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Do Dogs Bother Birds?
During Negotiated Rulemaking Committee meetings, there were repeated claims that dogs, and especially off-leash dogs, pose a significant danger to plants, birds and other wildlife. These claims were stated as fact, and were used to justify the need for significant restrictions on access to beaches and other areas in the GGNRA by off-leash dogs.
The reality is that there is no scientific consensusthat off-leash dogs have a significant impact on bird and wildlife populations.Some studies have indicated dogs have an impact. But others have found no significant effect on bird diversity and populations.
A recent study by Forrest and Cassady St. Clair (2006) studied diversity and abundance of bird and small mammals at 56 sites in urban parks in Edmonton, Alberta. Half of the sites were visited by off-leash dogs, half were on-leash or no dogs. City officials reported the on-leash sites had high public compliance with leash laws. Before beginning the study, the researchers fully expected “that designated off-leash areas would represent comparatively poor habitat and would negatively influence diversity and/or abundance of birds and small mammals relative to nearby habitat where dogs were required to be leashed within the same urban park system.”
To their surprise, they discovered that whether a site was on- or off-leash had “no measurable effect on the diversity or abundance of birds and small mammals.”This lack of difference between on- and off-leash sites was seen even when they considered only those species that appeared to be breeding, or only those species that nested on the ground or in low shrubs.
This study may be more relevant to the GGNRA than other studies of impacts on diversity because both the GGNRA and the parks studied in Edmonton are urban parks. Indeed, one possible explanation the researchers give for why there was no observed difference is that “wildlife, particularly birds, in suburban and urban areas exist there because they are fairly tolerant of moderate levels of human activity.”
Even studies conducted in the GGNRA itself indicate that dogs have no significant negative impact on the population of snowy ploversat Ocean Beach. The November 15, 1996 report “Western Snowy Plover (a Federally Threatened Species) Wintering Population and Interaction with Human Activity on Ocean Beach, San Francisco, GGNRA, 1988 through 1996” by Daphne Hatch found that there was an increase of more than 100% in the number of snowy plovers in the years after the 1979 Pet Policy went into effect (allowing dogs off-leash on Ocean Beach and elsewhere). Hatch could not find any negative relationship between the number of dogs on the beach at a given time and the number of plovers on the beach at the same time.
Indeed, the 1996 Hatch Report states: “Factors other than the number of people or dogs, possibly beach slope and width, appear to exert greater influence over Snowy Plover numbers on Ocean Beach.”
Unable to prove that dogs affect the numbers of plovers, the 1996 Hatch Report argues that dogs “disturb” plovers. In fact, in the entire year-and-a-half study, only 19 out of a total of 5,692 dogs – less than one-third of one percent – were observed deliberately chasing plovers, and none was reported to actually catch or harm a bird.
The Hatch Report makes the claim that “Disturbance [of plovers by dogs] results in lost energy intake due to reduced foraging and feeding efficiency, and increased energy expenditure as a result of fleeing from disturbance.” The very next sentence is “Little research has been conducted on the energetic expenditure as a result of fleeing from disturbance.” The first sentence is stated as fact, as a reason to ban off-leash dogs, but the second statement is proof that the first sentence is an untested assumption. Basing restrictions on untested assumptions makes no sense. [Note that when this assumption was tested several years later, it was proven to be false; see below]
A follow-up 2006 Hatch Report considers effects on the numbers of plovers after two Federal Court rulings reinstated the 1979 Pet Policy, allowing off-leash dogs back on Ocean Beach. The maximum number of plovers ever recorded was in 1994, a time there were no restrictions on off-leash dogs on Ocean Beach. Numbers have varied since then (from a low of 14 in 2000 to 35 in 2005), but there is no correlation between when numbers were low and when dogs were allowed off-leash.
For comparison, there has been a similar change in plover populations at a no-dog beach at Half Moon BayState Park (designated as Critical Habitat for the birds) (personal communication from plover monitoring group). At that beach, there was once a maximum of 60 plovers, but currently only 25-30 are present. This decrease cannot be blamed on dogs (since they’re not there), and appears to mirror what Hatch reported at Ocean Beach. Therefore, it’s possible that some larger issues are responsible for plover numbers, not the local conditions (dog or no dog) at each beach.
Indeed, data from the 2006 Hatch Report posted by the GGNRA on its website actually show an increase in plover numbers in 2005, the year after the Court Ruling. The annual snowy plover mean (total number of plovers observed during all the surveys in a year, divided by the number of surveys done that year) is 26.55 in 2004, and 31.30 in 2005, an increase after the Court ruling. The annual snowy plover median listed (the median for numbers of plovers counted in a single survey, with half of the surveys counting more plovers than the median number, and half of the surveys reporting less) is 28 for 2004 and 33 for 2005. The GGNRA’s own data indicate that there was no negative impact on plover abundance after the court ruling allowed off-leash dogs back on Ocean Beach; indeed, the numbers actually increased.
Figure 3 in the 2006 Hatch Report shows median and maximum snowy plover numbers at Ocean Beach from 2000 to 2005. A closer look at the data, however, show that the median numbers graphed were recorded only in the winter, while the maximum numbers graphed are based on annual data. Comparing numbers for one season with those from an entire year is essentially comparing apples and oranges. This is suggestive that the way the data was presented was chosen to make the case against dogs, not as part of an objective scientific analysis.
This is reminiscent of the recent controversy over data that staff at the Point Reyes National Seashore (PRNS), an autonomous entity within the GGNRA, claimed proved that there were significant negative impacts on the environment of Drakes Estero from an oyster farm. Corey Goodman, a microbiologist at UC Berkeley, member of the National Academy of Sciences, and a former Chair of the National Research Council’s Board of Life Sciences, analyzed the raw data used in the studies cited by PRNS staff and found that for nearly every negative impact claimed, the actual data did not support the claim.
On the September 27, 2007 episode of the KQED-FM program “Quest”, Goodman said, about the published claims by PRNS staff: “Essentially every one of the scientific claims that they made are refuted by their own scientific data…. They have made intentionally misleading claims, statements about data that are untrue, claims of cause and effect that are untrue. I think this is serious because they have misused science to mislead the public.”
GGNRA staff involved in the snowy plover data analysis, to the best of our knowledge, were not involved in the Drakes Estero fiasco, but there may be a GGNRA-wide approach to data analysis that allows bias – not facts – to determine analysis.
The 2006 Hatch Report also focuses on the idea of an increased number of “disturbances” of plovers after dogs were again allowed off-leash on Ocean Beach. The report quotes from a US Fish and Wildlife Service memo: “Such disturbances at overwintering sites require an increase in energy expenditure that mayadversely impact individual survival and reproductive success, thereby affecting the species at the population level” (emphasis added).
But the data does not show any negative correlation between numbers of dogs and numbers of plovers. The data do not show any significant negative affect on the population levels of the plovers. Therefore, the assumptions behind this statement must be called into question. Indeed, many assumptions about the effects of “disturbances” are simply conjectures, with no hard data to back them up.
The 1996 Hatch Report noted that “Little research has been conducted on the energetic effects of disturbance, and on whether individuals can compensate for this lost energy intake and increased energy expenditure.” Yet the assumption that any disturbance of plovers or other shorebird causes significant problems for the birds is repeatedly stated as fact. Clearly, more research testing these assumptions is desperately needed.
One recent study, conducted as part of a Senior Research Seminar at UC Berkeley, tested a commonly repeated assumption and found the data did not support it. Megan Warren (2007) studied whether recreational disturbances changed the feeding behavior of the snowy plover at Crissy Field and two sites at Point Reyes. She had expected the data to show that as the frequency of disturbance increased, the birds would spend less time actively foraging and more time alert. Instead, she found no significant relationship between feeding behavior and direct disturbance by people recreating on the beach. “The Crissy Field study did not provide any relevant results, however, the data from the two Point Reyes study sites do not support the hypothesis that western snowy plovers in more heavily disturbed areas devote less time to actively foraging and more time to being alert.” Any effects must be indirect, she suggests, such as habitat disturbance or food source quality.
What other assumptions about the effects of “disturbances” on plovers and other shorebirds will be similarly disproved when studies are done that put them to the test?
Another study that tested common assumptions disproved the idea that off-leash dogs on trails roam widely and frequently disturb plants, wildlife, and other park visitors. Bekoff and Meaney (1997) observed the behavior of dogs in six parks in and around Boulder, Colorado. They positioned themselves at various vantage points along trails and recorded everything they saw. They also followed individual dogs during the entire time they were in the park, recording everything the dogs did. Finally, they gave a questionnaire to all park visitors, obtaining more responses from non-dog owners than dog owners
Their data showed that off-leash dogs generally did not travel far off trail, and when they did, it was for short periods of time. “There is no doubt that somedogs go off trail for various amounts of time and that somedogs do occasionally disturb people, wildlife, and habitat. However, compared to people, dogs did not seem to do much damage to vegetation or bodies of water, and they only rarely chased wildlife… People disrupt wildlife more frequently than dogs, and people cause more damage to vegetation and to bodies of water.”
Bekoff and Meaney note that: “In Boulder and perhaps in other areas, reports of unruly dogs seem to attract a lot of attention, but of course, people do not report when dogs are well-behaved.” It is human nature to remember when something bad happens, but not to notice all the times nothing bad occurred. That’s not a problem unless you take the remembered bad incident and assume it is “typical.”
For example, people see a dog chase a plover and assume all dogs chase plovers or that dogs chase plovers all the time. But, as the 1996 Hatch Report noted, only six percent of dogs observed during the surveys deliberately chased plovers. Assumptions of negative impacts from “disturbances” of shorebirds are frequently based on anecdotal observations (and anthropomorphic descriptions of what the birds are “feeling”), not actual data. It is never a good idea to base public policy on anecdotal evidence untested by scientific studies.
It is useful to remember that, at the February 17, 2007 meeting of the Technical Subcommittee of the Negotiated Rulemaking Committee, US Attorney Barbara Goodyear discussed what constitutes an unacceptable “take” with regard to the Migratory Bird Treaty Act. Goodyear said that people could be cited for a violation of Treaty if they intentionally violate the Treaty by, for example, hunting or poaching birds, or training their dog to chase birds. You’re not going to be cited, she said, if you’re walking along the beach with your dog and you happen to pass by some birds that then flush. Deliberate behavior (training your dog to chase birds) should be the target of a management policy, according to Goodyear, but incidental behavior (walking by a bird and causing it to flush) should not.Yet incidental behavior is exactly what GGNRA staff frequently cite as justification for banning off-leash dogs.
Goodyear also made it clear that while all parks are managed at the same level (conservation of resources), there is flexibility in how that is done from park to park. She cited as an example, that you don’t manage Yosemite Valley with the expectation that people will have a solitary wilderness experience there. You manage it with the knowledge that people will bump into each other in that part of Yosemite. The GGNRA, an urban park located immediately adjacent to a large city, does not have to be managed in the same way as Yosemite.
As was noted earlier, there are some studies that indicate dogs have an impact on birds and other wildlife. And, as shown here, there are some studies that indicate dogs do not have a negative impact. Given this lack of consensus within the scientific community, and absent any overwhelming evidence against dogs, there can be no justification for restricting off-leash dogs from beaches and other parts of the GGNRA.
The studies referenced in this summary are:
1) “Effects of dog leash laws and habitat type on avian and small mammal communities in urban parks”, Andrew Forrest, Colleen Cassady St. Clair, Urban Ecosyst(2006) 9, p. 51-66
Abstract: “Remnant natural areas within urban settings can act as important refuges for wildlife, substantially increasing local biodiversity. However, habitat suitability for these species is potentially affected by human recreational activities including the presence of free-running dogs. To compare the diversity and abundance of songbird and small mammal communities between areas with bylaws that require, or do not require, dogs to be leashed, point counts and live-trapping surveys were conducted in three habitat types (deciduous, coniferous, and meadow) in the river valley parks of Edmonton, Alberta. Among birds, there was no difference between areas with different leashing bylaws in species diversity for any of the three habitat types. Similarly, there was no difference in bird diversity for a subset of species that were plausibly breeding at these sites. However, higher bird diversity was recorded in deciduous and coniferous sites than in meadow sites, regardless of leash designation, probably as a function of the horticultural practice of mowing meadows. Among both birds and small mammals, there was no difference in the abundance of individuals as a function of leashing bylaws. Our results suggest that off-leash dogs have no effect on the diversity or abundance of birds and small mammals in urban parks, but it is also possible that other factors, such as leash law compliance, reduced or obscured the effects of off-leash dogs in this study.”
Before beginning the study, the researchers “hypothesized that designated off-leash areas would represent comparatively poor habitat and would negatively influence diversity and/or abundance of birds and small mammals relative to nearby habitat where dogs were required to be leashed within the same urban park system… [On-leash sites] were believed by city officials to have high public compliance with leash laws. Off-leash sites were either in officially designated off-leash areas or, in two cases, in areas that were designated as on-leash but were known to experience frequent use by off-leash dogs and their owners.” (p. 53)
Researchers conducted bird surveys in all 56 sites (half off-leash, half on-leash) a total of three times between May and July 2002. Each survey involved a 5-minute, 100 m, fixed radius point count, followed by a 5-minute playback of a black-capped chickadee mobbing call (known to attract several bird species and used to increase detection of less vocal species). A 5-mintue post-playback point count concluded the survey. Researchers recorded all birds that were seen or heard during the 15-minute period. They only counted birds if they interacted with the environment (that is, they did not count birds flying over the survey site). Small mammals were live-trapped at a randomly selected subset of 32 of the original 56 sites.
They found that “Designation of sites for dogs to be on- or off-leash had no measurable effect on the diversity or abundance of birds and small mammals within the sites that we surveyed in the Edmonton River valley. There was a similar lack of difference in bird abundance when we restricted analyses to only those species that appeared to be breeding, only those species that nest on the ground or in low shrubs, and only the most abundant species.” (p.61)
2) “Interactions Among Dogs, People, and the Environment in Boulder, Colorado: A Case Study”, Marc Bekoff and Carron A. Meaney, Anthrozoos, (1997), 10(1), p. 12-31.
Abstract: “From September 1995 to April 1996 we studied interactions among dogs, people, and the environment in Boulder, Colorado, Data on behavioral disturbances by off-leash dogs who were accompanied by a person were collected with respect to dog-dog and dog-human interactions, dog-wildlife encounters, dogs trampling vegetation, and dogs entering and disturbing bodies of water. A questionnaire also was administered. Behavioral data showed that off-leash dogs generally did not travel far off trail, that when they did it was for short periods of time, and that they rarely were observed to chase other dogs, disturb people, chase wildlife, destroy vegetation, or enter bodies of water. Results from analyses of the questionnaire (skewed toward non-dog owners) showed that dog owners and non-dog owners agreed that people were more disruptive to the environment than dogs and that unruly people were more problematic than unruly dogs. We conclude that the well-being and interests of dogs should not summarily and dismissively be compromised when dogs and people attempt to share limited space that can be used by all parties for recreational purposes. Indeed, a higher percentage of people reported that the quality of dogs’ experience of the outdoors would be compromised more than their own enjoyment if dogs could not walk off-leash in areas where this is currently permitted. The methods used and the results from this case study can serve as a model for other locations in which dogs and people compete for limited spatial resources.”
In this study, the researchers observed the behaviors of dogs in six parks in and around Boulder. They positioned themselves at various vantage points along trails and recorded what they saw. They also followed individual dogs during the entire time they were in the park, recording everything they saw the dogs do. They administered a questionnaire they designed, with the help of professional pollsters, to all visitors entering the parks being studied. More non-dog owners (53.2%) responded to the questionnaire than did dog owners (46.8%).
“There is no doubt that somedogs go off trail for various amounts of time and that somedogs do occasionally disturb people, wildlife, and habitat. However, compared to people, dogs did not seem to do much damage to vegetation or bodies of water, and they only rarely chased wildlife… People were more disruptive than were dogs, and when dogs did go far off trails they often were lured off by people [e.g., by chasing a thrown stick]…” (p.26) “People also reported (and direct observations confirmed the fact) that people disrupt wildlife more frequently than dogs, and people cause more damage to vegetation and to bodies of water.” (p. 27)
“Recreation Disturbance Does Not Change Feeding Behavior of the Western Snowy Plover”, Megan Warren, UC Berkeley Environmental Sciences 196, Senior Research Seminar, May 7, 2007
Abstract: “The Western Snowy Plover (Charadrius alexandrinus nivosus) is a small shorebird that has many scattered wintering populations along the Pacific Coast of the United State, including several in the Bay Area. This species has been listed as threatened since 1993 under the federal Endangered Species Act of 1973. For this study I measured disturbance rates, types, plover responses and feeding time in three different sites in the San Francisco Bay Area to explore the link between recreation disturbance and feeding behavior. I predicted that as frequency of disturbance increased, the birds would spend less time actively foraging and more time alert. However, data showed no significant relationship between feeding behavior and direct disturbance by human recreators. Instead, I now predict that recreation has a more indirect effect on the western snowy plover feeding behavior. Future research should focus on indirect effects of recreation, such as habitat disturbance and food source quality.”
Warren observed plover behavior at Crissy Field (high-use recreational site), Limantour Beach (medium-use recreational site), and Abbott’s Lagoon (low-use recreational site). Surveys were made of birds’ responses to recreational activity in four categories – no response, mild response (causing a resting plover to stand), moderate response (causing a plover to stand up and/or walk away), and major response (causing the plover to flush). Feeding behavior surveys quantified how the plovers budgeted their time during the dusk feeding period. Plovers were observed: 1) searching for food, defined as movement along the shoreline with its head down visually scanning for prey; 2) actively foraging, defined as head down with its beak in the sand eating the prey; and 3) time spent alert, defined as a bird standing still with its head up visually scanning the beach. A linear regression was used to test the relationship between frequency of disturbance and foraging, alert and searching time.
“The Crissy Field study did not provide any relevant results, however, the data from the two Point Reyes study sites do not support the hypothesis that western snowy plovers in more heavily disturbed areas devote less time to actively foraging and more time to being alert… These results suggest that direct recreation disturbance is not as significant as earlier thought, and that links between recreation and western snowy plover feeding behavior are more subtle.” (p. 9)