COMMENTARY Disturbance, Habituation, and Management of Waterbird Colonies
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0051105 COMMENTARY Disturbance,Habituation, and Managementof WaterbirdColonies IANC. T. NISBET I.C.T. Nisbet & Company, 150 Alder Lane, North Falmouth, MA 02556, USA Internet: [email protected] Abstract.-This Commentary presents a critique of studies of effects of human disturbance on breeding colonial waterbirds, including a recent review by Carney and Sydeman (1999). It challenges the mind-set that the effects of disturbance are always adverse, and the resulting management principle that disturbance should be minimized. I argue that many studies do not withstand critical scientific scrutiny, and that published papers and reviews system- atically overstate the adverse effects of human disturbance. I propose definitions of the terms "disturbance", "habit- uation" and "tolerance", as well as classifications of types of disturbance and types of effect. Contrary to prevailing opinions, there is little scientifically acceptable evidence that human disturbance causes substantial harm to terns (Sternaspp.), gulls (Larus spp.) or herons (Ardeidae), although it is likely that sporadic incidents of harassment and vandalism are under-reported. Convincing evidence of adverse effects has been presented for several other species and groups of species; most well-documented cases have been early in the nesting cycle and/or mediated by diurnal avian predators. Although there are no formal studies of habituation, many or most colonial waterbirds can become extremely tolerant of repeated human disturbance. I recommend that, where appropriate, waterbird colonies should be managed for multiple uses (including research, education, and recreation) by deliberately promoting habituation. Although many field biologists are careful to investigate the effects of their activities and are successful in minimizing them, others appear insufficiently aware of the potential for harm, so that there is a need for more complete guidelines and better training. Key words.-Behavior, breeding, colony, disturbance, habituation, investigator, management, terns, tolerance, visitor, waterbirds. Waterbirds 23(2): 312-332, 2000 This journal (formerly Colonial Water- valued. I believe that waterbird colonies are birds) has published more papers on the ef- important resources for scientific research, fects of human disturbance on colonial education, and recreation, but that these waterbirds than any otherjournal, including resources are under-used because the scien- a symposium (Rodgers and Burger 1981) tific community repeatedly overstates the ad- and several reviews. This Commentary ar- verse effects of human disturbance, so that gues that many findings reported in the liter- managers unnecessarily restrict the activities ature and cited by reviewers do not of investigators and visitors. withstand critical scientific scrutiny. Many This Commentary has been stimulated studies did not show adverse effects, or by the review by Carney and Sydeman (1999) showed effects only in special circumstances and includes a critique of that paper. How- that are easily avoided; many other studies ever, my comments on that paper and the were poorly controlled, poorly reported, or studies cited therein are intended to apply otherwise inconclusive. I believe that the also to other reviews and other studies. I pre- basic concepts and terms are ill-defined, and cede this critique with a discussion of term- that the scientific questions and manage- inology, definitions, and classification of ment issues have been poorly framed. I be- effects. I continue with my own summary lieve that important effects are under- of the available information on effects of dis- reported, but that the published studies and turbance on terns, the species with which I reviews are biased and overstate the signi- am most familiar. I discuss briefly the litera- ficance of human disturbance, especially ture on other colonial waterbirds, and con- investigator activity. I believe that the impor- clude with a discussion of management tant phenomena of tolerance and habitua- implications and recommendations for man- tion have been under-reported and under- agement and further research. 312 0051106 DISTURBANCE,HABITUATION AND MANAGEMENT 313 My comments and conclusions are limit- magnitude of the effects, and whether they ed to the geographical areas where most of are significantly adverse. the published studies have been conducted: 3. The proposed definition includes all North America, Europe, Australia, and Ant- forms of activity, including deliberate perse- arctica. It is likely that human persecution cution and vandalism, as well as activities and disturbance of colonial waterbirds are such as casual intrusions that are not direct- more pervasively harmful in other areas ed at the birds in any way. Hence, it is neces- (e.g., Gonzailez 1999), but there is little pub- sary to classify and describe the activities lished information to support conclusions or before meaningful conclusions can be generalizations. drawn about effects of "disturbance". 4. The proposed definition is intended to TERMINOLOGY,DEFINITIONS, exclude habitat modification (e.g., removing AND CLASSIFICATIONOF EFFECTS nest-trees or erecting buildings on an is- land), which makes sites that were previously Disturbance occupied by colonial waterbirds unsuitable or unavailable. Although the act of modify- So far as I can determine, the term "dis- ing the habitat may disturb birds at the time turbance" has not been defined in any of the it is carried out, I distinguish this immediate prior reviews. Within the context of effects effect of disturbance from the permanent ef- on colonial waterbirds, I propose the follow- fect of human development or other forms ing definition: of habitat modification. This distinction is obscured in many previous discussions of the Human disturbance is any human activity subject. that changes the contemporaneous behavior or physiology of one or more individuals within a breeding Types of Disturbance colony of waterbirds. Most previous reviews (e.g., Carney and This definition has four important fea- Sydeman 1999) have made a binary distinc- tures: tion between "investigator disturbance" and 1. "Disturbance"is defined as human ac- "visitordisturbance", but this classification is tivity, not as the response of birds to this ac- insufficient because both classes include tivity. In the literature on colonial widely varying activities, and investigators waterbirds, the term is usually used in the perform many of the same actions as non-in- former sense, but is sometimes used in the vestigators. I propose the following classifica- latter sense. For example, the caption to Fig. tion of human activities, recognizing that 3 in Anderson and Keith (1980) includes the finer subdivisions may be required to ad- phrase "Disturbance can be seen every- dress some management questions: where", referring to birds flying in response 1. "Research procedures" are defined as to human intrusion. In that and other pa- activities by investigators that are applied to pers, the term is used in both senses, or am- individual birds or nests (e.g., marking nests, biguously. For clarity and precision, I trapping, banding, taking blood, applying recommend that it should be used only in radio transmitters). The focus of studies of the sense proposed here, i.e., as the human these procedures is determining the toler- activity that disturbs birds. ance of individual birds or pairs and, if nec- 2. Under the proposed definition, "dis- essary, modifying the procedures to reduce turbance" always results in some effect on or eliminate adverse effects. the birds. In my opinion, it makes no sense 2. "Investigatorintrusions" are defined as to call activity "disturbance" if the birds do activities by investigators (e.g, counting not respond in any way.Hence, it is meaning- nests, banding chicks, walking through the less to ask whether disturbance causes ef- nesting area to enter blinds, etc.) that affect fects: the important issues are the nature and birds other than those individually targeted. 0051107 314 WATERBIRDS The focus of studies of these activitiesis de- help to interpret information on effects of termining the effects of intrusions on the other types of disturbance and harassment. colony as a whole (e.g., the extent to which 8. "Persecution, harassment, and vandal- entering the colony repeatedlyand conduct- ism" is defined as activity by persons (other ing researchmakes birds other than those di- than managers) intended to harm the birds rectly targeted neglect or abandon their (e.g., taking eggs, destroying nests or nest- nests, or facilitatespredation). trees, or pursuing birds in vehicles). 3. "Visitorintrusions" are defined as ac- tivities visitors than by (other investigators) Types of Effect within a waterbirdcolony. These can be sub- classified into "deliberateintrusions" (e.g., Different types of effect that have been by people who enter the nesting area specif- reported in the literature are listed here in ically to see or photograph the birds) and approximate order of increasing severity: "casualintrusions" (e.g., by people who en- 1. Physiological effects (e.g., increases in ter the nesting areafor recreationalor other heart rate) without overt changes in behav- purposes); the latter activities are usually ior. These effects, where demonstrable, show more varied and more difficult to control. that the birds are aware of the human activity "Deliberate intrusions" include cases in and may be "stressed" by it, but should not whichwaterbirds establish