Factors affecting the responses of female Canada

Journal of Field Ornithology J. Field Ornithol. 84(2):171–180, 2013

DOI: 10.1111/jofo.12015

Factors affecting the responses of female Canada Geese to disturbance during incubation Valerie Miller,1,3 Kenneth F. Abraham,2 and Erica Nol1 1

2

Department of Biology, Trent University, Peterborough, Ontario K9J 7B8, Canada Ontario Ministry of Natural Resources, Trent University DNA Building, Peterborough, Ontario K9J 7B8, Canada Received 12 December 2011; accepted 28 January 2013

ABSTRACT. During incubation, Canada Geese (Branta canadensis) and other waterfowl flush from their nests in response to the approach of potential predators and subsequently return to nests after the threat of predation has abated. Differences among individuals in their responses to such disturbance (e.g., how close a potential predator approaches before flushing) are thought to reflect variation in female age, the reproductive value of clutches, and nest site characteristics. From 26 April to 26 May 2010, we examined the possible effects of these factors on the behavior of female Canada Geese (B. c. interior) on Akimiski Island, Nunavut. We used humans as surrogate predators and flushing distance and return time after disturbance as response variables. The distance at which females flushed in response to approaching humans was best explained by the density of vegetation around nests, with females on better concealed nests flushing at closer distances. We also found a weak relationship between return time and clutch size, with females with larger clutches returning to nests sooner. The frequency of human visits did not affect either female flushing distance or return time. Female Canada Geese in our study appeared to minimize risk of their own injury or death (future reproductive potential) in escape decisions, whereas return times appeared to minimize the risk of nest predation (current reproductive investment). RESUMEN. Factores que afectan las respuestas de las hembras del Ganso Canadiense ´ (Branta canadensis) a disturbios durante la incubacion Durante la incubación, el Ganso Canadiense (Branta canadensis) y otras aves acuáticas salen rápidamente del nido en respuesta a la aproximación de potenciales depredadores y regresan al nido después de que la amenaza de la depredación ha disminuido. Se cree que las diferencias en las respuestas ha estos disturbios (e. g., que tan cerca se aproxima un depredador potencial antes de salir rápidamente del nido) entre individuos son ocasionadas por la variación de edad entre las hembras, el valor reproductivo de las nidadas y las caracter´ısticas de los lugares de anidación. Desde el 26 de Abril a el 26 de Mayo del 2010, examinamos el posible efecto de estos factores en el comportamiento de las hembras de Ganso Canadiense (B. c. interior) en Akimiski Island, Nunavut. Usamos humanos como depredadores sustitutos, y distancias de salidas rápidas del nido y tiempo de regreso después de un disturbio como variables respuesta. Las distancias a las cuales las hembras salen rápidamente del nido en respuesta a una aproximación de humanos fueron mejor explicadas por la vegetación alrededor del nido, hembras en nidos más ocultos salieron volando a distancias más cortas. También encontramos una relación débil entre el tiempo de regreso y el tamaño de la nidada, en donde hembras con tamaño de nidadas más grandes regresaron al nido más rápido. La frecuencia de la visitas humanas no afecto la distancia a la salida del nido o el tiempo de regreso. Hembras del Ganso Canadiense en nuestro estudio parecen minimizar el riesgo de sus lesiones o muerte (futuro potencial reproductivo) usando decisiones de escape, mientras tiempos de regreso parecen minimizar el riesgo de depredación (inversión reproductiva en el presente). Key words: Akimiski Island, Branta canadensis interior, disturbance, flushing distance, Nunavut, return time

Incubating waterfowl respond to the approach of potential nest predators by flushing from their nests. Individual variation in flushing distances (a measure of risk-taking) has been attributed to variation in the reproductive value of clutches, with shorter flushing distances associated with larger and older (higher value) clutches (Sjöberg 1994, Albrecht and 3 Corresponding author. Email: valeriemiller@ trentu.ca

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Klvaˇna 2004, Quillfeldt et al. 2005, Osiejuk and Kucyński 2007). Female age might also influence flushing distance and return times because older birds likely have more experience and typically have both greater nest success (Brakhage 1965, i.e., current reproductive value), and lower residual reproductive value (Montgomerie and Weatherhead 1988, Redondo 1989; but see Sjöberg 1994). Proximate factors, like concealment by vegetation, may also help explain variation in flushing distance. For example, female Mallards (Anas

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platyrhynchos) were found to remain on more concealed nests longer (Albrecht and Klvaˇna 2004). However, whereas nest survival for Canada Geese (Branta canadensis) was positively correlated with concealment, female survival was negatively correlated (Miller et al. 2007). Responses may also vary among populations due to differences in predator communities. For example, in the absence of significant predators of adults, females may tolerate more risk from nest predators. Habituation to nonthreatening predators may also vary among populations, e.g., humans may cause no direct harm (Sjöberg 1994, Albrecht and Klvaˇna 2004, Osiejuk and Kucyński 2007). The results of previous studies of Canada Geese suggest that reproductive value, as determined by nest age and clutch size, can also influence flushing distances, with geese flushing at shorter distances when nests are older and clutches are larger (Sjöberg 1994). Factors that influence flushing distance have been examined in several species, including Canada Geese. However, the possible effects of vegetation cover and reproductive value on return times to nests after disturbance (an alternate measure of risk-taking) have not been examined. The length of time females are off nests can influence nest survival because nest exposure increases the probability that a nest may be discovered by a predator (Weston et al. 2011). Unless female Canada Geese detect approaching predators early enough to cover eggs before leaving, unattended nests are more visible because eggs are white. Prolonged absence also interrupts incubation, which can negatively affect embryonic development and hatching success (Weston et al. 2011). Canada Geese are ground-nesting birds that form long-term pair bonds and, during incubation, females incubate eggs and males guard females and nests (Bellrose 1976). Predation is a major cause of nest loss in ground-nesting birds (Ricklefs 1969), including Canada Geese (Bellrose 1976, Bruggink et al. 1994). However, female geese are long-lived and thus rarely risk their lives to protect clutches that can be replaced (Schmutz et al. 1997, Ghalambor and Martin 2000, Miller et al. 2007). Adult geese must, therefore, determine the degree of risk they are willing to assume at the approach of a predator and adjust their flushing distances and return times accordingly.

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We examined factors affecting flushing distances and return times of incubating female Canada Geese on Akimiski Island, Nunavut, Canada. We flushed incubating female Canada Geese by approaching their nests on foot, assuming an approaching human would be analogous to a predator dangerous to both adults and eggs. We hypothesized that reproductive value, female age (using the proxy of laying date; Hamann and Cooke 1987), and nest site characteristics would influence responses. We predicted that flushing distance would decrease with increasing female age, nest age, and clutch size (e.g., Sjöberg 1994, Albrecht and Klvaˇna 2004, Quillfeldt et al. 2005, Osiejuk and Kucyński 2007), as well as with mean egg volume, because larger eggs potentially result in chicks in better condition and with increased chances of survival after hatching (Ankney 1980, Pelayo and Clark 2003). We predicted that these same factors would decrease return times. We also expected that flushing distance would decrease and return time increase with greater nest concealment. Previous investigators have examined the possible effect of repeat visits to nests by observers on flushing distance (i.e., habituation; Forbes et al. 1994, Sjöberg 1994, Albrecht and Klvaˇna 2004, Osiejuk and Kucyński 2007) and we did so as well to determine if visit frequency might confound interpretation of the results based on our other predictor variables. METHODS Study area. Akimiski Island, Nunavut (53.10◦ N, 80.96◦ W), is a 3800 km2 uninhabited island located in the west-central region of James Bay, 16 km from the mainland of Ontario, Canada. Geese nested near small ponds and rivers. Dominant vegetation included alkali grass (Puccinellia phryganodes), red fescue (Festuca rubra), Baltic rush (Juncus balticus), sedges (Carex spp.), and willows (Salix spp.) (Blaney and Kotanen 2000). Geese nest on the ground in most vegetation types, providing a gradient of nest concealment. Potential nest predators in our study area included American Crows (Corvus brachyrhynchos), Common Ravens (C. corax), Herring Gulls (Larus argentatus), red foxes (Vulpes vulpes), and polar bears (Ursus maritimus).

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Responses of Incubating Geese to Disturbance

Nest searching. Our study was conducted from 26 April to 26 May 2010, although nest monitoring continued until 4 June. We searched for nests with three to 10 researchers spaced 50–75 m apart walking parallel to the shoreline of James Bay, extending from the tidal flats to the tall willows inland. The Akimiski Island population has been studied annually since 1993 using similar methods (Leafloor et al. 2000). When found, nests were assigned a number, marked with a 90 cm pin stake with orange flagging placed 10 m to the north, and the location was recorded on a Garmin 72H GPS (Garmin International, Olathe, KS). The mean internest distance was 123 m (Gan 2012). We recorded the clutch size and assessed the laying order of eggs based on differential staining, with the dirtiest egg assumed to be laid first and the cleanest last (Raveling and Lumsden 1977). We floated the presumed first and last laid eggs in a nearby pond to determine relative nest age; this method predicts nest age with an accuracy of ± 4 days (Walter and Rusch 1997). Egg and nest numbers were written on each egg with a permanent marker. We measured the length and width of most eggs using digital calipers (± 0.1 mm). Female response to disturbance. We quantified female behavior in response to disturbance by recording the distance between the nest and an approaching researcher when females left nests (hereafter flushing distance) and the time it took for females to return to nests after the researcher withdrew (hereafter return time). Based on a protocol established for a concurrent study (Gan 2012), nests were visited two or three (combined: N = 6), four (N = 10), five (N = 8), or six (N = 4) times. During each visit, a researcher approached the nest at a normal walking gait from the windward direction to avoid possible biases in behavior due to olfactory and aural cues. We determined flushing distance by either counting the number of paces to reach nests (later converted to meters) or recording the UTM of the researcher’s position when the female flushed using the GPS. We acknowledge that there could have been differences among researchers in their gait and their awareness of the location of nests because many nests were not visible from a distance. In addition, differences in the direction faced by incubating females during trials varied and that may have also influenced our results. A

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female goose was present and flushed during 75% of our nest visits. For the remaining nest visits, we could not determine if females were absent before we arrived or, if present, they left nests undetected by researchers at our approach. If the latter was true, it may have biased our results to shorter flushing distances. At nests where both the number of steps and GPS distance were recorded, flushing distances were highly correlated between methods (r = 0.97, P < 0.001, N = 8). Return times were determined for a subset of nests using motion-triggered cameras (Scoutguard SG550/SG530 5 megapixel digital scouting camera [N = 31], Reconyx RC55 Rapid Fire TM Color IR Camera [N = 10], and Moultrie Game Spy 1-60 Digital Game Camera [N = 9]). Cameras were located within 3 m of nests and placed either on the ground or on an elevated stand ( 0.05). Clutch size at each visit was treated as a continuous variable. Cumulative lateral vegetation density at 10 m was used because all lateral vegetation density variables were correlated (r > 0.70); tallest vegetation was significantly correlated with vegetation density at 10 m (flushing distance, rs = 0.75, and return time, rs = 0.69) and omitted. We used laying date as a proxy for female age because older female Canada Geese tend to lay eggs earlier than younger females and produce larger clutches (Brakhage 1965, Cooper 1978). For example, female Canada Geese (B. c. maxima) in Missouri that were ≥ 5 yr old tended to lay in the first or second week of nesting with a mean clutch size of 5.9 eggs whereas younger females (age two) laid during the third or fourth week and had a mean clutch size of 4.5 eggs (Brakhage 1965). None of these final predictor variables were significantly correlated, except clutch size and laying date (r = −0.63, P < 0.001, N = 108 for nests where we measured flushing distance; r = −0.61, P < 0.001, N = 31 for nests where we measured return time). Tolerance was tested (flushing distance, 0.63; return time, 0.66) and was greater than the suggested limit of 0.1 (Quinn and Keough

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2002), so both variables were retained. A subset of 32 nests where we had both measures was used to test the Pearson correlation between flushing distance and return time. We used average and final flushing distance to test the effect of visitation frequency on flushing distance. For average flushing distance, we calculated the mean for all visits at each nest, excluding one outlier (N = 108 females) that had a value for flushing distance above the 99th percentile of the dataset (Grubbs 1969). For final flushing distance, the flushing distance from the last visit was used for a subset of nests with multiple visits (N = 28) whose first visits were between 8 and 12 May and final visits were between 22 and 26 May, the period that contained the greatest sample of nests. Nest age did not differ among the four groups of nests with different visitation frequencies (mean = 23.2 ± 0.7 [SE] d, range = 15–29 d; F3,24 = 1.4, P = 0.26), and so did not confound results on the effects of visitation frequency on flushing distance. For both average and final flushing distances, we used ANOVA to compare among the four visitation frequency categories. Values are presented as means ± SE. Because hatching success rates were high (> 88%), we did not have enough nest failures to allow any comparisons of successful and unsuccessful nests.

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Table 1. Subset of 32 candidate models estimating the flushing distance of female Canada Geese during incubation using five reproductive, vegetation, and female age variables; models within two AICc units of the top model (VD) are listed. Minimum AICc was −249.282, with a null model AICc of −241.819 and a global model AICc of −245.848. Modelsa Kb RSSc AICcd wi e VD 3 9.211 0.000 0.117 VD + NA 4 9.040 0.192 0.107 VD + TCS 4 9.076 0.603 0.087 VD + MEV 4 9.079 0.648 0.085 VD + TCS + NA 5 8.893 0.672 0.084 VD + NA + MEV 5 8.912 0.905 0.075 VD + TCS + MEV 5 8.922 1.014 0.071 VD + TCS + NA + MEV 6 8.743 1.137 0.067 VD + LD 4 9.150 1.463 0.057 VD + NA + LD 5 8.987 1.779 0.048 a NA = nest age, MEV = mean egg volume, TCS = clutch size, VD = lateral vegetation density at 10 m, and LD = laying date. b K = number of estimable parameters. c RSS = residual sum of squares. d AICc = difference between each model AICc and the minimum AICc. e wi = model weight.

RESULTS Flushing distance. Mean flushing distance was 21.0 ± 0.9 m (N = 105 nests, one visit randomly selected from each nest). The top model explaining flushing distance contained vegetation density, as did all of the additive models within 2 AICc units from the top model (Table 1). Females at more concealed nests flushed when observers were closer to nests (Fig. 1). Other predictor variables were less important in explaining mean flushing distance and the confidence limits of their parameter estimates all included zero (Table 2). Return time. Return time averaged 45.4 ± 3.9 min (N = 35 nests, one visit randomly selected from each nest). We first compared return times of females after our initial disturbance when setting up cameras to those for subsequent disturbances and found no difference (paired t = 0.1, P = 0.93, N = 9). Clutch size was the parameter that explained the most variation in

Fig. 1. Relationship between lateral vegetation density at 10 m and log10 flushing distance of female Canada Geese for 105 randomly selected visits. Vegetation density had the highest importance value (wi = 0.975) and had a significant effect on flushing distance based on parameter estimate confidence intervals. Thus, females at nests with greater cover had shorter flushing distances than females with less concealed nests. The line was fitted using ordinary least squares regression.

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Table 2. Total weight or importance of each independent variable for flushing distance of female Canada Geese and model averaged parameter estimates with standard error and upper and lower 85% confidence intervals based on 32 candidate models assessed with parameters ordered based on importance. Cumulative vegetation density at 10 m had the greatest weight and was the only significant parameter. Parameter Intercept Lateral vegetation density at 10 m Nest age Mean egg volume Clutch size Laying date

Total weighta n/a 0.975 0.476 0.429 0.420 0.291

b

Ratio n/a 1.000 2.050 2.272 2.324 3.357

Estimate 1.143 −0.001 −0.006 0.004 −0.031 0.003

Standard error 0.574 0.0003 0.005 0.003 0.025 0.007

85% CI Lower Upper 0.299 1.987 −0.0014 −0.0005 −0.0129 0.0003 −0.0006 0.0080 −0.0677 0.0064 −0.0071 0.0138

a

Total weight was calculated by summing the wi for each model containing the variable. Ratio suggests the likelihood of a model containing the top variable, cumulative lateral vegetation density at 10 m, being more plausible than a model containing the relevant variable for explaining flushing distance.

b

Table 3. Subset of the 32 candidate models estimating the return time of female Canada Geese during incubation using five reproductive, vegetation, and female age variables; models within two AIC units of the top model (TCS) are included. Minimum AICc was 259.455, with a global AICc of 266.140. Modelsa TCS Null VD + TCS TCS + NA TCS + MEV

Kb 3 2 4 4 4

RSSc 47,800.63 52,818.29 45,904.44 46,342.98 46,985.56

AICcd 0.000 1.094 1.142 1.475 1.957

wi e 0.152 0.088 0.086 0.073 0.057

a NA = nest age, MEV = mean egg volume, TCS = clutch size, VD = lateral vegetation density at 10 m, and LD = laying date. b K = number of estimable parameters. c RSS = residual sum of squares. d AICc = difference between each model AICc and the minimum AICc. e wi = model weight.

return time (Table 3) and was the only parameter estimate that did not include 0 (Table 4), although the relationship was weak because the AICc of the null model was within 1.0 unit of the top model. The negative relationship suggests that females with more eggs returned to nests faster (Fig. 2). Flushing distance and return time were not correlated (N = 32, r = −0.07, P = 0.72). Individual variation. We found significant added variance among females for both flushing distance (F90,251 = 2.5, P < 0.001) and return time (F16,24 = 2.3, P = 0.034). Among-female differences explained 29.4% of

the variation in flushing distance (log10 ) and 31.5% of the variation in return time (log10 ). Visit frequency. Neither average flushing distance nor final flushing distance varied with the number of nest visits (average flushing distance: N = 108 females, F3,24 = 0.9, P = 0.50; final flushing distance: N = 28 females, F3,24 = 1.1, P = 0.35). DISCUSSION

Incubating female Canada Geese in our study remained on nests longer in the presence of an approaching threat when they were better concealed by vegetation. Concealing vegetation can reduce the likelihood of detection of nests and incubating female Canada Geese by predators (Miller et al. 2007). Thus, nest site selection represents an important antipredator strategy (Albrecht and Klvaˇna 2004, Osiejuk and Kucyński 2007). Vegetation can also restrict the movement of ground-searching birds and mammals, representing a physical barrier that reduces their ability to forage on eggs and young efficiently (Hines and Mitchell 1983, Johnson et al. 2005, Miller et al. 2007). In our study area, the low, dense vegetation around nests would probably only be a barrier for foxes because aerial predators and polar bears would likely not be deterred by such vegetation. Vegetation may also act as a scent barrier to predators that hunt using olfactory rather than visual cues (Albrecht and Klvaˇna 2004, Johnson et al. 2005). Concealed nests may thus have a greater chance of survival (Hines and Mitchell 1983, Johnson et al. 2005, Albrecht et al. 2006).

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Table 4. Total weight or importance of each independent variable for return time of female Canada Geese and model averaged parameter estimates with standard error and upper and lower 85% confidence intervals based on the 32 candidate models assessed with parameters ordered based on importance. Clutch size had the greatest weight and was the only significant parameter. Parameter Intercept Clutch size Nest age Lateral vegetation density at 10 m Mean egg volume Laying date

Total weighta n/a 0.640 0.350 0.330 0.277 0.241

b

Ratio n/a 1.000 1.830 1.937 2.311 2.656

Estimate 120.059 −11.606 −1.380 0.082 −0.612 −0.071

Standard error 113.983 6.206 1.223 0.080 0.763 1.992

85% CI Lower Upper −47.496 287.613 −20.729 −2.483 −3.178 0.417 −0.035 0.200 −1.734 0.510 −2.999 2.856

a

Total weight was calculated by summing the wi for each model containing the variable. Ratio suggests the likelihood of a model containing the top variable, clutch size, being more plausible than a model containing the relevant variable for explaining return time.

b

Fig. 2. Relationship between clutch size and return time of female Canada Geese for 35 randomly selected visits. Clutch size had the highest importance value (wi = 0.525) and had a significant effect on return times based on parameter estimate confidence intervals. Females with more eggs had shorter return times than females with fewer eggs. The line was fitted using ordinary least squares regression.

We found no effect of laying date, used as a proxy of female age in our study, on either flushing distance or return time, and Sjöberg (1994) reported similar results for 2- to 4-yr-old female Canada Geese in a study conducted in Sweden. The effects of adult age on reproductive performance, which may include responses to disturbance, may only be detectable in older individuals. For example, although flushing distances and return times of Lesser Snow Geese (Chen caersulescens caerulescens) were not mea-

sured, Cooke et al. (1995) examined several aspects of reproductive performance and found that age was inversely correlated with only two (hatchability and total brood loss) and these were only reduced in birds > 9 yr old. Average age of adult geese in our population was 3.6–5.5 yr (Leafloor et al. 2000, Abraham et al. 2008). We found no relationship between flushing distance and nest age. Sjöberg (1994) also examined the responses of incubating Canada Geese to human disturbance and found a weak (rs = 0.14), but significant, inverse relationship between flushing distance and nest age (measured as days to hatching). In other species of geese, this negative relationship has been reported as either weak (Upland Geese, Chloephaga picta; measuring egg density rather than nest age, Quillfeldt et al. 2005) or moderately significant (Greylag Geese, Anser anser; Osiejuk and Kucyński 2007). In addition, a negative relationship between flushing distance and nest age was found to be significant for one of eight species of ducks and nearly significant for a second species (Forbes et al. 1994, Mallory et al. 1998). One possible explanation for the different results among studies is that some researchers may have excluded observations made during hatching whereas others did not. Canada Geese (and other species) tend to flush at closer distances, and stay closer to nests when eggs are hatching (KFA, pers. obs., Mallory et al. 1998). Alternatively, other measures of attachment to nests (e.g., distance from nests once disturbed, their behavior upon disturbance, and return times) may more closely track relative reproductive value than

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flushing distances (Forbes et al. 1994, Sjöberg 1994). We found no effect of clutch size on the flushing distances of female Canada Geese, but females with larger clutches returned to nests more quickly after disturbance. Although the relationship was weak, this result supports Triver’s (1972) predicted relationship for parental investment and clutch size as a measure of reproductive value (Sjöberg 1994, Albrecht and Klvaˇna 2004). After experimental clutch reduction, Ackerman and Eadie (2003) showed that female Mallards with older nests and more eggs deserted nests less frequently. Similarly, with partial predation, female Mallards, Gadwalls (Anas strepera), and Northern Pintails (Anas acuta) were less likely to desert when the proportion of eggs remaining was larger and the nest was older (Ackerman et al. 2003). The results of these studies indicate that females assessed clutch size (reproductive value of the current nesting effort) and favored expected benefits of current offspring over those of future reproduction. Our results contrast with those of a previous study of Canada Geese in Sweden where females with larger clutches flushed at shorter relative distances (Sjöberg 1994) and postdisturbance behavior (i.e., moving to water, staying on land, or aggressively defending a nest) was not influenced by clutch size. Although egg volume did not appear in top models for either flushing distance or return time, we included this variable because it had been identified as a measure of reproductive value in previous studies (Albrecht and Klvaˇna 2004, Quillfeldt et al. 2005). Larger eggs require more energy to produce (Alisauskas and Ankney 1992), but large eggs produced by large females may, with respect to the proportion of reserves used (Brown et al. 1978), be relatively less valuable to them than a similarly large egg produced by smaller females. Thus, total clutch mass as a proportion of female mass (Ankney and MacInnes 1978, Forbes et al. 1994, Osiejuk and Kucyński 2007) may better represent female reproductive investment than egg volume. Repeated visits to nests had no influence on the female flushing distance in our study, and similar results have been reported by Sjöberg (1994) for Canada Geese and Osiejuk and Kucyński (2007) for Greylag Geese. Previous authors have suggested that incubating geese might respond to repeated visits by humans in

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two different ways (Forbes et al. 1994, Sjöberg 1994, Albrecht and Klvaˇna 2004, Osiejuk and Kucyński 2007). First, shorter flushing distances over time might indicate either that the geese become habituated to humans (perceiving them as less threatening and tolerating closer approach), or that they assessed themselves to be more effective defenders than they actually were because they experienced no negative consequences from earlier visits. Second, greater flushing distances over time might indicate that geese become more wary of humans and perceive them as a greater threat, as was the case for Mallards, American Wigeons (Anas americana), and Northern Shovelers (Anas clypeata) (Forbes et al. 1994, Albrecht and Klvaˇna 2004). We used only a human predator in our study because of the logistical advantages. However, examining the response of incubating geese to the approach of predators that represent different risks to adults and their young (e.g., avian vs. mammalian predators) would likely improve our understanding of the possible tradeoff between protecting current investment and surviving to reproduce in a subsequent breeding season (Miller et al. 2007). In summary, our results suggest that different factors are important in determining when incubating Canada Geese flush from nests and when they return; vegetation density (nest concealment) for the former and reproductive value for the latter. The decision to leave a nest appears related to the probability of detection and thus a female’s own risk of predation. On the other hand, when females return to nests after disturbance appears to be weakly determined by the reproductive value of clutches (clutch size). Female Canada Geese in our study appeared to place the potential risk of injury or death to themselves (future reproductive potential) ahead of risk of predation to their eggs in escape decisions, whereas minimizing risk of predation to their eggs, or current reproductive investment, motivated their return times. ACKNOWLEDGMENTS

We are grateful for funding provided by the Ontario Ministry of Natural Resources, the Mississippi Flyway Council, the NSERC Undergraduate Student Research Award program, NSERC and the Northern Scientific Training Program and to the Government of Nunavut for allowing access to the field sites. We are especially grateful to S. Gan, who led the Akimiski Island nest

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monitoring program in 2010, and S. Hagey and other MNR employees and volunteers of the MNR Waterfowl Program for assistance with logistics and field work.

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