, df = 3, P<0.0001) of disturbances (number of disturbed
birds) indicating that disturbances were concentrated in moist and saturated sand
(Figure 7). The same pattern was evident for disturbance events and disturbers. These
results were likely due to the easily observable pattern that more humans and birds
(except snowy plovers) were on the lower beach (though these data were not specifi-
cally taken for humans unless a disturbance occurred).
The proportion of birds disturbed increased with the amount of activity in each
beach sector (Spearman ρ=0.41, n=366, P<0.01). The average distance that
birds reacted to humans increased with the proportion of birds that were disturbed
on a particular day (r=0.49, n=37, P<0.01), suggesting disturbance sensi-
tized birds. In contrast, the distance that birds reacted to dogs was independent of
the amount of disturbance on a particular date (r=−0.03, n=37, P>0.05). The
proportion of all birds feeding did not decline significantly with increased disturbance
rates (r=−0.18, n=45, P>0.05) or with increased beach activity (r=−0.14,
n=45, P>0.05), although for some common bird species (black-bellied plov-
er, r=−0.47, n=27 and willet, r=−0.42, n=21) the association between
disturbance and feeding was stronger.
1958
Figure 7. Location of disturbances among substrate type (observed) relative to available substrate type
(expected). Expected values for each substrate type are the total number of disturbed birds times
the proportion of a particular substrate type recorded for the beach (averaged over all dates). Peo-
ple and birds were generally lower on the beach (moist and saturated), with the exception of a sunbathing
area, where most of the people were on the dry sand. The departure from expected, therefore, is most
likely because people and birds did not use the habitat evenly (because we did not record habitat use,
I could not evaluate this quantitatively).
When averaged over the course of the year, there was no association between the
spatial distribution of birds and the spatial distribution of people along the transect
(r=0.12, n=11, P>0.05). Although disturbed birds always moved away from
the activity that disturbed them (see also Smit and Visser 1993), an analysis of the
distribution of birds among sectors and dates did not reveal that birds increasingly
occupied less populated sectors as overall beach activity increased (r=0.0, n=45,
P>0.05), a trend that was consistent for all common species. This was true for
an independent study of snowy plovers which found that plovers did not find more
isolated locations to roost as human activity increased from the early morning to the
afternoon (Lafferty 2001).
Discussion
Large-scale seasonal variation and habitat features such as a lagoon and rocky inter-
tidal area determined the distribution of birds at Coal Oil Point. Work/school sched-
ules influenced patterns of human activity within the study area. Although people
disturbed birds, their presence did not significantly alter the large-scale distribution of
birds. Disturbances were frequent and varied according to the type of human activity.
Birds were particularly sensitive to dogs. Most disturbances occurred on the wet sand,
the area where many birds fed and humans walked and jogged.
1959
Distribution
At Coal Oil Point, a lagoon mouth (Devereux Slough) in the center of the transect
(sector E) attracted birds around its margin (and snowy plovers that roosted on the
dry sand of the delta) and a rocky point provided rich foraging habitat at low tide for
many species, especially in the winter where rocks were exposed. Crows and western
gulls may have been more common near the college student community of Isla Vista
because these species will feed on garbage (Ward and Low 1997). The change in
sector use with season by birds was most likely due to the fact that rock was more
exposed at the eastern sectors in the winter and due to the lower abundance of snowy
plovers (the species with the highest site fidelity to the lagoon mouth) in the summer
months.
The weekday–weekend effect was the main factor determining human density.
Unfortunately, due to the several day spaces between counts, I could not determine
whether bird densities along the transect actually declined in response to weekend
activity. In comparison to birds, spatial variation in how people used the site was
relatively low except for high numbers of people sunbathing at a sector called Sands
Beach, particularly on weekends (the spatial distribution of people in the water was
strongly influenced by two surfing areas – we did not count surfers if they were in
the water). Although one might expect summer beach crowds, winter months had as
much activity, presumably due to good winter surfing conditions, overcast summer
weather and the fact that many students were away during summer break.
The lack of an association between the spatial distribution of birds and the spa-
tial distribution of people along the transect suggests that habitat features may be
more important in determining the distribution of birds than human activity, at least
at the spatial scale at which I divided the transects into sectors. When disturbed birds
moved, they did not often move out of the sector where they were disturbed, making
the effect of disturbance on displacement difficult to detect on the scale of a sector.
This is consistent with McCrary and Pierson (2000) who did not see an effect of
human activity on shorebird abundance when they limited their analysis to a partic-
ular beach; only when they compared human and bird use among beaches did they
see a negative association. Burger (1986) also saw an effect of disturbance on bird
distribution when comparing sites at large spatial scales.
Disturbance
Fitness impacts to birds from single acts of disturbance are difficult to assess (Burger
1986), except for nesting birds, which may suffer dramatically from a single event.
Along this stretch of beach it was clear that each bird was disturbed, on average,
dozens of times per day. Such disturbances may come at the expense of feeding and
rest for species that are making energetically demanding migrations (Nudds and Bry-
ant 2000). The lack of an association between feeding (for most birds) and human
1960
activity contrasts with the results of Burger and Gochfeld (1991) who found that hu-
man activity altered foraging rates of sanderlings, underscoring that species specific
differences (as seen in this study) may be important in this regard (Burger and Goch-
feld 1998). That birds reacted to humans at a greater distance on days where the risk
of getting disturbed was high suggests that birds can be hypersensitized to humans.
It is also interesting that birds changed their sensitivity to humans but not to dogs,
perhaps because being chased always gives birds a valid concern about the presence
of dogs. These data differ from Fitzpatrick and Bouchez’ (1998) observation that
shorebirds can become habituated to disturbance. This might be because habituation
may require predictable patterns of human activity which birds can learn pose no
threat to them (Burger 1989; Burger and Gochfeld 1991). At Coal Oil Point, human
activity is neither predictable nor inconsequential for birds. Other factors shown to
increase sensitivity of birds, but not investigated here, include time of day (Burger
and Gochfeld 1991), watercraft (Burger 1998), noise levels (Burger and Gochfeld
1998) and location to location variation (Burger 1986; McCrary and Pierson 2000).
Dogs disturbed birds disproportionate to their numbers due to the tendency for
some dogs to chase birds and the possibility that some birds, such as snowy plovers,
are more sensitive to dogs than humans (Lafferty 2001). The observation of 11 dogs
to every 100 people was slightly less than the 15 dogs per 100 people observed at 13
Ventura County beaches (40 miles south of the study), where three beaches had over
30 dogs per 100 people (McCrary and Pierson 2000). Although the countywide leash
law was posted at the main beach entrance, this law was not enforced, explaining the
near absence of compliance by dog owners.
The differential susceptibility among bird species to disturbance was partially ex-
plained by habitat use. Most disturbances occurred at the lower beach where many
birds were foraging or resting and many people were walking or jogging. Birds that
tended to roost (snowy plovers) or forage (whimbrel) in the upper beach were less
frequently disturbed. This is best explained by the likelihood of a disturbance greatly
increasing as the distance between the disturber and the bird decreases. Fitzpatrick
and Bouchez (1998); Burger (1981) also note that different species responded differ-
entially to disturbances. Fitzpatrick and Bouchez (1998) suggest that this relates to
differences among species in cryptic plumage. Although it is not clear that plumage
explains most of the variation seen in my study, such a pattern is consistent with the
observation that snowy plovers rely on cryptic coloration and remaining motionless to
avoid predators and were much more hesitant to fly (25%) from a disturbance relative
to other species (75%).
Conservation
Given the high rates of disturbance and the resulting implications for shorebird con-
servation, what actions could reduce impacts? The main finding from this study is
that the rate of disturbance at a particular location was primarily a function of: (1) the
1961
type, location and frequency of human activity and (2) the distribution, abundance
and species composition of the bird community. Managing any of these factors could,
therefore, reduce disturbance rates. One goal might be to minimize overlap between
birds and humans by concentrating human activity away from preferred shorebird
habitat (such as lagoon and rocky intertidal areas). Possible management actions to
accomplish this might include the strategic distribution of parking lots and beach-
access points. Where birds and humans do overlap, reducing the frequency of high-
impact activity, such as unleashed pets, could also substantially reduce disturbance.
Changing human behavior is likely to be a challenge, requiring sustained efforts of
education, notification and enforcement.
Although little is presently done specifically to protect shorebirds, the guiding
land-use document for coastal California, The California Coastal Act, acknowledges
the need to ‘regulate the time, place and manner of public access’ to protect the ‘fra-
gility of the natural resources in the area’ (California Public Resources Code Section
30214(a3)). This goal is consistent with the Southern Pacific Coast Regional Shore-
bird Plan that proposes limiting human disturbance to shorebirds and, in particular,
restricting dogs from beaches with important shorebird habitat and leashing dogs
on all other beaches (Page and Shuford 2000). As conflicts between wildlife and
human recreation become more acute, coastal policy, planning and implementation
may benefit from studies such as this.
Acknowledgements
Special thanks to Darcie Goodman, Nick Kalodimos, Kathleen Whitney and sever-
al volunteers for participation in surveys. Jenny Dugan, Dave Hubbard, Jack Mel-
lor and Kathleen Whitney provided helpful comments. Nick Kalodimos helped with
manuscript preparation. The Coal Oil Point Reserve of the University of California
provided access and support.
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... Free-ranging dogs were the most greatest source of disturbance to great bustards Otis tarda, with the probability of disturbance exceeding 50% (Rees et al. 2005). Similarly, shorebirds show considerable sensitivity to unleashed dogs and react by fleeing at longer distances to dogs than to pedestrians (Lafferty 2001). Such sensitivity of birds toward free-ranging dogs may be due to the unpredictable movements of dogs, which is often accompanied by approaches and chasing (Lafferty 2001, Rees et al. 2005. ...
... Similarly, shorebirds show considerable sensitivity to unleashed dogs and react by fleeing at longer distances to dogs than to pedestrians (Lafferty 2001). Such sensitivity of birds toward free-ranging dogs may be due to the unpredictable movements of dogs, which is often accompanied by approaches and chasing (Lafferty 2001, Rees et al. 2005. Manoeuvres of military jets also increased the proportion of vigilant herons and egrets. ...
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This study examined the effects of different types on anthropogenic disturbance on behaviours of grey herons Ardea cinerea, and great egrets Ardea alba, that gather in an Important Bird Area near Belgrade (Serbia), during their autumn migration, with the goal of assessing how diverse human-caused stimuli affect the behaviours of foraging and resting birds. I obtained behavioural data through scan sampling, with six categories of behaviour distinguished: vigilant, flying, feeding, comfort, inactive and other. In total, I collected 5,065 observations of individual birds: 1,293 for grey herons and 3,772 for great egrets. Significantly more birds were vigilant or in flight when they were disturbed by construction vehicles, military jets, and rural free-ranging dogs, whereas no statistical significance was associated with shooting and passing cars. Using a linear mixed model, it was shown that a greater proportion of birds was vigilant during disturbance than following disturbance or in the absence of disturbance, whereas air temperature and wind speed were not statistically significant. This study demonstrates that anthropogenic disturbance can alter the behaviour of the study species, which could aid future management and conservation planning.
... Occasional high levels of traffic (e.g. during razor clam seasons, July 4 th , etc.) at Midway Beach, Copalis Spit, Connor Creek, and Leadbetter Point, can result in destruction of nests (Pearson and others 2014, C. Sundstrom 2021, pers. comm.), and likely higher levels of abandonment and loss to predation, and reduced chick survival (Lafferty 2001b(Lafferty , 2006Ruhlen and others 2003;USFWS 2007). Razor clam season days are popular and require deliberate and continued management, outreach, and enforcement attention to minimize conflicts with nesting plovers. ...
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Population status update for the Snowy Plover in Washington
... Shorebirds may be unable to gain mass and build fat reserves required for long-distance migration because of exclusion, interrupted access to, or changes in the timing of access to food resources or roosting locations (Lafferty, 2001). ...
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Shorebird populations have declined due to several threats throughout their annual cycle. Anthropogenic disturbance is one of the most ubiquitous threats to shorebird conservation in North America. Here, we studied the influence of human disturbance on shorebird community dynamics during migration and winter in Ensenada de La Paz, a subtropical coastal wetland in Mexico. We used negative binomial generalized linear mixed models to investigate the associations between spatial, biological, and anthropogenic variation and local shorebird abundance that accounted for shorebird body size (small, medium, and large) and foraging strategy (visual and tactile) of 22 shorebird species. After controlling for these different correlates of abundance, human disturbance (people, vehicles, and dogs) was negatively associated with shorebird abundance. During winter, all shorebird species were negatively related to human disturbance but positively associated with presence of raptors. However, small, tactile foraging birds exhibited a proportionally larger negative response to human disturbance than other shorebird types, indicative of guild‐level sensitivities to human disturbance regimes. The positive association between shorebird abundance and disturbance from predators was unexpected. Shorebirds likely concentrate in large groups to reduce predation risk, resulting in higher densities of shorebirds occurring in areas with high predation risk. Understanding factors influencing the abundance and habitat use of shorebirds on their non‐breeding grounds is paramount to support management and conservation policies for shorebirds and their habitats. Abstract in Spanish is available with online material. Las poblaciones de aves playeras han disminuido debido a varias amenazas a lo largo de su ciclo anual. El disturbio antrópico es una de las amenazas más evidentes para la conservación de las aves playeras en Norteamérica. Se estudió la influencia del disturbio humano en la dinámica de la comunidad de aves playeras durante la migración y el invierno en la Ensenada de La Paz, un humedal costero subtropical en México. Se utilizaron modelos lineales generalizados mixtos, considerando una distribución binomial negativa para investigar las asociaciones entre la variación espacial, biológica y antropogénica y la abundancia local de aves playeras, considerando su tamaño corporal (pequeño, mediano y grande) y la estrategia de alimentación (visual y táctil) de 22 especies de aves playeras. Después de controlar diferentes covariables de abundancia, el disturbio antrópico (personas, vehículos y perros) se asoció negativamente con la abundancia de aves playeras. Durante el invierno, todas las especies de aves playeras se relacionaron negativamente con el disturbio humano, pero se asociaron positivamente con la presencia de rapaces. Sin embargo, las aves pequeñas y táctiles exhibieron una respuesta negativa al disturbio humano mayor que otros grupos de aves playeras, lo que indica sensibilidades al disturbio humano a nivel de gremio. La asociación positiva entre la abundancia de aves playeras y los depredadores fue inesperada. Es probable que las aves playeras se concentren en grandes grupos para reducir el riesgo de depredación, lo que resulta en una mayor densidad de aves playeras en áreas con alto riesgo de depredación. Comprender los factores que influyen en la abundancia y el uso del hábitat de las aves playeras en sus áreas de no reproducción es fundamental para apoyar las políticas de manejo y conservación de las aves playeras y sus hábitats. We studied the influence of human disturbance in shorebirds, a subtropical coastal wetland in Mexico. During the winter, all shorebird species were negatively related to human disturbance but positively associated with the presence of raptors. Understanding the factors influencing the abundance and habitat use of shorebirds on their non‐breeding grounds is paramount to support management and conservation policies for shorebirds and their habitats.
... ). Raven in boerenland die vaak hun nesten kwijtraakten aan vernielingen (vervolging), kwamen al van hun nest op 450 meter afstand, terwijl raven die op geïsoleerdere plekken broedden en niet met dergelijke vernielingen te maken hadden, pas van hun nest kwamen op 90 meter afstand(Knight 1984). Vergelijkbare toenames in verstoringsafstanden traden op bij Amerikaanse strandplevieren (snowy plover), zwarte scholeksters en kelpmeeuwen (Zuid-Afrika) bij toenemende verstoringsdruk(Lafferty 2001a, Van de Voorde et al. 2015. Pinguïns in een kolonie die het voorgaande jaar intensief onderzocht en gefilmd was, hadden in het jaar daarna een veel sterkere verhoging van de hartslag dan pinguïns die eerder niet verstoord waren (Ellenberg et al. 2012) (snares penguin Nieuw-Zeeland). ...
Chapter
The successful conservation of bird species relies upon our understanding of their habitat use and requirements. In the coming decades the importance of such knowledge will only grow as climate change, the development of new energy sources and the needs of a growing human population intensify the, already significant, pressure on the habitats that birds depend on. Drawing on valuable recent advances in our understanding of bird-habitat relationships, this book provides the first major review of avian habitat selection in over twenty years. It offers a synthesis of concepts, patterns and issues that will interest students, researchers and conservation practitioners. Spatial scales ranging from landscape to habitat patch are covered, and examples of responses to habitat change are examined. European landscapes are the main focus, but the book has far wider significance to similar habitats worldwide, with examples and relevant material also drawn from North America and Australia.
Chapter
The successful conservation of bird species relies upon our understanding of their habitat use and requirements. In the coming decades the importance of such knowledge will only grow as climate change, the development of new energy sources and the needs of a growing human population intensify the, already significant, pressure on the habitats that birds depend on. Drawing on valuable recent advances in our understanding of bird-habitat relationships, this book provides the first major review of avian habitat selection in over twenty years. It offers a synthesis of concepts, patterns and issues that will interest students, researchers and conservation practitioners. Spatial scales ranging from landscape to habitat patch are covered, and examples of responses to habitat change are examined. European landscapes are the main focus, but the book has far wider significance to similar habitats worldwide, with examples and relevant material also drawn from North America and Australia.
Chapter
The successful conservation of bird species relies upon our understanding of their habitat use and requirements. In the coming decades the importance of such knowledge will only grow as climate change, the development of new energy sources and the needs of a growing human population intensify the, already significant, pressure on the habitats that birds depend on. Drawing on valuable recent advances in our understanding of bird-habitat relationships, this book provides the first major review of avian habitat selection in over twenty years. It offers a synthesis of concepts, patterns and issues that will interest students, researchers and conservation practitioners. Spatial scales ranging from landscape to habitat patch are covered, and examples of responses to habitat change are examined. European landscapes are the main focus, but the book has far wider significance to similar habitats worldwide, with examples and relevant material also drawn from North America and Australia.
Chapter
Recreational disturbance is an increasingly significant impact on the survival of birds, especially in coastal environments. The way on how birds respond to different recreational disturbances has been detailed in earlier chapters. This chapter explores the range of planning and impact management strategies that can and have been employed to protect birds from disturbance in coastal environments. Furthermore, applicability of different management measures to protect birds in coastal recreation zones in Tropical Asia, along with avenues for future research to bridge the existing knowledge gap at Tropical Asian regional context, are discussed.KeywordsDisturbance managementImpactsRecreation ecologyTropical AsiaCoastal birds
Chapter
Human recreational disturbance to shorebirds is an important topic of concern owing to increasing human-environmental interactions in the coastal environments. In this chapter, we use a systematic quantitative review of the literature to synthesize available information on the impact of human recreation on birds inhabiting coastal environments with specific emphasis on Tropical Asia. The review highlights that despite Tropical Asia being an important region for threatened and endangered migratory and resident shorebird species of the coastal zones, less than 3% of the published research into the recreational disturbance of shorebirds came from Tropical Asia. This suggests a significant knowledge gap and need to advance research regarding the complex human-environmental relationships of recreation disturbance of shorebirds in Tropical Asia. In contrast, almost three-quarters of the peer-reviewed articles that report research and management strategies for the recreational disturbance of shorebirds are focused on coastal zones in North America (36%), Oceania (20%), and Europe (20%). Most studies reported negative impacts arising from the recreational disturbance of shorebirds. Approximately 20% of the included articles report that recreational disturbance affects the abundance of shorebirds, the diversity of shorebird communities, or how shorebirds select and use habitat in coastal environments. Alertness, locomotion, aggression, and habituation were the commonly reported behavioural responses of shorebirds to recreational disturbances.KeywordsSystematic reviewPRISMACoastal habitatsShorebirdsDisturbance
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The habitat of beach-nesting birds often overlaps with areas heavily used for human recreation. Human activity has been linked to negative behavioral and reproductive consequences for shorebirds; therefore, it is important for managers to understand how to best mitigate disturbance. In Florida, there is concern that human disturbance negatively affects the state-threatened population of Snowy Plovers (Charadrius nivosus). We measured response probabilities and flight initiation distances (FIDs) of Snowy Plovers at sites experiencing a range of human use. Snowy Plovers responded at longer distances to pedestrians and dogs than to competitor and predator species, except for incubating birds which responded at longer distances to predators. At all distances below 50 m, plovers had a response probability of > 0.2 for pedestrians. Dogs induced such strong reactions at close distances that plovers always displaced before they came within 20 m. Brood-rearing plovers were more sensitive to anthropogenic disturbance than plovers engaged in other behaviors. Plovers at sites with high disturbance generally had lower FIDs than birds at sites with less disturbance. Our findings illustrate the importance of accounting for differences in disturbance regimes among sites when setting buffer distances, and for protecting brood-rearing areas in addition to nesting habitat. Due to the severity of responses prompted by dogs, managers should strongly consider dog prohibitions at sites with breeding Snowy Plovers, as reasonable buffers may not be adequate.
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CONTENTS Fig. I. Map of Langebaan Lagoon showing study areas. total of 30 h each month on a 500 m stretch of the lagoon shore at Bottelary and on 500 m 2 of the Sarcocornia marsh at Geelbek (Fig. I) over the period March 1974 -March 1975, by the Instan-taneous Scan method (Altmann 1974). Observa-tions were made at the sandflats when these were exposed by the tide, and at the marsh both at low and high tides. The birds were counted and their activity noted every 15 min, spaced over all day-light hours. Activity was classified into foraging, flying, standing (including preening) and roost-ing.
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-we,examined,ways,in which,American Crows (Corvus brachyrhynchos),for- aging in an urban environment,balance the conflicting demands,of finding food and avoiding predators. As individual vigilance (i.e., scanning) decreased, time devoted to foraging in- creased. Significant predictors of vigilance varied with location and included time of day, temperature, food availability, distance to nearest source of disturbance, cover distance, and size of foraging group. Group size and, secondarily, distance from cover accounted for most of the variability in vigilance. Crows were,more,vigilant in areas of high human,disturbance than in areas of low human disturbance. Received 21 June 1996, accepted 10 Feb. 1997. Vigilance (used interchangeably,with scanning) and foraging are mu-
Article
Many small birds perform short flights, for which takeoffs, ascents and descents form a targe component of the total flight time and which are characterised by low airspeeds. Using the doubly-labelled water technique, zebra finches Taeniopygia guttata engaging in repeated short flights were found to expend 13.65 kJ more than 'non-flying' controls, which equated to a flight expenditure of 27.8 times their basal metabolic rate. This is over three times the predicted flight expenditure derived from existing aerodynamic models. These data were used to determine a coefficient (0.11) for converting the mechanical power derived from aerodynamic models into metabolic power. An equation is presented, based on body mass, which can be used to predict the costs of short flights in ecological and behavioural studies of birds.
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The author subjected waterbirds to experimental disturbance on Sanibel Island, Florida. Approaching birds on foot was the most disruptive of the usual activities of refuge visitors. Photographers were most likely to engage in this activity. -from Author
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Sterna antillarum is endangered in New Jersey and New York and is being considered for the US Federal List as threatened along the Atlantic Coast. Like many coastal, ground-nesting species, it has suffered habitat losses, increased predation, and increased human disturbance with increased human population. This paper presents an overview of 10 yr of monitoring and managing of least terns in New Jersey. The program involves monitoring population levels and reproductive success, protecting colonies from people and predators, manipulating vegetation and habitat, and actively attracting least terns with decoys. In successive years a trend has indicated increased population levels, and reproductive success, and decreased and then increased number of colonies. -from Author
Article
We studied the foraging behavior of Sanderlings (Calidris alba) in the winter of 1986, 1988 and 1990 in Florida to determine whether the presence of people influenced foraging behavior, and whether foraging behavior varied as a function of time of day. We used a focal animal sampling approach. For all three years, the models explaining the greatest variation in seconds per minute devoted to feeding included the number of people within 100 m of foraging Sanderlings. Although the number of people within 10 m of foraging Sanderlings during the day did not increase from 1986 to 1990, the number of people within 100 m rose dramatically, and foraging time per minute decreased. Sanderlings continued to feed through dusk into night and the time devoted to foraging and to aggression was greater at night, while the time devoted to avoiding people was less at night than during daylight or dusk.
Article
I examined the direct and indirect effects of human activity on birds at a coastal bay refuge along the Atlantic Coast. Over the year, human activity varied at different sample sites on the refuge, but people were present on part of the refuge every day, although activity was concentrated on designated paths around a freshwater pond and at a fishing pier. On the refuge (exclusive of the ponds) people were present at the sample sites 17% of the time, birds were present 42% of the time when people were present, but birds were present 72% of the time when people were absent. Human activities, such as jogging or grass mowing, which involved rapud movement or close proximity to roosting birds, usually caused them to flush. Slow-walking bird watchers and clammers did not usually cause birds to flush. Gulls and terns were least affected as they usually relanded where they had been, ducks usually flushed and flew to the centre of the pond, and herons, egrets and shorebirds were most disturbed and flushed to distant marshes. These results suggest that if management objectives include providing roosting areas for migrating shorebirds then some areas must be protected from close and fast-moving human activities.